Fuel and diluent effects on entropy generation in a constant internal energy–volume (uv) combustion process

Recently, Teh et al. (2008) showed that constant internal energy–volume (UV) combustion (with equilibrium products) is the optimal strategy for minimizing entropy generation (Sgen) 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, N2, and O2) on Sgen in constant UV combustion. With CH4 as the fuel, increasing reactant temperatures by 100 K decreased Sgen by 6–9%, while reactant pressure had a negligible effect on Sgen. Specific entropy generation, calculated per-unit-mixture-mass and per-unit-fuel-mass, followed the same trends as total Sgen for reactant temperature and pressure variations. However, mixture-mass-specific Sgen decreased with decreasing equivalence ratio and increasing diluent fraction while total and fuel-mass-specific Sgen exhibited the opposite trends. Of the diluent species examined, H2O and CO2 had the most (up to 65%) and least (∼40%) significant effects on Sgen, respectively. Among fuels, C8H18 exhibited the highest Sgen (four-times higher than C2H5OH and six-times higher than CH4), indicating the strong effect of fuel type and structure on Sgen. Finally, the implications of the present results for practical IC engine combustion processes are also discussed.

► Entropy generation in constant internal energy–volume combustion is studied.
► Reactant temperature and equivalence ratio strongly affect entropy generation.
► Diluent addition increases combustion-generated entropy.
► Combustion-generated entropy is strongly dependent on fuel type.
► Entropy generation must be optimized for best efficiency–emissions–power tradeoffs.