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.

不同体积配比的生物柴油-醇类混合燃料对柴油机性能的影响已得到广泛研究。由于混合燃料组分变化会同时改变碳氢氧元素比例，因此将醇类分子结构的影响与氧含量的影响分离开来，是一项极具挑战性的工作。本研究提出一种元素约束型燃料调配方法，基于现有生物柴油-乙醇混合燃料开发新型燃料配方。研究以生物柴油、甲醇、丁醇及戊醇为原料，制备了三组与生物柴油-乙醇混合燃料（BE：碳质量分数72.74%、氢12.26%、氧15.00%）元素质量比完全一致的混合燃料，并对其十六烷值、滞燃期、密度、粘度及冷滤点（CFPP）进行了测试。在柴油机试验台架上，分别于56Nm、140Nm及224Nm三种负载工况下，对三种混合燃料的燃烧与排放性能开展了试验评估。试验结果表明，三种混合燃料的理化性质相近，燃烧性能也较为相似。但气态与颗粒物排放则呈现出显著差异。其中生物柴油-甲醇-戊醇（BMP）混合燃料在56Nm与224Nm负载工况下，分别将燃油消耗量降低3.3%与3.7%，氮氧化物（NOₓ）排放量降低0.84g/kWh与0.23g/kWh，颗粒物质量浓度降低10.9mg/kWh与67.9mg/kWh；同时颗粒物数浓度分别提升0.1×10^7个/立方厘米与0.8×10^7个/立方厘米。