air-compressed-energy

The laws of physics dictate that uncontained gases will fill any given space. The easiest way to see this in action is to inflate a balloon. The elastic skin of the balloon holds the air tightly inside, but the moment you use a pin to create a hole in the balloon's surface, the air expands outward with so much energy that the balloon explodes. Compressing a gas into a small space is a way to store energy. When the gas expands again, that energy is released to do work. That's the basic principle behind what makes an air car go.

The first air cars will have air compressors built into them. After a brisk drive, you'll be able to take the car home, put it into the garage and plug in the compressor. The compressor will use air from around the car to refill the compressed air tank. Unfortunately, this is a rather slow method of refueling and will probably take up to two hours for a complete refill. If the idea of an air car catches on, air refueling stations will become available at ordinary gas stations, where the tank can be refilled much more rapidly with air that's already been compressed. Filling your tank at the pump will probably take about three minutes [source: Cornell].

The first air cars will almost certainly use the Compressed Air Engine (CAE) developed by the French company, Motor Development International (MDI). Air cars using this engine will have tanks that will probably hold about 3,200 cubic feet (90.6 kiloliters) of compressed air. The vehicle's accelerator operates a valve on its tank that allows air to be released into a pipe and then into the engine, where the pressure of the air's expansion will push against the pistons and turn the crankshaft. This will produce enough power for speeds of about 35 miles (56 kilometers) per hour. When the air car surpasses that speed, a motor will kick in to operate the in-car air compressor so it can compress more air on the fly and provide extra power to the engine. The air is also heated as it hits the engine, increasing its volume to allow the car to move faster [source: Cornell].

Air Car Advantages

Lionel Cirroneau/AP Photo
MDI's Guy Negre shows off the AirPod One prototype in January 2009.

One major advantage of using compressed air to power a car's engine is that a pure compressed air vehicle produces no pollution at the tailpipe. More specifically, the compressed air cars we're likely to see in the near future won't pollute at all until they reach speeds exceeding 35 miles per hour. That's when the car's internal air compressor will kick in to achieve extra speed. The motor that runs this air compressor will require fuel that'll produce a small amount of air pollution. Some fuel (you can use eco-friendly biofuels or fossil fuels) will also be used to heat the air as it emerges from the tank. The newest compressed air engines also offer drivers the option of using fossil fuels or biofuels to heat the air as it enters the engine. Nonetheless, this technology represents a marked improvement over cars powered by internal combustion engines that produce significant amounts of pollution at any speed.

Air cars are also designed to be lighter than conventional cars. The aluminum construction of these vehicles will keep their weight under 2,000 pounds (907 kilograms), which is essential to making these vehicles fuel efficient and will help them go faster for longer periods of time.

Another advantage of air cars is that the fuel should be remarkably cheap, an important consideration in this era of volatile gas prices. Some estimates say that the cars will get the equivalent of 106 miles (171 kilometers) per gallon, although compressed air will probably not be sold by the gallon. A more meaningful estimate is that it may take as little as $2 worth of electricity to fill the compressed air tank, though you'll also need gasoline to power the electric motor that compresses air while driving [source: Cornell].

The vehicles themselves also will be relatively cheap. Zero Pollution Motors, which plans to release the first air cars in the United States and estimates a sticker price of about $17,800, which would make these cars affordable to budget-conscious American buyers [source: Max].

Air Car Disadvantages

Clive Streeter/Getty Images
Could this happen to you in an air car crash?

While an air car produces no pollution running on already compressed air in its tank, pollution is nonetheless produced when the air is compressed, both while the car is moving and while it's being refueled. As we mentioned earlier, the vehicle's air compressor will probably run on gasoline, and this gas will produce pollution when burned.

