H2 effects on diesel combustion and emissions with an LPL-EGR system

In this study, we examined H2 effects on the combustion and emissions of a diesel engine with low-pressure loop (LPL) exhaust gas recirculation (EGR). We converted a 2.2-L four-cylinder direct-injection diesel engine satisfying Euro5 for H2 supply. An LPL-EGR system replaced the high-pressure loop (HPL) EGR system. For all tests, the brake mean effective pressure (BMEP) was kept at 4 bar and the EGR ratio was varied from 9 to 42%. The H2 energy percentage was varied from 0 to 7.4% independently to evaluate the H2 effects and EGR effects separately. The heat release rate was calculated from the measured cylinder pressure. We found that substitution of H2 for diesel fuel made the premixed burn fraction larger, and reduced the nitrous oxide (NOx) and particulate matter (PM) emissions simultaneously. For example, the NOx emissions were reduced by 36% for an EGR of 42% and an H2 percentage of 7.4%. PM emissions were reduced by 18% for an EGR of 35% and an H2 percentage of 7.4% compared with diesel fuel only cases.