In the present article, a Computational Fluid Dynamics (CFD) method and a home-made FORTRAN code have been utilized to investigate the effects of injection timing under various equivalence ratios on the first and second laws of thermodynamics terms in a hydrogen fueled Direct Injection Spark Ignition (DISI) engine. The results show a good agreement with the experimental data. Exergy terms such as exergy transfer with work, exergy transfer with heat, exergy transfer with exhaust gas and fuel chemical exergy were computed based on principles of the second law. Also Entropy generation per cycle is calculated. Special attentions are given to recognize and quantify the irreversibility of combustion process basing on the different injection timings and equivalence ratios. The obtained results indicated that combustion irreversibilities and exhaust gas availability are more affected by varying the equivalence ratio and amount of fuel availability that transfers to environment with exhaust gases increased by increasing the equivalence ratio. Varying the equivalence ratio had different effect on the accumulated work availability reduced to fuel availability at the late and early injection strategies. Also, entropy generation reduced by retarding the hydrogen injection timing and decreasing the equivalence ratio. Changing in injection timing has its maximum effect on Phi = 0.6 equivalence ratio. Crown Copyright (c) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.