A BRIEF HISTORY OF AIR CARS

For half a century the air-powered locomotive was a serious contender for the top spot in transportation because of its obvious advantages: simplicity, safety, economy, and cleanliness.  Air engines were built first during a period of experimental daily use in metropolitan street transit during the 1880s and 1890s, by companies organized by inventors and air car advocates such as General Herman Haupt.  In New York City a building-sized 1500 horsepower compressing station was constructed for the use of the transit locomotives that were being tested there on daily routes.  Air-powered mining locomotives were manufactured routinely by steam locomotive companies.  Until the 1930s and 1940s the air mule had no serious competition from electric or internal combustion engines in mining because the heat and spark made them unsafe in closed-in and gassy places.

The term "air engine" disappeared from engineering textbooks between 1931 when William Lawrence Saunders died, and the end of the second world war.  Gas engines had been perfected, the power of the oil industry was established, and gas was cheap.

Serious interest in air cars was rekindled by the petroleum shortages of the 1970s.  There are now hundreds of patented designs for conventional, hybrid, closed cycle, and self-fueling air cars, as well as conversions for existing engines.

Categories of air cars (some categories overlap depending on the design):

• Conventional air cars stop every 50 miles or less to refill with very high pressure air in large tanks that take up a lot of space in a car that is probably underbuilt for lightness.  The car weighs a lot less when the tanks are empty than when the tanks are full.

• Hybrid air cars have both an air engine and a gas engine.  The gas engine runs a compressor and the air engine runs the wheels.  There is no need for large high pressure tanks since the car has a gas tank that is filled up periodically, the same as a Toyota Prius or any hybrid.  Heat from the gas engine can be used to increase the efficiency of air use in the air engine.

• Closed cycle air cars capture the air engine exhaust and recompress it.  Since the air is never expanded to its largest volume (atmospheric pressure), the compressor is smaller, so this would be a good feature in a hybrid.  Among self-fueling air cars (below), many designs are partially closed-cycle, re-compressing only a portion of the air engine exhaust.

• Conversion air cars use an existing gas or diesel engine that is modified to run on compressed air.

• Self-fueling air cars, which should be called extended range air cars, carry their own compressor.  While any air car can and should carry a compressor for regenerative braking, this class of air car is unique in that its compressor or at least one of its compressors runs almost all the time.  Probably not during startup but after the car is underway and moving down the road, it has a means of decreasing the energy cost of keeping the tanks "full" (= useful) compared to conventional compressors.  This class of air car and stationary air power plants with similar capabilities are the main point of my current research but this page ignores them completely to focus on the less controversial designs.

The Pneumatic Railway, 1880s to today

Like modern electric subway trains, the power supply was provided continuously by a pipeline laid along the track.  This concept was not practical at the time it was invented (1820s) because the materials were not available to make it work reliably.  A modern version appeared in Brazil in the 1980s, invented by Oskar H. W. Coester, and developed by Aeromovel Global Corp.

Preceding this was New York City's first attempt at a subway, in which a lightweight car fits more or less airtight in a wind tunnel and is blown along by very large fans from one end or the other of the tunnel.  Scholar Slawomir Lotysz is writing his doctoral thesis on the origins of air as a transport medium.  His study covers developments worldwide in the pneumatic locomotives of the 19th century.

The Mekarski Compressed Air Locomotive, 1886-1900

The Mekarski air engine was used for street transit.  It was a single-stage engine (air expanded in one piston then exhausted) and represented an advance in air engine technology that made air cars feasible: the air was reheated after leaving the tank and before entering the engine.  The reheater was a hot water tank through which the compressed air bubbled in direct contact with the water, picking up hot water vapor which improved the engine's range-between-fill-ups.

