Numerical Investigation of the Combustion Kinetics of Partially Premixed Combustion (PPC) Fueled with Primary Reference Fuel 2020-01-0554
This work numerically investigates the detailed combustion kinetics in a gasoline compression ignition (GCI) engine using three fuel injection strategies, including single-injection, double-injection, port fuel injection and direct injection (PFI+DI). A reduced Primary Reference Fuel (PRF) chemical kinetics mechanism was coupled with CONVERGE-SAGE CFD model to predict GCI combustion under various operating conditions. To provide insight into key reaction pathways, a post-process tool was used. The validated Converge CFD code with the PRF chemistry and the post-process tool was applied to investigate how the ignition occurs during the low-to high-temperature reaction transition and how it varies due to single- and double-injection and PFI+DI injection strategies. Three characteristic GCI combustion features were selected: (1) initial low temperature heat release (LTHR); (2) intense LTHR, where both iso-octane and n-heptane were converted to intermediates through oxygen-related reactions; (3) early stage high temperature heat release (HTHR) with CH2O as the core source species. It is found that the heat release was primarily dominated by the reaction H+O2 (+M)=HO2 (+M) and AC8H¬17+O2=AC8H17O2 during LTHR. For single- and double-injection, the high reactivity fuel/air mixture and bulk gas movement play an important role in the initial auto-ignition kernel characterized by the region of the representative destruction reaction (RDR) of HO2. The RDRHO2 region featured with medium temperature (around 1000 K) produces more H2O2/HO2 radical before the auto-ignition than low-temperature combustion. The rapid dissociation of H2O2 provides a large amount of OH radical that enhances the chain branching reaction as well as heat release process which then initiates the autoignition of n-heptane. The H atom is also found to promote the chain branching during auto-ignition.
Yuanyuan Zhao, Hu Wang, Xinlei Liu, Daojian Liu, Wang Chen, Hongyan Zhu, Mingfa Yao
Tianjin University, King Abdullah University of Science & Technology