Recollections of my meetings with Abner Doble in 1930
As recounted to Bill Lloyd on 13 - 19 September, 1999
My first glimpse of Abner Doble and E-24
I was born on 8th July, 1911 in Auckland, New Zealand. As a young lad in the 1920’s I had a keen interest in steam cars and had read of the legendary cars manufactured by Abner Doble in San Francisco. One day about 1930 I was greatly surprised to see one of these cars in Auckland city. It was parked on the northern side of Vulcan Lane off Queen street, just a stone’s throw from where I occasionally helped my father in his accountancy practice. I asked if he could photograph the car for me using his quarter plate camera and he did this on two different days with the car in the same place on both occasions. I often saw the car in the same area and in the same parking spot over several months. It was a pale yellow coupé with black mudguards and I noticed that the paint was blistered in a circular patch on the rear part of the front bonnet. The license plate was 8-341 and on another occasion 171031. The right hand window was partly down and a spectator once reached in and blew the horn. I was immediately interested in the instruments and noticed the steam pressure was reading 600 psi on a small gauge. I don’t remember the exact colour of the car interior but I do recall that the seat leather wasn’t black. To find out more about the car I got in touch with my cousin Charlie Jonas who was a mattress manufacturer with an office in Lorne street. He had built a small model steam locomotive and was active in the model engineering society. Doble attended an exhibition of this society and there is a photo of Mrs. Doble beside my cousin’s locomotive. He told me that Abner Doble was in New Zealand to supervise a joint venture with A&G Price at Thames for the manufacture of steam buses for the Auckland Transport Board and the White bus company at Thames. He also thought that Doble was importing the fuel for his car. It wasn’t running on petrol. It had a very distinctive and seductive odour of oil and steam that only a steam car can have. I believe it was running on diesel oil which was very difficult to get in those days. It was proposed to run the buses on diesel, which was much cheaper than petrol.
Doble’s car E-24 was parked in a side road in the busiest part of Auckland and usually attracted a lot of attention. I always had a close look at the car whenever I could and on one occasion I saw a tall and distinguished looking gentleman getting into it. He had a fair complexion and was neatly dressed in city clothes with a felt hat. He was noticeably stooped for a young man of about 35 and I immediately noticed a conspicuous and rather horrible scar that ran diagonally down one side of his face. It came from eye level down to his jaw and looked like a bad piece of facial surgery that hadn’t been stitched. It was particularly noticeable on his rather pallid features. There were several theories - a far fetched one that it came from a sword duel but the more likely explanation subsequently given in an article in Light Steam Power was that it arose from a boiler explosion. I am a pianist myself and instinctively look at a person’s hands when I first meet them. I noticed that his hands were unmarked, not the hands of a manual worker. He had the hands of a musician rather than a manual engineer. I would have liked to speak to him but was only about 19 at the time and was too shy to approach him directly. Fortunately the opportunity arrived by accident a little later. On this first occasion I watched as he got into the car and I heard a soft, deep rumble as the burner ignited. A faint blue haze came away from under the car and left a delightful odour of steam, oil and flue gases. The car moved off silently, except that when it was about 20 feet away there was a sudden “crack” like the knock of a hammer on metal. Neither my father nor I knew what this was at the time but I now realise that this was one of the high pressure relief valves discharging condensed water from the cylinders back to the water tank. I watched with my father as the car moved away in almost total silence. I had just had my first glimpse of one of the most famous engineers of the steam age.
Chauffeured by Abner Doble
A little later I had the opportunity of meeting Abner Doble in person and riding in his car. I was in a garage in Chapel Square in Auckland city to see a home built steam car with a Locomobile engine owned by “Steam” Stewart. H.H. Stewart had been a joint agent with the Treloar Milking Machine Co which had been the sole or primary agents for the Stanley Company some years before. Stewart also had some connection with the Doble/Price venture and had received around £750.00 in commission for introducing Doble to Prices. I was chatting to Mr. Stewart and Jim Lawler the garage owner in the enclosed garage office when Abner Doble wandered in. He had parked his car in the street outside the garage and was apparently expecting to meet Stewart there because he said to him “I want to make an appointment with you for lunch.” After a little discussion, Stewart introduced me to the first American I had ever met in the flesh. I noticed his accent but nothing otherwise remarkable about his voice. It was average, unhurried but business like. He was neatly dressed in a business suit with his felt hat and was smoking a cigarette in a short holder, something I hadn’t seen before. He and Stewart spoke on first name terms and when Abner was about to leave I took an indirect approach and hurriedly asked Stewart “Do you think he’d give me a lift?” “Give him a ride!” said Stewart in a rather obliging tone, possibly using the opportunity as a convenient way of removing an over-enthusiastic teenager from the office. Doble immediately agreed and we walked out towards the car. But before we got there he stopped to look at the experimental steam chassis that Stewart had built and which was being stored in the garage. “I like the idea of your single spoked steering wheel!” he joked at the hasty construction. As I got into the right hand side of his left hand drive car I noticed a small white wire haired terrier occupying the shelf behind the single front seat. These were fashionable at the time and someone had given it to him as a present. My next impression as I lowered myself onto the single bench seat was something of a surprise when the cushion hissed at me. I had never seen a pneumatic cushion before. He switched on and we turned around. He had been parked on the “wrong” or right hand side of the road. The car moved to the end of the short Chapel Square with the Catholic church on our right and we turned left into Wyndham street, then eastwards down to Queen street where he turned right. He stopped some distance up Queen Street, on the eastern side, directly in front of what was then the Auckland Savings Bank and said “I’ll be here for about 10 minutes.” He then reached across me to shut the passenger’s window to prevent the dog from escaping and excused himself with the comment “Just so he won’t elude you.” I definitely remember him using the elegant expression “elude”. He went into the bank leaving me and the dog in charge of this remarkable machine. I was careful not to touch anything. He returned from the bank and we proceed up Queen street to the Wellesley street intersection, occupied by the traffic officer since there were no traffic lights at the time. Abner leaned across me again and said to the officer “Can I go right round?” There was no reply but we were waved around and he made a complete U-turn at the intersection, going around the officer. “You’ve got a car to be proud of” I remarked as we gathered speed. “Oh yes, it’s a fine car” he answered with justifiable pride. I was a bit shy and asked what I feared might have been a silly question. “Can you drive with the hand brake on?” “Oh no, it’s just like a locomotive” he answered immediately. But then he hesitated a moment and as an afterthought said “Oh yes you could ..” and added something that now escapes me. It might have been “but it wouldn’t be desirable.” We turned right into Quay street and he put on a short turn of speed along by the wharves. There was a distinct and effortless surge of power which was most impressive, even though the conditions were too restrictive for anything more than about 40 mph. He switched off the burner and said “We’re coasting now.” Then a moment later he asked “How much further can I take you?” When I replied that I was going to Upper Queen street he was somewhat surprised and quickly exclaimed “We’re getting further from Upper Queen street every moment!” but I was so taken with the unique experience that I just said “No, just keep going.” We stopped a few moments later outside the Auckland premises of A&G Price on the left, about half a mile along Quay street. As we pulled up he said “I shall be here for about an hour” and extended his hand in a courteous manner which indicated that my unique journey was at an end. “Pleased to have met you Mr. Jonas” were his last words as he opened the door and stepped out. I walked back to the Baptist Tabernacle where I had left my father’s car or my push bike after my organ practice from 8 to 9 am. Not only had I willingly traveled well out of my way but my father was less than pleased to hear that I had also broken an appointment he had arranged for me with a potential employer, just when the depression was beginning to bite. But any pangs of conscience were more than adequately recompensed. At last I had had my first ride in a steam car and in all the world there was no greater steam car than the Doble and I had been chauffeured by none other than the deity Abner Doble himself. It was like meeting the almighty. I felt like the King of England had taken me on a tour of Buckingham Palace.
My last meeting with Abner Doble
I met Abner Doble on one other occasion. Possibly around August, 1930 my mother saw in the Table Talk column of the New Zealand Herald that Mr. and Mrs. Doble were now staying at the Grand Hotel in Prince’s street near the university. I telephoned the hotel and asked to speak with Mr. Doble. I was put through to him and asked if I might come down to see him. He agreed and when I asked when could I come he replied “Right now.” I wasted no time in getting there and found him and his wife sitting in chairs on the steps approaching the front door. We had a pleasant conversation in which he mentioned that he didn’t like living in Auckland and preferred Thames. Thames is a much smaller town. In the same breath he mentioned that he enjoyed tennis. I recall asking him about the burner and he spoke about the venturi but I didn’t really follow because I had never seen one. I told him that I was hoping to make up a steam car from a Mobile engine that I had. “You’ll find it damn hard!” he replied. “What speed could I expect from it?” I asked him. “Oh, about 25 miles per hour.” He also suggested “Why don’t you go down to Hamilton and see Jim Trelor? He’s got a lot of junk!” He was alluding to Stanley material, for which he appeared to have little regard. I asked if he could lend me any information but he said “It’s all packed up.” He was very patient and gave me about 20 minutes to half an hour. Then he ended the interview with the words “How much more can I tell you because I propose to take my wife out for an airing?” I remember these exact words because I thought it was an unusual expression. His wife had sat patiently throughout our discussions, saying virtually nothing. I later heard from Stewart that she may not have been his wife. Her name may have been Alene. He mentioned that he was the hand brake on?” “Oh no, it’s just like a locomotive” he answered immediately. But then he hesitated a moment and as an afterthought said “Oh yes you could ..” and added something that now escapes me. It might have been “but it wouldn’t be desirable.” We turned right into Quay street and he put on a short turn of speed along by the wharves. There was a distinct and effortless surge of power which was most impressive, even though the conditions were too restrictive for anything more than about 40 mph. He switched off the burner and said “We’re coasting now.” Then a moment later he asked “How much further can I take you?” When I replied that I was going to Upper Queen street he was somewhat surprised and quickly exclaimed “We’re getting further from Upper Queen street every moment!” but I was so taken with the unique experience that I just said “No, just keep going.” We stopped a few moments later outside the Auckland premises of A&G Price on the left, about half a mile along Quay street. As we pulled up he said “I shall be here for about an hour” and extended his hand in a courteous manner which indicated that my unique journey was at an end. “Pleased to have met you Mr. Jonas” were his last words as he opened the door and stepped out. I walked back to the Baptist Tabernacle where I had left my father’s car or my push bike after my organ practice from 8 to 9 am. Not only had I willingly traveled well out of my way but my father was less than pleased to hear that I had also broken an appointment he had arranged for me with a potential employer, just when the depression was beginning to bite. But any pangs of conscience were more than adequately recompensed. At last I had had my first ride in a steam car and in all the world there was no greater steam car than the Doble and I had been chauffeured by none other than the deity Abner Doble himself. It was like meeting the almighty. I felt like the King of England had taken me on a tour of Buckingham Palace.
