This work is aimed at study of maximum available work and irreversibility (mixing, combustion, unburned, and friction) of a dual-fuel diesel engine (H-2 (hydrogen)-diesel) using exergy analysis. The maximum available work increased with H-2 addition due to reduction in irreversibility of combustion because of less entropy generation. The irreversibility of unburned fuel with the H-2 fuel also decreased due to the engine combustion with high temperature whereas there is no effect of H-2 on mixing and friction irreversibility. The maximum available work of the diesel engine at rated load increased from 29% with conventional base mode (without H-2) to 31.7% with dual-fuel mode (18% H-2 energy share) whereas total irreversibility of the engine decreased drastically from 41.2% to 39.3%. The energy efficiency of the engine with H-2 increased about 10% with 36% reduction in CO2 emission. The developed methodology could also be applicable to find the effect and scope of different technologies including exhaust gas recirculation and turbo charging on maximum available work and energy efficiency of diesel engines. (C) 2014 Elsevier Ltd. All rights reserved.