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An experimental investigation was performed to find out the fuel properties including specific gravity, density, and viscosity of diesel and biodiesel fuel in the temperature range from 0 to 200°C. Test fuels used were a conventional diesel, neat biodiesel (100% methyl ester of soybean oil), and their blends with blending ratios of 20%, 40%, 60%, and 80%. In order to analyze the fuel properties, the experiments were carried out at various temperatures for each of the six test fuels and the resulting measurements of the biodiesel and its blends were compared with the properties of conventional diesel fuel. In this work, the specific gravity of biodiesel fuel increased with the increase of the blending ratio of biodiesel and gradually decreased as the fuel temperature increased linearly. The density value measurement was correlated as a function of fuel temperature and blending ratio by an empirical equation. The viscosity of the test fuels was found to decrease linearly with increasing temperature and decreasing blending ratio. The kinematic viscosity obtained by this investigation agrees well with the empirical equation which is derived from the measured results.

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An experimental investigation was performed to analyze the effects of undiluted biodiesel fuel (100% methyl ester of soybean oil) on spray, combustion, and exhaust emissions characteristics in a direct injection (DI) common-rail diesel engine with a cooled-EGR system. The macroscopic and microscopic injection characteristics for test fuels such as injection mass, injection rate, droplet diameter, and spray tip penetration were measured by using an injection rate meter, a spray visualization system, and a droplet measuring system. The study of combustion and exhaust emission characteristics was carried out under various engine operating conditions for biodiesel fuel, and the results were compared to those of ultra low sulfur diesel (ULSD). In this work, the injection characteristics of test fuels such as injection rate and mass results are very similar for diesel and biodiesel fuel derived from soybean oil. However, when comparing the start of injection, biodiesel resulted in short injection delay. The Sauter mean diameter (SMD) of biodiesel fuel is higher than that of diesel fuel, and biodiesel showed longer spray tip penetration as compared to that of diesel fuel. Combustion of diesel and biodiesel fuels indicated similar patterns of combustion pressure and rate of heat release. However, the combustion of biodiesel showed lower peak combustion pressures and peak heat release rates than those of diesel fuel becase of its LHV (lower heating value). The comparison of emission characteristics of biodiesel and diesel fuel shows that the biodiesel fuel emitted higher indicated specific NO x and a remarkably low level of soot emissions.