The Doble Steam Buses
Since my ride with Abner Doble, I have ridden in eight other steam vehicles including the buses. I had two rides on the buses, both on bus Number 10 as a fare paying passenger around Auckland. Once was to Point Chevalier and later along Mountain Road past the grammar school, which I had attended just a couple of years before. Only three complete bus units were built, all different in detail. The first was sold to the Auckland Transport Board, installed in a converted AEC bus as described and illustrated in the newspaper cutting. This was the only bus I rode in. They were all conversion units, although one had a special body built by Cousins & Cousins and ran the 70 or 80 miles from Auckland to Thames for about 3 months for the White company. I saw this one once on the road coming from Auckland as I was returning from Thames. This one had the auxiliary unit driven by a donkey engine behind the condenser rather than by shaft drive from the main engine. I once owned the complete power plant out of this Thames bus and sold it to a Mr Alexander in Sydney in 1948 or early 1949. I later went to Sydney on the Wanganella in 1949 to exchange a turbo booster unit from Number 10 bus for a White steam car engine. I can’t recall his name. He wrote to me about a pressure atomizing burner that he had designed and how he found it.
The number 10 bus appears in the newspaper photograph and is the one which had the most use. This was the first bus I saw. It had a forward driving control, half way over the boiler room. I first saw it in Commerce street in the city, coming in to its terminus and was impressed by the silence of the bus as it made a U-turn in Commerce street. Riding was equally smooth, with a faint sound from the exhaust but much quieter than the old AEC bus engine. It had that subtle and attractive odour of steam and oil. I later saw the Thames bus coming from Auckland toward Thames as I returned. This Thames bus was sold to the Thames Authority, which was separate from the Auckland Transport Board that owned the Number 10 bus. I later visited the Price works in Thames after the project had been terminated and took stereo photos of one of the chassis. Everything lay there for some time, until Price had a big clean up, possibly when they became Cable Price. Even Doble’s workshop and drawings were there.
There were some problems with the buses because they were under-powered except that the third one, the Thames bus, had a bigger boiler. It had an auxiliary engine to take some of the electrical load. Jo Bell said that this took too much steam. It went at 1,500 revs and sounded like a petrol engine working. I think it was a little compound V-engine. The failure of the project was a combination of the lack of performance and the depression. Fuel economy with Number 10 bus was said to have been about the same as conventional buses but with cheaper fuel.
The fate of the steam buses
The compensator came from the Number 10 bus unit and some other parts from this unit ended up in my Chev steam car. I don’t recall if the third unit, the Thames bus, had a compensator. The second unit was lying idle for about 9 years but no one bought it. I don’t know what happened to that second unit. A chap in Hamilton, a Mr. Grinter bought the Thames power unit and I bought it off him. This is the one I sold to Alexander without ever taking delivery of it. I bought it with the idea of reselling it. I paid about 90 pounds for it and only saw it in pieces in the railway yards. It was just the power unit. I think the engine of the third unit, the Thames bus, went to a museum in the UK because I got a letter from them about it.
“Bo” Bollond at Thames bought my Stanley about 1945 after I stripped a lot of stuff off it. He got Prices to put a bus engine into it. I don’t know what bus engine this was. Brian Rankine has this engine at the moment. Bollond might have got one separately from Prices. He is the one who cut the auxiliary unit in half. Sadly, he eventually committed suicide by gassing himself, I believe as a result of women trouble.
Jo Bell, one of the guys who was in charge of the mechanics on the bus project at Thames said he once had the use of Doble’s car (E-24) for a weekend. If the project had continued he would have made the control boxes. A relation of his appears in a group photograph of the works people. At Gary Summerhayes’ prompting I wrote 48 pages of memoirs of my steam car experiences for the Model Engineering Society, now the Steam Engine Society.
I rode in Doble E-13 once in Christchurch when Alec Gudsell had it and remember being most impressed at the way it went through thick sand on a sandy road, like a locomotive pulling up hill. Joe Bell, who had worked on the bus project, said there could have been a third Doble car brought in by a tourist but only briefly. He had seen the word “Doble” on the back of an electrician’s jacket.
Stanley Mixing Tube Fires by Pat Farrell (aka SSsssteamer) SACA
NW Steam Clinic September 27, 2019
What are mixing tube fires? The mixing tubes of the Stanley steam car are where the vaporized fuel and atmospheric air mix to produce a combustible flame to fire above the burner grate. When the fire presents itself below the burner grate in the plenum, or in the mixing tubes below, that is not acceptable. This generally is called a mixing tube fire. What are the causes? Most common tube fires are started by a fire leak from around the burner to boiler seal. The pilot light inspection hole not being fire tight, as well as the super heater exit at the rear of the burner can also start mixing tube
fires. A fuel flooded mixing tube fire is usually caused by a flooded burner. The flooded burner can
be flooded either by the main fuel jets, or by the pilot light being out causing raw fuel to build up in the mixing tubes and plenum. Mixing tube fires can also be started by forcing the burner too fast at firing up and flooding the burner with raw fuel. Instead, preheat well and build a slow hot fire. Tube fires can be caused by the fire dropping down out of the burner and into the plenum by the way of a cracked burner grate. The burner’s slots or its drilled holes can become too big and therefore dropping the fire down through them and into the plenum. A warped or heat damaged burner grate can be the cause for the over-sized slots. The burner grate’s plenum not being sealed tight enough around the burner grate, can also allow the fire to descend into the plenum. Flooding of the burner plenum can be caused by using too heavy of fuel for the too large of main jets being used. Thin your fuel with gasoline or reduce the size of your jets to help reduce fuel flooding. This flooding is also a problem found at higher elevations where the oxygen is thinner. Sometimes, old fuel will refuse to vaporize, and until that fuel is disposed of, the old fuel will be a problem. Partially plugged main jets can cause drooling that will accumulate creating flooding of the mixing tubes. Misaligned main fuel jets within the mixing tubes can flood a side of a mixing tube and thereby flooding the mixing tubes. Also a resulting fog of vaporized fuel blowing back outside of the mixing tube can result in a puddle of raw fuel and an eventual tube fi re. The main jets vapor spray should always do a perfect bull’s eye inside of the mixing tubes. What should be done? A roaring mixing tube fire should be extinguished as soon as possible to prevent further damage to the Stanley burner grate. The first thing to do is to eliminate the fuel source by turning off your main burner valve. If I have a roaring tube fire, I prefer to quickly pull off of the road and try to let the excess fuel burn itself off in a small flame. Continued driving fans the tube fire making it a hotter tube fi re and possibly doing excessive damage to your burner grate. Sometimes if my mixing tube fi re gets too large, I will use my Halon fire extinguished to keep the fire from getting too big and doing collateral damage. Never use a powdered fire extinguisher in your mixing tubes as that will plug your burner grate up solid with extinguisher powder. To resume firing properly, the excess fuel has to be burned off, so a smaller fire is encouraged into eliminating the excess fuel. If the burner has lost its fi re and it is blowing raw fuel fog into the air, turn the main fuel valve off immediately and drive until the fueled smoke screen has subsided and then pull over to relight the burner. The first lighting attempt is to light the fire from the top at the smoke bonnet’s access door. To prevent your body from being burned, stand upwind from the fuel vapor cloud when lighting. Next is to check your pilot light at the peek hole for being lit. Light the pilot light if it is still out. What is the collateral damage? Too much roaring burning of a mixing tube fire will eventually crack your burner grate. Plenum fires can also destroy all of your refractory materials located in your burner. Excessive tube
fires with fuel left uncontrolled can eventually burn your Stanley up. Always shut off your main fuel valve when leaving your Stanley unattended. Try to shut off your main fuel valve a quarter mile before arriving at your destination. That should clear out any stored fuel in your steam automatic system and prevent your main fuel from later cycling on and drooling fuel while the Stanley is parked. What can be done to continue driving while tube fi res persist? Sometimes while on the road, a quick fix for tube
fires is just not available. To survive this problem and to continue driving, these steps can be taken. Reduce your fuel pressure so as not to create too much internal pressure inside of the burner/plenum area. Reducing your fuel pressure to below 100 PSI can sometimes get you home. Get your Stanley rolling up to about 18 MPH or faster before slowly turning on your main fuel valve. This creates a draft so as to keep the fire burning above the burner grate and not in the plenum or mixing tubes. Some Stanley's have a stack blower that can be used to duplicate this need for a draft. Before using your main fuel valve, by using your firing up valve you can gently bring your fire temperature up to a good
firing rate following with firing with the main fuel valve. If your burner grates become sooted up from tube fires and it restricts the passage of the air/fuel vapor, remove your main fuel jets and if you have one, use your steam enema with full steam to clear your burner grate of any soot. I have also removed my smoke bonnet, and by blasting down each fire tube with an air nozzle, I cleared the sooted up the burner grate below of its blocking soot. Once I was in a blinding dust storm that blocked my burner grate with dust. My steam enema saved me that day too. Hopefully something in my above SSsssteamer experiences will help you in your steam car adventures. <
From bill Bill Lloyd 2011
Only today I had actually made a start at sorting through all my own Dungog photos, apart from just picking out a few here and there – like the ones attached. I still have hopes of making a disc of all my rally photos of the past decade, but something always seems to interrupt the process. I’m sure it will happen, eventually.
The Model K was delivered here to Denistone in Sydney to give me more time to “bond” with it. It’s been stone cold since it left Dungog, but we’ll be taking it out again on Friday so a couple of friends from the Road Steam Engine Association can have a ride and officially certify it for its annual club registration. The Doble went back to Trevor’s for some new plumbing. Trevor’s currently on holidays somewhere in central NSW for a few weeks. I nearly killed myself getting ready for the rally. Now I’m killing myself catching up afterwards. One of my friends went to London on Sunday. Another left for Japan today. He asked if I wanted to go with him, as I did once in the past, but alas, I’ve used up all my leave points for a while.
I’ve asked the body people to get me the Model K paint colour code which Basil wanted, so please tell him it will be forthcoming in due course. They’re currently working on the 1915 Detroit electric, which was dropped off in the same truck which then loaded the Model K for Dungog. The Detroit springs and wheels need stiffening up in a few places, with powder coating on the wheels. Incidentally, I made contact with your friend Don Davidson, first to buy a reproduction motor plate for the Detroit and then to see about having some Doble hub cap badges made. I told him how much I had enjoyed both the articles you sent me about his Detroit and Stanley.
