Shock tube/laser absorption measurements of ethylene time-histories during ethylene and n-heptane pyrolysis

Ethylene concentration time-histories were measured behind reflected shock waves in ethylene/argon and n-heptane/argon mixtures using 10.5 μm CO2 laser absorption. Reflected shock conditions covered temperatures between 1350 and 1950 K, pressures between 1.3 and 3.3 atm, and fuel concentrations of 1% ethylene and 300 ppm n-heptane in argon. The ethylene absorption cross-section at this wavelength was determined over similar pressures and temperatures using both absorption measurements in a heated-cell FTIR and laser absorption/shock tube measurements. Measured ethylene concentration time-histories during ethylene pyrolysis were compared to constant volume simulations using the Marinov et al. (1998) mechanism. A sensitivity of the measured profiles to the rate constant of the primary ethylene decomposition reaction, C2H4 → C2H2 + H2 was demonstrated, allowing a determination of the rate constant for this reaction using the ethylene time-histories. Ethylene concentrations, measured during n-heptane pyrolysis, were also compared to simulations using the Sirjean et al. (2009)/JetSurF 1.0 mechanism. Incorporation of the new reaction rate constant k1 provided better agreement between the measured ethylene concentration profiles and the simulations for both ethylene and n-heptane pyrolysis.