A quasi-dimensional model has been developed for an SI engine fuelled with natural gas/hydrogen blends, the combustion chamber was divided into two zones by the flame front, and a turbulent entrainment combustion model was conducted. This paper investigates the effects of calibration coefficients on the model, which includes the turbulence intensity coefficient C(2), the Taylor length scale coefficient C(3), and the Ignition lag coefficient C(ig). Validation by experiments is carried out under various operating conditions including different ignition timing, excess air ratio, manifold ambient pressure (MAP) and fraction of hydrogen enrichment. The results show that C(ig) always stay the same at 1.52. When the fuel is pure natural gas, C(3) plays an important role in the simulation which changes from 0.95 to 2. The main factor changes from C(3) to C(2) when the hydrogen fraction increases from 30% to 55%. When the engine is fuelled by pure hydrogen C(2) to changes from 1.65 to 2.1. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.