The air compressor at the gas station will probably be powered by electricity. The production of that electricity may or may not pollute, depending on how that electricity is generated. For example, coal-powered electricity could produce substantial amounts of pollution. Cleaner sources of electricity, such as nuclear power or hydropower, will result in far less pollution. According to the Web site Gas 2.0, an air car in the United States would create about .176 pounds of carbon dioxide emissions per mile based on the average mix of electric power sources during refueling. By comparison, a Toyota Prius Hybrid, which combines a battery-powered electric motor with an internal combustion engine, generates about 0.34 pounds of carbon dioxide per mile. So, while the air car is not quite pollution free, it still represents an improvement over one of the most popular hybrid cars on the market [source: Nuccitelli].

Distance could also become a disadvantage, depending on your travel habits. The distance that an air car can cover without refueling is crucial because very few filling stations will have compressed air pumps available at first. If you only plan to use your air car for short commutes -- distances less than 100 miles --will be fine. However, the one-to-two hour wait for the car's built-in air compressor to compress a tank full of air could become a problem on cross-country trips. Zero Pollution Motors -- the American arm of MDI and the company likeliest to produce the first air car for the U.S. market -- aims to have a car available soon able to travel between 800 and 1,000 miles on one tank of air plus 8 gallons of gas [source: Cornell]. Early prototypes, however, have traveled distances closer to 120 miles -- good enough for your daily commute, but not quite adequate for longer trips [source: Motavalli].

What will happen if an air car suffers damage in an accident? After all, compressed air tanks can be dangerous. To reduce this danger, the air tanks are made of carbon fiber and are designed to crack, rather than shatter, in a crash. This crack would allow the "fuel" to escape harmlessly into the surrounding air. Manufacturers feared that air escaping from one end of the tank could produce a rocket-like effect and propel the car on a jet of air. The valve on the cars' fuel tanks has been placed on the side to minimize this effect.

Despite these precautions, there is some concern that the air cars' lightweight construction might make it difficult for them to pass stringent American safety requirements and that this could hold up the arrival of air cars in the U.S. marketplace. Other factors have come to the forefront as well, and we'll learn about those next.

Air Cars in the Marketplace

Lionel Cirroneau/AP Photo
A look inside the AirPod One prototype.

India's Tata Motors will likely produce the first air car in the marketplace in the next few years. Tata Motors' air car will also use the CAE engine. Although Tata announced in August 2008 that they aren't quite ready to roll out their air cars for mass production, Zero Pollution Motors still plans to produce a similar vehicle in the United States. Known collectively as the FlowAIR, these cars will cost about $17,800. The company, based in New Paltz, N.Y., says that it will start taking reservations in mid-2009 for vehicle deliveries in 2010. The company plans to roll out 10,000 air cars in the first year of production [source: Max]. MDI also recently unveiled the joystick-driven AirPod, the newest addition to its air car arsenal. Although the AirPod generates a top speed of only 43 mph, it's also extremely light and generates zero emissions.

Major automobile makers are watching the air car market with interest. If the first models catch on with consumers, they'll likely develop their own air car models. At present, a few smaller companies are planning to bring air cars to the market in the wake of the MDI-based vehicles. These include:

K'Airmobiles -- French company K'Air Energy has built prototypes of an air-fueled bicycle and light road vehicle based on the K'air air compression engine [source: K'air]

Air Car Factories SA -- This Spanish company has an air car engine currently in development. The company's owner is currently involved in a dispute with former employer MDI over the rights to the technology [source: MDI].

Initially, the MDI cars will be the only air vehicles on the market. However, MDI has reportedly licensed the technology to manufacturers in a dozen different countries, so air cars should be available around the world soon.

v For more details visit:

Ø http://auto.howstuffworks.com/fuel-efficiency/vehicles/air-car1.htm

Air compressed engine

Wed, 04 Nov 2009 11:09:40 +0100

Mike Smyth's Compressed Air Engines

Welcome to my compressed air engine page! Below you'll find information about the V-twin and radial air engines that I designed and constructed.

