Study of Exhaust Re-Breathing Application on a DI SI Engine at Partial Load Operation

Using Exhaust Gas Recycling (EGR) on internal combustion engines enables the reduction of emissions with a low or even no cost to the engine efficiency at part-load operation. The charge dilution with EGR can even increase the engine efficiency due to de-throttling and reduction of part load pumping losses. This experimental study proposed the use of late exhaust valve closure (LEVC) to achieve internal EGR (increased residual gas trapping). A naturally aspirated single cylinder direct injection spark ignition engine equipped with four electro-hydraulic actuated valves that enabled full valve timing and lift variation. Eight levels of positive valve overlap (PVO) with LEVC were used at the constant load of 6.0 bar IMEP and the speed of 1500 rpm. The results have shown that later exhaust valve closure (EVC) required greater intake pressures to maintain the engine load due to the higher burned gases content. Hence, lower pumping losses and thus higher indicated efficiency were obtained. The higher charge dilution lowered the combustion temperatures and hence the formation of oxides of nitrogen (NOx). Unburned hydrocarbon emissions reduced as well, while a slight increase on carbon monoxide emissions was observed. Spark assisted compression ignition (SACI) combustion was identified at the longest exhaust valve opening durations tested due to increased in-cylinder temperature.