Sustainable Gossypium arboreum biodiesel production using an industrial waste heterogeneous catalyst for RCCI engine...

Industrial waste-based catalysts provide a sustainable and cost-efficient solution for biodiesel production, improving yield, quality, and environmental impact. When this biodiesel is used in advanced reactivity-controlled compression ignition (RCCI) mode, it enhances the combustion process within direct injection (DI) diesel engines. These strategies effectively reduce nitrogen oxide (NO_x) emissions and smoke without compromising engine performance. This study used cottonseed (Gossypium arboreum) methyl ester (CSME) as the pilot injection fuel. It was produced under optimal conditions of 2 wt% industrial waste dolomite catalyst, an 8:1 methanol-to-oil molar ratio, and heating at 55 °C for 45 min during transesterification through the response surface methodology (RSM) with central composite design (CCD). The catalytic potential of the industrial waste dolomite catalyst is validated through X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) analyses. Next, the n-butanol was injected into the intake manifold of the diesel engine at different energy shares of 10%, 20%, and 30% using an electronic primary fuel injection (EPFI) system in the RCCI mode. The fuel blends of diesel, CSME10 (10% CSME + 90% diesel), CSME20 (20% CSME + 80% diesel), and CSME100 (100% CSME) were tested as single-fuel in conventional mode, and CSME100 + 10% n-butanol, CSME100 + 20% n-butanol, and CSME100 + 30% n-butanol were tested in RCCI mode under variable load settings. Compared to the single-fuel operation, the RCCI combustion mode improved the performance and reduced emissions characteristics for all n-butanol energy shares. Especially, the CSME100 + 30% n-butanol mixture boosts brake thermal efficiency (BTE) by 22.25% and lowers brake specific fuel consumption (BSFC) by 23.33%. The unburnt hydrocarbon (HC) and carbon monoxide (CO) emissions were slightly increased by 28.13% and 27.37%, respectively. Also, the RCCI mode could simultaneously reduce smoke opacity (up to 58.07%) and NO_x emission (up to 41%) through lower peak cylinder pressure and heat release rate (HRR) at 18 kg in 100% engine load operation. Based on these analyses, it is suggested that the RCCI mode with n-butanol injection by the EPFI system shows efficient fuel combustion and significantly reduced tailpipe emissions in DI diesel engine applications.