CFD Modelling of Soot Formation and Entrainment Processes in Diesel Engine Combustion of Soy, Palm and Coconut Methyl Esters

The aim of this work is to employ computational fluid dynamics (CFD) modelling to elucidate the soot formation and entrainment processes when diesel as well as soy, palm and coconut methyl esters (biodiesel) are used in a light-duty diesel engine under varying operating conditions. ANSYS FLUENT 13, which is linked to a chemical kinetic model via CHEMKIN-CFD, a plug-in chemistry solver, is utilised. The soot entrainment focuses on thermophoretic soot deposition on the cylinder liner and soot transport into the crevice region via blowby. During the closed cycle combustion process, the mass of soot deposited on liner via thermophoresis is more significant than that transported into the crevice region through blowby, representing at least 95% of the total soot entrained. The percentage of entrained soot from the net amount of exhaust soot is dependent on the methyl ester type. Diesel results in the maximum soot entrainment with the largest averaged diameter while coconut methyl esters with short hydrocarbon chain length produces the smallest amount and size of entrained soot. Different saturation levels give rise to different soot entrainment processes under varying operating conditions. Overall, this work provides detailed insights into the main in-cylinder processes controlling soot entrainment for biodiesels.