(2 of 2)
Jack-Rabbit Start. Free piston engines are still full of bugs, but their seemingly indirect way of generating power has its points. Since the combustion gases start their work cycle at extremely high pressure and temperature, the thermal efficiency of the engine (the amount of mechanical energy that it gets out of the fuel) can be very good. It has no flywheel, crankshaft or connecting rods. It has many valves to shunt air through the various chambers, but they are all self-operating, and none are exposed to high temperature. The engine can be made to run on almost any combustible liquid, even thick black bunker oil. Since the gases that spin the turbine have been mixed with scavenging air, they are not very hot (800-900° F.), so the turbine need not be made of expensive, heat-resistant metals.
For use in automobiles, trucks, etc. the free piston engine has special advantages. The gasifier, its heaviest part, can be placed under the hood while the turbine can be in the rear at the end of a gas pipe. This eliminates the drive shaft that clutters low-slung cars, and it distributes the engine's weight in a desirable way. Unlike straight gas turbines, free piston engines have quick response. The man whose self-confidence is supported by making jackrabbit starts when the traffic light turns green will not suffer deflation if his dream-car of the future has free pistons in it.