Waste plastics pyrolytic oil is a source of diesel fuel: A recent review on diesel engine performance, emissions, and combustion characteristics

Abstract

Most waste plastics can be converted into automobile fuel through the pyrolysis process. Plastic pyrolysis oil (PPO) has a heating value comparable with commercial diesel. The properties of PPOs depend on parameters such the plastic and pyrolysis reactor types, temperature, reaction time, heating rate, etc. This study reviews the performance, emissions, and combustion characteristic of diesel engines fuelled with neat PPO, PPO and diesel blends, and PPO with oxygenated additives. PPO has higher viscosity and density, higher sulphur content, lower flash point, lower cetane index and an unpleasant odour. PPO displays a higher delay in ignition during the premixed combustion phase. The literatures reported that diesel engines can run with PPO without any modification to the engine. This paper reveals that the brake specific fuel consumption can be lowered by 17.88 % by using neat PPO in the engine. Brake thermal efficiency can be reduced by 17.26 % while blends of PPO and diesel are used. Some studies say NOx emission can be reduced up to 63.02 %, however, others indicate that it can be increased up to 44.06 % compared to diesel when PPO is used in engines. The highest reduction in CO₂ emission was found to be 47.47 % using blends of PPO and diesel; conversely, the highest increase was documented as 13.04 % when only PPO is used as fuel. In summary, PPO has very high potential as a substitute for commercial diesel fuel through further research and by improving its properties through post-treatment processing such as distillation and hydrotreatment.