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Engineair's Ultra-Efficient Compressed Air Motor


Elegant minimalist design eliminates most of the working parts traditionally associated with internal combustion engine; offers nearly 100% energy efficiency for a variety of transport and stationary applications.

by Mary-Sue Haliburton
Pure Energy Systems News
Copyright © 2006

Imagine a vehicle with nothing under the hood (or bonnet), no gearbox, no transmission, no carburetor or other fuel feeds. Yet it converts virtually all the energy fed to its motors into actual motion. With the elegance of absolute simplicity, this concept makes traditional internal-combustion cars look like the Rube-Goldberg contraptions they are: using way too many parts and stages to do what is really a simple task.

All we have to do is to get wheels to turn, preferably with as little wasted motion and energy as possible.

By comparison, the traditional car’s engine uses up to about 65% of the energy potentially available from the fuel, just to move all its parts such as pistons and cams, plus what is wasted generating excess heat. Then the transmission uses 6%, the accessory load 2% and idling losses come to about 11%, leaving about 16% of the energy actually engaged in making the wheels turn. Because of the weight of all these structures, the engine block, crankshaft, gears, transmission, etc., that 16% of the energy is having to move a vehicle weighing perhaps a ton and a half – which may have only one person sitting in it, weighing only 150 lb.

There is a lot wrong with that 100-year-old picture. It should be laughed off the road as unsuitable for the 21st century.

In Melbourne, Australia, an Italian-born mechanical engineer named Angelo Di Pietro has been experimenting for many years to find a more efficient design than the traditional reciprocating combustion engine. Inspired by his earlier work on Wankel rotary engines at Mercedes Benz in Germany, he pursued the notion of a rotary engine with fewer parts. Since his 1999 breakthrough, Di Pietro has been testing and perfecting his unique design which also eliminates traditional pistons and their housings. Though it weighs only 13 kilograms (28.6 lb), this rotary air motor is capable of powering a car without creating any pollution.

The Rotary Piston Unit

What he has done is to combine the pistons into a single rotary unit running on compressed air. With air to cushion the moving parts, there is no wearing of surfaces. And because this motor is designed to be mounted immediately beside the wheel with no intermediate parts to transmit motion, almost all energy is actually used to power the wheel itself.

Six expansion chambers and pivoting dividers effectively convert this single rotary piston into a six-cylinder expansion motor.

Turned by air pressure on its outer wall, the asymmetric cylindrical shaft driver turns an axel using two rolling elements mounted on bearings on the shaft. A thin film of air cushions the parts from wearing. To optimize performance parameters for the intended application, the motor can be easily adjusted by altering only the slotted timer (shown in yellow in the animated cutaway diagram above. (Ref.)

If more torque is desired, the timer is set for a longer air inlet period. With the air supply limited by a shorter inlet period, the air in the chamber will perform expansion work at a much higher efficiency.

The Di Pietro motor gives instant torque starting from zero RPM. The user controls motor speed and torque by throttling the air intake up or down; the controls are precise enough to allow for a soft start and gradual acceleration. (Ref.)

In addition to controlling power output, the timer also determines the sound made by the motor. These motors are capable of running nearly silently; however, most people prefer to have cars make some noise as warning of their approach. Whatever the sound level chosen by the user for his application, one thing is certain: vehicles with dipietro motors will not need mufflers – eliminating yet another weighty structure that takes energy to move it around.

Automotive Futures

Engineair of Australia is not a car manufacturing company, Mr. DiPietro admits. He plans to license the technology to car builders with the background and expertise to design cars that will meet the needs of consumers, and that they will want to drive.

Although he has retrofitted an existing vehicle, he says that due to its excess weight and the heavy chassis designed to accommodate parts his motor does not need, the older cars are not really worth upgrading. The time and money are better spent on a new concept designed to take advantage of his motor’s best capabilities.

Although interested buyers from China have signed a letter of intent, they are still planning to retrofit older vehicles, and Di Pietro wants to convince them to think farther ahead. But China lies under a pall of severe air pollution, exacerbated by sandstorms in some areas. When he was there recently, Di Pietro could barely make out the sun in the sky; “It looked more like the moon,” he says. So if Chinese engineers are desperate for a rapid reduction in fuel consumption and don’t want to take time to redesign the whole vehicle, they have good reason. They may be hoping to do a total redesign at a later stage when at least some improvement in their country’s atmosphere has been established.

