Achieving efficient and clean combustion of biodiesel as a renewable source of energy requires a fundamental understanding of the effects of the different thermophysical properties on the fuel injection process at conditions relevant to diesel engines. In this study, the spray characteristics of two fatty acid esters, methyl oleate and ethyl oleate, are compared to a baseline diesel fuel using high-speed imaging of the sprays in a constant volume chamber. A single hole fuel injector with a nozzle diameter of 280 μm was used with a single injection event with a duration of 1.0 ms. The spray development was investigated for fuel-rail pressures of 40, 60, 80 and 100 MPa and the chamber gas densities of 1.15 kg/m3, 5.75 kg/m3 and 11.5 kg/m3. High-speed shadowgraph imaging of the non-vaporizing sprays was performed at 15,000 frames per second. Image processing algorithms were developed to quantify the spray penetration distance, penetration rate and cone angle as a function of time for the injection process. Penetration distance and penetration rate results were similar for the esters and diesel fuel for the range of experimental conditions studied. However, diesel had a larger spray cone angle compared to both esters. Additionally a novel metric for air entrainment was developed based on the macro-scale features of the spray. The integrated mixing volume metric showed no difference in air entrainment between the fuels, which is in good agreement with the behavior expected based on spray theory.

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