Development of a Reduced Chemical Reaction Kinetic Mechanism with Cross-Reactions of Diesel/Biodiesel Fuels

Abstract

Biodiesel is a clean and renewable energy, and it is an effective measure to optimize engine combustion fueled with biodiesel to meet the increasingly strict toxic and CO₂ emission regulations of internal combustion engines. A suitable-scale chemical kinetic mechanism is very crucial for the accurate and rapid prediction of engine combustion and emissions. However, most previous researchers developed the mechanism of blend fuels through the separate simplification and merging of the reduced mechanisms of diesel and biodiesel rather than considering their cross-reaction. In this study, a new reduced chemical reaction kinetics mechanism of diesel and biodiesel was constructed through the adoption of directed relationship graph (DRG), directed relationship graph with error propagation, and full-species sensitivity analysis (FSSA). N-heptane and methyl decanoate (MD) were selected as surrogates of traditional diesel and biodiesel, respectively. In this mechanism, the interactions between the intermediate products of both fuels were considered based on the cross-reaction theory. Reaction pathways were revealed, and the key species involved in the oxidation of n-heptane and MD were identified through sensitivity analyses. The reduced mechanism of n-heptane/MD consisting of 288 species and 800 reactions was developed and sufficiently verified by published experimental data. Prediction maps of ignition delay time were established at a wide range of parameter matrices (temperature from 600 to 1 700 K, pressure from 10 bar to 80 bar, equivalence ratio from 0.5 to 1.5) and different substitution ratios to identify the occurrence regions of the cross-reaction. Concentration and sensitivity analyses were then conducted to further investigate the effects of cross-reactions. The results indicate temperature as the primary factor causing cross-reactivity. In addition, the reduced mechanism with cross-reactions was more accurate than that without cross-reactions. At 700–1 000 K, the cross-reactions inhibited the consumption of n-heptane/MD, which resulted in a prolonged ignition delay time. At this point, the elementary reaction, NC₇H₁₆+OH<=>C₇H₁₅-2+H₂O, played a dominant role in fuel consumption. Specifically, the contribution of the MD consumption reaction to ignition decreased, and the increased generation time of OH, HO₂, and H₂O₂ was directly responsible for the increased ignition delay.

Keywords

Marine engines and fuels / Renewable energy / Biodiesel / Diesel / Reduced mechanism / Cross-reactions

RIGHTS & PERMISSIONS

Harbin Engineering University and Springer-Verlag GmbH Germany, part of Springer Nature