An internal combustion engine 10 wherein only some compression is carried out in the engine 10 and including a tank 30 of compressed air, a pressure regulator 34, a fuel injector 28, and means 40 and 50 for connecting the foot pedal 38 to the pressure regulator 34 and the fuel injector 28, for controlling air and fuel feed to the combustion chambers 22 in response to throttle demand during high power demand conditions. The engine 10 compresses its own air for cruise conditions but uses stored compressed air (charged from a wayside source) for higher power demand. The engine can use spark or heat ignition, provides full expansion, can be two or four stroke and of the diesel or gasoline type. Compressed air can be generated more efficiently using central station power with a vast savings in the amount of oil consumed. Oxygen enriched (60-80% O.sub.2) compressed air can be used without high temperature problems because of the only partial compression and the high (cooling) expansion ratio and higher rpm.