Impact of waste-plastic-derived diesel on the performance and emission characteristics of a diesel engine under low load conditions

In recent years, hybrid (e.g. diesel-renewable) power systems have been implemented in many isolated regions (e.g. remote areas and islands) to reduce dependency on diesel generation. Nevertheless, low load (up to 30% of the maximum rated power) at variable speed operations is considered flexible and relevant for maximum renewable energy penetration because of the high cost and complexity of the conventional mode with fixed speed operation in the hybrid system. Given the increasing emphasis on fossil fuels in power generation sectors, plastic-derived diesel can be a suitable alternative. In this study, plastic-derived diesel was used for engine testing. It was produced from plastic crude oil from high-density polyethylene, polypropylene and polystyrene in a 1:1:1 ratio by using a vacuum distillation technique via the pyrolysis process. The pyrochemical properties of plastic-derived diesel were tested after distillation. The present work focused on validating the two-zone thermodynamic model for investigating engine performance and emissions at variable speeds (i.e. 1200, 1500, 1800 and 2100 rpm) at 5, 10, 15, 20, 25 and 30% load conditions fuelled with ultra-low sulphur diesel and plastic-derived diesel blends (5, 10 and 20). The simulation and experimental results showed good agreement. The maximum variation of 17.2% was found between the experimental and simulated results at mentioned speeds and loads for all tested fuels. Compared with ultra-low sulphur diesel, plastic-derived diesel showed a significant improvement in brake power, torque, brake thermal efficiency and brake-specific fuel consumption. The maximum brake power variation was 9.85% for plastic-derived diesel (20%) at 1200 rpm at 5% load. Moreover, the minimum brake specific fuel consumption variation was 4.15% for ultra-low sulphur diesel at 1500 rpm and 25% load. Compared with the commercial ultra-low sulphur diesel, 20% of plastic-derived diesel blends exhibited maximum reductions of 4.75, 5.95, 4.45 and 4.35% in NOx, CO2, CO, and HC emissions, respectively, under any tested conditions. Plastic-derived diesel blends showed less particulate matter emission compared to ultra-low sulphur diesel. Therefore, up to at least 20% of the plastic-derived diesel blends tested in this study can be used as an alternative fuel for ultra-low sulphur diesel. Further study should be carried out to test more than 20% plastic-derived diesel blends and reach a conclusion.