Methane and ethylene time-history measurements in n-butane and n-heptane pyrolysis behind reflected shock waves

CH4 and C2H4 concentration time-histories were measured behind reflected shock waves during the pyrolysis of two n-alkanes: n-butane and n-heptane. Experiments were conducted at temperatures of 1200–1600 K and at pressures near 1.5 atm, with fuel concentrations of 1% in Ar. A mid-IR scanned-wavelength laser absorption diagnostic with a difference frequency generation (DFG) laser near 3.43 μm was used to measure CH4 concentration time-histories. C2H4 was measured using a fixed-wavelength absorption scheme at 10.532 μm with a CO2 laser. The mechanism of Wang et al. with a constant volume gasdynamic model was used to calculate temperature and pressure profiles and the mole fraction time-histories of CH4 and C2H4. The measured CH4 and C2H4 time-histories in n-butane pyrolysis were compared to simulations based on the comprehensive n-alkane mechanism by Wang et al. and the detailed n-butane mechanism by Marinov et al. Based on these comparisons, the n-butane decomposition rates measured by Oehlschlaeger et al. were incorporated into the Wang et al. mechanism and two additional butane abstraction reaction rate constant adjustments were also made. The measured CH4 and C2H4 time-histories during n-heptane pyrolysis were also compared to simulations based on the mechanisms by Wang et al. and Curran et al. The overall n-heptane decomposition rate measured by Davidson et al. was incorporated into the Wang et al. mechanism, and the two methyl abstraction reactions from n-heptane were adjusted, and the H-abstraction reaction rate from ethylene was updated. Using these modified mechanisms the agreement between simulation and experimental time-histories of CH4 and C2H4 were both significantly improved for n-butane and n-heptane pyrolysis.