High-Pressure Spray Dynamics of Palm Oil Biodiesel–Diesel Blends: Numerical Simulation and Experimental Validation

Spray quality directly determines the mixture formation and therefore combustion and emissions in diesel direct-injection engines. Biodiesel obtained from palm oil is a viable replacement for mineral diesel, which is renewable. However, due to its high viscosity and surface tension, the performance of biodiesel in terms of atomization quality is poor. This paper presents a validated CFD analysis of sprays for pure diesel (D100), pure palm oil biodiesel (P100), and three other fuel blends (P20, P50, and P80) at ultrahigh injection pressures of 100, 200, and 300 MPa. CFD simulations were conducted using ANSYS Fluent software version 2019with a Euler–Lagrange discrete phase model (DPM) approach, the realizable k-ε turbulence model, a plain-orifice atomizer, and the Kelvin–Helmholtz/Rayleigh–Taylor (KH-RT) hybrid atomization model in a constant-volume combustion chamber. The spray tip penetration and spray cone angles predicted by the developed model were validated against those provided by previous experiments conducted. The model prediction accuracy was up to 22%, with the largest error for the tip penetration of the spray. It seems that the Ranz correlation is inaccurate due to the exclusion of viscosity and surface tension from the prediction of the cone angle. Parametric analyses show that the SMD reduces significantly with increasing injection pressures, which confirms that ultrahigh injection pressures lead to enhanced atomization of all tested fuel blends. In addition, there exists a nonlinear relationship between injection pressure and spray tip penetration, which is attributed to the drag force acting on a jet of high velocity. Pure palm oil biodiesel (P100) always showed the largest SMD and longest spray tip penetration due to its high viscosity compared to diesel.