Examining the Effects of Neem Leaf Extract Additive on Biodiesel Blends for Improved Fuel Efficiency and Engine Performance in a Low Heat Rejection Engine

This research assessed the performance, combustion behavior, and emission characteristics of three biodiesel sources—Pongamia pinnata, Juliflora, and Calophyllum inophyllum—blended with conventional diesel in a low heat rejection (LHR) engine. It also examined the impact of neem leaf extract as an additive. B20 blends (20% biodiesel, 80% diesel) were formulated and tested under different load conditions in a single-cylinder diesel engine, where key components were coated with partially stabilized zirconia. The neem leaf extract concentration was varied using a central composite design to evaluate its effects. Essential fuel properties, including oxidation stability, viscosity, cetane number, and flash point, were analyzed. The study also investigated combustion parameters such as brake thermal efficiency, fuel consumption, exhaust gas temperature, cylinder pressure, heat release rate, and ignition delay, alongside CO, HC, NOx, and particulate matter emissions. Results indicated that biodiesel blends exhibited superior brake thermal efficiency compared to pure diesel, particularly at higher loads, with Pongamia pinnata biodiesel showing the best performance. Adding 2.5% neem leaf extract further improved efficiency across all blends. Biodiesel blends led to lower CO, HC, and particulate emissions but caused a slight increase in NOx emissions due to elevated combustion temperatures. However, neem leaf extract helped counteract the rise of NOx. Higher cylinder pressures and heat release rates were observed with biodiesel blends, indicating enhanced combustion, while ignition delays were reduced, with neem extract further minimizing them. The findings highlight the potential of these biodiesel feedstocks as sustainable diesel alternatives, with neem leaf extract serving as a natural additive to enhance fuel properties, combustion efficiency, and emissions control in LHR engines.