Biodiesel Spray Characteristics and a CFD Simulation Study of Injection Timing Effects on the Combustion Process in a Biodiesel-Fueled, Direct-Injection Rotary Engine

Abstract

Energy conservation is important in this modern era because of its high demand in transportation systems coupled with the depletion of fossil fuels. Biodiesel is thus an alternative fuel to replace conventional diesel. This study investigates the effect of chamber pressure (Pamb) and chamber temperature (Tamb) on biodiesel spray penetration length (SL) and spray pattern (SP) characteristics in a constant-volume vessel, under rotary engine working conditions, using spray visualization and image processing techniques. Furthermore, a three-dimensional (3D) direct-injection rotary engine model was developed and used for computational fluid dynamics (CFD) simulation studies of biodiesel distribution, mixture forming, and combustion process at different injection timing (IT) in the cylinder. Results indicate that increasing Pamb decreases SL and broadens SP, while increasing Tamb decreases SL and narrows SP. At advanced IT, biodiesel diffuses and disperses, and at retarded IT, which is the suitable rate for combustion, biodiesel concentrates and narrows. Compared with the original scheme [80° crank angle before top dead center (CA BTDC)], Pmax increases by 16.79%, ϕmax decreases by 28.75%, NO and CO change a little, and CO2 decreases. Its drawback is a 15.65% increase in soot formation.