The effects of vegetable oil properties on injection and combustion in two different diesel engines

Four different vegetable oils, each in at least 3 different stages of processing, have been characterized according to their physical and chemical properties, their injection and atomization characteristics, and their performance and combustion characteristics in both a direct‐injection and an indirect‐injection diesel engine. The injection and atomization characteristics of the vegetable oils are significantly different than those of petroleum‐derived diesel fuels, mainly as the result of their high viscosities. Heating the oils, however, results in spray characteristics more like those observed with diesel fuel. The 2 engine types demonstrated different sensitivities to the composition of the various oils. The combustion characteristics and the durability of the direct‐injection engine were affected by the oil composition. The indirect‐injection engine, however, was not greatly affected by composition. Two different preliminary specifications have been proposed: a stringent specification including compositional requirements for direct‐injection engines, and a less stringent specification for indirect‐injection engines. The specifications are discussed in terms of the data and the rationale used in their development. Some precautions concerning the application of the specifications are also presented.