Optimising Injection Strategies and EGR in Modified Piston Diesel Engines Fuelled with Waste Plastic Oil

Growing concerns over plastic pollution and fossil fuel depletion have driven research toward alternative fuels and engine optimisation strategies. The transition from fossil-based fuels to alternative fuels is imperative for reducing greenhouse gas emissions and addressing plastic waste. This study investigates the synergistic effects of injection pressure, ignition timing and exhaust gas recirculation on a single-cylinder diesel engine with modified piston bowl geometry using waste plastic oil-diesel blends. Waste plastic oil, derived via pyrolysis of municipal plastic waste, was blended with diesel in varying propor-tions (25–100%). Tests on engines were performed with varying injection pressures (200–500 bar), ignition timing (17°−23° before top dead centre) and exhaust gas recirculation rates (0–9%). Results reveal that the D25WP75 blend at 500 bar and 23° before top dead centre offers a peak brake thermal efficiency, minimum brake specific fuel consumption, and reduced emissions of CO, HC, NOx and smoke opacity. Optimal exhaust gas recirculation at 6% further reduced NOx. The maximum cylinder pressure and heat release rate are obtained at 73.02 bar and 52.66 J/deg. The improvement percentage in brake thermal efficiency at 500 bar for the D25WP75 blend compared with D100 is 10.8%, with a reduction in brake specific fuel consump-tion of 11.76%. It is also observed that NOx reduces by 5.46%, CO by 44%, HC by 8.82% and smoke by 35.38%. The combined impact of piston geometry modification and injection strategies improved combustion uniformity and emission control. The findings suggest that integrating fuel modification with combustion optimisation offers a viable pathway to cleaner diesel engine operation.