Combustion Kinetics

The chemistry that drives combustion is a highly complicated web of reactions. To describe the combustion of a single fuel compound, say iso-octane, in full chemical detail requires detailed knowledge of hundreds of chemical species that participate in thousands of individual chemical reactions. Each of these reactions, in turn, has a detailed description in terms of fundamental physical principles. The combustion kinetics research at the CRF is aimed at discovering and characterizing important elementary reactions at this most fundamental level.

Which elementary reactions are important for understanding and controlling combustion? When nineteenth-century inventors were creating the first internal combustion engines, chemists didn’t even have the fundamental knowledge that combustion is governed by chain reactions of radicals. Diesel and Otto didn’t need to know any chemistry beyond fuel + air = heat! However, in the intervening years the operation of engines has become far more sophisticated, and the demands on engine performance have vastly increased. Important modern engine design considerations such as minimizing pollutant formation or controlling autoignition, require models that can reliably predict chemical species that occur at sub-part-per-million levels in the combusting mixture. The two subjects of pollutant formation and autoignition chemistry are areas where the details of the chemistry make a difference in predicting the performance of real devices, and much of the CRF’s recent chemical kinetics research has focused on reactions that are relevant to one of these topics.

Even within these two areas, the challenges for detailed combustion chemistry are vast. Rate coefficients and branching fractions for individual reactions must be known over wide ranges of temperature and pressure – far wider than is practical to experimentally investigate. Moreover, when one considers that petroleum distillates like gasoline may already include thousands of chemically distinct fuel compounds one clearly sees that we can’t simply measure every individual reaction in detail, or even every important reaction! Fundamental chemistry research can make a timely contribution to combustion modeling, and hence to the design of future clean and efficient combustion technologies, by defining the underlying physical principles that will allow confident prediction of chemical reactions under unexplored conditions.