The Australian engineer envisions a vehicle redesigned from the ground up, with a motor to drive each front wheel. The axels can be much smaller and lighter, as can just about everything else. Or, perhaps a 4WD light truck or SUV could have one rotary air motor on each wheel. If the four wheels are independently powered, then with four short, independently-turning axels, a car that can be parked by driving sideways may really become feasible.

The new vehicle should be aerodynamic, with a carbon-fiber shell and structural components also made light but sufficiently strong to protect passengers.

Di Pietro says that he has been contacted by an independent small carmaker in the United States who expressed interest in the technology as an ideal fit for what they were trying to do. This caller stated that his company was dissatisfied with lithium-ion batteries. In addition to taking eight hours to recharge, they would need to be replaced in only three to four years, at a considerable cost amounting to the price of a whole new motor vehicle.

The Big Chill

Monash University in Melbourne tested an earlier dipietro motor in 2002, and provided a complete report. This is no longer published as the motor design has further advanced, based on insights gained from the independent tests.

To understand how this technology differs so completely from the familiar dinosaur of an internal-combustion engine, and therefore how it functions in different climate conditions, we have to think about refrigeration technology.

When air is compressed, the molecules rub together, creating heat. When the compressed air performs expansion into the engine, the air becomes cold. So when running, instead of heating up, the dipietro motor gets colder. Much colder. So instead of having excess heat that must be dissipated as in an internal combustion engine, the dipietro motor becomes like a sponge absorbing heat. Heat is energy, and we can harness this energy for free from the atmosphere or from the sunlight.

It seems that another efficiency is available nearly for free here, a serendipitous bonus for good design. If the exhaust air is circulated into the passenger compartment, the motor itself would function as an air-conditioning unit. No environmentally-questionable freon would be required. And of course the weight of a refrigeration system would also be eliminated from the car, along with the need to consume energy for cooling the passenger compartment.

It has been found that for most efficient operation, the Di Pietro’s original concept of the air motor is ideally suited to operating in warmer climates. More recently, Engineair has applied for a patent on a technological enhancement that is as astute and minimalist as the motor itself, making the question of climate irrelevant. With this added factor, the efficiency of operation will be improved in colder regions as well.

Cost-Savings Galore

When envisioning this stripped-down power system, it’s not hard to imagine the reduction in cost to manufacture and ship vehicles with dipietro motors in them. Far fewer parts are needed to begin with, and those that are used will last much longer. Because of the lighter weight, for example, tires that, on a current car weighing two tons would last only 3 to five years, might end up lasting for a couple of decades, depending on factors such as climate and driving habits.

First in Line: the Mining Industry

It has never been possible to use internal-combustion power tools or vehicles underground due to the risk of explosions and air contamination in a closed space. Therefore, the mining industry has had to rely on compressed-air power for the past century; 10% to 30% of electricity is used to generate compressed air in this and other industries. Billions of dollars per year are poured into obtaining equipment such as air power tools, and further billions of dollars are spent to pay for electricity usage to compress air.

The dipietro system will cut such a cost to at least half and, will extend other savings such as a reduction in the size of the compressor at least by half.

In the cost-plagued business of mining as well as in other industries, the chance to reduce costs dramatically opens up using the dipietro motor. Much less material is required to make the device. Less electricity is required to manufacture and operate it. The first product from Engineair will be motors for the mining, pharamacuetical and chemical industries, as these can be plugged into existing systems and uses with little need for redesign, unlike what will be required for cars and other vehicles.

Comparing Apples & to Other Apples, or to Oranges?

In an episode of Beyond Tomorrow, an Australian television program about advances in technology, both Di Pietro’s motor and the French version of a compressed-air car were explored.

To ensure adaptability and to promote its adoption by the public, the French version of a compressed-air vehicle is intended to run on ordinary fuel when its supply of compressed air is used up, and therefore has the more complicated drive train, transmission, and other weighty structures. In the footage filmed of the reporter riding in the French vehicle, the motor noise overwhelms other impressions. Whether this vehicle design, which uses the same engine block and pistons as a standard internal-combustion engine, is always that noisy, or whether this is just a demonstration model and new muffler designs can compensate for it, is not stated in that televised report. Therefore, although it offers a pollution-free drive while running on compressed air, this vehicle does not achieve the same high efficiency as Di Pietro’s design.

