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

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 (NOx) 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 NOx 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.