On the effect of injection pressure on spray combustion and soot formation processes of gasoline/second generation biodiesel blend

Abstract

70GB, which comprises 70% gasoline and 30% biodiesel, shows excellent potential for application in gasoline compression ignition due to its superior lubrication capability, renewability, environmental friendliness, high ignitability contributed by biodiesel namely as Hydrogenated catalytic biodiesel (HCB), and high volatility conferred by gasoline. However, the spray combustion and emission characteristics of 70GB fuel have not yet been quantitatively evaluated. In this work, we performed a comprehensive simulation focusing on the ignition delay, heat release rate, flame lift-off length, flame structure, and soot formation of 70GB in a constant volume chamber under various fuel injection pressure. Numerical results showed that, different injection pressure strongly impact the HRR without affecting the maximum temperature. Increasing the injection pressure from 80 to 120 Mpa, increased the heat release rates by 23. %. The ignition delay was marginally affected by increasing injection pressure, while a 5.7 mm increase in flame lift-off length observed with higher injection pressure. Additionally, 65% lower soot formation was typically predicted for higher injection pressure 120MPa. In particular, the soot mass is primarily controlled by enhancing the atomization and evaporation processes, as well as improving fuel-air mixing rate, which was achieved by increasing the injection pressure. Furthermore, the role of soot oxidation was insignificant in reducing soot with increasing injection pressure, while the soot initiation step and soot surface growth step play an important role in soot suppression with increasing injection pressure for 70G fuel.