Ingersoll-Rand built the largest-ever Wankel engine, with two rotors, which was available between 1975 and 1985, producing . A one rotor version was available producing . The displacement per rotor was 41 liters, with each rotor being approximately one meter in diameter. The engine was derived from a previous, unsuccessful Curtiss-Wright design, which failed because of a well-known problem with all internal combustion engines: the fixed speed at which the flame front travels limits the distance combustion can travel from the point of ignition in a given time, thereby limiting the maximum size of the cylinder or rotor chamber which can be used. This problem was solved by limiting the engine speed to only 1200 rpm and the use of natural gas as fuel. That was particularly well chosen, since one of the major uses of the engine was to drive compressors on natural gas pipelines.