A Feasibility Study of Reciprocating-Flow Super-Adiabatic Combustion Engine(<Special Issue>Emerging Fields in Thermal Engineering)

Super-adiabatic combustion engine proposed here has a high thermal efficiency of 57.5% over a wide range of operation conditions. The engine consists of a displacer piston, a power piston and a porous medium in a cylinder. These create reciprocating motions with a phase relation angle. After scavenging, a mixture introduced is compressed by the displacer piston and preheated by the porous medium, and then, ignited in the vicinity of the downstream end of the porous medium. The main reaction occurs in the power piston side cylinder. By the heat recirculation from the residual combustion-gas enthalpy to the enthalpy increase in the mixture, the maximum temperature becomes higher than the theoretical (adiabatic) flame temperature. As a result, the system has such a high thermal efficiency and extends the flammability limit to a concentration of 1.58 vol.% methane in air.