Two years ago, results of a study carried out at Chalmers University, Gothenburg, Sweden, were intensively discussed in the public. In this study the authors – belonging to the group of Olsson – claimed that they had found up to tenfold higher emission rates of benzene and ozone precursors when using biodiesel (rapeseed oil methylester) compared to Swedish diesel fuel MK1. The experiments were carried out in a very small reactor that was heated to 550 °C and fed with a constant air stream into which the fuels were injected. The exhaust gas analysis was carried out by GC/MS. In their conclusion, the authors stated that "Hitherto, the disadvantages of renewable products have been neglected in research and development. The advantages of renewable products are advocated strongly by their proponents urging for a quick and subsidized market introduction." (Pedersen et al., 1999).
Many researchers in Europe and the U.S. were sceptical concerning a transfer of the results obtained in this small reactor to the real combustion in a diesel engine. Needless to say the temperature, pressure, and droplet size are not comparable, which should result in different chemical reaction pathways. However, nowhere in the world experiments had been carried out with the aim to compare the emissions of biodiesel and Swedish diesel fuel MK1 from real diesel engine combustion.
This was the motivation for this study, to compare in a dedicated research project different fuels regarding their exhaust emissions from a modern DaimlerChrysler diesel engine. Since diesel engine particles are likely to pose a lung cancer hazard to humans, the determination of mutagenic potentials of particulate matter was carried out to estimate possible carcinogenic health effects.

By: J. Krahl, A. Munack, O. Schröder, H. Stein, J. Bünger

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