Some Aspects of Chemical Kinetics in Chapman-Jouguet Detonation: Induction Length Analysis

The influence of complex chemical kinetics on the induction length in Chapman-Jouguet detonation was studied, with emphases on hydrogen chemistry and applications in pulse detonation engines (PDEs). Problems studied include the role of branching-termination reactions on the overall reaction rate, the reduction of the detailed hydrogen oxidation mechanism to simpler ones without compromising comprehensiveness of description, the coupled influence of chemical reactivity and the upstream speed of sound on ignition, and the use of hydrogen as a potential ignition enhancer. Results show that the presence of the pressure-sensitive and temperature-insensitive three-body termination reactions can significantly prolong the ignition delay, that an operation map for PDE operation can be constructed based on the crossover temperature so that operation regimes with excessively long ignition delays can be avoided, and that while the extent of chemistry reduction for the hydrogen/air PDE system depends on the degree of parametric comprehensiveness required, a two-step reduced mechanism appears to be adequate for near-stoichiometric descriptions. Furthermore, it is demonstrated that the benefit of the fast hydrogen chemistry is moderated by hydrogen's high speed of sound, which reduces the detonation Mach number and thereby the postshock temperature.