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The effects of the physical and chemical properties of biodiesel fuels on the combustion process and pollutants formation in Direct Injection (DI) engine are investigated numerically by using multi-dimensional CFD models. In the current study, methyl butanoate (MB) and n-heptane are used as the surrogates for the biodiesel fuel and the conventional diesel fuel. Detailed kinetic chemical mechanisms for MB and n-heptane are implemented to simulate the combustion process. It is shown that the differences in the chemical properties between the biodiesel fuel and the diesel fuel affect the whole combustion process more significantly than the differences in the physical properties. While the variations of both the chemical and the physical properties between the biodiesel and diesel fuel influence the soot formation at the equivalent level, the variations in the chemical properties play a crucial role in the NO emissions formation.

The current work aims to develop a reliable numerical model simulating the depletion and decomposition process of urea-water solution (UWS) droplets injected in a hot exhaust stream as experienced in an automotive urea-based selective catalytic reduction (SCR) system. The depleting process of individual UWS droplets in heated environment is simulated using a multicomponent vaporization model with separate depletion law for each component. While water depletion is modeled as a vaporization process, urea depletion from the UWS droplet is modeled using two different approaches. The first approach models urea depletion as a vaporization process with an experimentally determined saturation pressure. The second approach models urea depletion as a direct thermolysis process from molten urea to ammonia and isocyanic acid using various sets of kinetic parameters. Comparison with experimental data shows the superiority of modeling urea depletion as a vaporization process.