A Study on Performance, Emissions, Durability and Optimisation of a Marine Diesel Engine Fuelled with Raw Microalgae Oil

Abstract

This study investigated the performance, emissions, durability, and optimisation of a single- cylinder diesel engine fuelled with Schizochytrium sp. microalgae oil (MAO), diesel oil (DO), and MAO/DO blends. The engine experiments were conducted under different operating conditions to produce a comparative study of the critical parameters of MAO and DO, including brake power (BP), brake specific fuel consumption (BSFC), brake thermal efficiency (BTE), in-cylinder pressure, heat release rate (HRR), exhaust gas temperature (EGT), nitrogen oxides (NOx) and carbon monoxide (CO) emissions. A key finding from this research project was a substantial reduction in NOx and CO emissions when the engine was fuelled with MAO. This is due to the higher viscosity of MAO which results in lower combustion efficiency and a reduced release of heat, causing a reduction in emissions. Moreover, the lower calorific value (CV) of MAO causes the fuel system to inject more fuel to maintain the same output power, which increases the BSFC. The study also identified reductions in engine brake power and BTE, in some test conditions, when the engine was fuelled with MAO. The difference in brake power and BTE is a result of the differences in properties between MAO and DO, in particular parameters such as CV, viscosity, and oxygen content. In terms of MAO engine durability tests, deterioration of piston rings was found within 60 hours operation. The polymerisation process, created by the MAO on the contacting surface of the piston ring and cylinder liner, may cause the top two piston rings to malfunction as the cylinder’s hottest point is from the crown to the skirt of the piston. Lubricant oil (LO) viscosity, density, total acid number, wear, and additive metal concentrations of the MAO fuelled engine were measured and it was concluded that no significant difference was observed, compared to the same DO fuelled engine. Further optimisation studies, using the Taguchi method, to improve the engine performance and emissions were conducted through an engine model developed using Ricardo Wave software. Experimental results were used to validate the developed model for all tested fuels. The chosen operational factors, which have the greatest impact on the system are injection pressure, start of ignition, injection duration, nozzle diameter, compression ratio, and injection temperature. The analysis and simulation indicate that the brake power, BMEP and BTE all increased by up to 10%. BSFC and NOx concentration are decreased by 10% and 44%, respectively, when the operational factors mentioned above were optimised in the validated numerical model. Overall, the experimental and simulation studies demonstrate the potential of MAO as a feasible alternative fuel that offers a promising solution to the decarbonisation of the marine sector.