The present work investigates experimentally the behavior of compression ignition engine while boosting the combustion by enriching air-intake manifold with hydrogen supplement at the atmospheric condition. The study reports the engine thermal efficiency, NOx emissions and engine exhaust temperature while varying hydrogen content, engine speed and ignition timing. The results show that thermal efficiency of the compression ignition engine increases as hydrogen content increases in the air-intake manifold for the same diesel mass flow rate. The effect of hydrogen supplement on engine efficiency is more pronounced at low engine speed and part-load. The hydrogen supplement causes an increase in NO emissions which is attributed to the increase in the combustion temperature and as a result, lower smoke opacity numbers are attained. (C) 2014 Elsevier Ltd. All rights reserved.