Experimental study on injection characteristics of fatty acid esters on a diesel engine common rail system

The injection processes of three fatty acid esters (methyl laurate, methyl oleate and ethyl oleate) are investigated on a high pressure common rail injection system and compared to that of diesel fuel. The cycle injection rate, cycle injection quantity and pressure fluctuation at the injector inlet during and after the injection event are studied across a range of injection pressure and injector energizing time. Test fatty acid esters show smoother rising slopes at the start of injection and lower injection rates at the stable injection period in the volumetric injection rate curves, but the mass injection rates among all test fuels are quite close. Fatty acid esters have longer injection delay than diesel fuel; while increased injection pressure causes reduced injection delay but prolonged injection duration. Injector energizing time significantly influences the shape of injection rate curve and the pressure fluctuation at the injector inlet. After the needle valve closure, pressure oscillation damps more rapidly for methyl oleate and ethyl oleate, due to their high density, viscosity and bulk modulus of compressibility.