| The energy shortage and environmental pollution are two concerns in the modern society. Biodiesel, a clean and renewable oxygenated alternative fuel, could greatly contribute to alleviating the energy crisis and environmental problems. However, for their diversity in feedstock sources, there inevitably exists distinct variance among their physical and chemical properties for different biodiesels. This work aims to identify the effect of biodiesel components on fuel injection and spray process. Therefore, the detailed injection and spray characteristics of three fatty acid esters with different carbon chain lengths(methyl oleate, ethyl oleate and methyl laurate) are studied and compared to those of fossil diesel.(1) The single injection characteristics of fatty acid esters and diesel are investigated with mono injection qualifier on the injection test system. It is found that four test fuels produce similar trends in pressure fluctuation at injector inlet, injection rate and cycle injection quantity. Also, the fuel properties pose important influence on those injection parameters.(2) On the same test system, the two stage injection processes of fatty acid esters and diesel are investigated. It is noted that the influences of fuel physical properties on the two stage injection process are similar with those on single injection process. In addition, pilot injection energizing time, main injection energizing time and injection dwell time place distinct effect on injection characteristics.(3) The simulation results using an injector model can agree well with experimentally obtained injection rate curves, injector inlet pressure fluctuation and cycle injection quantity in the two stage injection process. It is found that fuel density and bulk modulus significantly affect the two stage injection process while a weak effect of fuel viscosity is found.(4) The macroscopic and microscopic spray characteristics of test fuels are measured on the spray test system with a high speed photography camera and a split laser particle size analyzer, respectively. The results show that fuel properties play important role in spray penetration distance, projected spray area, spray cone angle and droplet sizes, thus influencing the fuel atomization process and the fuel-air mixing quality. |
