Development of a reduced multi-component chemical kinetic mechanism for the combustion modelling of diesel-biodiesel-gasoline mixtures

Abstract

In this study, a compact combined reaction mechanism for diesel-biodiesel-gasoline mixtures (CDBG) is developed, comprising n-heptane, methyl butanoate (MB) and methyl decanoate (MD) as well as toluene and isooctane to represent the combustion characteristics of diesel, biodiesel and gasoline fuels, respectively. The mechanisms are separately reduced prior to combining by means of directed relation graph (DRG), directed relation graphs with error propagation (DRGEP) and full species sensitivity analysis (FSSA). The reduced mechanisms are then combined, and extensive validations are carried out for closed homogenous reactor application under the following conditions: T = 600–1700 K, P = 1–50 atm, and equivalence ratios (Φ) of 0.25–1.5 (156 setups in total). To boost the accuracy of the CDBG mechanism, cross-reaction analysis is performed to identify the important intermediate species and reactions. The identified species and reactions are subsequently integrated into the CDBG mechanism, resulting in significant improvements in ID timings up to 30%, 18% and 16% for the CDBG sub-mechanisms of diesel, biodiesel and gasoline, respectively. In addition, Arrhenius rate constant optimisation is also employed to further improve the ignition behaviour of the proposed kinetic mechanism. The results revealed that the dual implementation of the cross-reaction analysis and Arrhenius rate constant optimisation diminished the maximum associated errors considerably, down to 14.6%, 16.9% and 14.9% for the CDBG sub-mechanisms of diesel, biodiesel and gasoline, respectively. Concisely, the best results achieved at T = 600–1700 K were P = 41 atm and Φ=1, P = 1,4 atm and Φ=1, and P = 50 bar and Φ=0.3 for diesel, biodiesel and gasoline surrogates, respectively.