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

An existing in-cylinder thermal regeneration concept for Diesel engines is examined for the roles of the porous insert motion and the fuel injection strategies on the fuel evaporation and combustion and on the engine efficiency. While the heated air emanating from the insert enhances fuel evaporation resulting in a superadiabatic combustion process (thus increasing thermal efficiency), the corresponding increase in the thermal $NOx$ is undesirable. A two-gas-zone and a single-step reaction model are used with a Lagrangian droplet tracking model that allows for filtration by the insert. A thermal efficiency of 53 percent is predicted, compared to 43 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 insert. During the regenerative heating stroke, the heated air enhances the droplet evaporation, resulting in a more uniform, premixed combustion and a higher peak pressure, thus a larger mechanical work.