French auto runs on compressed air technology

French engineers have designed a low consumption and low pollution engine for urban motoring that runs on compressed air technology. The CATS (Compressed Air Technology System) "air car" from Motor Development International is a significant step for zero-emission transport, delivering a compressed air-driven vehicle that is safe, quiet, has a top speed of 110 km/h and a range of 200 km. Costing next to nothing to run, the Zero Emission Vehicle (ZEV) range - which includes a pick-up truck and van - is set for release in early 2005.

Cyril Nègre is the head of Research and Development at Moteur Developement International (MDI) cars, where the Zero Emission Vehicle (ZEV) prototype has been in production since 1994. The two-stroke engine is powered by compressed air stored in tanks at about 150 times the pressure of tyres on a car. The expansion of the compressed air drives the pistons to create movement, replacing the burning of fossil fuel in a conventional engine. In an air-refilling station (currently unavailable as service stations have not been fitted yet) it is estimated to take between three and four minutes to re-fuel. At home, with a 220V plug, it takes three and a half hours.

Nègre estimates a full tank of air will cost around 1.50 euros to fill and that the extra reward is knowing that you are pumping nothing harmful into the atmosphere. The hidden environmental cost with the CATS is that electricity must still be generated and the means of that production may still employ fossil fuels that discharge pollutants. Still, the savings to the pocket and environment appear well worth investigating. Four models are available for the commercial market - the MiniCAT car at approximately €6 860 euros, or the CitiCATs, including a taxi (with room for up to 5 passengers), a Pick-Up truck and a van, all retailing for approximately €9,460 euros plus taxes.

Air powered engine

This engine uses an innovative system to control the movement of the 2nd generation pistons and one single crankshaft. The pistons work in two stages: one motor stage and one intermediate stage of compression/expansion. The engine has 4 two-stage pistons, i.e. 8 compression and/or expansion chambers. They have two functions: to compress ambient air and refill the storage tanks; and to make successive expansions (reheating air with ambient thermal energy) thereby approaching isothermic expansion. Its steering-wheel is equipped with a 5kW electric moto-alternator. This motor is simultaneously:

• the motor to compress air • the starting motor • the alternator for recharging the battery • an electric moderator/brake • a temporary power supply (e.g. for parking)

No clutch is necessary. The engine is idle when the car is stationary and the vehicle is started by the magnetic plate, which re-engages the compressed air. Parking manoeuvres are powered by the electric motor. The CAT´s 34 P04 engine is equipped with patented variable-volume butts and a dynamic variable-volume volumetric reducer.

The dual energy system

The Series 34 CAT´s engines can be equipped with and run on dual energies - fossil fuels and compressed air - and incorporate a reheating mechanism (a continuous combustion system, easily controlled to minimise pollution) between the storage tank and the engine. This mechanism allows the engine to run exclusively on fossil fuel, which permits compatible autonomy on the road. While the car is running on fossil fuel, the compressor refills the compressed air tanks. The control system maintains a zero-pollution emission in the city at speeds up to 60 km/h. The MDI con-rod system allows the piston to be held at Top Dead Centre for 70º of the cycle.This way, enough time is given to create the pressure in the cylinder. The torque is also better so the force exerted on the crankshaft is less substantial than in a classic system.

...continued