Simulation and Analysis of In-Cylinder Soot Formation in a Low Temperature Combustion Diesel Engine Using a Detailed Reaction Mechanism

摘要

3-D Computational Fluid Dynamics (CFD) simulations have been performed using a detailed reaction mechanism to capture the combustion and emissions behavior of an IFP Energies Nouvelles optical diesel engine. Simulation results for in-cylinder soot volume fraction (SVF) have been compared to experimental data reported by Pires da Cruz et al. [1] for the engine operating in low-temperature combustion (LTC) mode with high EGR, and for varied operating conditions. For the simulations, a 4-component surrogate blend containing n-hexadecane, heptamethylnonane, 1-methylnaphthalene, and decalin was used to represents the chemical and physical properties of the standard European diesel used in the engine tests. A validated detailed surrogate mechanism containing 392 species and 2579 reactions was employed to model the chemistry of fuel combustion and emissions. In addition, a new pseudo-gas soot model was developed and coupled with the fuel chemistry to simulate in-cylinder soot nucleation, growth, and oxidation processes. A 60° sector mesh containing 53500 cells was used for the engine simulations using the FORTE CFD simulation software. Comparisons of calculated incylinder soot volume fractions to those measured show good agreement for crank-angle-resolved SVF. Soot production nominally begins as soon as the combustion starts around 6 crank angle degrees (CAD) after TDC, and peaks approximately 12 CAD after TDC when soot oxidation begin to dominate. Simulations captured the location of soot in the center of the bowl just above the wall, and trends in SVF with variation in operating parameters, including fuel loading, EGR, injection timing, and intake temperature. Advancing injection timing and increasing fuel loading increases peak soot levels, whereas lower EGR and lower intake temperatures lower peak soot levels. Simulations also capture the trends in other emissions for varied operating conditions. Further analyses have been performed to understand the combustion and emissions processes.