Best regards to you both
FLYING STEAM ENGINESHomeHistoryMy Recent EffortsGenerating the SteamFuelDesigns for aircraftHydroplanesPracticalSkylarkI.C. EnginesCompressed Air
In their simplest form a boiler is a round tank of water with a fire underneath and in the case of my first engine (designed in 1967 by David Parker) it is little more than that. What we can do with these little boilers is to improve on the material normally used on model locomotives and to look at just how big a safety factor we really need. Model locomotives sometimes have a boiler shell that is twenty, thirty, even forty times stronger than it needs to be! ! The modern aircraft which we happily board and in which we fly away on our holiday works very safely on much lower factors of mechanical strength than forty to one! It is really quite safe to use a factor of four to one on a boiler of only 50 mm diameter which operates at perhaps 150 C. David's 'Comet' engine (see photograph and drawings) has a quite generous safety factor of 5:1 and the boiler is free of any long term danger due to corrosion. The boiler is made of 0.5mm nickel silver sheet, silver soldered with very simple water tubes of 6mm copper to increase its heating surface. It is spirit fired and I hydraulically tested mine to 3 times the working pressure with no problems, it worked consistently for over five years.
My experience with 'Comet' has led me to believe that it is perfectly feasible to build a model speed boat engine along similar lines as the airborne engine. Add reversing gear and a throttle valve and you could build a fast planing steam boat that is quiet, controllable and above all absolutely unique.. This is not silly thinking, the Comet's engine directly coupled to a 12''x8'' propeller turns at 3200 RPM. and develops, a static thrust of about 600 grams. The weight of this engine and boiler is little more than a 540 size electric motor and a standard 7cell 1500 ma Ni/Cad battery pack. The fastest steam powered model boats in the world are the tethered flash steam hydroplanes which reach speeds of up to 170 kph this brings me to a different kind of boiler that offers huge improvements in performance for model aircraft, the flash or Monotube Steam Generator.
Small monotube theory and practice
What is Flash Steam? There are two basic ways of generating high pressure steam almost everyone is familiar with the locomotive boiler and the land and sea born variants of the pressurised container, heated with either water or fire tubes and an external source of heat. In a flash boiler the heating surface is a single or it may be a series of tubes into which the cold feedwater is pumped against the developed pressure. The heat source is usually an oil, petrol, or gas flame directed against the tube. The tube is normally coiled and housed in a thin light weight case of stainless steel and the flame is directed through the centre of the coil. The development of high pressure steam is virtually instantaneous, hence the term flash steam. The little Groves 1936 engine that I have built goes from cold to full power in 8-10 seconds and the power is turned out all the time there is water and fuel. Throttling works within fairly narrow limits just by turning the heat supply down, the response is instant. The narrow band of power available can be satisfactorily extended using a more elaborate control system. The Groves engine is very simple and intended for free flight only where one power setting is all that is needed. The steam so generated can be superheated to the point of the engine's self distruction, where the lubricating oil is turned into carbon before it reaches the cylinder walls. I am fascinated by monotubes and in 2002 when the offer came I could not resist the temptation to buy all 15 feet of Skylark with its oil fired Monotube steam source. Like all experimenters I had to get it going ASAP in search of the first modification or improvement I could introduce. I am quite sure the previous owner would have been disappointed in me if I hadn't! There was one major departure from normal monotube practice; it was not a monotube at all it was a bi-tube, two parallel tubes wound alongside each other. (There is a theoretical advantage in doing this which I will not go into at this point.)
I have no complaint about Skylark, I launched her in the Chichester Ship Canal in April 2003 and everything operated much as the previous owner had said it should except, try as I might all I could get was 25psi and a slow walking pace. I was told that Skylark steamed well at 80-100psi and produced enough power to run at full hull speed which should be say 3.5mph, a fairly good walking pace. That is, it did when it had a monotube. I tried all I could to get that bi-tube to operate but it would not play ball. The previous owner gave me his bi-tube pressure equalising valve along with Skylark when I bought her and I experienced no sign of overheating of one tube with the other tube running much cooler. I can look down the funnel straight into the flame area and if anything is red hot I can see it at once. My impression is it did divide the flow exactly as intended. All I got was 25psi.
After a few weeks I gave up and made a new monotube from the self same two 20 foot (6.1 M) lengths of 3/16" (4 mm) Kunifer (copper alloy) brake pipe. They were joined with a screwed compression joint some way up the chimney out the way of the direct heat of the flame. Result, 60 psi whoopee progress!
(At this point I changed the propeller for a bigger one and as expected the pressure rose because the load was greater and now the boat operated exactly as its builder described. This matter of Balance between load and heat input will be covered under "Controls" when I write it!)
I do not think it was the bi-tube as a device that was the problem, my firm belief is that by switching from bi-tube to monotube I had DOUBLED the velocity of the feed water through the 3/16" (4 mm) Kunifer tube. This matter of water velocity has been discussed in the book "Experimental Flash Steam", it is so relevant to these notes that I have included the results in my table, I quote verbatim from the book:-.
Quote from Experimental Flash Steam, by Benson and Rayman my copy being published by Argus Books Ltd in 1973. The Experiments themselves were carried out by Mr Edgar T Westbury one of the most well known writers and designers of model engineering projects in UK. He is known the world over, the world of model engineering that is; (not a very big world!). Page 59.
“Tests carried out on three copper boilers each 11 Feet in length and 3/16" (4 mm), 1/4" (6.3 mm) and 5/16" (7.9 mm) diameters respectively and with a wall thickness of 0.03" (0.7 mm). Each coil was wound upon a circular tapered form, 2 1/4" (57 mm) inside diameter down to 1 1/2" (38 mm) diameter and spaced 1/8" ( 3.2 mm) apart. The casing left 1/8" (3.2 mm) gap at the largest coil. Water was fed from a water pump driven by an electric motor. Each boiler was fired by the same air-gas blowpipe 1 7/8" (48 mm) diameter, and various evaporation tests were conducted with a spring loaded outlet valve set to blow at 500psi.
In each test the 3/16" dia. boiler gave the best results and on a maximum evaporation test managed 27 cu. Inches per minute with the gas blowpipe flat out and the steam highly superheated. This represents about 1 lb per minute and seems a remarkable figure for only 11 feet of tube and the fact that this boiler had the lowest heating surface. In every test the 5/16" boiler gave the worst results. On repeating the experiments using thicker walled tube the relative results were confirmed but evaporation increased by about 12%! End of quote.
E.T. Westbury's test results on 3/16" tube is included in the table which follows. SO what is going on? 60lbs of highly superheated steam per hour from about 1/2 sq. ft heating surface! It must be said at once that this sort of hard driven performance is VERY wasteful of heat using only a few hundred degrees Centigrade from the flame. A Gas-Air torch typically burns at about 2200 degrees C at the flame cone. A thin piece of steel wire at the outlet to my tiny boilers glows red, about 800-900 C. We do not want red hot exhaust on a steam boat and I certainly do not get it on Skylark.
Why is velocity so obviously critical in the performance of monotubes? The previous owner of Skylark has a theory which I believe to be correct. As the water flows and heats at some variable point along the tube it begins to form tiny steam bubbles on the inside wall. These must tend to stick to the surface just as they do to the bottom of a saucepan when you boil water in it. The steam bubbles seem obstinately glued to the metal. In order for a monotube to operate efficiently the water must flow fast enough to scour bubbles away IMMEADIATLY they form. The conductivity of any vapour is thousands of times worse than water and maybe 100,000 times worse than copper alloys like Kunifer. If as I believe the dramatic increase in performance is due to the increased water velocity then I thought maybe I can juggle a few numbers and come up with a very interesting, if empirical figure that represents a likely MINIMUM velocity to aim for when designing very small monotubes like Skylark's and the really tiny tubes I have in Tiddler's Monotube.
Another result of this scouring is that scale and oxides do not form on the inside of the tube. Indeed if you cut open a well used section of a monotube you will see that the inside surface looks as if it had been lightly etched.
I could have directly compared the results of the bi-tube and monotube and left it at that but in addition to Westbury's 3/16" diameter tube experiment, a further source of data is available in an article published in the Model Engineer magazine in 1992. This was written by Bob Kirtley covering in great detail the construction of his world record breaking hydroplane Pisces II which raised the Class B Steam record from about 80 mph to 104 mph in one step. I have seen her go and it is a joy to behold, the noise is like no other, music to my ears and any other Monotubist's.
What I did was to compare directly the water velocities of the four separate cases and tabulate them as follows. The different values for Monotube area (Ma) for Pisces and Westbury are because of the differing tube wall thickness.
ParameterSkylark Bi Tube
3/16” Dia.Skylark Monotube
3/16” Dia.Pisces II Monotube
3/16” Dia.Westbury Test Monotube
3/16” Dia.Pump Ram
area (Ma)0.141cm20.075cm20.103cm20.081cm2H2O Velocity (WV)
It was with smug satisfaction that I noticed the close tally between Skylark and the Westbury test data. To other Monotubists everywhere please give me the current particulars of your system so we can acquire a data bank for future use by others. All the tabled parameters plus pressures, temperatures, fuels, burners anything you can think of that may help others who will follow on after us.
I don't pretend that my observation and experience is a scientific study but it may prove more concrete than any other data that I have seen to date. It is further born out by the fact that if I slowly reduce the heat input setting on Skylark there comes a point at about 50 psi when the pressure drops very quickly from 50 to 25 psi; without a commensurate reduction in fuel flow. With the available data I would suggest that anyone contemplating a small monotube design for normal cruising speeds and pressures a WATER INPUT VELOCITY of about 50 metres per minute (0.8 Metres per second) should be a safe minimum to aim for at the systems normal 'cruising' power.
The importance of the above statement cannot be over emphasised as I believe it may be the key to solving much of the hit and miss approach that seems to dog this subject and is perhaps the root cause of the commonly heard mystique surrounding design and application of very small monotube steam plants. To design a plant we can now start from the same point as steam plant designers have always started; the steam consumption, this basic calculation is very clearly explained elsewhere in text books and I spare myself the need to repeat it here. This value can also be gained from users of the same and similar engine designs of course and it is perhaps a more reliable guide as well! In any case it is a good way of checking your own calculations. From the mass of steam reguired per hour the pump ram diameter and stroke can be decided and then the tube bore for a given water feed velocity becomes an additional but simple calculation. From my experience with Skylark and tiny monotubes for aircraft models I can suggest that it is an advantage if the water feed velocity drops well BELOW 0.8 metres per second for slow speed work, maybe as low as 0.4. I still get a reliable flow of steam at maybe 80 revolutions per minute but it is wet, as one would expect but very controllable.
