Symmetric Ethers as Bioderived Fuels: Reactivity with OH Radicals

Abstract

Environmental pollution and greenhouse gas emissions are major challenges faced by our society. One possible way to mitigate global warming is to cut CO2 emissions by taking a shift from conventional fuels to renewable fuels for future sustainability. Carbon neutral fuels produced in a sustainable carbon cycle can close the carbon cycle and reach net zero-carbon emission. To this end, ethers are promising renewable fuels and/or additives for future advanced combustion engines. Therefore, understanding the oxidation behavior of ethers under engine-relevant conditions is of utmost importance. In this work, the reaction kinetics of hydroxyl radicals with dimethyl ether (DME), diethyl ether (DEE), di-n-propyl ether (DPE), and di-n-butyl ether (DBE) were investigated behind reflected shock waves over the temperature range of 865–1381 K and the pressure range of 0.96–5.56 bar using a shock tube and a UV laser diagnostic technique. Hydroxyl radicals were monitored near 306.7 nm to follow the reaction kinetics. These reactions did not exhibit discernible pressure effects. The temperature dependence of the measured rate coefficients can be expressed by the following modified Arrhenius equations in units of cm3 mol–1 s–1: k 1(DME+OH) = 1.19 × 1014 exp­(−2469.8/T), k 2(DEE+OH) = 1.27 × 107 T 2 exp­(327.8/T), k 3(DPE+OH) = 1.64 × 107 T 2 exp­(368.4/T), k 4(DBE+OH) = 9.12 × 1011 T 0.65 exp­(−843.5/T). Our measured rate data were analyzed to obtain site-specific rates and branching ratios. Our results are compared with the available literature data wherever applicable. Furthermore, the ability of Atkinson’s structure–activity relationship (SAR) to predict the kinetic behavior of the reactions of dialkyl ethers with OH radicals was examined.

Virtual Special Issue of Recent Advances in Fundamentals of Biomass and Biofuel Combustion

“…Of those, five papers focused on a recently proposed class of biofuels, linear ethers heavier than dimethyl ether. Belmekki et al 18 used a shock tube to investigate reaction kinetics of hydroxyl radicals with dimethyl ether, diethyl ether, di-n-propyl ether, and di-n-butyl ether. Mulvihill et al 19 proposed a high-level theoretical study of non-Boltzmann effects on the formation of ketohydroperoxides during the lowtemperature oxidation of diethyl ether.…”

Shock Tube/Laser Absorption Measurements of the High-Temperature Spectra and Decomposition of Propyl Ethers

“…and Belhadj et al using a JSR. The only available shock tube study was performed by Belmekki et al, where they measured the rate constants of H-abstraction reactions of DnPE by OH radicals over the temperature range of 865–1381 K and the pressure range of 0.96–5.56 bar. A theoretical study of H-abstraction reactions of DnPE by H, CH 3 , HO 2 , and OH radicals was performed by Gao et al He et al performed a theoretical study on the O 2 addition reaction of the DnPE radical.…”

“…Oxidation studies of DnPE were conducted by Serinyel et al 10 and Belhadj et al 11 using a JSR. The only available shock tube study was performed by Belmekki et al, 12 Gao et al 13 He et al 14 performed a theoretical study on the O 2 addition reaction of the DnPE radical. To the best of the authors' knowledge, no other literature is available on the hightemperature kinetics of DnPE and DiPE, emphasizing the need to investigate the combustion kinetics of these isomers.…”