A Study of Flow Characteristics on the Diesel-Gasoline Dual-Fuel Combustion by 3-D CFD 2019-24-0117

Various advanced combustion concepts, which can achieve higher thermal efficiency and emissions reduction, have been suggested as the emissions regulation gets stricter. Dual-fuel combustion that operates by using different fuels having both premixed and non-premixed combustion characteristics is one of the viable alternatives. In dual-fuel combustion, it is critical to understand air-fuel mixture distribution as it determines the ignition spot and following combustion phase. The fuel distribution in the engine is affected by various factors, such as chamber geometry, injection strategy or in-cylinder flow motion. Furthermore, among them, in-cylinder motion, usually described in terms of swirl or tumble motion, is mostly affected by in-cylinder port geometry.

In this paper, 3-dimensional Computational Fluid Dynamics (CFD) was used to investigate the effect of in-cylinder flow motion in dual-fuel combustion. Two head and port geometries were used in the simulations. One is the conventional diesel engine shape that has a flat head and intake ports with swirl-inducing shape; the other one has a pent-roof shape with straight intake port geometry. For the combustion model, the Representative Interactive Flamelet (RIF) model and G-equation were combined to solve the auto-ignition of direct-injected diesel fuel and the flame propagation of premixed gasoline fuel. For the chemical mechanism, the reduced Primary Reference Fuel (PRF) mechanism with 73 species and 296 reactions was used. The flow analysis was first conducted with different geometry cases under a full-mesh condition and was followed by the combustion analysis which was conducted under a sector mesh condition by using the flow simulation results as initial conditions. This paper illustrates the effect of difference in in-cylinder flow motion on the fuel distribution and combustion characteristics.