Compressed-Air Vehicles

Updated: 10 May 2013

Mekarsky Wikipedia link added

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This page refers expressly to road vehicles that are driven by stored compressed air to provide independent locomotion. Compressed-air locomotives now have their own page in the Unusual Locomotive section of the Museaum.

The principle of compressed-air propulsion seems very simple. Pressurise your storage tank, connect it to something very like a reciprocating steam engine, and off you go. At least you are spared the difficulties, both technical and medical, of using ammonia, petrol, or carbon disulphide as the working fluid.

Unfortunately there are still serious problems. If you have ever pumped up a bicycle tyre, you will know that the pump body gets uncomfortably hot quite quickly. Compressing a gas generates a lot of heat, and all this energy is lost when you store the air and it cools down. The losses can be reduced by compressing the air in two or more stages, and cooling it between the stages, but they are still substantial.
At the other end of the process, using compressed air to run an engine, the main problem is keeping the system working at all. When a gas expands it gets colder, and unless the stored air is perfectly dry (which it won't be) ice will start forming in the pipework and engine, and things will soon grind to a halt.

Compressed-air systems flourished, insofar as they did, in situations where the smoke, sparks and steam of the much more effective steam engine were not acceptable- in city streets, and down coal mines- and at a time before electricity was a viable means of propulsion. There were several compressed-air tram systems, though none proved very successful, and most were quickly abandoned. Compressed-air locomotives in mines lasted longer, but they too were eventually replaced by electric haulage. Now read on...

FIRST STEPS
The first compressed-air vehicle I have found so far was devised by Bompas, a patent for a locomotive being taken out in England in 1828. There were two storage tanks between the frames, with conventional cylinders and cranks. It is not clear if it was actually built. (Knight, 1880)

The first recorded compressed-air vehicle in France was built by the Frenchmen Andraud and Tessie of Motay in 1838. A car ran on a test track at Chaillot on the 9th July 1840, and worked well, but the idea was not pursued further.

Left: The Parsey compressed-air locomotive of 1847

The reservoir A was filled with air "compressed to as great an extent as was compatible with safety" which fed chamber B, kept at engine pressure by automatic reducing valve C. Pipe D fed the double-acting engine E. At F is the air recharge valve, and G is the safety valve. The locomotive was intended for coal-mine work, but again it is not clear if it was actually built.

In 1848 Barin von Rathlen constructed a vehicle which was reported to have been driven from Putney to Wandsworth (London) at 10 to 12 mph.

At the end of 1855, a constructor called Julienne ran some sort of vehicle at Saint-Denis in France, driven by air at 25 atmospheres. (350 psi)

THE MÉKARSKI SYSTEM

Most of the images and much of the information on the Mékarski system are displayed by courtesy of John Prentice, whose stunning exposition of the history of compressed-air trams can be seen at Tramway Information. Do not miss it.

Louis Mekarsky (the exact spelling is uncertain) was born in 1843 in Clermont-Ferrand , in the south of France, of Polish origin.

In Louis Mekarski built a standard gauge self-contained tramcar which was tested in February 1876 on the Courbevoie-Etoile Line of the Paris Tramways Nord (TN), where it much impressed the current president and minister of transport Marechal de MacMahon. The tramcar was also shown at the exhibition of 1878 as it seemed to be an ideal transport method, quiet, smooth, without smoke, fire or the possibility of boiler explosion.
Following this success, Tramways Nord used compressed air locos to pull horse trams on their Route E, Saint Denis to Place Clichy, beginning in February 1879. Air at 25 atmospheres (350 psi) was stored in eight reservoirs 0.3 m or 0.4 m in diameter, mounted transversely under the vehicle. These were in two sets, a main and a reserve set. The two-cylinder engine drove the front axle through the usual cranks set at 90 degrees to avoid stalling at dead centre; cylinder dimensions were a modest 125 mm bore and 260 mm stroke.