This study, whilst interesting may be of very limited use much outside of the tube diameters in the table, I would hazard a guess that all would be well up to 3/8" (9 mm) bore tube. I have done some calculations on turbulant flow at the temperatures and pressures at which Skylarks monotube normally cruises and it seems to be that turbulent flow will occur at all the water flow rates we are likely to work at and it is unlikely to fall outside that rule of Thumb up to maybe 3/8" (9 mm) bore. More is needed in this arena to prove anything. It may just be that in full size practice perhaps the known point of turbulence is the lower end of any particular monotube's efficient and useful working range. Do we have a proffessional Monotubist out there ready to help us?
At this point it may be of interest to put a few figures together to illustrate what this all means to me. Skylarks boiler certainly produces about 50 lbs. of steam per hour at 100 psi and it is reasonably dry, the bore of the tube is 3mm (7square mm area) and there is about 10 metres of tube in the flame area. Now if we double the diameter of the bore from 3 to 6mm the area quadruples to 28 square mm and at about 1 metre per second water velocity you will get 200lbs of steam at 100 psi and I would expect you could do this with only 10 metres of tube if you throw enough heat at it. However more tube of greater diameter added as a feed water heater if you like to separate the sections mentally, will give a very good return in higher efficiency. This is exactly how Doble and others built their car monotubes; I am confident they knew exactly what they were doing and why! Looking at Dobles monotubes they had about 25- 30% of tube length at the smallest diameter and usually had a total of three diameters of tube in the furnace which must have helped reduce pumping frictional effort by perhaps 30-50%. When I build a bigger monotube I will do exactly what the old masters did.
Pisces has a water velocity twice that in Skylark and produces at least eight to ten times the power. I know this because Class B boats have similar rules be they Steam or IC Powered, the IC boats are usually fitted with 30cc racing two stroke glow motors which are known to be capable of 5 HP. A point I must make here Bob Kirtley's engine has a displacement of 13cc and yet has a performance comparable with 30cc IC engines!. A good steam Hydro is not that much slower than an IC boat and yet is generally 2-4 lbs heavier. I doubt if Skylark needs more than half a horse power to drive her as she goes at the moment.
Some Monotubes go and others Don't
The simple analysis given above is I believe the key to first time success in the construction of a small steam generator that performs in a very satisfactory manner and one that doesn't. I have seen on the net and in books many notions and designs, one of which involved the use of 300 feet of 1/4" copper tube to run a Stuart 5A, Westbury's experiment proved that tube length alone is not the answer to success in making steam but it must have a place in raising overall efficiency.
In some discussions about flash boilers the separation from a feedwater heat function and the steam raising and superheating area is viewed as a physical point of some mystic significance. If you look at Doble, White and Serpollet cars they certainly were efficient but never as far as I am aware did any of these great engineers write about the critical nature of water velocity at that transitional stage where the absorbtion of the latent heat takes place. Nor do they seem to consider that point of any significance in their designs. Their boilers had long lengths of tube of several diameters and ended up with a section where the velocity certainly was in excess of a metre per second. Without experiment into this we will never know the point where transition from liquid to gas takes place and how dynamic the change of that point along the tube will be as power (heat input) is changed by the operator; and having discussed it before with others and thought about it at length; I don't think it matters one jot! Of one thing I am certain, once the smallest bore tube has been reached that tube section must remain the same until it reaches the engine. I have seen set ups where the steam leaves the monotube and goes into manofolds and convoluted passages and is therefore allowed to expand cool and slow down as it gets to the engine----Why? Why do that? One answer I got was, "Well to me it is obviously being too hopefull expecting the steam to get to the engine through that tiny tube"! To my mind it has already gone through 30 or more feet of it, what effect is another two feet going to have? The small tube loses heat far slower than big tube and it is far more efficient to lag that diameter so my 4 mm steam tube goes straight to the steam chest. Get the steam to the engine ASAP and let as much expansion as possible take place there rather than en route, that is my view at the moment.
The crucial thing is in the design of the heat source, there is obviously an area/volume where the heat will be the most intense and that is where the small bore section has to be. If the water begins to vapourise in the feedwater heater so what, it will soon be accellerating along the hot bit and it won't stay liquid for long. When I fit the feedwater heater section it will be up what is now the funnel; it will be 6mm or 8mm tube and will be fed through a cone into the 4mm diameter tube until it gets to the steam chest.
This brings me back to the question of tube length. The longer the tube, the more heating area = greater efficiency. Yes, but there are limitations and in small sizes pumping effort is a very significant limitation. I want to try a feedwater heater section above the monotube in the smoke stack and because this area is unlikly to have boiling water in it, feedwater velocity is of much less significance. This then permits the use of bigger bore tube for the feedwater heating section of the system which will help with reducing pumping effort. Accepting that there is NO WAY of predicting where along the tube the water actually boils from measurement the exhaust temperature at the chimney top is only about 300 C. and boiling point at 100 psi is about 170 C. it is far less likely to boil water in the chimney than right in the fire. That is as far as the argument needs to go in my view.
The relative merits of flash or conventional Boiler
Conventional boiler merits.
1. The containment of a mass of heated water makes power control as simple as a carburettor on an IC engine.
2. The complications of pumps and pump control on a flash plant make the conventional boiler more reliable especially in the smallest sizes. 3. Pressure control in a heated pressurised tank, using a safety valve is essential for safety and very useful when throttling with a simple valve. 4. The pressure controlled tank of heated water is a store of instantly available energy in its latent heat. This latent heat is the source of the destructive power of a conventional boiler explosion.
1. Requires regular pressure testing.
2. Is heavier than any self respecting flash unit of the same power.
3. Limited in its capacity to safely contain very high pressures and temperatures
The Latest Monotube I have Built
The pictures in this paragraph depict a monotube I built quite recently for use by a student at Southampton University and I make no apologies for the fact that it is a bigger version of H H Groves typical airborne Monotube design. The frame is of 1" x 1/16" 316 Stainless steel strip made to operate mounted in a vertical furnace of lagged stainless steel tube of about 5" bore. The most tedious job was striking all those slots in the spacers. I did this by mounting a 4mm thick angle grinder wheel in my off hand bench grinder and making a special tool rest which is grooved to support the thin material as it is cut. I wore out two wheels to get the job done which I thought was reasonable thin stainless is very hard on the wheel. I tried stacking all four up together and do them all in one go but it was far more hard work on the wheel and on me getting the cut made. The University TIG welded the frame together after I had tacked it with my Oxy/Acetylene.
The tube was 3/16 Dia. Copper/Nickel brake pipe which serves well enough as a monotube but I did melt the one I built for my little launch so the new monotube will be of Stainless Steel. I thought the Stainless would be a frightful price but it was not much more than the brake tube! Twelve Metres of 4mm stainless cost £40 and the same length of Copper/nickel was going to set me back £28---no contest!
A new Monotube for Skylark
The following pictures depict the new Skylark monotube as I built it and made the small adjustments necessary to make everything fit.
Frame Stretchers (3 of 4) The frame stretchers and rings are of the same 1" (25mm) x 16swg. (1.6mm) 316 st/stl. that I mentioned in the previous paragraph. The struts or Stretchers have to be cut with 30+ slots in their 16" (406mm.) length. The whole assembly is inserted into a piece of 4" (100 mm) Mild Steel tube which is well insulated with Mineral Wool and layers of alluminium foil. The heated core is 4" (100 mm) Diameter and the outer case of the boiler is 15.5" (340 mm) diameter giving a total of 5.5" (140 mm) of surrounding insulationStretchers, Rings and 2 clamp jigs The first two pictures shows the components of the frame, four spacer rings four vertical stretchers and two spacers which I made to hold the stretchers in position for welding. The third picture is the simple right angle section steel jig to which I clamp the rings and stretchers before welding. I have no TIG welder and I use Oxy/ Acetylene for all my stainless welding which of course uses much more heat in the process---which causes more distortion. Alignment Welding Jig Not surprisingly the biggest problem I found in making this particular frame WAS distortion; made much worse because I did not think about it enough! Last time, for Southampton University I just tacked it together using minimal tacks with Oxy/Acetylene, the University TIG welded it permanently which itself uses far less heat so there was very little distortion. The complete new monotube Next time I may use a piece of tube to line the rings up and I will weld from ONE END. This will allow the weld to distort the stretchers as much as it needs to and permit correction as required before welding the next ring into position. Gas welding stainless is not a big problem but it uses a glass flux which goes black and is a devil to remove so the appearance of the finished product is not wonderful. However a furnace rarely improves the appearance of anything so this is not too much of a worry! It ended up reasonably straight and was a good fit in the furnace tube.
The hot end and concentric coilsI changed the design at this stage as a little arithmetic told me I could get the whole of one 20 foot (6 metre) length of tube into an inner core only 16" (400 mm) long less a metre or so for lead out length. Looking at typical albeit lightly blown oil heaters it is very noticable that the flame tongue streaks straight through the middle of the furnace space so this time I tried to pack as much tube in that area as I can. This is why the outer coils look a bit ragged and badly spaced because there was space to spare on the outside. I am convinced that how the tubes are presented to the heat source and how near optimum the fuel/air ratio is kept is very important to overall efficiency in monotube steam sources.
How not to run Monotubes This is born out by the fact that in the steam model hydroplane, changing from one big burner to three smaller ones yielded more steam and higher speeds. Skylark's outer boiler casing was made by the previous owner who deliberately made it look as much like a coal fired boiler as he could, just for the fun of doing it, I may change it one day but for the moment I quite like the joke of explaining how little coal it uses! I have now made two cores for this boiler and each was smaller than the last and smaller than the one which was in the boat when I bought it. This is how and why I created space for so much insulation. All the added insulation and concentration of heat proved too much for this the second core in Skylark! The copper/nickel alloy monotube became blocked with black copper oxide powder and caused this failure which melted the tube and damaged the pressure gauge. It made a pop no louder than opening a can of lager and made me one of the worlds totally converted monotubists. The new core whilst more compact carries an identical length of tube about 36 feet (10 metres) actually in the fire, I have done this deliberatly to gauge any increase or loss of boiler efficiency that may be caused by the changes of monotube form and insulation. This latest core has modified form being of the same overall diameter but 2" (50 mm) shorter and with more tube concentrated in the centre, nothing else has been done of any significance. I really want to know what is going on in these steam systems. If this change betters things, the next change will be a blue flame burner then a chimney feed water heater. All being modifications of the same boat, engine and propeller.
