Experimental and numerical studies on the performance and emission characteristics of waste cooking oil biodiesel fuel and its blends in a direct injection diesel engine

Bahmanisangesari, Sajjad (2024) Experimental and numerical studies on the performance and emission characteristics of waste cooking oil biodiesel fuel and its blends in a direct injection diesel engine. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Internal combustion engines, especially diesel engines, have sustained the transportation industry for over a century. As the global emphasis shifts towards renewable energy sources and improved air quality, biodiesel especially from waste cooking oil (WCO) emerges as a potential solution to the inherent challenges of emissions from diesel engines. This research endeavours to address the prevailing gaps in the understanding of combustion characteristics and emissions of Waste Cooking Oil Biodiesel (WCO B100) and its blends. While previous studies have primarily focused on vessel models and overlooked real-world dynamics like piston movement and the splash model, this research illuminates these vital elements by incorporating them into the ANSYS Fluent IC Engine model. To further deepen our understanding, a detailed chemical reaction sensitivity analysis was executed using the 0-D ANSYS Chemkin-Pro DI Engine diesel reactor simulation. Methodologically, the research combined experimental platforms, a 0-D Direct Injection engine model on ANSYS Chemkin-Pro, and Computational Fluid Dynamics (CFD) simulations via ANSYS Fluent. Core findings reveal that waste cooking oil biodiesel has a shortened ignition delay, attributed to its reduced heat capacity and enhanced evaporative characteristics. Additionally, this fuel exhibits accelerated evaporation rates and superior thermal conductivity, especially noticeable at heightened temperatures during the piston bowl's ascent. Notably, there's an initial extension in its liquid penetration length, quickly followed by a significant decrease. This pattern suggests a potential for a more localized and richer combustion zone. Compounding these observations, waste cooking oil biodiesel displays shorter liquid and vapour penetration lengths, a characteristic likely influenced by its lower heating value. This suggests less energy availability for propelling the vapour cloud further into the chamber, further affecting the vapour penetration length adversely. In terms of emissions, waste cooking oil biodiesel significantly reduced HC particulate and NOx emissions. Sensitivity analyses revealed key reactions influencing emissions, such as formaldehyde production through reactions involving OH and O radicals and the intricate nature of combustion chemistry, highlighted by interactions of acetylene and other hydrocarbons. In conclusion, this study provides vital insights into waste cooking oil biodiesel's combustion, spray, and emission dynamics, underscoring the importance of diesel engine optimization for a cleaner and sustainable future.