Simulation and experimental study of the Otto and Stirling combined cycle

Gasoline engines currently reject up to 40% of the total fuel energy in their exhaust. Because of increasing petroleum costs, there is a growing interest in techniques that can use this waste heat to improve the overall system efficiency. In this paper, a combined cycle system is proposed where a high-speed gasoline engine acts as the topper of the combined cycle with exhaust gases used for a bottoming cycle based on a Stirling cycle. This paper describes a mathematical model of the Stirling engine to evaluate the combined performance of the gasoline engine and the Stirling engine driven by waste heat. Simulation and experimental studies of the combined cycle system of the gasoline engine and Stirling engine reveal that the Stirling engine is a good candidate for small-scale power generation. Maximum shaft power of 535 W is recovered when the temperature of the exhaust gas reaches approximately 1000 K and the gasoline engine operates at 3000 RPM and 90% load with 50.7 kW output power. The operating pressures and temperatures of the Stirling engine are monitored in the experiment by placing three pressure sensors and 34 thermocouples in the heat exchangers.