Combined influence of injection timing and EGR on combustion, performance and emissions of DI diesel engine fueled with neat waste plastic oil

Disposal of waste plastic accumulated in landfills is critical from the environmental perspective. The energy embodied in waste plastic could be recovered by catalytic pyrolysis as waste plastic oil (WPO) and could be recycled as a fuel for diesel engines. This method presents a sustainable solution for waste plastic management as the gap between global plastic production and waste plastic generation keeps widening. The present study investigates the combined influence of EGR and injection timing on the combustion, performance and emission characteristics of a DI diesel engine fueled with neat WPO. Experiments were conducted at three injection timings (21 degrees, 23 degrees and 25 degrees CA bTDC) and EGR rates (10, 20 and 30%) at the engine's rated power output. When compared to diesel, the combustion event occurred closer to the TDC when the injection timing is delayed from 25 degrees CA bTDC to 21 degrees CA bTDC. The peak in-cylinder pressures and HRRs dropped gradually as the injection timing was delayed from 25 degrees CA bTDC to 21 degrees CA bTDC at all EGR rates. The engine delivered diesel-like fuel consumption with 5.1% higher brake thermal efficiency. NOx decreased up to 52.4% under 30% EGR when WPO was injected lately 21 degrees CA bTDC. Smoke density remained lower by 46% and 9.5% for 10% and 20% EGR rates respectively for WPO only at early injection timing of 25 degrees CA bTDC. HC and CO emissions stayed lower at early injection timing of 25 degrees CA bTDC under 10% EGR. WPO injected at the advanced injection timing of 25 degrees CA bTDC and low EGR rate of 10% was found to simultaneously reduce smoke and NOx by 46% and 38% respectively.