The compressed-air locos were soon withdrawn due to a number of accidents, possibly caused by icing in the pipes of the brakes, which were also worked by compressed air. This strikes me as an inherently flawed concept; if you ran out of air the brakes didn't work. A car where the brakes stopped working completely if you ran out of petrol would probably not be a saleable proposition. The servo brakes fitted to almost all cars these days retain enough engine vacuum for at least one serious stop if the engine ceases to run, and when that is exhausted the brakes still work, even if some serious foot effort is required.

Left: A bouillotte mounted on the front of a tram built by Mekarski and used in early trials in Paris. (Drawing 1875)

One solution to the freezing problem was the use of the bouillotte which apparently can be translated as either "hot-water bottle" or "hotpot". This was a vertical cylinder mounted on the front platform and was 0.35 m in diameter and about 1.5 m high. It was 3/4 full of water at about 180 degC, and at about 7 atmospheres of pressure. This warmed the air and also saturated it with water vapour. As the water vapour condensed on expansion, it gave up its considerable latent heat and limited the temperature drop in the engine cylinders. The condensation may also have helped to lubricate the cylinder walls of the engine, but I would suggest it diluted the lubricating oil and caused more friction than it saved.

Note the two pressure gauges, one showing the pressure of the stored air and the other the pressure of the air leaving the bouillotte and going to the engine.

According to La Nature, the storage capacity was 2640 litres, holding kg of air at 80 kg/cm2. This weighed 262 kg at 15 degC. The range was about 16 kilometres, by which point the storage pressure had dropped to 12 kg/cm2.

Left: The air control valve on top of the bouillotte.

The water in the bouillotte cooled quickly, and was initially reheated by blowing steam through it when the tram stopped to recharge the air tanks. Later a certain Monsieur Bonnefond introduced an internal coke firebox to provide continuous reheating of the water. This approach appears to have only been used in the Paris operations. See below.

Left: The Bonnefond bouillotte.

The Bonnefond system is all very well, but you immediately lose the main advantage of compressed-air power; ie the absence of smoke, ashes and potentially hazardous sparks. There is also the stimulating possibility of a boiler explosion. Considering that the driver already had his hands full dealing with the uncertain braking system, to expect him to stoke and supervise a small steam-boiler as well seems rather rash.

Note the butterfly valve at B to close off the chimney while dropping coke into the firebox.

According to La Nature again, the Bonnefond bouillotte consumed 0.6 kg of coke per kilometre.

Mékarski went on to run an extensive compressed air tram system in Nantes, opening in 1879. The first trams had ten steel storage cylinders between the frames and were charged to 30 atmospheres, reduced to 4 to 6 atmospheres at the engine, which was very similar to the Paris engine. An additional 32 trams were bought between 1898 and 1900; these were more powerful than the first series, with air storage at 60 atmospheres (840 psi) and with both axles driven to improve adhesion. The compressed-air trams were replaced with electric trams in 1911.

Left: A Nantes tram recharging with air and blowing steam through the bouillotte.

The bouillotte, with its distinctive handwheel, can be seen to the left of the driver.

Mékarski system tram networks were also built in other towns in France: Vichy (1895), Aix-les-Bains (1896), La Rochelle (1899), and Saint-Quentin (1901).

There is a Wikipedia article on the Mekarski system.

COMPRESSED AIR TRAMS IN GREAT BRITAIN

Compressed-air trams were tried in East London, Wantage, the Vale of Clyde, Liverpool and Chester. Various designs were used. None of the trials lasted long; the cost of operation proved excessive.

The Wantage experiments used two Mékarski-type trams built by the Compressed Air Engine Co Ltd, of 19 St Swithins Lane, London EC. The air was preheated by some sort of bouillotte, which raised its temperature to 312 degF, doubling its volume. Compressing plant costing Ł2000 was installed at Wantage Town tram terminus. A single-acting compressor pressurised six large air receivers to 450psi. Recharging a tram took 15 minutes. Quite why it took that long to fill the compressed air tanks is not easy to understand- for me anyway.

