While there is now much interest in electric vehicles or various hybrids, the most benefit may result from a revolutionary modification and efficiency improvement of the conventional internal combustion Otto cycle engine, by recovering a large portion of the availability that exists at the end of the power stroke. This paper will describe the theory and a potentially practical method for achieving a 50% improvement in power output and fuel efficiency. While the topping cycle will remain the internal combustionpiston/cylinder engine, a two stage bottom cycle will be used. The first bottom stage is a single process consisting of a turbine installed in the exhaust stream to extract power from the excess pressure that exists when the engine exhaust valve opens. The second bottom stage is a complete external combustion gas turbine cycle consisting of a compressor, exhaust gas to compressed air heat exchanger and a turbine. Such a two stage bottoming cycle can be practical and may increase the power output by about 50%. This means that a car that achieves 30 mpg without a bottoming cycle can achieve 45 mpg with this bottoming cycle. Alternatively if the performance of cars can be improved to 66 mph by means of decreasing the power requirements by with smaller size and frontal area, better aerodynamics, lower rolling resistance tires and better transmission and drive trains, this vehicle can be extended to 100 mpg with this combined cycle engine.
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