Optimization of cashew nut shell biodiesel production with industrial waste catalysts and butanol additives for ecofriendly CRDI engine applications

Stringent emission regulations and the depletion of conventional fuel sources drive research on green fuels, additives, and the optimization of fuel injection and exhaust gas recirculation. This study analyzes the impact of butanol additives in diesel and cashew shell liquid biodiesel (CSLB) blends under optimal operating conditions. CSLB was produced with an 85.43% yield from waste cashew nut shell liquid under optimal conditions: a methanol/CSL molar ratio (MR) of 20:1, a process temperature (PT) of 70 °C, and a 4 wt% industrial waste-derived heterogeneous catalyst (IC), using the desirability function approach in the RSM-CCD model. The catalyst was characterized using XRD, FTIR, and BET analyses to confirm its catalytic activity. Engine performance improvements were achieved with specific modifications, including 4° CA timing retardation, 15% split injection, and a 20% exhaust gas recirculation rate when using CSLB blends. In common rail direct injection (CRDI) experimental investigations, diesel and CSLB blends were combined with butanol additives (2.5%, 5%, and 10%) and compared to the baseline test. Incorporating 10% butanol, with its higher latent heat, resulted in a lower combustion temperature, reducing NO_x emissions by 47.09% in CSLB10. Additionally, the additive's lower viscosity and higher oxygen content enhanced atomization, reducing CO (33%) and smoke (23.02%) emissions. However, a slight increase in CO₂ (8.92%) and a decrease in HC emissions (27.14%) were observed in CSLB10. Improved combustion characteristics, reflected in higher peak pressure and heat release rate, resulted in a 4.75% increase in brake thermal efficiency and a 13.92% reduction in brake-specific energy consumption compared to ideal conditions. Overall, this study explores the impact of butanol additives on the performance and emissions of CRDI engines fuelled with CSLB blends derived from waste cashew nut shell liquids, providing insights for sustainable fuel optimization.