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

This paper presents the work on a carburetted gasoline engine, in particula r the complete modelling of an engine in-cylinder thermodynamics under high values of ignition retard (HVIR). The "combustion" is a two-zone burnt/unb urned 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 crit ical change in pressure distribution in the cylinder due to the abnormal sp ark retard. An empirical correlation for cylinder pressure variation during the mass blowdown process, which occurs between the exhaust valve opened a nd bottom-dead-centre, was included in the simulation to enhance the predic tive capability of the engine model. The complicated mass blowdown process across the exhaust valves was simplified by two processes. (i) isentropic e xpansion from the cylinder pressure to the constant exhaust manifold pressu re, and (ii) constant pressure throttling which gives rise to increased exh aust gas temperature due to the recovery of kinetic energy. (C) 2001 Editio ns scientifiques et medicales Elsevier SAS.