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6208027 
Journal Article 
Effect of dimethyl ether, NOx, and ethane on CH4 oxidation: High pressure, intermediate-temperature experiments and modeling 
Ano, TA; Dryer, FL 
1998 
0 
Symposium (International) on Combustion
ISSN: 0082-0784 
Elsevier 
27 
1 
397-404 
The effects of small amounts of dimethyl ether (DME), NO, and NO2 on the autoignition and oxidation chemistry of methane, with an without small amounts of ethane present, were experimentally studied in a flow reactor at pressures and temperatures similar to those found in spark- and compression-ignition engines (under autoignition conditions). The reactions were studied at pressures from 10 to 18 atm, temperatures from 800 to 1060 K, and equivalence ratios from 0.5 to 2.0. It is found that 1% DME addition is as effective in stimulating the autoignition and oxidative behavior of methane as 3% C2H6 addition, and that NOx at even ppm levels is more effective than hydrocarbon additives. For the same reaction time and temperatures below 1200 K, addition of small amounts of NOx lowered the temperature at which reaction becomes significant by more than 200 K. Chemical kinetic mechanisms in the literature for the interactions of methane, ethane, and NOx do not predict the reported observations well. The most significant rate-controlling reactions for CH4 autoignition is found to be CH3+HO2=CH3O+OH. Good agreement, with and without NOx perturbations can be obtained by modifying the rate constants of three reactions (CH3+HO2=CH3O+OH; CH3+HO2=CH4+O2: CH2O+HO2=HCO+H2O2) and by adding the reaction CH3+NO2=CH3O+NO to the GRI-Mech v2.11 mechanism. These modifications do not significantly affect predictions for shock tube, flame, and other results used in developing GRI-Mech v2.11. Results strongly suggest that exhaust gas residuals and/or exhaust gas recirculation can have as profound an effect as natural gas contaminants on the apparent octane and cetane behavior.