Shaft horsepower output associated with a prime mover for driving a component of a transport refrigeration system may be selectively augmented through an auxiliary power apparatus. In an embodiment, a compressed air engine is provided and selectively operable to augment the shaft horsepower output for driving the component. At least one storage tank is provided for storing compressor air and at least one air compressor is provided for generating and supplying compressed air to the at least one compressed air storage tank. In an embodiment, the prime mover is a fuel combustion engine and the compressed air is heated by exhaust gas from the fuel combustion engine. The driven component may be a refrigerant compressor. The driven component may be an electric generator.