Insight into the Ozone-Assisted Low-Temperature Combustion of Dimethyl Ether by Means of Stabilized Cool Flames

Abstract

The low-temperature combustion kinetics of dimethyl ether (DME) were studied by means of stabilized cool flames in a heated stagnation plate burner configuration, using ozone-seeded premixed flows of DME/O 2 . Direct imaging of CH 2 O* chemiluminescence and Laser Induced Fluorescence of CH 2 O were used to determine flame front positions in a wide range of lean and ultra-lean equivalence ratios and ozone concentrations, for two strain rates. Temperature and species mole fraction profiles along the flame were measured coupling thermocouples, gas chromatography, micro-chromatography and quadrupole mass spectrometry analysis. A new kinetic model was built on the basis of the Aramco 1.3 model, coupled with a validated submechanism of O 3 chemistry, and was updated to improve the agreement with the obtained experimental results and experimental data available in the literature. Main results show the efficiency of the tested model to predict the flame front position and temperature in every tested condition, as well as the importance of reactions typical of atmospheric chemistry in the prediction of cool flame occurrence. The agreement on the fuel and major products is overall good, except for methanol, highlighting some missing kinetic pathways for the DME/O 2 /O 3 system, possibly linked to the direct addition of atomic oxygen on the fuel radical, modifying the products distribution after the cool flame.

An experimental and kinetic modeling study on the low-temperature oxidation of oxymethylene ether-2 (OME-2) by means of stabilized cool flames

“…A heated stagnation plate burner configuration was used in the present study to acquire experimental data from stabilized, ozone-seeded OME-2/DME/O2 premixed cool flames. The experimental unit was extensively described in previous studies [30,31] and only the most important aspects are mentioned here.…”

“…An ICCD Princeton PI-MAX 3, equipped with a band-pass filter (396 -450 nm) was used to collect the excited formaldehyde (CH2O*) chemiluminescence signal of the cool flames. The obtained images were further processed via three-point Abel inversion [30] to extract axial CH2O* profiles and to precisely determine the cool flame positions. The latter is defined as the position above the burner at which the emission of CH2O* reaches a maximum.…”

“…A symmetric and flat cool flame is observed, positioned well below the heated stagnation plate. To investigate the decomposition pathways during OME-2 low-temperature oxidation, DME cool flames containing small quantities of OME-2 were studied with conditions close to those reported in earlier work by Panaget et al [30]. OME-2 had to be seeded in DME, because of the low OME-2 vapor pressure and because the burner body was kept at room temperature.…”

“…The geometric strain rate, defined as the ratio of the inlet velocity and the distance between the burner and heated plate, was kept fixed at 50 s -1 for both cool flames. As the equivalence ratio of the fuel mixture decreases, the required ozone mole fraction has to increase to stabilize the cool flame [30]. OME-1 was found to be the main impurity in the OME-2 fuel (≈ 98.5 mol% OME-2, 1.5 mol% OME-1) and was therefore considered as part of the inlet feed for the kinetic model simulations [15].…”

A detailed experimental and kinetic modeling study on pyrolysis and oxidation of oxymethylene ether-2 (OME-2)

“…In the case of conflicting thermodynamic or kinetic parameters, the input of the AramcoMech model is retained to maintain the integrity of this experimentally fitted model. The AramcoMech 1.3 mechanism is chosen over more recently extended versions based on the experience of earlier studies by the authors [12,48]. The complete kinetic model for pyrolysis and oxidation, consisting of 301 species and 2251 reactions, is available in the Supplementary Information in CHEMKIN format.…”