Waste plastic pyrolysis oils as diesel fuel blending components: detailed analysis of combustion and emissions sensitivity to engine control parameters

Abstract

Efforts to reduce greenhouse gas emissions and ensure energy security have led to increased interest in renewable energy technologies, particularly pyrolysis for converting waste into fuel. This study examines the use of polypropylene (PPO) and polystyrene (PSO) pyrolysis oils as diesel fuel (DF) blending components. Single-cylinder engine tests were conducted on PPO and PSO, each blended with DF in mass proportions of 20%, 40% and 60%. The engine featured a state-of-the-art compression ignition combustion system, including an 8-hole high-pressure injector and precisely controlled air and exhaust gas recirculation paths. Results proved that both PPO and PSO could be efficiently combusted in modern compression ignition systems, provided their admixture with reference DF did not exceed 60%. For optimal performance, the engine control map needed to be re-calibrated to prevent over-homogenization of the pilot spray, caused by higher volatility and reduced fuel reactivity. When maximising waste-derived components, PPO provided optimal emission results (1.37 g/kWh NOX and 0.04 g/kWh PM) when combined with heavy EGR and advanced injection timing. In this case, the total emissions overlimit value was 3.7, compared to 7.3 in the best-case DF scenario (a 50% reduction in cumulative emissions). For minimizing emissions, small additions (20%) of highly volatile PSO were found to offer the greatest potential for co-optimization. Compared to the optimal DF configuration, a cumulative emissions reduction of 81% was achieved in the same calibration map region as for PPO.