Cooled EGR for a Turbo SI Engine to Reduce Knocking and Fuel Consumption 2007-01-3978

Cooled exhaust gas recirculation is emerging as a promising technology to address the increasing demand for fuel economy without compromising performance in turbocharged spark injection engines. There are a number of different possible architectures, each with its specific characteristics. The objectives of this study are to quantify the increase in knock resistance and to decrease the enrichment at full load in order to target stoichiometric operation over the full operating range, and to define a vehicle compatible cooling system to meet the demanding heat rejection requirements.

Based on our knowledge in EGR and air loops, the benefits and risks of various cooled EGR turbocharged systems were evaluated and compared in a preliminary phase. Two architectures, one with high pressure EGR and the other with low pressure EGR, were selected and tested on a 2L turbocharged gasoline engine on a stationary test bench and the performance was compared to the serial production engine. The EGR gas and the turbo compressed intake air were cooled by high efficiency compact water cooled heat exchangers, allowing an accurate control of the gas temperatures. As predicted, using cooled EGR at high load enabled operation at lambda one with the same serial engine performances, which offers substantial advantages: BSFC reduction (up to 14%), exhaust gas temperature reduction (up to 100°C), and emission reduction (CO, HC). In addition, a significant advantage of the low pressure EGR system was observed in comparison to the high pressure system typically applied to diesel engines, in particular at lower engine speed. Finally, the cooling requirements of both EGR systems were analyzed for vehicle integration.