Ignition and Flame Propagation Modeling With an Improved Methane Oxidation Mechanism

An improved chemical mechanism for methane combustion has been developed which describes a broad range of ignition and combustion phenomena. Simulations of shock tube induction times, atomic oxygen and atomic hydrogen concentrations in shock tube oxidations, flame speeds, and flame compositions have been carried out with a reasonable degree of success. In addition, the rate-determining reactions for each of these processes have been determined with sensitivity analyses The mechanism is used here to perform two types of ignition calculations for which no experimental information is available: (1) induction times in mixtures ignitied with different ignition energy distributions; (2) the minimum ignition energy as a function of equivalence ratio for spherical ignitions where the ignition energy is added in the form of heat. These calculations provide information on the chemical processes which are important to the success of flame initiation in methane-air mixtures. The H + O 2 = OH + O is shown to play a dominant role in determining the minimum ignition energy. In addition, the timing of chemical heat release and its magnitude are shown to be important considerations in the description of the flame initiation process.