Got a question? Check out the FAQ page:

Air Engine FAQ

SF376

Configuration: 5 cylinder radial

Bore: 0.4375 in (7/16")

Stroke: 0.500 in

Displacement: 0.376 cu in

Intake Valves: Rotary

Intake Dia.: 0.0938 in

Intake Duration: 44 deg

Exhaust Valves: Rotary

Exhaust Dia.: 0.125 in

Exhaust Duration: 60 deg

Weight: 6 oz.

This is a 5 cylinder radial engine that has the same displacement as the V-twin below. The radial cylinder configuration has the advantage that at least one cylinder is on a power stroke at all times. This allows the engine to self start from any position and it also allows the engine to run at very low RPM without a flywheel. The valve design is similar to the V-twin except the valves are integrated with the crankshaft. This eliminates the need for the external timing gears. The intake and exhaust timing are independently adjustable.

The construction of the SF376 is very similar to the V-twin. All of the metal parts are made from brass tubing and sheet from a local hardware store. The white parts are made from a plastic cutting board. All of the parts were made with basic tools - drill press, belt sander, bench grinder, hacksaw, dremel tool and a vise. The brass parts were soldered together using a small butane torch and plumbing solder.

The videos below show how the engine performs under different conditions. All the videos except the first one include sound. The first video shows engine with one side of the crankcase removed. The crankshaft is slowly rotated through a full rotation to show the connecting rod configuration. If the video player is put on continuous repeat it will look like the engine is turning continuously.

In the second video, the engine is idling at only a couple hundred RPM on about 1-2psi. without a flywheel. The third video shows the engine revving with no load, and the fourth shows the engine spinning an 18" 3-blade propeller. Even with the fairly heavy load, the engine accelerates rapidly. The maximum pressure in this video was about 45psi. The engine would easily generate enough thrust to lift it's own weight vertically.

Video 1 (340Kb) Cutaway view showing the internal movement

Video 2 (1.8Mb) Engine idling slowly with no flywheel

Video 3 (2.0Mb) Engine revving with no load and no flywheel

Video 4 (2.6Mb) Engine powering an 18" 3-blade propeller

I am working on a set of plans with step by step instructions for the SF376. These will be available from this web site for a small fee.

V-Twin

Configuration: 70deg V-Twin

Bore: 0.563 in

Stroke: 0.750 in

Displacement: 0.373 cu in

Intake Valves: Rotary

Intake Duration: 167 deg

Exhaust Valves: 0.125 in dia. port at bottom of stroke

Exhaust Duration: 122 deg

Timing Shaft: Gear drive

The bottom end of the engine (pistons, connecting rods, crankshaft) is very similar to engines found in everyday automobiles. However, the top end normally consisting of multiple poppet valves, springs, at least one camshaft, rocker arms and push rods (unless it's an overhead cam design) is replaced by a rotary valve that controls the timing of airflow into the cylinders. All of the above mentioned components are replaced by a single hallow shaft with cutouts in strategic locations. The picture below shows the timing shaft, timing gear and the intake manifold.

Compressed air is injected at the left end of the intake manifold tube. When the timing shaft is turned so the ports do not line up with the cylinder ports (the two tubes on the side of the main tube) the intake valves are closed and no air flows because there is nowhere for the air to escape (the end of the timing shaft by the gear is plugged). When the timing shaft is turned so that either of the ports is lined up with the cylinder ports, the intake valves are open and compressed air flows into the respective cylinders. By changing the location of the ports in the timing shaft, the firing order and relative timing can be adjusted. Changing the mesh of the timing gear and the crankshaft gear allow intake timing adjustment relative to the crankshaft position. Fine adjustments to intake timing can be made by rotating the intake manifold in the plastic friction mounts in either end of the block. This can be done while the engine is running.

The exhaust ports are simply tubes at the bottom of the piston stroke that open to the atmosphere to relieve the pressure in the cylinder. This is very similar to a 2-stroke engine. With this design, the exhaust timing is dependent on the location of the port in the cylinder and the duration is a function of the diameter of the port (a larger diameter port will have a longer duration).

