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. Engine tests of PPO and PSO blended with DF were conducted using a single-cylinder research engine equipped with 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 from DF-tailored engine calibration showed that PPO and PSO blends, up to 60%, did not cause significant changes in oxides of nitrogen (NOX) emissions compared to DF. PPO admixture did not affect particulate matter (PM) emissions, whereas PSO increased it by 20%. The lower viscosity and higher volatility of pyrolysis oils, combined with lower reactivity, improved mixture homogenization before auto-ignition, albeit with a slight increase in CO and HC emissions. These properties enhanced the potential for waste plastic pyrolysis oil blends with dedicated engine calibration. It was determined that advanced fuel injection combined with high exhaust gas recirculation shifted combustion to a premixed mode, significantly reducing emissions of NOX and PM compared to DF.

Keywords: diesel engine, waste plastic, pyrolysis oil, emissions, engine calibration