Comparative Study of Diesel Oil and Biodiesel Spray Combustion Based on Detailed Chemical Mechanisms

A master combustion mechanism of biodiesel fuels has recently been developed by Westbrook and co-workers [1]. This detailed mechanism involves 5037 species and 19990 reactions, the size, which prohibits its direct use in computational fluid dynamic (CFD) applications. In the present work, various mechanism reduction methods included in the Reaction Workbench software [2] were used to derive a semi-detailed reduced combustion mechanism maintaining the accuracy of the master mechanism for a desired set of engine conditions. The reduced combustion mechanism for a five-component biodiesel fuel was implemented in the FORTÉ CFD simulation package [3] to take advantage of advanced chemistry solver methodologies and advanced spray models. The spray characteristics, e.g. the liquid penetration and flame lift-off distances of RME fuel were modeled in a constant-volume combustion chamber. The modeling results were compared with the experimental data. Engine simulations were performed for the Volvo D12C heavy-duty diesel engine fueled by RME on a 72° sector mesh. Predictions were validated against measured in-cylinder parameters and exhaust emission concentrations. The semi-detailed mechanism was shown to be an efficient and accurate representation of actual biodiesel combustion and emissions formation. Meanwhile, as a comparative study, the simulation based on a detailed diesel oil surrogate mechanism were performed for diesel oil under the same conditions.