Numerical modeling of soy biodiesel to maximize engine power and efficiency while minimizing pollutant emissions
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Biodiesel is a renewable fuel that can help to reduce dependence on foreign petroleum and to help control the negative environmental effects of combustion engines. This work develops a numerical model for soy biodiesel combustion in diesel engine applications. A comprehensive breakup model for diesel and biodiesel combustion calculations using the KIVA- 3V is presented. The primary breakup model calculates the outcome of the initial breakup stage using flow conditions, nozzle geometry, and liquid fuel characteristics, and assigns the Sauter Mean Radius (SMR) values to injecting droplets. The Kelvin-Helmholtz/Rayleigh-Taylor(KH-RT) model acts as the secondary model to break up injected particles. Good agreement between simulation and the experimental results was found for both diesel and soy biodiesel fuels. The model was capable of accurately predicting liquid length, spray angle, and steady liquid penetration.The results showed that the Taylor Analogy Breakup (TAB) model under predicts the spray behavior, while deactivating the secondary breakup model tends to over predict these behaviors. Soy biodiesel fuel property estimation techniques were validated indirectly using experimental spray data and one set of fuel property models capable of predicting accurate liquid length for soy biodiesel was presented.Results revealed a significant difference in estimation techniques, with the highest discrepancy found in enthalpy calculation techniques. The results also showed that a higher average fuel particle temperature will result in smaller spray. Almost all the cases tend to over estimate the liquid length with some extreme cases predicting wall impingement. A computationally efficient, two step reaction, pre-calculated chemical kinetic model for soy biodiesel combustion, capable of predicting both power and NOx emission in diesel engine configuration was proposed. The results showed that the model is capable of accurately predicting ignition delay, maximum cylinder pressure, and NOx emissions. Two single step global kinetic reactions were investigated and compared against experimental data. Both models under predict ignition delay, maximum cylinder pressure, and NOx emission. The two step mechanism model was utilized in a soy biodiesel injection timing optimization study. Start of injection (SOI) of 2 degrees before top dead center (BTDC) was reported as the optimized injection timing.