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Four different vegetable oils, degummed soybean, once refined cottonseed, peanut and sunflower oils, were injected into a high-pressure, high-temperature environment of nitrogen. The environment was controlled to resemble, thermodynamically, conditions present in a diesel engine at the time of fuel injection. Samples were removed from the sprays of these oils while they were being injected. A sonic, water-cooled probe and a cold trap were used to collect the samples. Chemical analyses of the samples indicated that significant chemical changes occur in the oils during the injection process. The major change is the formation of low-molecular weight compounds from the C18:2 and C18:3 fatty acids.

Vegetable oils are candidates for alternative fuels in diesel engines. These oils, such as soybean, sunflower, rapeseed, cottonseed, and peanut, consist of various triglycerides. The chemistry of the degradation of vegetable oils when used as alternate diesel fuels thus corresponds to that of triglycerides. To study the chemistry occurring during the precombustion phase of a vegetable oil injected into a diesel engine, a reactor simulating a diesel engine was constructed. Pure triglycerides were injected into the reactor in order to determine differences in the precombustion behavior of the various triglycerides. The reactor allowed motion pictures to be prepared of the injection event as the important reaction parameters, such as pressure, temperature, and atmosphere were varied. Furthermore, samples of the degradation products of precombusted triglycerides were collected and analyzed (gas chromatography / mass spectrometry).

During the 1980's, vegetable oils, microemulsions containing fatty alcohols as surfactants, and fatty esters have been extensively investigaed as alternative fuels to #2 diesel fuel (DF-2) used in farm tractors. Despite the importance of vegetable oils (mainly triglycerides) and fatty derivatives to the alternative fuel program, cetane numbers for pure triglycerides and many fatty derivatives were not reported. In the current study, estimated cetane numbers of these materials have been determined by use of a constant volume combustion bomb. Prior research has shown that this equipment can produce cetane numbers that correlate satisfactorily with engine cetane numbers as determied by ASTM D 613. The influence of chemical structure on ignition delay and cetane number was investigated. Evidence is presented that shows the current cetane number scale is not always suitable for these fatty materials. Suggestions are made as to what might be done to remedy this problem.