The diesel engine is the prime mover of choice for locomotives in operation on Canadian railways. Combustion takes place in a diesel engine by compressing the fuel and air mixture until auto-ignition occurs. It has found its niche as a result of its fuel-efficiency, reliability, ruggedness and installation flexibility. Two diesel prime mover installation arrangements are currently in use: Medium-speed diesel engine: This engine is installed in versions from 8 to 16 cylinders at up to 4,400 HP, with an operating speed of 800 to 1,100 RPM. Multiple 'GenSet'diesel engines: This 'stand alone' generating set (GenSet) is each powered by a 700 HP industrial diesel engine driving separate generators, which are linked electronically to produce up to 2,100 traction horsepower, with an operating speed up to 1,800 RPM. For switching locomotive applications, the advantage of this arrangement is that individual GenSet engines can be started or stopped according to the power required