Predictive modeling and optimization of a CI engine's performance and emission responses to methanol/pentanol/diesel blends using RSM approach

Considerable experimental effort has been devoted to identifying environmentally compatible fuels capable of reducing exhaust emissions while meeting increasing global energy demand. Among alcohol fuels, methanol has attracted significant attention; however, its limited miscibility with diesel restricts its direct application in compression ignition engines. In this study, pentanol was employed as a co-solvent to enhance blend stability, enabling the preparation of homogeneous methanol–pentanol–diesel ternary fuels. A single-cylinder diesel engine was experimentally operated using neat diesel and three ternary blends containing 5%, 10%, and 15% methanol (with a fixed pentanol ratio of 5%) under varying engine loads. Response Surface Methodology (RSM) was applied to identify optimal operating conditions by simultaneously considering performance and emission responses. Compared with baseline diesel operation, the optimized ternary blend (15% methanol at 60% engine load) resulted in an improvement in brake thermal efficiency while reducing carbon monoxide (CO) and hydrocarbon (HC) emissions; although a moderate increase in NO x was observed. Under optimal conditions, brake thermal efficiency (BTE), brake mean effective pressure (BMEP), and brake specific fuel consumption (BSFC) were obtained as 32.51%, 380.62 kPa, and 0.285 kg/kWh, respectively, with CO and HC emissions reduced to 0.025% and 146.34 ppm. The results demonstrate that methanol–pentanol–diesel blends can offer a favorable compromise between performance and emission characteristics when evaluated relative to conventional diesel fuel.