Shock tube measurements of methane, ethylene and carbon monoxide time-histories in DME pyrolysis

High temperature dimethyl ether (DME) pyrolysis was studied behind reflected shock waves by measuring time-histories of CO, CH4 and C2H4 in mixtures of 0.5%, 1%, and 2% DME in argon respectively. Experiments were conducted at temperatures of 1300–1600 K and pressures near 1.5 atm. A direct absorption strategy with a fixed wavelength (2193.359 cm−1) using a quantum cascade laser (QCL) was used to measure CO concentration time histories. 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 two-wavelength absorption scheme at 10.532 μm and 10.675 μm with a CO2 laser. The mechanism of Curran et al. with a constant volume gasdynamic model was used to calculate temperature and pressure profiles and to infer the mole fractions of CO, CH4 and C2H4. The concentration time-histories of CO, CH4 and C2H4 were all found to be strongly sensitive to the DME decomposition rate k1 (CH3OCH3 (+M) → CH3 + CH3O (+M)), which was recently measured by Cook et al. at conditions similar to the current work. This measured k1 value was incorporated into two major DME decomposition mechanisms of Curran et al. and Zhao et al. The modified Curran et al. mechanism was found to predict the time histories of CH4 and C2H4 significantly better than the modified Zhao et al. mechanism.