An ignition delay and kinetic modeling study of methane, dimethyl ether, and their mixtures at high pressures

Abstract

The development of accurate chemical kinetic models capable of predicting the combustion of methane and dimethyl ether in common combustion environments such as compression ignition engines and gas turbines is important as it provides valuable data and understanding of these fuels under conditions that are difficult and expensive to study in the real combustors. In this work, both experimental and chemical kinetic model-predicted ignition delay time data are provided covering a range of conditions relevant to gas turbine environments (T = 600 − 1600 K, p = 7 − 41 atm, φ = 0.3, 0.5, 1.0, and 2.0 in 'air' mixtures). The detailed chemical kinetic model (Mech 56.54) is capable of accurately predicting this wide range of data, and it is the first mechanism to incorporate high-level rate constant measurements and calculations where available for the reactions of DME. This mechanism is also the first to apply a pressure-dependent treatment to the low-temperature reactions of DME. It has been validated using available literature data including flow reactor, jet-stirred reactor, shock-tube ignition delay times, shock-tube speciation, flame speed, and flame speciation data. New ignition delay time measurements are presented for methane, dimethyl ether, and their mixtures; these data were obtained using three different shock tubes and a rapid compression machine. In addition to the DME/CH 4 blends, high-pressure data for pure DME and pure methane were also obtained. Where possible, the new * address:

Quantification of the Keto-Hydroperoxide (HOOCH2OCHO) and Other Elusive Intermediates during Low-Temperature Oxidation of Dimethyl Ether

“…This section of the paper also includes a discussion of the limitations of our approach to determine PICS with respect to the separation and quantification of isomeric species. Figure 3 has revealed that all three DME mechanisms (USTC, 19 NUI, 18 and Nancy 5 ) considered here differ already significantly in their predictions for the main species profiles. In the following discussion only a few comparisons between the mechanisms' different description of the detailed chemistry are provided and instead we refer the reader to the papers, in which the mechanisms have been described, for the origins of the different predictions.…”

“…In order to validate the low-temperature part of the DME combustion chemistry mechanisms 5,18,19 and to identify opportunities for improvements, the quantification of the combustion reactants, intermediates, and products is crucial. The experimental mole fraction profiles of the main species (H 2 O, CO, O 2 , Ar, CO 2 , and DME) as a function of the reactor temperature were shown in Figure 3 and discussed together with the model predictions in the experimental section 2.2 as part of the data evaluation procedures.…”

“…To first add confidence to our data evaluation procedure, we compared our experimentally obtained main species profiles with simulated concentration profiles using the three widely accepted DME mechanisms from ref 19 (USTC mech), ref 18 (NUI mech), and ref 5 (Nancy mech). The calculations were performed using the perfectly stirred reactor model within CHEMKIN-PRO.…”

“…In order to give a more complete data set, a total of 15 reactants, products, and intermediates (including key intermediates like H 2 O 2 , HCOOH, and CH 3 OCHO) were also quantified. The new mole fraction profiles are then compared to model predictions using the most widely validated and accepted detailed chemical kinetic mechanisms for DME oxidation, 5,18,19 to illustrate their capabilities and possibilities for an improved description of DME's low-temperature chemistry.…”

Development of a water-cooled multi-hole calibration burner for optical measurements of flames with high pressures and temperatures

“…A CH4/DME(Dimethyl ether) model composed of 113 chemical species and 710 elementary reactions (Burke et al, 2015) was used for the reaction kinetics. The radiation heat loss was modeled using Planck mean absorption coefficients [Barlow et al, 2001].…”