Recently, Teh et al. (2008) showed that constant internal energy-volume (UV) combustion (with equilibrium products) is the optimal strategy for minimizing entropy generation (S-gen) in idealized internal combustion (IC) engine processes. The present paper examines the effects of fuel type (CH4, C2H5OH, and C8H18), reactant temperature (300-1200 K), reactant pressure (101.325-10132.5 kPa), equivalence ratio (0.3-1.5), and diluents (CO2. H2O, N-2, and O-2) on S-gen in constant UV combustion. With CH4 as the fuel, increasing reactant temperatures by 100 K decreased S-gen by 6-9%, while reactant pressure had a negligible effect on S-gen. Specific entropy generation, calculated per-unit-mixture-mass and per-unit-fuel-mass, followed the same trends as total S-gen for reactant temperature and pressure variations. However, mixture-mass-specific S-gen decreased with decreasing equivalence ratio and increasing diluent fraction while total and fuel-mass-specific S-gen exhibited the opposite trends. Of the diluent species examined, H2O and CO2 had the most (up to 65%) and least (similar to 40%) significant effects on S-gen, respectively. Among fuels, C8H18 exhibited the highest S-gen (four-times higher than C2H5OH and six-times higher than CH4), indicating the strong effect of fuel type and structure on S-gen. Finally, the implications of the present results for practical IC engine combustion processes are also discussed. (C) 2012 Elsevier Ltd. All rights reserved.