Injection Pressure Characteristics of Palm Methyl Ester and Diesel in Solenoid Injector under Common-Rail System 2016-01-1729

Nowadays, the diesel engine models are developed from a unit pump to a common-rail injector. With palm methyl ester (commonly known as biodiesel) with higher viscosity and density than conventional diesel being used as alternative fuel for diesel, palm methyl ester may affect the injection characteristics. Injection pressure is one of the important parameters of common rail injector. Because of its effects on the pressure between command port and control volume, which activates a needle lift during injection process. This paper presents injection characteristics of solenoid injector experimented in a Zeuch’s chamber with a focus on injection pressure frequency, injection pressure amplitude, injection pressure stable duration. Commercial diesel (with mandate of 5% biodiesel blend or B5) and palm methyl ester (B100) were used as the test fuels at various injection pressures (40, 80, 120 and 160 MPa). The back pressure was kept constant at 4.5 MPa in the Zeuch’s chamber while energizing durations were altered (0.5, 1, and 2.5 milliseconds). The single hole injector with diameter of 140 micron was applied throughout the experiment.

Higher density of palm biodiesel caused lower elastic fuel deformation and higher bulk modulus, which contributed to faster approximate sound velocity and larger pressure difference. For injection pressure characteristic, longer energizing time (ET) caused reduced injection frequency and increased injection pressure amplitude due to pressure difference in the injection pipe. When compared to diesel (B5), B100 showed reduced injection frequency but larger injection frequency amplitude in all injection pressure values because higher viscosity and density directly affected fuel flow in the injection pipe. In addition, injection pressure stable duration increased with increasing injection pressure. At high injection pressure and ET of 0.5 ms, injection pressure stable duration increased, as expected from decreased injection pressure difference in the pipe, as well as Water-Hammer phenomenon from needle closing impacting injection pressure. Similarly, B100, with higher bulk modulus causing faster approximate sound velocity, yielded longer injection pressure stabile duration.