Effects of Inlet Air Heating and EGR on Thermal Efficiency of a SI Engine at Part Load

The common method for achieving less than full power operation in a spark ignition (SI) engine is reducing charge density via a throttle. However, a significant fuel economy penalty is associated with the pumping losses across the throttle valve. An alternative method to aid in reducing fresh charge density has been investigated on an Oldsmobile Quad-4 engine: exhaust gas recirculation in combination with inlet air heating. Brake thermal efficiency gains of about 6% were realized. The exhaust hydrocarbon increases associated with EGR were mitigated largely by inlet air heating.