A Few Words about Materials
The core of the new boiler is 100% stainless steel however even this remarkably heat resistant steel is no match for prolonged use at red heat and beyond. If you look at the burnt out end of the last monotube the case is made of stainless steel chimney liner which I thought might last 40 hours, it began to fail well before that and I had to fit another inner liner to prolong its life. The problem is much worse than in a racing hydroplane where the boiler may only be used for a few hours in a years testing and racing. I want 100 hours continuous use as a starting point. The outer case (or liner) was of 0.005" (0.12 mm) thickness and it began to fail after maybe 10 or 15 hours of use, the new liner is of 0.062" (1.6 mm) mild steel which has an inner liner of 0.024" (0.06 mm) Stainless steel protecting the first 6" (152 mm) of the hot end of the assembly. You can see from the damage that not only the tube has burnt out, so has the frame which was made of 0.010" (0.25 mm) stainless steel sheet. Notably all this damage is concentrated in the first lower 5" (127 mm) of the assembly's total length of 18" (456 mm). In fact I am quite impressed by the longevity of mild steel in the furnace area clearly it lasts less time than stainless but not say 100 times less it has maybe a third the life of stainless in the same circumstances, with the lower 6" of the mild steel monotube case protected by the replacable inner liner I am fairly confident that I will get maybe 50-100 hours of use out of it.
Changing Materials and Metal Sections
The above notes on building this new monotube is not a recomendation for anyone to follow! I am already looking to new ways of making my next furnace and monotube built for 1000 hours of continuous use, provided the pump never fails to deliver feedwater I do believe the steel of the monotube itself will make it for 1000 hours but the steel liner and sheet frame no chance. Nimonic steels are a possibility but I do not want to bother with that, I think simpler and cheaper methods will work just as well. The tube itself is super cooled by the flow of water and steam through it. The outer case has no such benifit but it also has no structural function either, it supports nothing but itself, all it does is keep the hot gases close to the tube. I can see nothing but benifit by dispensing with a metal liner altogether and making a close fitting furnace space of furnace brick and genuine furnace cement with the monotube on a frame suspended concentricly within it. The frame has a support function which is of real utility especially if overheating does occur; in my experience it almost certainly will, one day. Sheet section steel is actually hopeless and although the new frame is over ten times thicker it will still only last perhaps 50 or 100 hours if current experience is anything to judge by. I am instead thinking in terms of using 0.187" (4.75 mm) or 5mm diameter stainless rod this will give a far greater thickness of material to waste away with far less exposed area per unit mass and an ever reducing area as it wears and burns away. I managed recently to aquire a few Stainless Steel welding rods of 2 mm diameter and provided one is reasonably deft and quick very sound welds can be made on this size (0.187") stainless rod with a standard ac welding set. The same basic form may remain with rings and stretchers but all made of stainless rod with the slots made of short lengths of straight rod. This construction may well allow use of spot welding to great advantage, a small jig of copper would help greatly to hold components at right angles. Food for thought.
At some future time I will also go into details like how to automatically control steam temperature (it is perhaps more important than the pressure). The likely limits to power up to the 3/8" (10 mm) bore to which the above table probably applies. Lubrication at the upper limits of temperature, the use of solid lubricants and posh oils. How to estimate a value for the real pressure inside the monotube, if indeed you want to know it
That is how I see small bore monotube design and is as far as I have taken it to date. More will follow as I have notes, pictures and drawings to make up perhaps a further 20 pages but the pay is not good and the workshop beckons at every idle moment but there will be additions to these pages as time permits.
(SACA Board member Tim Nye, learning that I was planning a visit to the University of Michigan’s Buhr Shelving Facility, asked me to scan the following article. It is an English translation of a Czech article, right at the end of WW2. It is fascinating in that the Czech engineers were running a stationary steam engine without cylinder lubrication, instead using carbon rings to seal the cylinders. Ed.)
HIGH SPEED STEAM ENGINE WITHOUT LUBRICATION
By H. Frank and J. Rais. (From VDI Seitschrift, Vol. 89, Nos. 5/6, February 3rd, 1945, pp.6466).
(Translation appearing in The Engineer’s Digest, October, 1945 Vol. 2, No. 10.)
A STEAM Engine to operate without cylinder lubrication has been designed and built by the Skoda Works (Czechoslovakia – Ed.) for a special purpose, where oil-free exhaust steam and highest economy at even partial loads are vital requirements. The engine was built for an output of 440 h.p., with live steam of 43 kg. per sq. cm. pressure and 380 deg. C. temperature, the back pressure being 7-9 kg. per sq.cm.
(steam at 612 lbs. per sq. inch, 716 degrees F and 100-128 psi back pressure. This engine was briefly mentioned by Stan Jakuba in the April/May/June 2000 issue of the Bulletin. He noted it had a water rate of 18.3 pounds per horsepower-hour. This poor water rate is undoubtedly due to the low expansion ratio responsible for the high back pressure. It’s almost certain this industrial engine was designed to produce a high back pressure so that the exhaust steam could be used in other industrial processes. Ed.)
Aiming to secure oil-free exhaust from a reciprocator, the Skoda Works had carried out extensive experiments with regard to the use of carbon seals. However, these experiments, conducted since 1935, had been confined to considerably lower pressures. Thus, when faced with the present task, a new approach to the problem had to be made. The new series of tests were concerned with finding the most suitable type of carbon material, most suitable, that is, with regard to mechanical strength, thermal expansion, wear, and ability to withstand high operating temperatures. The most suitable material for the piston and the piston rod had also to be ascertained. Furthermore, an existing engine was equipped with carbon seals in order to measure leakage and other data. Carbon is adversely affected by the presence of oil, a sticky mass being formed which exerts an abrasive action upon the piston rings and wears them down with great rapidity. Particular attention had therefore to be paid to preventing lubricating oil from the crank case, from reaching the carbon seals. In this respect the provision of duplex scraper rings with inter-drainage proved most helpful. These rings are now made of sintered iron in place of bronze, as hitherto used.
(This section can be interpreted to mean that the piston was affixed to a piston rod which, in turn, was reciprocated by a crosshead. It’s impossible to speculate on whether it was single or In this manner the crankshaft, connecting rod and crosshead could all be oil lubricated without fear of introducing oil to the carbon rings. Since the piston has no appreciable side loads, likely not even contacting the cylinder wall, no lubrication would be required for anything but the piston rings. Ed.)
Carbon is a very good material for sealing purposes and by no means inferior to a metallic seal provided the rubbing parts to be sealed are as hard as possible and have a mirror-type surface finish. Should this not be the case, carbon particles will lodge in any existing pores and wear of the carbon rings will be inevitable.
A horizontal engine design had to be ruled out for reasons of cost, and a vertical design had therefore to be resorted to. A multi-cylinder design had to be chosen, since large size carbon seals are net feasible because of danger of breakage. It was, moreover, necessary to decide upon a single-acting engine type in order to eliminate the stuffing boxes. The specified engine output called for a six-cylinder design with a bore of
199 mm. and a stroke of 200 mm., the engine speed being 750 r.p.m. This results in a mean piston speed of 5 m. per second, which is a high value hitherto rarely used in steam reciprocator practice.
(bore of 7.835 inches, stroke of 7.874 inches at a speed of 984 feet per minute, similar to that of some Doble engines – Ed.)
(The magazine illustrations weren’t sometimes too clear. The magazine was almost 70 years old and it’s possible that British wartime rationing didn’t help as regards paper and ink quality.
The drawings have been either modified or replaced as possible. Absolute reliance on the images should not be taken as they are best interpretation. Ed.)
Upon removal of the cylinder head, the carbon rings (a), as shown in Fig. 1, are slipped over the piston (d) together with the ring carriers (b). Circular leaf springs (e) serve to press the carbon rings lightly against the wall (f) of the cylinder. The piston crown is connected with the piston rod by means of the bolts (h). As these bolts exhibited fissures after short time in service, they were subsequently replaced by longer ones. The method employed for sealing the valve spindles is outlined in Fig. 2. Here it will be seen that the carbon bush (b) serves both as guide for the spindle (a) and as first stage gland, the steam pressure being throttled to a certain extent by the labyrinth-action of the grooves provided in the carbon bush. Sealing of this carbon bush against the valve body is effected at top and bottom of the bush by means of the elastic copper packings (c), the required degree of compression being exerted by the threaded gland (d).
The stuffing box proper is constituted by the ring carriers (e)containing the carbon rings (f). Each of the latter is composed of three circular segments, the segments of adjacent rings being staggered by 60 deg. (Detailed section A-B in Fig. 2). The carbon segments are pressed against the valve spindle by means of the insular leaf springs (g). Furthermore, locating pins are provided to keep the carbon segments from rotating. In order to prevent the leakage of steam to atmosphere, distance piece (h) is inserted below the two topmost rings, this annular distance piece connecting with the back-pressure steam space by means of the duct (m). The two topmost carbon rings therefore act only as seals against the back pressure of the engine. In this way steam loss is kept to a minimum.
The rings (i) and (k) act as oil wipers, with the leakage oil being led away through the opening (l).
The mutual angular disposition of the six cranks of the engine crankshaft is indicated in Fig. 3. The connecting rods are forged and milled in order to keep their weight to a minimum. The big end bearings are made in cast steel halves, while the crosshead bearings are of the box type. The light metal crossheads have wrist pins of special bronze. The crank case is a single welded piece in order to avoid bolting the crank shaft bearings; the latter are bolted to pedestals enabling the withdrawal of the crankshaft to one side without lifting it. The cylindrical crosshead guides are made in halves and can be easily removed together with the crossheads through the openings provided in the engine casing. In the original engine the piston rods and certain other parts were made of stainless steel, but this precaution was later found to be unnecessary.
The employment of a mechanical governor had to be ruled out because of the high engine speed and the large controlling forces required, and a pressure oil governor system was therefore adopted, as shown in Fig. 4. The pressure oil pump as well as the gear type lubricating oil pump are driven from the engine shaft.
