Experimental investigation of combustion and emission characteristics of biodiesel-alcohol blends with identical C/H/O mass ratio

The effects of biodiesel-alcohol blends with varying volume ratios on diesel engine performance have been extensively studied. Isolating the impact of alcohol molecular structure from oxygen content presents a significant challenge due to concurrent changes in the C/H/O ratio with blend composition. This study introduces an elemental-constrained fuel blending approach to develop new fuel formulations based on an existing biodiesel-alcohol blend. Two blends with identical elemental mass ratios of biodiesel and ethanol (BE: C 72.74% wt, H 12.26% wt, O 15.00% wt) were prepared using biodiesel, methanol, butanol, and pentanol. Their cetane number, ignition delay, density, viscosity, and cold filter plugging point (CFPP) were measured. Combustion and emission performance were experimentally evaluated on a diesel engine test bench under 56 Nm, 140 Nm, and 224 Nm conditions. The results show close physiochemical properties and similar combustion performance among the three blends. However, significant variations were observed in gaseous and particulate emissions. The biodiesel-methanol-pentanol (BMP) blend reduced fuel consumption by 3.3% and 3.7%, NOₓ emissions by 0.84 g/kWh and 0.23 g/kWh and particle mass concentration by 10.9 mg/kWh and 67.9 mg/kWh, while it increased particle number concentration by 0.1 × 10⁷ and 0.8 × 10⁷ #/cm³ at 56 Nm and 224 Nm loads, respectively.