| Biodiesel is a promising alternative to petroleum-based diesel fuel because it is renewable and its extensive use in unmodified engines has proved to be very successful. However, its future use may be limited by the higher oxides of nitrogen (NOx) emissions that are typically generated relative to petroleum diesel. The purpose of this research was to increase the scientific understanding of the fundamental mechanisms of NO x generation in diesel engines fueled with biodiesel through modeling of the spray, ignition and combustion process of biodiesel, and to evaluate some strategies for reducing NOx emissions.; Computational methods were developed to estimate the physical and thermodynamic properties of biodiesel for combustion modeling. A computer software program, BDProp 1.0, was developed based on the property estimation methods. The estimated results were compared to measured or published data where available and were found to be sufficiently accurate for use as a fuel definition for biodiesel combustion modeling efforts.; The computational modeling of the spray, ignition, combustion, and NO x emissions of biodiesel in diesel engines was conducted. Several sub-models were developed for KIVA-3V to include biodiesel in the fuel library. The predicted cylinder pressure, heat release and NOx emissions from the modified KIVA-3V model were compared to and were found to be in close agreement with experimental data that were collected from a John Deere 4045T diesel engine fueled with diesel (D2), soybean methyl ester (SME), yellow grease methyl ester (YGME), and genetically modified soybean methyl ester (GMSME). Higher overall cylinder temperatures were observed for SME compared to D2, which was regarded as a direct cause of the higher NOx emissions of SME. Based on the computational modeling results, the higher overall cylinder temperatures of SME were attributed to the earlier start of injection and decreased spray cone angle, which were seen as the leading reasons for higher NOx emissions.; Computational modeling was applied to evaluate strategies for reducing NOx emissions from biodiesel combustion. The results indicated that increasing spray cone angle, retarding start of injection, applying exhaust gas recirculation (EGR) and charge air cooling were all effective in reducing NOx emissions from biodiesel. |
