The effect of simple halogenal hydrocarbons on ignition delay

The ignition delay of CH4/O2 and H2/O2 diluted in argon has been studied behind reflected shock waves. Silane, bromomethane, and chloromethane were added to the mixtures to investigate their influence on ignition for the condition 1∼3atm, 1600∼2200K for CH4/O2 mixtures, and 1000∼1600K for H2/O2 mixtures. Laser absorption technique was used to monitor the onset of OH to identify the times for ignition delay. Detailed chemical kinetic modeling was used to simulate the shock tube conditions in order to study the effects of different additive on radical growth. In CH4/O2 mixtures, addition of bromomethane and chloromethane reduced the time for ignition delay by 20% to 70%, while addition of silane reducing it by 80%. The effect was more pronounced at lower temperature for both haloid additives and silane. Pressure has negative effect on the reduction of ignition delay for haloid additives, but not obvious for silane. In H2/O2 mixtures, additions of haloid additives prolonged the ignition delay, however, addition of silane had reduced 80% of the ignition delay time. The effect is also pronounced at lower temperature. The kinetic simulation showed the increase of the production rate of the chain carrier in the induction period with the presents of additives were basically caused by early C-Cl and C-Br bound breaking followed by hydrogen abstraction of methane fuel by Cl and Br atoms.