Overcoming diesel engine emissions trade-off effects, especially NOx and Bosch smoke number (BSN), requires investigation of novel systems which can potentially serve the automobile industry towards further emissions reduction. Enrichment of the intake charge with H-2 + N-2 containing gas mixture, obtained from diesel fuel reforming system, can lead to new generation low polluting diesel engines. This paper investigates the effect of simultaneous H-2 + N-2 intake charge enrichment on the emissions and combustion of a compression ignition engine. Bottled H-2 + N-2 was simultaneously admitted into the intake pipe of the engine in 4% steps starting from 4% (2% H-2 + 2% N-2) up to 16% (v/v). The results showed that under specific operating conditions H-2 + N-2 enrichment can offer simultaneous NO, BSN and CO emissions reduction. Apart from regulated emissions, nitrogen exhaust components were measured. Marginal N2O and zero NH3 emissions were obtained. NO/NO2 ratio increases when speed or load increases. Under low speed low load operation the oxidation of NO is enhanced by the addition of H-2 + N-2 mixture. Finally, admission of H-2 N-2 has a detrimental effect on fuel consumption. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.