Modelling of engine in-cylinder thermodynamics under high values of ignition retard

This paper presents the work on a carburetted gasoline engine, in particular the complete modelling of an engine in-cylinder thermodynamics under high values of ignition retard (HVIR). The "combustion" is a two-zone burnt/unburned model with the fuel burning rate described by a Wiebe function. Under extreme spark timing retard conditions, the Wiebe function describing the heat release of the fuel-air reactions was modified to account for the critical change in pressure distribution in the cylinder due to the abnormal spark retard. An empirical correlation for cylinder pressure variation during the mass blowdown process, which occurs between the exhaust valve opened and bottom-dead-centre, was included in the simulation to enhance the predictive capability of the engine model. The complicated mass blowdown process across the exhaust valves was simplified by two processes. (i) isentropic expansion from the cylinder pressure to the constant exhaust manifold pressure, and (ii) constant pressure throttling which gives rise to increased exhaust gas temperature due to the recovery of kinetic energy. (C) 2001 Editions scientifiques et medicales Elsevier SAS.