Shock-tube study of the ignition and product formation of fuel-rich CH4/ozone/air and natural gas/ozone/air mixtures at high pressure

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The influence of ozone on the ignition delay times and product formation of methane and natural gas was determined in a high-pressure shock tube at fuel-rich conditions (ϕ = 2 and 10), ozone concentrations of 550 ppm, temperatures between 850 and 1700 K and pressures of about 30 bar. The addition of ozone causes a strong reduction of the ignition delay times for temperatures below 1100 K. Product concentrations were determined with fast sampling and GC/MS analysis for the experiments at ϕ = 10. Experiments and simulations show that CO, H2, H2O, C2H2, C2H4, C2H6, CO2, C3H6, and benzene are the main products. A comparison to similar studies with additives such as n-heptane, dimethyl ether, diethyl ether, dimethoxymethane and experiments without additives shows that C2H2, C2H4, and benzene concentrations are decreased, whereas CO concentrations are increased when ozone is used as additive. The experimental results were compared to simulations with chemical kinetics mechanisms from literature. The measured ignition delay times agree well with the simulations. A comparison of measured and simulated product distributions shows that the temperature dependence of the product formation is predicted well but that there are deviations of the absolute concentrations up to a factor of two for acetylene and benzene contrary to studies with other additives.