In the related segment of the same program, Di Pietro appears, driving an assortment of adapted vehicles, including an adapted road car, a “minicat” for hauling supplies in a vegetable market, and an outboard motor. One can imagine how fishermen would appreciate a quiet, pollution-free motor. A motor scooter using the rotary piston has also been created. As the primary area for trading fresh fruits and veggies, the Melbourne market is incongruously highly polluted due to the numerous small tractors and forklifts all running on gasoline. Therefore the managers of this food-trading centre are reported to be keen on adopting his technology.

Other engineers and inventors are applying different approaches to compressing air to run a motor. The Gun Engine of Kazimierz Holubowicz uses the explosive force of fuel to compress the air. His design of a four-stroke cycle during startup switches automatically to a twelve-stroke cycle that converts all the energy released from any type of combustible fuel into work. Fuel flexibility is being touted as “alternative” energy, though combustion and emissions are still the result.

When running full tilt, the gun-engine’s induction stroke supplies fuel vapor with air into the explosion chamber where heat and compression occur. Then a primary power stroke feeds four compression and four extra power strokes, which convert all the energy into extra work. (Ref.) This concept has a central drive motor with the usual gears and transmission, so although it has more of the energy converted to power, it will still be using a significant percentage of that extra power to move its own parts rather than only to turn wheels. Also, an engine that is driven by explosions will be inherently noisy.

Another version by Raphial Morgado, replaces a 3000-lb engine with one weighing 150 lb., hinting at the reason for his naming of it as the MYT or “Massive, Yet Tiny”! In his design, the pistons move stepwise, each following the other in a toroidal cylinder while allowing openings for air intake. By firing 16 times in one rotation, he makes the equivalent of a 32-cylinder four-stroke engine. In demonstrations, the MYT engine is using pressurized air; it has not been extensively tested yet running on fuel, though they have run it on diesel briefly.

Morgado has achieved a power to weight ratio forty times better than conventional motors, and also shows a reduced parts count, smaller size and weight, and high mechanical efficiency. He envisions the MYT Engine installed in aircraft, big ships, tractor trailers and big-rig trucks, pumping stations, and power generator applications. The MYT Engine as a pump/compressor exceeds existing pumps and compressors in providing massive pressure, volume, and flow, all in one unit. (Ref.)

Which compressed-air engine is better?

The answer might be in completing the question and asking, “better for what purpose?” The new inventions offer greatly improved extraction of power from available fuel or electricity converted to compressed air at one stage or another, with air cushioning operation and reducing wear on engine parts. It may be that each of the above motors will fill a niche in the overall market, being ideal for some applications and situations, but not in others.

If all of these new, more efficient designs come into production and compete directly, the public will have a wider choice of motor options that save fuel and emit fewer or no polluting gases or particles. People can then choose the one that best fits their needs, considering such factors as noise level, size and weight, overall power output, and whether they wish to avoid burning or exploding fuel at any stage of the operation.

The Company

Engineair Pty Ltd was established on 9 September 2000 to research and develop Di Pietro’s design first built in 1997. They have facilities close to Melbourne in Australia, with state-of-the-art equipment for testing and measuring performance. Entering the stage of commercializing its technology, the company is doing quality checks on the first lot of motors, which are destined for the mining industry and for various stationary applications.

The company has several partners and investors. They have been receiving enquiries from around the world. Since their intention is to license the product for various applications, they are willing to consider further partnerships and will entertain offers from car manufacturers. Additional investment partners may be able to participate to expand production and to develop new applications.

See: http://www.engineair.com.au

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  1. I would convert it into a stirling with methyl chloride or just as a steam engine or lee rogers type of compressed air motor.

  2. Air powered cars are not practical. Anyone who tells you otherwise is either ignorant, insane, or lying.

    There are two problems:
    1) Air is a lousy energy storage medium. ATW, it takes almost 200 times the volume to store the equivalent of gasoline, and that is at a whopping 4500 psi. In other words, it would take a 400 gallon tank to get the range of a car with a mere 2 gallons of gas. Or call it liters if you like. Either way, that’s a freaking huge air tank, which will weigh rather a lot. And it will be extremely dangerous… see Mythbusters for what happens if a high-pressure air tank springs a leak. A catastrophic failure of 400 gallon tank should take out a good sized building.

