Modelling of combustion and emissions of a direct injection compression ignition heavy-duty engine fuelled with cashew nutshell liquid biodiesel

Abstract

Several studies have shown that the efficient use of bioenergy can reduce greenhouse gas emissions and keep global temperatures below 2°C. Among biofuels, cashew nut shell liquid (CNSL) biodiesel from inedible feedstock is considered sustainable, environmentally friendly, and economically beneficial. However, knowledge gaps exist regarding how to improve in-cylinder combustion phenomena and reduce emissions with the use of CNSL biodiesel in diesel engines. This research aims to explore the potential of CNSL for the production of biodiesel and further determine the combined effects of combustion chamber geometry and injection parameters on the combustion and emission characteristics of CNSL biodiesel in a direct injection compression ignition diesel engine using CFD software, ANSYS FORTE. The RNG k- ε turbulence model was used to examine physical phenomena associated with kinetic energy changes. To reduce time and cost, a sector mesh at a 45° angle with periodic boundary conditions is used instead of the entire engine geometry. The substitute for diesel fuel was n-heptane, which was modelled and simulated in five different combustion chamber piston bowl designs with varying injection parameters. Simulation results were similar to the experimental data for in-cylinder pressure, temperature, heat release rates, and exhaust emissions of CO, UHC, NOx, and soot. ANSYS CHEMKIN-PRO was used to solve complex chemical and gas reaction models by implementing the properties of CNSL biodiesel-diesel blends using methyl palmitate and methyl oleate with the merger of n-heptane in ANSYS FORTE to conduct simulations. In turn, two optimized piston bowl designs were used to model and simulate the impact of CNSL biodiesel and diesel blends (B10, B20, B30, and B50) on combustion and emissions. Results show that diesel engines can utilise CNSL B10 and B20 without significant engine modifications. A CNSL biodiesel blend emits fewer CO and UHC compared to diesel, and further reductions occur as the blend percentage increases. With an increased proportion of CNSL biodiesel in the blends, the gross indicated specific fuel consumption (GISFC) increased significantly. A larger spray-included angle and advanced injection timing increased NOx emissions marginally but reduced soot emissions and GISFC.