A detailed combined experimental and theoretical study on dimethyl ether/propane blended oxidation

Abstract

In this work, a binary fuel model for dimethyl ether (DME) and propane is developed, with a focus on engine-relevant conditions (10-50 atm and 550-2000 K). New rapid compression machine (RCM) data are obtained for the purpose of further validating the binary fuel model, identifying reactions important to low temperature propane and DME oxidation, and understanding the ignition-promoting effect of DME on propane. It is found that the simulated RCM data for DME/propane mixtures is very sensitive to the rates of C3H8 + OH, which acts as a radical sink relative to DME oxidation, especially at high relative DME concentrations. New rate evaluations are conducted for the reactions of C3H8 + OH = products as well as the self-reaction of methoxymethyl peroxy (in competition with RO2 = QOOH isomerization) of 2CH3OCH2O2 = products. Accurate phenomenological rate constants, (,), are computed by RRKM/ME methods (with energies obtained at the CCSD(T)-F12a/cc-pVTZ-F12 level of theory) for several radical intermediates relevant to DME. The model developed in this work (120 species and 700 reactions) performs well against the experimental targets tested here and is suitable for use over wide range of conditions. In addition, the reaction mechanism generator software, RMG, is used to explore cross-reactions between propane and DME radical intermediates. These cross-reactions did not have a significant effect on simulations of the conditions modeled in this work, suggesting that kinetic models for high-and low-reactivity binary fuel mixtures may be assembled from addition of their corresponding submodels and a small molecule foundation model.

n-Heptane cool flame chemistry: Unraveling intermediate species measured in a stirred reactor and motored engine

“…Interestingly, the acetic acid concentration was significantly underestimated, even when the rate constant of the Korcek reaction calculated by Jalan et al [81] was increased by a factor of 10. Dames et al [82] Fig. 9 are taken from quantum chemistry calculations by Goldsmith et al [83].…”

“…The experimental results in this work provide additional insights into the sequential third O2 addition to P(OOH)2 radicals and subsequent reactions, bimolecular reactions of C7 intermediates, e.g., C7H14Ox (x=0-5) and C7H12Ox (x=0-4), and the formation of C2-C6 diones from the decomposition of the C7 keto-alkoxy radicals. However, these pathways were seldom considered in the aforementioned kinetic models, or those from other teams [33,56,82,90]. Our next goal is to include these pathways in an n-heptane kinetic model [11], and to test their effect on the species distribution in n-heptane JSR oxidation and on n-heptane ignition delay measurements in shock tubes and rapid compression machines.…”

Computer-generated isotope model achieves experimental accuracy of filiation for position-specific isotope analysis

“…RMG, an open-source software tool which enables the construction of detailed reaction mechanisms that model a wide array of radical chemistry processes such as pyrolysis, oxidation, and catalytic systems. (Gao et al, 2016a;Goldsmith and West, 2017;Allen et al, 2014;Dames et al, 2016;Class et al, 2016;Gao et al, 2015) Thermochemical and kinetic parameters of species and reactions in the reaction mechanism originate from structure-based estimation methods using databases of parameters known from experiments or high-level quantum chemistry calculations.…”

UConnRCMPy: Python-based data analysis for Rapid Compression Machines

“…The cti_file argument to Condition must point to a file in the CTI format that contains the thermodynamic and reaction information for the species in the mixture. The experiments in the following example were conducted with mixtures of propane, oxygen, and nitrogen [7]. The CTI file necessary to run this example can be found in the Supplementary Material of the work by Dames et al [7].…”

“…Ellipses indicate input that was truncated to save space; the truncated input is present in the file available with the work of Dames et al [7]. The mole_fractions must be set to the appropriate values.…”