Referring to Fig. 4 it will be seen that the small fly-ball governor (b) acts upon the pilot valve (c) of the slave cylinder (d). Valve control is effected in a novel manner, there being a cut-off control lay-shaft in addition to the main lay-shaft. The admission valves (e) are controlled by the cams (g) and the exhaust valves by the cams (h). The main lay-shaft revolves at constant speed, while the angular position of the cut-off layshaft relative to the main lay-shaft can be adjusted by shifting the pinion (i) by the movement of the piston of slave cylinder (c). Electrical remote engine speed control is provided. The engine is equipped with lubricating oil and pressure oil coolers, oil filters, and an emergency governor with oil hydraulic operation of the throttle valve. A manually operated pressure oil pump to set up the required oil pressure for starting is also provided. Provision for the absorption of thermal expansion is made at all vital points, including the steam piping.
The steam supply line from the boiler was laid out with a minimum of bends, a distributing header being provided close to the cylinders. From observations made at points of the live steam connections close to the admission valves, it was found that there prevailed a weak steam oscillation of a frequency corresponding to the rotational speed of the engine. In addition to this, higher harmonics and a certain amount of non-harmonics were also found to prevail. The most suitable means for the suppression of these oscillations has not been found as yet. As the compression amounts to about two-thirds of the admission pressure, there also occurred a small amount of vibration of the admission valves, but this could be eliminated by changing the valve springs.
Compared to a slow speed poppet-valve engine of equal power at 125 r.p.m., the present engine affords a saving in weight of some 60 per cent. At the end of August,1944, the engine had been in service for about 8,000 hours without showing any marked wear of the carbon rings. The amount of cylinder lubricating oil saved during this period amounts to more than 5,000 kg. The guaranteed specific steam consumption was 11.2 kg. per kW.-hr. (18.4 lbs. per h.p.-hr. - Ed.) with a tolerance of +5 per cent, with a load of 410 h.p. This compares with a measured consumption of 11.95 kg. per kW. hr.,(19.6 lbs. per h.p.-hr. – Ed.) that is, +6.7 per cent in excess of the guaranteed consumption. From diagrams taken at a later date, it was, however, found that two cylinders showed insufficient compression owing to faulty adjustment of the valve control. It is therefore confidently expected that after proper adjustment has been made the guaranteed steam rate will be met without tolerance. The indicator diagrams reproduced in Figs. 5 and 6 were taken with an electrical indicator. They clearly show the resonant oscillations occurring during the admission period.
(A couple of notes seem worth mention. It mentions that the cylinder walls should be quite hard and as smooth as possible. This seems reasonable as graphite is soft and would wear away against an even mildly abrasive surface. Industrial hard chrome (not the stuff put on cars and motorcycles for the sake of being shiny) sounds like it might fit the bill, if polished. To be clear, this would be the kind of chrome plated onto injection molds to reduce wear … and other such heavy-duty work.
Hopefully the article has been of interest. It would seem to follow that, if this approach worked on engine cylinders, it might also be valid for piston valves. It becomes more debatable for slide valves given the pressure applied to the sealing surfaces.
After having slaved over a hot keyboard to put the article into a computer, and reworking some drawings, Tim Nye pointed out that that I had missed the fact that Josef Rais, one of the authors, had previously taken out patents on carbon piston rings and seal. The US patent, which is probably the most easily accessed, was applied for in March of 1934 (originally April 21, 1933 in Czechoslovakia) and was granted on April 4, 1939. It carries the title “Packing Ring for Sealing the Pistons and Piston Rods and was assigned to the Skoda Works in Pilsen, Prague, Czechoslovakia. I have to thank Tim for this observation, it brings the article into much clearer focus. Rais makes the case for his patent, as follows:
“This invention relates to a new and improved type of packing ring for sealing the pistons and piston rods of reciprocating engines and machines using working cylinders and reciprocating pistons. The known constructions of engines and machines of this type suffer from the disadvantage that the packing members must of necessity be lubricated with some special lubricant supplied from without. This requirement results in a considerable increase in the cost of running, and expensive means are necessary for reducing the quantity of lubricating oiI to the minimum. In steam engines, the lubricating oil contaminates the exhaust steam, so that the latter cans not be used for certain purposes, since it contains excessively large quantities of oil.
In the case of compressors, the lubricating oil can be caused to ignite. In consequence of the increased air temperature, thereby resulting in an explosion and hence the destruction of the entire machine. (When working with 5,000 psi air compressors, while in the Navy, we used special vegetable based oils for cylinder lubrication specifically to avoid these explosions. Ed.) Furthermore, the coolers are apt to become fouled by the lubricating oil, so that a special oil eliminating device becomes necessary. In the case of compressors in which a lubricant other than oil is employed, the pistons must be provided with soft packing means, for example cups, which are, however, comparatively short lived. In the case of refrigerating machines also, the lubrication with oil, glycerine, and other lubricants often gives rise to troublesome disturbances. Similar inconveniences due to the necessity for lubrication occur in the case of internal combustion engines also.
The present invention overcomes these drawbacks by virtue of the arrangement that the packing members of the pistons or piston rods, or of both, consist of rings of carbon, graphite, or similar frictionless self-lubricating material, which rings are so resiliently mounted relatively to spring metallic supporting or holding means, that the necessary radial resiliency is provided without any independent lubrication whatever.
These carbon rings are inserted in metal holding bushes, both the ring of self-lubricating matter's and also the resilient metal holding means being cut through by a single cut, for the purpose of enabling the entire packing member to be resilient radially.
The packing ring according to the invention is rendered particularly well able to withstand the strains and stresses to which it is subjected by virtue of the arrangement that the ring consists of two coaxial independent rings loosely mounted one upon the other.”
Rais notes: “In the hitherto known constructions of packing rings of carbon, graphite, or similar material the ring is either divided into a plurality of segments or else is rigidly connected to a metallic base. The first mentioned principle of construction does not ensure a perfect seal nor a uniform pressure of the packing ring against the co-operating surface, whereas with the second principle of construction the Independent stressing of the carbon packing ring is prevented, and in addition detrimental stresses are transmitted from the underlying base to the carbon ring whereby either the connection between the carbon ring and the metallic underlying base or else the carbon ring itself is damaged.
These disadvantages are overcome by the present invention, by virtue of the arrangement that the metallic ring is loosely inserted in the carbon ring, with possible locking against lateral displacement. In accordance with the invention, the packing ring may for this purpose consist of two coaxial and independent rings loosely mounted one upon the other. These two rings are mounted one upon the other without any rigid interconnection whatever, with the result that the resilient action of the metallic ring is uniformly transmitted to the carbon packing ring. The sealing action of a packing ring constructed in accordance with the invention can be increased or reduced as required in the various cases of utilizing the rings in machines by choosing suitable metallic resilient material for the production of the resilient metallic ring. The seating surface between the two rings can be cylindrical; but may with advantage be provided with one or more grooves of any desired cone figuration for the purpose of preventing axial displacement. Packing rings constructed in this manner permit of radial movement of the ring performing the packing function. In this case, however, if the grooves be of dovetail or other shape, it is necessary to provide such connection between carbon ring and metallic ring with an amount of play which admits of displacement within limits permitting of perfectly uniform resilience of the packing ring.
The resilient packing ring according to the invention is cut through in a normal manner at one point on its periphery, the cut in the packing ring and that in the metallic ring but either coincident or in offset relation to each other.”
The following illustrations are all derived from the patent, while the abbreviations in the table replace the number designations used to describe patent features (on the theory that it might be easier to remember MR stands for “metallic ring” rather than the number 13, or whatever).
Figure1 shows three rings installed in the piston while Fig. 2 describes the rings themselves.
Figures 3 through 8 show a number of variations on the piston ring, these differing in the manner used to locate the carbon ring inside the metal ring; with Fig. 3 having no mechanical retention whatsoever other than contact with adjoining rings or piston grooves.
Figures 9 and 10 consist of packing assemblies holding multiple carbon rings.
Figures 11 through 13 show pistons built up in segments, which serve to entrap the packing elements. The bushings are either a springy retainer or are backed by leaf or helical springs. The stops distribute the spring load against the bearing surface after the carbon rings have reached the worn in state. Thus, the springs are actually a temporary expedient used to break in the packing element.
Figs. 14, 15, 17 and 18 also show sections of modified forms of packing rings inlaid in the material of the shell of the piston. Fig. 15 is a plan view of Fig. 14, and Fig. 18 a plan view of Fig. 17. In both instances, the split halves of the bushings connect with a tongue and groove to provide tighter joints.
Generally speaking, the above embodiments are used with split, built-up pistons. Figures 21 and 22 are designed to be installed into the groove of a solid piston. Leaf springs underneath force the carbon ring against the cylinder walls while the stops are pins driven into holes drilled into the piston grooves from either the top or bottom of the piston. The rings are made in halves and use tongue and groove joints to promote tightness.
Rais noted: “In accordance with the invention the packing ring may be constructed in such a manner that its resiliency in a radial sense is effected by metallic means provided beneath the ring.” This implies that he understood the metallic ring would supply the resiliency required to hold the carbon packing in contact with the sealing surface but did not rule out the natural resiliency of the graphite itself.
Today, we might have a greater range of options. At least two companies manufacture carbon materials engineered with an array of properties. Graphitar products are manufactured by US Graphite in Saginaw, Michigan while Superior Graphite is headquartered in Chicago, Illinois.
Superior Graphite has been in business since 1917 while US Graphite was a spinoff of the Wickes lumber business and was founded in 1895 to exploit then-recent graphite discoveries in Mexico.
The following comes from the Superior Graphite website found at: http://graphitescarbons.superiorgraphite.com/Asset/RGC-Brochure.pdf
(RGC stands for ‘Resilient Graphitic Composites’, Ed.)
US Graphite sells what appear to be similar engineered graphite products under the tradename ‘Graphitar’. There are a wide variety of Graphitar products with specific properties for a range of applications. These can be molded directly to shape, or machined, whichever is advantageous. The company website shows their products being used for mechanical seal faces, as bearings (dry and water lubricated) and to form vanes, rotors and pump pistons. Perhaps some of these engineered carbon products have a place in modern steam automobile engineering.
Data sheets for their various products include such data as resilience, strength, hardness, porosity, temperature limits, PV factors, oxidation and chemical resistance can be found at: http://www.usggledco.co.uk/Resources.
The Bulletin staff would enjoy any experiences you may share regarding carbonaceous materials as applied to steam engines.
The Development of a Steam Powered Motorcycle
The following article covers the basic design philosophy for an attempt at the land speed record for a steam powered motorcycle and perhaps the outright record for any steam powered vehicle.
