In this study, we examined H-2 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 H-2 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 H-2 energy percentage was varied from 0 to 7.4% independently to evaluate the H-2 effects and EGR effects separately. The heat release rate was calculated from the measured cylinder pressure. We found that substitution of H-2 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 H-2 percentage of 7.4%. PM emissions were reduced by 18% for an EGR of 35% and an H-2 percentage of 7.4% compared with diesel fuel only cases. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.