Effect of EGR on NOx and Thermal Efficiency Improvement in a D.I. Methanol Engine for Light Duty Vehicles

Exhaust gas recirculation (EGR) was applied in a spark-assisted, direct-injection (Dl) neat methanol engine for light duty vehicles. An experimental study has been carried out to analyse for major factors of EGR that influence in the reduction of NOx mass emission and improvement in brake thermal efficiency.

EGR on the Dl methanol engine alters intake charge, especially increasing the concentrations of H₂O and unburned methanol with rising intake charge temperature. The results of qualitative analyses show that this phenomenon suppresses rapid heat generation at the initial combustion stage, therefore lowering the combustion temperature in the cylinders and leading to a reduction in NOx production. It was also found out that brake thermal efficiency is improved by raising in the intake charge temperature with recirculating the unburned methanol to the cylinder, which not changes start of combustion and accelerates combustion in the following combustion stages with less change in the combustion duration.

Combining the EGR rate control, fuel injection timing control, spark timing control and an oxidation catalyst, the Dl methanol engine will satisfy the 1994 Japanese Vehicle Emission Standards for trucks and buses.