As a starting place for a steam powered land speed record, a motorcycle is a terrible idea. The restricted space envelope and poor aero-dynamic characteristics make it the worst possible concept. However, not to be daunted that is what we chose. The decisive factor was because we had this small Bower and Bell engine, which was an Abner Doble inspired design, it is too small for a car, but deserved to be used in something. Our love of motorbikes and the idea of a steam powered motorbike is more appealing to us than the ultimate record itself, we have used a Suzuki Hayabusa as the donor vehicle.
The basic formula pertaining to drag is: Drag = Cd x (1/2 x density of air x velocity2 x Area), where Cd is the co-efficient of drag and Area is the projected frontal area. As we can see, drag increases by the squared function of speed. The two most important factors that we can control in design space is frontal area and the Cd.
A motorbike has a relatively small frontal area, which is good,. However, even fully faired racing motorbikes struggle to achieve better than a Cd of 0.6. This compares to 0.3 for a modern road car, a Streamliner can have Cd as low as 0.12.From the RSR Bonneville Aero-Horsepower & Drag Loss Calculator: available online at: -
Coefficient of Drag: Street, faired motorcycles are notoriously inefficient aero-devices with Coefficient of Drag (Cd) figures in the 0.6 range. For example, a Suzuki Hayabusa has a Cd of .561 whereas a Kawasaki ZX-12 has a Cd of 0.603. Modern cars often have paid close attention to aerodynamics and may have Cd figures of 0.3. Streamliners may have Cd figures of under 0.2, perhaps as low as 0.15 or in some cases figures of 0.10 have been achieved.
Frontal Area: Reducing frontal area is key to going fast as the horsepower requirements go up exponentially as you push that "barn door" through the air. You'll need a close approximation of your vehicle's frontal area in square feet to make this calculator entry. A Suzuki Hayabusa has a frontal area of 6.01 square feet. A Kawasaki ZX-12 has a frontal area of 6.09 square feet. Some streamliners like the Lambky Vincent have only 4 square feet frontal area.
Vehicle Weight: On shorter courses with asphalt surfaces and good traction weight is more of an issue than it is at Bonneville, where weight can aid traction on the slippery salt surface. Short courses are more of a drag race and accelerating extra mass is not a good idea. At Bonneville the big dogs will be on the long course with over six miles of salt with the clocks at the 2, 4, and 6-mile markers, so weight is not nearly as much of an issue.
Figure 1: An example of a record setting Streamliner at Bonneville
Figure 2: At Elvington airfield UK setting 80mph run
The engine was chosen due to availability and suitability (mainly size). In some respects this is not an ideal engine for the task. However, it was suitable and most importantly available!
The engine in question is a double acting Bower and Bell V twin, a modest 1.25 in diameter high pressure cylinder and 2.5-inch diameter Low pressure cylinder, the stroke is 1.5 inches with a fixed 50% cut-off. Various figures are bandied around for its power, approximately 30hp at 3000rpm with 1500psi has been quoted.
One owner from Scotland who carried out trials with a Dynamometer, has stated that he achieved 22hp at 840psi and a constant 1890rpm. Calculations carried out indicate correlation with the reported test results from Scotland. Interestingly using the same calculator with the quoted 1500psi and 3000rpm show around 32Hp from the Hp cylinder only. Alternatively calculating for both cylinders (including subtracting the negative work from the HP cylinder on its exhaust stroke) shows ~29HP as a single acting engine, if allowing for double acting, then power is ~58Hp.
We intend to push it as far as we can, using the spreadsheet I have created using 840psi, 1890rpm it predicts 20.8hp compared to the 22hp reported. At 3600 rpm, 2000psi and 900F, it predicts 94hp. I’m somewhat sceptical that the engine will produce this or indeed hold together.
However, that is what we intend to trial on the Dyno. As far as the spreadsheet goes, it is quite complex and is not a simple pro-rata affair. When data from other verified engines is entered, it predicts values commensurate with those reported. So, until proven otherwise, we have to believe the numbers at this stage!
The water and fuel usage are calculated at 743lb/hr of water and 8.96US-Gallon/hr of Kerosene at full power. The bike carries 53lb of water, enough for about 4 minutes running at full power. However, to go from a standing start to one mile only takes around 30 seconds, so this is ample for the purpose. Fuel has rather more in reserve, as fuel is consumed even when water isn’t, to maintain temperature and pressure, for example on the paddock stand before a run.
In theory the engine should hold together, as it has been proven to be quite happy at 3600rpm. The small (0.75 inch) crank throw, means that piston velocity is no higher than other steam engines with longer throws and maximum torque is generated at low rpm.
Therefore, if it doesn’t break at the start up, then there is no reason to believe it will fail at the high revs. However, since engine failure must be quite a credible possibility, the engine output shaft has been fitted with a bespoke free wheeling hub such that if the engine locks up, the rear wheel will remain free to rotate. See Figure 3 below
Figure 3:Sprag clutch freewheeling hub with water pump output shaft.
A mechanical water pump is fitted to the end of the free-wheeling hub output shaft. This delivers all of the water necessary. The capacity of the water pump is approximately 200% of theoretical demand, ensuring the ability to rapidly increase the water level within the steam generator if steam temperature is too high.
The water pump is driven by an eccentric, which can be changed to provide different water delivery, should testing reveal changes are required. Water must be added to the steam generator at start up by external means, as no electrical or hand pump is provided on the bike.
We have chosen to run the steam generator at between 900 and 950 Fahrenheit. The steam lubricating oil limit is 1000F. This increase in temperature results in reduced water consumption for a given power. Abner Doble typically used 850lb/hr at 850F as the requirement for a 100Hp engine. This aligns with the water consumption predicted by my spreadsheet.
The steam generator has been designed to output sufficient steam for 96Hp, which is 750lb/hr at 950F. The basis for all fluid velocities and required surface area has been calculated from the work of Abner Doble, including the required combustion volume. The steam generator has ~430 feet of 8mm OD tube for the water coils, 180 feet of 12mm OD tube for the steaming coils, 30 feet of ½ OD tube for the Normaliser and 30 feet of ½ OD tube for the super heater. The water and steaming coils are carbon steel for improved heat transfer properties. This minimizes the required tubing and the Normaliser and Superheater coils are 316L stainless steel to withstand the higher temperatures. The total weight of tubing is 120lbs and the internal volume is 0.3 cubic feet. If one considers that the required output of 727lb/hr equals 12lb/min and the internal volume is sufficient for ~9.5lb of water/steam, then simplistically the approximate time that a molecule of water entering at the inlet to the generator takes to subsequently exit the generator at 950F is (9.5/12) *60 = 47.5 seconds. At full power the velocity in the water tubes is 9ft/ sec, in the steaming coils 50ft/sec and in the superheater 75 ft/sec. Therefore, notionally the water spends 48 seconds in the water coils, 3.6 seconds in the steaming coils and 0.8 of a second in the superheater.
This might seem incredibly fast. However, comparing to Abner Doble’s design for a 100Hp generator producing 850lb/hr of steam at 1000psi, (steam at this temperature and pressure has a density of ~1.39lb/cubic foot).
Producing 850/3600 = 0.236lb/sec.
The super heater and normaliser coils are 3/4inch OD, 9/16inch ID and 39 feet total length. The cross-sectional area is therefore 0.2485inch2. The volume in the superheater is (39*0.2485/144) = 0.0673feet3, so contains 1.39*0.0673 = 0.0936lbs of steam. Therefore, to produce 0.235lb per second, requires the superheater to be emptied 0.235/0.0936 = 2.5 times per second, 2.5 times 39 is 98 feet per second velocity!
Figure 4: Steam generator casing
For the generator controls we have a temperature sensor (referred to as TC1) at the end of the steaming coils, a Normaliser inlet at the start of the Normaliser coils for adding water to the top coils, should steam temperature be excessive. This is sized to allow for approximately 10% of feed water, followed by a pressure sensor (P1) and second temperature sensor (TC2) at the outlet from the generator. This follows broadly other successful control systems for monotube steam generators
Figure 5: Schematic of plumbing
At the steam chest on the engine, a third temperature sensor (TC3) and second pressure sensor (P2) is located. This is important for the generator control system as will be described later. The regulator is a fly by wire control. A suitably rated regulating stem needle valve is located between the generator and the bike engine.
The twist grip throttle is in fact a potentiometer. This electrical signal is used via a controller to move a stepper motor, which actuates the valve. The controller is within a military spec case for protection and has its own Uninterruptable Power Supply (UPS).
This consists of a stack of Super Capacitors, which charge as soon as power is connected to the bike. Should input signal or external power be lost, the controller automatically runs a valve close procedure, using the stored electrical energy within the Super Caps.
The control and power cables to and from the stepper motor and control box, are run within an armoured sheath.
As a back up to the regulator, a second valve is positioned upstream and is actuated by a hydraulic cylinder from the clutch lever. This ensures that the rider can manually shut of steam to the engine. However, once used, this valve can only be reset after all pressure is drained from the generator.
The water pump has a pulsation damper fitted at the outlet and a relief valve set at 2300psi to protect the pump and damper.
Between the water inlet to the generator and the water pump, are two check valves. Closest to the pump is a poppet check valve with polymeric seal.
At the generator inlet is a metal seat lift check valve, rated for 3280psi at 900F. Immediately after the metal seat check valve is a relief valve set at 2500psi. Should the pressure exceed this within the generator, this will ensure the liquid content of the generator is immediately released, (albeit flashing of to steam in the process), therefore collapsing the pressure.
The lower set water water-pump relief ensures that the mechanical pump can’t deliver water should the generator pressure be high enough to lift the generator relief.
The main electrical power for the bike is provided by 3 in number 24v Lithium batteries each containing ~10Ahr. They can sustain a continuous discharge of 15 amps (each) with 70amps peak.
At full load the fuel pump draws 8 amps, the air fan 20 amps, the control system 6 amps and the electrical boost pump (water suction delivery for mechanical pump) 3 amps. Total 37 amps.
The burner consists of a single flame tube containing an atomizing oil nozzle by DELAVAN. This is a Variflow nozzle that allows for modulation.
Figure 6: Burner schematic
This system allows for a minimum firing rate of just over 1gal/hr, up-to a maximum of 9.9gal/hr> This is achieved via three control modes. At constant pressure (100psi) the bypass line is controlled via pulse width modulation (PWM) of a solenoid controlled PRV.
This allows (with the nozzle we have selected) a firing range from 1.2 to 6 gal/hr. With the bypass line fully closed, fuel pressure can be increased (max 300psi) to give up-to 9.9gal/hr.