The Hardie Compressed Air Locomotive, 1892-1900

Robert Hardie's air engine was a going concern in street transit in New York City.  Air car advocate General Herman Haupt, a civil engineer, wrote extensively about the advantages of air cars, using the Hardie engine as his source material and providing much of the impetus for the New York experiment to gain support and succeed.  The engine was a one-stage expansion engine using a more advanced type of reheating than the Mekarski engine.  One of its new features was regenerative braking.  By using the engine as a compressor during deceleration, air and heat were added to the tanks, increasing the range between fill-ups.  Check valves were installed on the engine cylinders to admit atmosphere to the cylinder in case over-expansion of the compressed air produced a partial vacuum, allowing the engine to operate with full expansion.  A 1500 horsepower steam-powered air compressor station was built in New York City to supply the Hardie compressed air locomotives and the Hoadley-Knight pneumatic locomotives.

The Hoadley-Knight Compressed Air Locomotive, 1896-1900

The Hoadley-Knight system was the first air powered transit locomotive that incorporated a two-stage engine.  It was beginning to be recognized that the longer you keep the air in the engine, the more time it has to absorb the heat that increases its range-between-fill-ups.  Hoadley and Knight were also supporters of Nikola Tesla's disc turbine, for which they formed a propulsion company that didn't get off the ground.

H. K. Porter Compound Air Locomotives, 1896-1930

Inventor Charles B. Hodges became the first and only air car inventor in history to see his invention become a lasting commercial success.  His engine was two-stage and employed an interheater between the two piston stages to warm the partially expanded compressed air with the surrounding atmosphere.  A substantial gain in range-between-fill-ups was thus proven attainable with no cost for the extra fuel, which was provided by the sun.  The H. K. Porter Company in Pittsburgh sold hundreds of these locomotives to coal-mining companies in the eastern U.S.  With the hopeful days of air powered street transit over, the compressed air locomotive became a standard fixture in coal mines around the world because it created no heat or spark and was therefore invaluable in gassy mines where explosions were always a danger with electric or gas engines.

The European Three-Stage Air Locomotive, 1912-1930

Hodges' design was improved upon by European engineers who increased the number of expansion stages to three and used interheaters before all three stages.  The coal mines of France and Germany and other countries such as Belgium were swarming with these locomotives, which increased their range-between-fill-ups 60% by the addition of ambient heat.  It might have become obvious to the powers-that-be that these upstarts were a threat to the petroleum takeover that was well under way in the transportation industry; after world war two the term "air engine" was never used in compressed air textbooks and air powered locomotives, if used at all, were usually equipped with standard, inefficient air motors.

In fairness to Hodges, the original inventor of this type of engine, my contact in Europe told me that the three-stage design didn't work out to be as flexible as the two-stage.  Probably the higher efficiencies were available under certain ideal conditions and the rest of the time the third stage was a drag on the first two.

The German Diesel-Pneumatic Hybrid Locomotive, 1930

Just before technical journals stopped reporting on compressed air locomotives, they carried stories on a 1200 horsepower full-size above-ground locomotive that had been developed in Germany.  An on-board compressor was run by a diesel engine, and the air engine drove the locomotive's wheels.  Waste heat from the diesel engine was transferred to the air engine where it became fuel again.  By conserving heat in this way, the train's range-between-fill-ups was increased 26%.  A modern train engineer tells me that all  train engines these days are hybrids: diesel-electric.  And we are supposed to consider the Toyota Prius a miracle of modern invention?

Terry Miller, air car advocate

In 1979, Terry Miller set out to design a spring-powered car and determined that compressed air, being a spring that doesn't break or wear out, was the perfect energy-storing medium.  From there he developed his Air Car One, which he built for $1500 and patented.  He showed his air car from coast to coast and then went on to other things.  In 1993 he picked up his air car project again with the help of Toby Butterfield of Joplin, Missouri.  They developed the Spirit of Joplin air car with parts mostly donated by manufacturers.  Terry's air engines demonstrated the feasibility of building air engines with off-the-shelf parts on a small budget.  His engines used up to four consecutive stages to expand the same air over and over.  They ran at a low speed so there was plenty of time for ambient heat to enter the system and the possibility of low-tech developers to build engines cheaply at home.  Terry was instrumental in educating the founder of Pneumatic Options on air car fundamentals.  Terry's greatest contribution--and what makes him an air car advocate, not just another inventor--was that he published and made easily available the complete details on how to build an engine like his.  No other inventor has done this.  Shortly before his death in 1997, Terry Miller gave all rights to his invention to his daughter and to Toby Butterfield.  Mr. Butterfield died in 2002.

