An investigation into spray combustion processes of waste cooking oil biodiesel fuel under diesel engine conditions using the LIF-PIV, shadowgraph, and chemiluminescence techniques

Abstract

In this study, WCO biodiesel and conventional diesel fuels were characterized fundamentally in the context of their spray, gas entrainment, and combustion characteristics under diesel-like engine conditions. This was achieved using laser-induced fluorescence and particle image velocimetry (LIF-PIV), shadowgraph, and chemiluminescence techniques under non-evaporating, evaporating, and reacting conditions. The impact of fuel injection pressure and nozzle diameter on spray and gas entrainment characteristics of the fuel were also investigated. Due to higher viscosity and surface tension, it was observed that WCO biodiesel produced longer spray penetration and narrower spray angle than diesel fuel under non-evaporating conditions. Furthermore, the quantity of gas entrained by WCO biodiesel spray was lower. Due to higher distillation temperature and less gas entrainment, the WCO biodiesel liquid length was longer. The combined effect of ultra-high injection pressure of 300 MPa with a smaller nozzle hole diameter of 0.08 mm was observed to enhance gas entrainment processes. Due to its higher cetane number, WCO biodiesel displayed a shorter ignition delay. While higher injection pressure influenced the combustion processes, with less air entrained upstream of the WCO biodiesel lifted flame, it was observed that fuel oxygen content played a crucial role in its soot formation.