    2) Compressing and expanding air is inefficient. As you know if you’ve ever pumped up a bicycle tire, the pump gets hot because the air heats when it is compressed. That’s energy wasted that you’re not likely to recover (except in cold climates). And, then when air expands, it cools down. Which you’d be well aware of if you’ve ever operated an air-powered tool. That might make for free air conditioning, but it’s liable to get the motor so cold it may ice up, particularly in cold climates where the compression heat is useful. The overall efficiency is far lower than that of charging a battery then running an electric motor.

  3. Air car is a good idea –
    The energy losses of compressing the air generates heat – you can use this heat overnight to warm a house or run a thermoelectric generator to recover some of this loss. A large home storage air tank (probably steel or carbon fibre tank) and compressor could run only at night when heat is actually needed then your compression losses are effectively zero since the pumping heat is not wasted at all – also running the compressor at night is more efficient since cool air is denser. ! Worst case you can run at offpeak times when electric power is cheapest.

    When you need the compressed air you refill from the home air tank in a few minutes – thats way faster than you can charge a battery – even the best Li-Fe-Po batterys take 5 minutes to reach 80% charge and these fast charge systems require special high power electricity connections.

    The best air motors – Not the MDI one Tata is planning to use – The Engine Air motor from Australian is far superior are low friction with high efficinecy and high torque, and capable of air based regenerative breaking. Large air motors have relatively low friction and mass so by limiting to 2 front or rear air drive motors mechanical complexity and friction losses are kept very low. – no differential, no clutch, no gearbox – Large Air motors can have excellent power to weight ratio even better than large DC electric motors.( note that small electric motors are far superior to small air motors though)

    Likly a hybrid 6 segment rotating air motor with computerised/electric valve control will be developed which gives higher efficiency than even engineairs excellent design.

    A vehicle with a combo system would be the best though.

    Lithium battery provides :-electric power steering ,headlights , indicators ,radio, fans, engine /air management computer, electric air valve actuators, electric windows and windscreen wipers, navigation system etc. The lithium battery would only need to run low power systems and so is quite small – no heavier than existing Lead acid car batterys and inexpensive – Small air motors have large friction losses and high complexity so by using small electric motors and batterys for these smaller items you can get the best of both worlds.

    Compressed Air: for main wheel motor’s and interior cooling. Compressed air energy storage is similar to current lithium batterys BUT the tanks last far longer than batterys, are cheaper, environmentally friendly and safer. Compressed air provides main motive fource -provides efficient storage of kenetic energy in a safe, low cost, long life carbon fibre bound tank- the larger the tank the better the storage-weight-cost ratio becomes. Also in warm weather the cool, clean air from the air motors can help cool passengers -this is an advantage air has over all other motors it’s provides inherent cooling.

    LPG or Propane: runs a heat exchanger to preheat the compressed air from the first stage air pressure regulator, and may also provide interior heating it only needs to heat air to low temperatures so this is actually far more efficient than the way an IC engine would use it for – and it’s optional – The LPG would be optional in warmer climates and very little would be needed anyway a 9Kg BBQ bottle tank would last well over 1000Km even in cold weather. – Yes the car may use some carbon fuel but it is used far more efficiently and sparingly than other vehicles.

    Lubricating oil – not actually burnt but helps the air motors run – probably a few drops per km and most it is recoverable with an air-oil filter.

    All up it would be light weight, long life and very efficient.

    It is of note that for smaller lighter sized vehicles pure electric will allways be best- Electric motors, battery cost and weight increases in an almost linear fasion with power output and for small sized vehicles electric is far simpler and cheaper – Electric motorcycles and light weight electric sports cars will certainly dominate the small vehicle market in the future.

    Air motor and air tank storage cost rolls off so that very large air motor only costs a little more than a smaller one and only weighs a little more, same with air storage tanks a tank with 4* the storage will only cost a little more to make. – So Air would be best suited for medium to VERY large vehicles where the size advantages of would give Air power a significant edge and the more complex air motors are both cheaper and ligher than an equivelant electric motors. I expect air power will be perfect for large/medium passenger vehicles, busses, trains and trams or even short haul trucks.

    One other thing will be Air refuel stations – how much do you charge for air -and if many people have home tanks then why not develop an air recharge network and payment system interesting.


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