This is achieved through PWM control of the fuel pump motor. Air is supplied via an Electric Ducted fan intended for radio-controlled aircraft. Again, through PWM, the air supply can be matched to the fuel delivery to give the correct air fuel ratio.
Figure 7: 3 phase 24V EDF
It should be stated at this point, that what has been described to date reflects the current status of the design. An earlier version of both the generator and control system have been physically trialled, and speeds of around 80mph achieved.
This was very disappointing to ourselves, as we hoped to easily break the 100mph mark. However, subsequent investigations revealed that the generator was woefully under tubed, containing only enough tube for around 25hp, the burner could only deliver 3gal/hr.
The piston rings were broken on the valve gear due to standing for a long time, such that the engine was severely compromised.
With a fixed cut-off engine, it is extremely important that the generator can provide as much steam as is demanded, without the ability to reduce cut-off there is no ability to reduce steam consumption if pressure and temperature are low, this creates a vicious circle when it comes to monotube steam generators.
The control and protection philosophy are as follows. The normal operational envelope is controlled via a small computer, vis a raspberry Pi, controlling fuel, water and air.
Figure 8: Test bed for Raspberry Pi control system
If the system strays outside of the normal operational envelope, there exists a hard-wired relay-based protection system. This utilises industrial process temperature and pressure controllers, which hold the power relays made.
Should protection limits be exceeded, power is removed from the relays, effectively shutting down the burner etc, regardless of what demand signals may be being sent by the control system. Should this hard-wired electrical system fail, then beyond this, we have physical mechanical pressure reliefs and an emergency steam shut of valve hydraulically operated via the clutch lever.
A thumb kill-switch and a kill-cord are also provided, which have the effect of removing all power (shutting fuel solenoids etc). As previously described the regulator will then automatically shut upon loss of signal or external power.
Figure 9: Dummy combustion chamber to trial control system
Demand for fuel is calculated from the steam chest conditions. i.e. temperature and pressure within the steam chest determine steam density and thus the heat content of the volume of steam used. Steam density is calculated in real time by the PLC using a five-order polynomial equation I developed from steam tables. It is sufficiently accurate across the permissible operating range of pressures and temperatures that we are using. Swept volume, inlet cut off and rpm are then used to calculate mass flow rate of steam.
Figure 10: Formula for steam density used by PLC
Figure 11: Actual values for steam at 850F and 2000psi from
Steam Mass flow rate = Swept volume x cut off x rpm x steam density. Since inlet flow conditions and the effectiveness of the piston and valve rings will affect the real value, a multiplying factor is utilised. This can only be determined for a given engine via experiment and we have assigned this the notation leakage factor.
From the pressure and temperature of the steam in the steam chest, the specific heat content can be calculated. Firstly, the saturated steam temperature is calculated using again a formula developed by ourselves,
Figure 12: Formula for calculating Saturated steam temperature
Using this the specific heat content of the saturated steam was derived initially using formula developed from the IAPWS Industrial Formulation 1997. Page 10 of 14
Figure 13: IAPWS Industrial Formulation 1997 for region 2.
However, we have found that suitably accurate results for our region of operation can be achieved through the use of the following formula developed by ourselves.
Figure 14: Formula for calculating specific heat of dry saturated steam
Then the degrees of superheat above the saturation temperature are used to calculate the specific heat content due to superheat using a fourth equation developed. The sum of these values, is the total specific heat content of the steam being used by the engine.
Figure 15: Formula for heat content due to superheat
Figure 16: Formula that calculates the heat content of steam within the steam chest
So the formula calculates the heat content of steam at 850F and 2000psi as 2.64x106 + 5.508x105 which equals 3.191x106 J/kg or 1372 Btu/lb, this compares to 1371.84Btu/lb from the SpiraxSarco web site, an error of 0.16Btu/lb or 0.01%. The error increases to a maximum of around 1.5%, at 750F and 800psi. Provided temperature is maintained at above 800F the error across the conceivable pressure range in the steam chest is <1%, the error is largely associated with the Superheat term hence the correction factor.
The PLC using the above formulas calculates the specific heat content of the superheated steam several times a second. The previously calculated steam density and swept volume is used to calculate the amount of steam being removed.
Then the heat removed from the generator is simply the mass flow rate x the heat content.
The generator efficiency is estimated from the relationship between mass flow rate/ heating surface area, the generator has been sized to achieve ~80% efficiency at full power. Since we now have a value for heat removed in BTU/hr the fuel demand is simply calculated from:
approximations within this approach, will be such that equilibrium is unlikely to be exactly achieved, as such temperature and pressure will rise or fall during operation in proportion to the errors within the calculations.
There are various permutations. However, in simplistic terms (for the sake of this article) there are four basic scenarios, temperature to low or too high, and pressure too low or too high.
1. If temperature is low but pressure is good, then there is excess water in the generator, i.e. the water to saturated steam transition is too high up the coils. The remedy is to reduce feed water input.
2. If temperature is too high but pressure is good, then there is excessive heat and insufficient water. The remedy is to reduce burner input, and increase feed water (a normaliser can be used to control excess temperature. However, additional feed water must also be added at the bottom end to remedy the situation.)
3. If pressure is low but temperature is good, then again there is insufficient water in the coils. The remedy is to increase feed water and heat together.
4. If pressure is high but temperature is good, then there is too much water in the coils. However, both water and fuel must be reduced together.
Formula for temperature and pressure correction factors have been created. These are used to bias the fuel demand and water delivery. Therefore, the initial fuel and water demand, which was calculated from heat/ steam being removed, is either increased or reduced according to the conditions in the steam generator relative to the operating set point.
Clearly if either the boiler efficiency or the steam usage is significantly out, then the system will find equilibrium away from the desired set point. Therefore, trim pots are provided on the control interface to allow the boiler efficiency and or the leakage factor to be adjusted to bring the convergence in line with the operating point. An error in efficiency would result in issues related to heat input, errors in steam usage would result in issues with feed water rate.
If steam usage was underestimated, then we will see an increase in temperature with a falling pressure. This is because there is a reducing water level in the generator. Therefore, the leakage factor must be increased. Should pressure be high and temperature low, then steam usage is overestimated and leakage factor should be reduced. Note the reduction in calculated steam removal has the effect of reducing both feed water and heat input proportionately. Therefore, pressure should reduce. However, temperature will be maintained via the reduced water level within the coils despite the proportional reduction in heat input.
Should boiler efficiency be underestimated then we will see over temperature and over pressure. In this case boiler efficiency factor should be increased, this will reduce the fuel delivery. Should temperature and pressure be low, then boiler efficiency has been over estimated and the boiler efficiency factor should be reduced, thus increasing fuel delivery.
So leakage factor increases or decreases feed water and fuel in proportion
Boiler efficiency either increases or decreases burner input alone.
There are three control modes:
At its lowest fuel pressure setting and with the return line fully open, the burner delivers approx. 1.2gal/hr. In this setting the burner cuts in and out at the operational point for pressure and or temperature, the fan continues to run at low speed to prevent a damaging heat soak, which could otherwise occur. The system stays in minimum burn, whilst demand is less than the minimum burn value (1.2gal/hr). Speeds in excess of 30mph will be required before demand exceeds minimum burn.
Once demand for fuel exceeds minimum burn mode, the system automatically switches to PRV control. Now the system varies the PRV position in the nozzle return line to match fuel delivery to demand. As the demand increases, the PRV progressively closes. The return flow meter is used to calculate fuel delivery. However, as the PRV approaches fully closed, the low flow starts to make the flow meter readings unreliable. As such, an algorithm is used to calculate return flow from PRV position at the final stages of closure. Unlike in minimum burn mode, the system modulates around the desired operating point. As previously described the fuel demand and water is modified based on generator conditions. Therefore, if pressure exceeds the operating point, this results in a reduction in fuel and feed water. The reduction progressively increases the further from the operating point the system gets. If this results in reducing steam temperature, then the feed water will be cut back further still. If the steam temperature actually rises due to the reduced feed water, then feed water is increased. Should the control system fail to keep the pressure and or temperature within the upper operating band around the set point, the system will drop into minimum burn mode. Once conditions return to within the operating band, the burner will ramp back up to the required demand again. Should, however, even minimum burn mode not prevent further pressure and or temperature rise, then upon reaching the safety limit the burner and feed water will fully shut down.
Speed Control mode:
Once fuel demand exceeds PRV mode, the return line valve and PRV are fully shut. Now fuel delivery is varied by increasing fuel pump speed. This has the effect of increasing fuel pressure in the fuel rail. Fuel pressure can be varied from 100 – 300 psi and at 300psi this gives 9.9g/hr. Modulation (including shut down) is as described for PRV control mode.
Feed Water control
The water pump is driven from the output shaft of the engine via the free-wheeling hub Therefore, even when coasting, the water pump is driven via the back wheel. However, no feed water is available when stationary. The outlet from the feed water pump has a recirculation line back to the inlet port of the pump via a solenoid valve. When this valve is open, no water is delivered to the generator. It is a simple task for the PLC to modulate the solenoid valve to control the proportion of water delivered. In addition, an offtake from the pump delivery goes to a second solenoid valve and from thence to the normaliser. Should the stem outlet temperature be too high, then the normaliser solenoid valve opens and allows cold water to injected to the top coils of the generator. The feed water entering at the bottom has an increased pressure compared to the steam leaving the generator at the top, due to the pressure drop related to velocity within the generator. As such the pressure delta increases with demand and so the fixed orifice in the normaliser nozzle has been sized to deliver approximately 10% of the feed water rate for any given speed and demand. The normalizer nozzle should consist of an orifice followed by approximately 3 inches of shroud within the steam main. This shroud is heated by the superheated steam. The water spray entering the shroud (via the orifice) is heated and turned to wet steam within the shroud before it mixes with the main steam flow, ensuring good mixing and efficient heat transfer between the gaseous fluids. If water is merely injected straight into the super heater coil, then the water droplets bead like water dropped on a hot plate and the effectiveness of the system is much reduced, (remember at full demand the velocity in the superheater is >75ft/sec), with a mix of wet and superheated steam leaving the generator outlet. The water pump is fixed displacement, thus the feed water rate is calculated from engine rpm and validated by a flow meter within the suction line to the pump. A non-return valve on the pump inlet ensures that when in bypass mode, the internal pressure in the pump is largely maintained and not just lost back to the water tank. An electric boost pump ensures that pump inlet conditions are maintained to prevent cavitation.
Part two will follow after further updates to design and testing.