The range of the compressed-air trams was barely sufficient for a round trip. Matters were not eased by the 1:47 gradient at the end of the route, when the air pressure was at its lowest. The first compressed-air journey was made on Thursday evening, 5th August 1880

Mr. G. Stevenson, the line's engineer, estimated that the compressor used about 24 cwt of coal per day, but on such a sparse service this was far too high, as steam locos would only use 5 cwt per day.

COMPRESSED AIR TRAMS IN AMERICA

These articles are taken from the journal Manufacturer and Builder:

Street Cars Run by Motive Power

Manufacturer and Builder / Volume 10, Issue 5, May 1878

"The Second Avenue Railroad of New York city, has one of the Pneumatic Tramway Engine Company's cars. Upon each platform is a steel lever, by means of which the car can be started, stopped or its direction reversed. The car is of the same general model as that of ordinary street cars. It has six tubular air receivers situated under the floor of the car. The air is compressed by an engine which is standing at the side of the depot, and is introduced by a rubber hose into these receivers. That air passes through an engine situated between the axles, and propels the car."

"The car lately ran from 63d to 95th street and back in about 20 minutes, with two or three stoppages. It is claimed for the car thus inspected that it can be stopped more readily than the horse cars, and that its rate of speed can be increased to 30 miles per hour, while it can make 9 miles per hour and still not appear to go faster than the horse cars. The car which was run is only a model, and it takes about four hours to charge its receivers with air, but machinery has been ordered which will perform the work in less than a minute."

"One of these air engines, it is said, can easily draw a whole train of ordinary street cars. A company composed of 25 capitalists has been formed to manufacture cars upon the above model. It has already received an order for five from the Second Avenue Company. These will be used on the upper part of the Second Avenue route."

Compressed Air Locomotives in New York City

From Manufacturer and Builder / Volume 11, Issue 11, November 1879

"The Third avenue horse railroad has now in operation one small locomotive, which is used instead of a span of horses to propel one of their ordinary cars. The machinery is partially on the front platform and partially below the bottom of the car and under the side seats, which will accommodate about half the number of passengers that the car will hold. The propelling power is compressed air, which is stored up at the depot up-town by a stationary engine, and tapped by the car from its reservoir at every trip, the capacity of the reservoir in the car being sufficient to contain compressed air enough for a down and up trip."

"It appears to give satisfaction so far, and if this continues, it will afford great relief to the horses, which, when used on street cars, suffer much from the continual stopping and starting connected with this mode of travel. The Society for the Prevention of Cruelty to Animals will, we hope, encourage this new enterprise."

Revival of the Use of Compressed Air as a Motive Power
By Dr. P. H. Van Der Weyde

From Manufacturer and Builder / Volume 26, Issue 12, December 1894

"Lately an important problem has again been brought to public notice -- namely, the propulsion of street cars by means of compressed air, carried on the car itself."

"The solution of the problem requires the execution of two kinds of contrivances -- first, a reservoir strong enough to withstand considerable pressure, and, secondly, a motor machine to be put in operation by this pressure. The reservoir is by preference made in the form of cylinders, of say one or two feet in diameter, so that they can be placed under the seats of the car, and of a length sufficient to utilize all the space afforded. The motor is best placed under the floor of the car, now a common method in the electric trolley cars, while the regulating devices are on both platforms where the motorman performs his duty."

"It is evident that this system offers peculiar advantages, especially by reason of its apparent simplicity. The cylinders containing the compressed air -- the motive power -- are charged at the station and need no further attention, as is the case with locomotive boilers, where the chances of safety depend on the engineer and stoker. All the heavy machinery used for the production of the primary power is stationary, and no power is wasted to move it about as in the case of the locomotive, the only weight to be transported is the motor and the cylinders containing the compressed air. Summing up the advantages, they are:"

1. No dead weight of coal or fuel on board.

2. No dead weight of water, boiler, furnace, and other material which has to he stabled, the real primary motor, which is a stationary structure of large dimensions, and therefore economical, as the economy increases at a very large ratio as the engines are increased in size.

3. The compression of air is going on continually in the reservoirs, and is always connected with the gauges, so as to insure safety.