This engine design worked (barely) the first time, but is very sensitive to the air pressure used. There is plenty of torque on the compression stroke even with very low air pressure, but because there is only an exhaust port at the bottom of the stroke much of the power is wasted as the pistons are traveling up. The high cylinder pressure from the power stroke is relieved once the exhaust port is opened, but when it closes off as the piston travels up, the remaining air in the cyclinder is compressed - robbing energy. This problem is made worse by the small amount of air that leaks into the cylinders around the rotary intake valve. Not only is the air in the cyclinder being compressed, the leaking air also exerts downward force on the cylinder robbing more power.

The main drawback to this design is the power loss on the upward stroke of the piston caused by the exhaust valving. On a 2-stroke engine, the upward stroke is the compression stroke. In this case, it's necessary to compress the fuel/air mixture and the compression is a good thing. The energy lost compressing the fuel/air is more than compensated for by the additional energy gained by igniting the fuel under pressure rather than at atmospheric pressure. However, in a compressed air engine, no additional energy is gained if the air in the cylinder is compressed on the upward stroke of the piston. Any additional energy gain due to the higher pressure on the power stroke can't be greater than the energy required to compress the air in the first place.

Because of this major drawback, I redesigned the valve system to relieve the pressure in the cylinders on the upstroke of the pistons. One way to alieviate this drawback would be to increase the exhaust duration by using a bigger exhaust port. This would allow the piston to travel up farther before the port is closed thereby reducing the power loss. However, this would also reduce the effective length of the power stroke because once the exhaust valve opens, there is no longer cylinder pressure to force the cylinder down.

Because I did not want the power loss caused by simply increasing the exhaust duration, I added exhaust valves to the timing shaft in addition to the intake valves. The picture below shows the redesigned valve. This configuration allows the exhaust valves to be closed during the entire power stroke and also allows them to be open through the entire upstroke.

The new timing shaft is plugged in the center between the intake and exhaust valves and is open at both ends. Air flows in the left side of the timing shaft and is distributed to the cylinders as before through the two left intake ports. Air is exhausted through the two ports on the right and out the gear-end of the timing shaft. There is also now a second port in the top of each cylinder that connects to the new exhaust ports on the manifold. On the upward piston strokes, the exhaust valves are open until the piston is nearly at TDC (top dead center). This corrects the drawback described above and allows wider adjustment of the exhaust timing and duration.

With the redesigned valves, the engine is not sensitive to air pressure and will easily run just by blowing into the intake manifold. I may make a small dyno with a DC motor to measure the actual power output of the engine at various intake air pressures. Below are revised engine specifications and pictures with the new valves.

V-Twin with Improved Valves

Configuration: 70deg V-Twin

Bore: 0.563 in

Stroke: 0.750 in

Displacement: 0.373 cu in

Intake Valves: Rotary

Intake Duration: 175 deg

Exhaust Valves: Rotary

Exhaust Duration: 175 deg

Timing Shaft: Gear drive

Not shown in the pictures above is the flywheel. The flywheel I've been using is simply a bar with a bolt in each end for weight. It serves the purpose, but is pretty ugly so I didn't include it in the pictures. Once I turn down a nice steel flywheel on the lathe I'll post some pictures with the flywheel. With the improved valve design, the engine will actually run without the flywheel, but it will need one if I do any dyno testing.

The engine could also use some crankshaft counterbalance to make it run smoother. I may try to add some weight to the crankshaft and maybe offset the flywheel weight a little.

Here is a video of the V-twin engine running with a simple flywheel. It is simply a piece of plastic with a large nut and bolt at each end. It's a little crude, but it offers a significant load as the engine accelerates. The picture below shows the flywheel.

Video 1 (1.4M) Engine accelerating with flywheel.

v For more details visit:

Ø http://home.ctlnet.com/~robotguy67/classic_cars/air_engines/V-Twin/air_engines.htm