The influence of straight vegetable oil fatty acid composition on compression ignition combustion and emissions

This paper presents experimental studies carried out on a modern direct injection compression ignition engine supplied with a range of straight vegetable oils to investigate the effect of oil fatty acid composition on combustion and emissions. Seven oils, those of corn, groundnut, palm, rapeseed, soybean, sunflower and the micro-algae species were tested, with all of the fuels heated to 60°C, at constant injection timing and constant ignition timing at a constant engine speed of 1200rpm. All of the vegetable oils exhibited a duration of ignition delay within ±0.6CAD of that displayed by a reference fossil diesel, but displayed much reduced rates of peak heat release rate. The duration of ignition delay was found to increase with an increasing carbon to hydrogen ratio of the vegetable oils, implicating the fatty acid alkyl chain as the primary driver of low temperature reactivity. Peak heat release rates decreased with decreasing vegetable oil viscosity, suggesting a significant degree of fuel cylinder wall and piston bowl impingement. At both injection timings, emissions of NO were lower for all of the vegetable oils relative to the reference fossil diesel, while those of CO, THC and particulate matter were higher and sensitive to the injection timing.

本文介绍了在一台现代直喷压燃式发动机上进行的实验研究，该发动机使用了一系列纯植物油，以研究油的脂肪酸组成对燃烧和排放的影响。对玉米油、花生油、棕榈油、菜籽油、大豆油、向日葵油以及微藻油这七种油进行了测试，所有燃料均加热至60°C，在发动机转速恒定为1200转/分钟的情况下，保持喷油定时和点火定时不变。所有植物油的着火延迟持续时间都在参考化石柴油的着火延迟持续时间±0.6°CA（曲轴转角）范围内，但峰值放热率大幅降低。研究发现，着火延迟持续时间随着植物油碳氢比的增加而增加，这表明脂肪酸烷基链是低温反应性的主要驱动因素。峰值放热率随着植物油粘度的降低而降低，这表明燃料与气缸壁和活塞凹坑的撞击程度较大。在两种喷油定时下，与参考化石柴油相比，所有植物油的氮氧化物排放都较低，而一氧化碳、总碳氢化合物和颗粒物的排放则较高，且对喷油定时较为敏感。