Hydrogen is expected to be one of the most important fuels in the near future to meet the stringent emission norms. In this experimental investigation, the combustion analysis was done on a direct injection (DI) diesel engine using hydrogen with diesel and hydrogen with diethyl ether (DEE) as ignition source. The hydrogen was injected through intake port and diethyl ether was injected through intake manifold and diesel was injected directly inside the combustion chamber. Injection timings for hydrogen and DEE were optimized based on the performance, combustion and emission characteristics of the engine. The optimized timing for the injection of hydrogen was 5 degrees CA before gas exchange top dead center (BGTDC) and 40 degrees CA after gas exchange top dead center (AGTDC) for DEE. From the study it was observed that hydrogen with diesel results in increased brake thermal efficiency by 20% and oxides of nitrogen (NO) showed an increase of 13% compared to diesel. Hydrogen-DEE operation showed a higher brake thermal efficiency of 30%, with a significant reduction in NOx compared to diesel. (C) 2008 Elsevier Ltd. All rights reserved.