A comprehensive biodiesel combustion model is presented for use in multi-dimensional engine simulations. The model incorporates realistic physical properties in a vaporization model developed for multi-component fuel sprays and applies an improved mechanism for biodiesel combustion chemistry.
Previously, a detailed mechanism for methyl decanoate and methyl-9-decenoate was reduced from 3299 species to 85 species to represent the components of biodiesel fuel. In this work, a second reduction was performed to further reduce the mechanism to 69 species. Steady and unsteady spray simulations confirmed that the model adequately reproduced liquid penetration observed in biodiesel spray experiments. Additionally, the new model was able to capture expected fuel composition effects with low-volatility components and fuel blend sprays penetrating further.
A new biodiesel chemistry modeling strategy was implemented that utilizes n-heptane to improve ignition behavior and two biodiesel experiments were chosen to validate the model under engine operating conditions. First, a low-speed, high-load, conventional combustion experiment was simulated and the model was able to predict the performance and NOx formation seen in the experiment. Second, high-speed, low-load, low-temperature combustion conditions were successfully modeled and the HC, CO, NOx, and fuel consumption were well-predicted for a sweep of injection timings. The LTC results included a comparison of biodiesel composition (palm vs. soy) and fuel blends (neat vs. B20). The model effectively reproduced trends observed in the experiments including a reduction in NOx with neat biodiesel at these conditions.