Effect of High and Low-Pressure Exhaust Gas Recirculation System on NOx Emissions in a Bus Diesel Engine

This study aims to design the exhaust gas recirculation (EGR) system for a bus diesel engine in order to reduce exhaust emissions. This includes the experiment and simulation of the test engine based on the Emission Test Cycles ECE-R49. The comparison of high and low-pressure exhaust gas recirculation systems fitted on a bus engine was conducted to analyze the effects of their control on fuel consumption, pollutant emissions. The research results showed that the test engine retrofitted high-pressure exhaust gas recirculation systems (H-EGR) results in a lower ratio of EGR in comparison with that of low-pressure exhaust gas recirculation systems (L-EGR). In addition, due to the higher intake gas velocity and pressure, the local loss in case of H-EGR is also higher than the one of the L-EGR at the venturi assembly position. The H-EGR was only effective at the engine load less than 75 %, consequently, the role in reducing NOx emissions was less effective than that of the L-EGR. The maximum reduction of NOx emissions in case of H-EGR was 41.27 % at a load of 75 % and a velocity of 1400 rpm. Meanwhile, the NOx emission can be reduced to 62.43 % in case of L-EGR.