Shock tube investigation of methyl tert butyl ether and methyl tetrahydrofuran high‐temperature kinetics

Abstract

The autoignition and pyrolysis of two C5 ethers, methyl tert butyl ether (MTBE) and 2‐methyltetrahydrofuran (2‐MTHF), are investigated using the shock tube reactor. The experiments are carried out at pressures of 3.5 and 12 atm at temperatures above 1000 K with argon as a diluent gas. By means of direct laser absorption, carbon monoxide time histories and associated chemical kinetic timescales are also determined. It is observed that the competition between ignition and pyrolysis times depends on the temperature and equivalence ratio of the ignition mixture, such that there is a temperature above which pyrolysis predominates oxidative kinetics. This crossover temperature shifts toward higher temperatures for reactive systems with a fixed fuel concentration but higher oxygen content. The resulting experimental observations are also compared with predictions of existing chemical kinetic models from the literature. The results point to differences in chemical reactivity, such that in pyrolysis conditions, the reactivity of the cyclic ether, 2‐MTHF, is generally higher than that of the aliphatic ether, MTBE. While agreement between experimental observations and model predictions is observed under certain conditions, significant variance between observations and predictions is observed under other conditions. With respect to prediction of the pyrolysis time used to capture the global kinetics of pyrolysis, it is observed that the relation of this time to the time needed to attain 90% of the equilibrium CO concentration varies greatly with the result that the models used in this work generally predict a faster initial formation of CO but a much slower approach to the equilibrium concentration. This is thought to arise from the slow transformation of intermediate CH2O and CH2CO to CO. The chemical kinetic models considered in this work are therefore not capable of predicting the CO time histories during pyrolysis.

Chemical kinetics of cyclic ethers in combustion

“…High-temperature IDTs of 2-MTHF were measured in STs by Wang et al [661,662] and Jouzdani et al [664,665]. Tripathi et al [663,669], Fenard et al [670], and Cai et al [672] reported IDTs obtained in STs for 2-MTHF, 2,5-DMTHF, and 2-BTHF, respectively.…”

“…An explanation for this trend is given in Part 5.2.2.4. High-temperature (> 900 K) products, as summarized in Table 16, were measured for 2-MTHF (FR and ST pyrolysis [658,664] and PLF [658,667,668]) and for 2,5-DMTHF (FR pyrolysis [671]). No speciation data was found for any other molecules of this class.…”

Exploring the Flame Chemistry of C5 Tetrahydrofuranic Biofuels: Tetrahydrofurfuryl Alcohol and 2-Methyltetrahydrofuran

“…The combustion chemistry of MTHF has been investigated extensively, ,,,,,− and various kinetic models have been reported, such as those by De Bruycker et al, Moshammer et al and Fenard et al, whereas the current knowledge of the oxidation chemistry of THFA is limited to the recent investigation by Tran et al The authors explored the THFA combustion chemistry of a low-pressure-burner-stabilized 20% THFA/methane flame. Only one fuel mixture (20% THFA) was investigated, and numerous intermediate and final products were identified and quantified.…”