Evaporation-Combustion Affected by In-Cylinder, Reciprocating Porous Regenerator

An existing in-cylinder thermal regeneration concept for the Diesel engines is examined for the roles of the porous regenerator motion and the fuel injection strategies on the fuel evaporation and combustion and on the engine efficiency. While the heated air emanating from the regenerator enhances fuel evaporation resulting in a superadiabatic combustion (thus increasing thermal efficiency), the corresponding increase in the thermal NOx is undesirable. A multi-gas-zone and a single-step reaction model are used with a Lagrangian droplet tracking model that allows for filtration by the regenerator. A thermal efficiency of 52 percent is predicted, compared to 45 percent of the conventional Diesel engines. The optimal regenerative cooling stroke occurs close to the peak flame temperature, thus increasing the superadiabatic flame temperature and the peak pressure, while decreasing the expansion stroke pressure and the pressure drop through the regenerator. During the regenerative heating stroke, the heated air enhances the droplet evaporation, resulting in a more uniform, premixed combustion and a higher peak pressure, and thus a larger mechanical work.