Effect of engine compression ratio, injection timing, and exhaust gas recirculation on gaseous and particle number emissions in a light-duty diesel engine

Abstract

Along with other particulate and gaseous emissions, particle number (PN) from diesel engines has also been stringently regulated in the latest emission regulations. The present study focuses on combined effects of various parameters such as engine compression ratio (CR), start of injection (SOI) timing, and exhaust gas recirculation (EGR) rate on performance and emissions from a single-cylinder diesel engine with a special focus on PN. Three test cases with varying engine load were selected for this study. The engine was tested for these loading conditions with various compression ratios varying from 13.3 to 17. SOI sweep was carried out from −16 deg aTDC deg to −4 deg aTDC deg to identify the optimum injection timing with the best compression ratio. EGR sweep was also carried out with increasing EGR from 0% to 30% to see the effect of changing the EGR rate with increasing compression ratio on various emissions. For all the loading cases tested in this study, an increase in the compression ratio resulted in higher in-cylinder pressure, reduced ignition delay along with a slight improvement in fuel consumption. Higher NOx production with increasing compression ratio was observed because of higher combustion temperatures. Interesting trends were observed for PN and soot emissions during this study. Soot emissions and PN reduced with increasing compression ratio till CR16. A further increase in the compression ratio resulted in a further increase in PN and soot emissions.