A chemical kinetic study of low alcohol/iso-octane blends in both premixed and partially premixed combustion

Abstract

The use of alcoholic fuels in both compression ignition and spark ignition engines has received much attention in recent years. Using these fuels, either in pure form or in a blended form with gasoline, not only reduces engine emissions but also improves engine performance. Therefore, a careful examination of the chemical kinetics of combustion of alcoholic fuels is of great importance. Since the run time of combustion chemistry calculations is proportional to the square of the total number of species in the chemical kinetic mechanism, the use of a detailed chemical kinetic mechanism for engine design and optimization is not practical. In this paper, first, the performance of a reduced mechanism has been investigated in terms of predicting ignition delay time and laminar flame speed. Then, the mechanism is utilized to study and compare three different blends of alcohol fuels (namely methanol and ethanol) and iso-octane with identical stoichiometric air to fuel ratio, volumetric energy content, octane numbers and latent heat. Combustion properties for both premixed and non-premixed diffusion flames, and homogeneous reactor configurations are studied. The results indicate that ignition delay and laminar flame speed are more defined by the iso-octane and methanol content rather than ethanol. Generally, blends with lower iso-octane and higher methanol give a longer ignition delay time and a higher laminar flame speed. The main source of pollutant formation for one of the blends are also discussed.