"The first application of this principle was seen some six or eight years ago at the Harlem station of the Second Avenue Railroad. It was intended for the propulsion of trains, and the compressed air reservoirs consisted of two huge cylinders placed horizontally, with a space between, through which the engineer could see the forward track while standing on the motor, and having the train of cars behind."

"A few years later I saw some interesting experiments of thie same character at the Delamater works, where pipes were laid to quite a distance from the works, and at which pipes the cylinders could take up new supplies of compressed air without going back to the supply station."

"A syndicate has been formed to introduce this system of street transportation, so that we will have another additional method in practice."

THE HARTLEY AIR-POWERED TRICYCLE

Left: A Compressed-Air Tricycle for mail delivery.

Nothing is currently known beyond the information in the New York Times article. No US patent appears to have been taken out by either Hartley or Stoll.

If the compressed-air-tank was installed "under the handle bars" this seems to indicate it wasn't very large, and it seems surprising that such a tricycle could cover thirty-three miles. Perhaps in reality it couldn't.

Thanks to Bill Levine for bringing this to my attention.

HISTORIC COMPRESSED-AIR CARS

Left: The Pneumatic Carriage Companie's compressed air car: 1898

The Pneumatic Carriage Company of New York City developed a car that ran on compressed air. The air is believed to have been stored in a steel cylinder running the length of the lower body; the storage pressure is not currently known.

From The Horseless Age for October 1898:

"In 1895, the Pneumatic Carriage Company was organized under the laws of West Virginia, with an authorized capital of $5,000,000, and with offices at 253 Broadway, New York. The organizers had been conducting experiments with compressed air motors for street railway service for several years, and naturally turned toward the motor vehicle when it received its first impetus in America. The president and manager of the company is A. H. Hoadley, who has been in charge of the experiments at the works of the American Wheelock Engine Company, Worcester, Mass.

The first carriage built by the company, illustrated herewith, was completed in November, 1896. It has seating accommodations for six passengers, weighs 2700 pounds, and will run 20 miles over ordinary good roads on one charge. A grade of 20 per cent is claimed to be surmountable. The wooden wheels are 30 and 42 inches respectively, and pneumatics of 4 inches diameter render riding as easy as possible. The motor, of the reciprocating type, weighs 400 pounds and operates at 350 revolutions, when the carriage is making 15 miles an hour. Ordinary compensating gear and hub steering are employed. In order to heat and expand the air before it enters the motor, it is surcharged with hot water, carried in the vehicle in a separate tank and kept at a temperature of 400 degrees Fahrenheit. Five pounds of water are required for each mile traversed. All the above machinery is spring-supported, to relieve it from the shocks of the road.

This carriage has been tested for the past year or more in the streets of Worcester and Washington, DC"

This account positively bristles with impracticalities. Note the very limited range, and the need to carry around a tank of hot water to heat the air; if five pounds of hot water were expended per mile, and the range was 20 miles, the contents of the full tank would have weighed 100 pounds. The engine appears to have been extraordinarily heavy at 400 pounds.

Note that the hot water was stored at 400 degF. The normal boiling point of water is 212 degF, so clearly it was stored under pressure. In fact, under considerable pressure, because water boils at 400 degF at about 230 psi- a greater pressure than that used in most steam boilers of the day. The water tank would have to withstand this pressure, so it would have to be a lot stronger and heavier than a simple tank. This clumsy and potentially dangerous setup seems to indicate that the Pneumatic Carriage Company had considerable difficulty in storing enough energy to heat the air, even for the very limited range that was claimed.

Therefore "filling up" would be quite a business. You would need a filling station that not only had a supply of compressed air (which I suspect was at considerable pressure- the later Mekarski system stored air at 60 atmospheres = 840 psi) but also a constantly-hot steam boiler working at an unusually high pressure. And with a 20-mile range you would need an awful lot of filling stations. You can see why this idea did not take off.