Guy Negre and MDI

For many years a French inventor named Guy Negre has been building an organization to market his air car designs in several countries.  A web search for air cars will turn up thousands of references to his company, Moteur Developpment International (MDI).  Mr. Negre holds patents on his unique air engine in several countries.  Along with other inventors like Angelo Di Pietro Terry Miller and, it is Guy Negre and his son Cyril Negre who have put air cars back on the map.

C. J. Marquand's Air Car Engine

Dr. Marquand  has taken the highly commendable step of incorporating heat pipes into his air engine design for the recovery of compression heat.  He also plans to use regenerative braking.  It is not clear whether his engine has been tested in a car yet.  Professor Marquand is a scientist with a number of published research articles to his credit.  For further information contact: C. J. Marquand or H. R. Ditmore, Dept. of Technology & Design, Univ. of Westminster, 115 New Cavendish St., London W1M 8JS, Tel. 0170 911 5000.

Tsu-Chin Tsao's Hybrid Air Engine for Cars

Tsu-Chin Tsao is a distinguished professor of mechanical and aerospace engineering at UCLA.  He has invented a camless gasoline engine that does not idle; it uses compressed air to start the car, and when the air is gone the engine runs on gasoline.  During deceleration, braking energy operates a compressor to fill the air tank for the next start.  This brings to mind Buckminster Fuller's reminder in his magnum opus Critical Path, wherein he tells us how many horses (as in horsepower) could be jumping up and down going nowhere for all the gasoline being pointlessly burned by cars sitting at red lights at any given time.  We have nothing but admiration and respect for Professor Tsao's serious step in a perfectly good direction, and apparently Ford Motor Company is in agreement: they are working with Tsao's team to look into the viability of putting a pneumatic hybrid on the road to compete with the Toyota Prius and other electric hybrids.  The pneumatic hybrid is expected to save 64% in city driving and 12% on the highway.

Angelo Di Pietro's Rotary Positive Displacement Air Engine

Everything I've heard about this air engine is positive.  Many people have written asking me to report on it, but the best I can do till I ride in his air car is to show you a picture and a link.  Based on what is said about the engine, I think it sounds like a good idea.  It seems like a good approach to simplifying the piston engine while lowering friction and wear.  Quoting from the website, http://www.engineair.com.au:

"The space between stator and rotor is divided in 6 expansion chambers by pivoting dividers. These dividers follow the motion of the shaft driver as it rolls around the stator wall. The motor shown is effectively a 6 cylinder expansion motor...Variation of performance parameters of the motor is easily achieved by varying the time during which the air is allowed to enter the chamber: A longer air inlet period allows more air to flow into the chamber and therefore results in more torque. A shorter inlet period will limit the air supply and allows the air in the chamber to perform expansion work at a much higher efficiency. In this way compressed air (energy) consumption can be exchanged for higher torque and power output depending on the requirements of the application...Motor speed and torque are simply controlled by throttling the amount or pressure of air into the motor. The Di Pietro motor gives instant torque at zero RPM and can be precisely controlled to give soft start and acceleration control." 

From what I've read, I think this sounds like what other people have  wished they could invent.  A lot of people are counting on Mr. Di Pietro to get an air car on the market.

Armando Regusci of Uruguay

In my correspondence with Mr. Regusci of Uruguay, I found him a sincere person and his design very appealing.  His invention does away with the crankshaft, using sprockets and chains and freewheeling clutches, to turn a shaft.  He has built bikes and small air cars of various descriptions and is very devoted to the cause.  His website, http://www.airenergycars.com, is extensive.  You can also see his video on YouTube.

When I first contacted Mr. Regusci, he was assisting a university in Texas with their plans to build an air car.

I want all you air car enthusiasts to become air car inventors and builder, like Angelo Di Pietro, Armando Regusci, Guy Negre, Terry Miller, and all the others.  Join forces with each other!  Let's get off the internet and onto the highway.  We know we have the best alternative, now let's get out there and prove it.