Utilization of waste plastic oil in diesel engines: a review

Abstract

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) which could be recycled as a fuel for diesel engines. This method presents a sustainable solution for (a) waste plastic management as the gap between global plastic production and waste plastic generation keeps widening, (b) replacing diesel partially or wholly which is currently extracted from fast depleting fossil crude oil. The present work attempts to bring together all the investigations pertaining to WPO usage either (a) as a neat fuel or (b) as a blend component with diesel or (c) with an oxygenated additive till date in diesel engines and reviews the engine’s performance, emission and combustion characteristics. Majority of the works utilised WPO extracted from mixed waste plastic as a feedstock using a laboratory scale batch reactor via catalytic pyrolysis. Silica, Alumina, ZSM-5 and Kaolin were used as catalysts. This method often yielded up to 80% of liquid WPO. This oil had a slightly lower cetane number than fossil diesel and hence produced longer ignition delays and higher heat releases during premixed combustion phasing. NOx emissions were higher with WPO which is addressed by modifying the injection timing or by means of EGR. Contrary to popular belief, smoke emissions are mostly lower with WPO and could be brought down further to Euro levels by the use of oxygenated additives. In summary, WPO was found to run smoothly in diesel engines and more work is necessary to study the PM characterisation and long-term durability of the engine when fueled with this oil.