Direct Measurement of High-Temperature Rate Constants of the Thermal Decomposition of Dimethoxymethane, a Shock Tube and Modeling Study

Abstract

Shock-tube experiments have been performed to investigate the thermal decomposition of the oxygenated hydrocarbon dimethoxymethane (DMM; CH₃OCH₂OCH₃). The primary initial reaction channels of DMM decomposition are considered to be the two bond fissions: CH₃OCH₂OCH₃ → CH₃O + CH₂OCH₃ (1) and CH₃OCH₂OCH₃ → CH₃ + OCH₂OCH₃ (2). In the present work, two shock-tube facilities and three different detection techniques have been combined: Behind reflected shock waves, we have carried out time-resolved measurements of (i) the formation of H atoms using the highly sensitive H-ARAS (Atomic Resonance Absorption Spectrometry) technique and (ii) the depletion of the DMM reactant by high-repetition-rate time-of-flight mass spectrometry (HRR-TOF-MS). In addition, (iii) the temperature-dependent composition of stable reaction products was measured in single-pulse shock-tube experiments via gas chromatography (GC/MS). The experiments span a temperature range of 1100-1430 K, a pressure range of 1.2-2.5 bar, and initial reactant mole fractions from 0.5 ppm (for H-ARAS experiments) up to 10 000 ppm (for HRR-TOF-MS experiments). Experimental rate constants k_total, k_total = k₁ + k₂, obtained from these three completely different methods were in excellent agreement among each other, i.e., deviations are within ±30-40%, and they can be well represented by the Arrhenius expression k_total( T) = 10^13.28±0.27 exp(-247.90 ± 6.36 kJ mol^-1/ RT) s^-1 (valid over the 1100-1400 K temperature and the 1.2-2.5 bar pressure range). By replacing the respective k_total values used in a recently published DMM chemical kinetics combustion mechanism (Vermeire et al. Combust. Flame 2018, 190, 270-283), it was also possible to successfully reproduce measured product distributions.