The following news item provides a little more information:

"A Compressed Air Carriage. Nov 1896"

"For some time past experiments in compressed air motors have been conducted at the factory of the American Wbeelock Engine Company, Worcester. Mass. These experiments have been very exhaustive, covering the application of compressed air motors to both track and road vehicles. To gather data for tbe latter class of vehicles, the Pneumatic Carriage Company, which is the name of the company working in this particular line, have just completed a two-seated carriage, which was publically exhibited in a procession held on Flag Day, Oct. 31, through the streets of Worcester, although close inspection was not allowed, inasmuch as tbe present vehicle is merely experimental and the company are not yet prepared to furnish specific information. President Hoadley states, however, that the experiments will be continued until a thoroughly satisfactory model is obtained, when steps will be taken to introduce compressed air vehicles for public service in cities."

"The Pneumatic Carriage Company has New York offices at 3S3 Broadway, connected with those of the American Wbeelock Engine Company."

CONTEMPORARY COMPRESSED-AIR CARS

There are several on-going projects for air-driven cars; see Wikipedia.

The French MDI Air Car is apparently no longer a live project; the domain name is for sale. Apart from straightforward compressed-air propulsion, they claimed to be also developing dual-energy engines, in which a fuel (petrol, diesel, oil, alcohol or gas) is burned in an external continuous combustion chamber to heat the air and give more range. The amount of toxic gases released is claimed to be very low.

One of the vehicles proposed had the following specs:

Weight Empty
220 kg
Max speed
70 km/h (43 mph)
Range (urban)
220 km (136 miles)
Reservoir Pressure
350 bar (5076 psi)
Reservoir Volume
175 litres
Refill Time
1.5 minutes

The claimed top speed was very modest, at 43 mph, and the range less than stunning at 136 miles. The company made the usual claims about the car being pollution-free, which is of course true in actual operation. But since compressed air is being used merely for energy storage, power will have to generated somewhere else. And proponents of air cars never mention that compressing air is inherently inefficient, with all the heat of compression lost.

The air storage tank was to be made of carbon-fibre wound on a thermoplastic liner. Kerry Stiff tells me:

"The storage vessel they were using is known as a Composite Overwrapped Pressure Vessel or COPV. COPVs are expensive, fragile and dangerous. They have a limited number of fill-discharge cycles. There is a pressure at which the overwrap fibre goes from compression to tension. Every time you cross this pressure value, rising and falling, you use up one cycle. COPVs must be filled very slowly to prevent overheating."

"NASA uses COPVs with great caution. The procedure for charging COPVs at KSC is so onerous that we charged them at CERN. These COPVs were not certified for transport under pressure on public roads. We had the road closed from CERN to the Geneva airport so we could transport AMS to the airport. AMS was airlifted to KSC by a US Air Force C5-M. The C5-M landed on the shuttle runway at KSC alleviating DoT issues in the USA. This was the coolest airplane ride I have ever had!"

OTHER COMPRESSED-AIR VEHICLES

The Odd Bicycle gallery of the Museum has a projected compressed-air bicycle as an exhibit. It looks completely impractical.

One of the most prestigious of the early motor cars was the French built Delaunay-Belleville. They built some big cars with 11.8 litre engines for the Russian Tsar in 1909. These were fitted with Saurer compresed-air starting gear, which could also be used to inflate tyres, jack up the wheels, or blow a whistle. However its most important feature was that the air reservoir was sufficient to drive the car for about 400 yards without even starting the engine, allowing the Tsar to make a quick getaway from an assassination attempt.
Given the history of Russia, this was not just a theoretical possibility. Tsar Paul I was murdered in his own bedoom in 1801. Alexander II survived assassination attempts in 1866, 1879 (twice), and in 1880, when the dining room of the Winter Palace was blown up, before finally running out of luck in 1881.

There is, of course, another and far less benign class of things very often powered by compressed air. Torpedoes.

EXTERNAL LINKS

Compressed air vehicles in general: aircaraccess.com
Interesting historical material, but some worrying references to what appears to be perpetual motion.

For French references, Google on "locomotive ŕ air comprimé". For example: tramways_mecaniques

Porter locomotive links:

www.railroadpix.com

www.pernet.net/~james1

www.cdmrr.com/porter.html

www.nrhs.com/web_exclusives/fireless_cooker

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