OSCILLATORY COOL FLAMES IN THE COMBUSTION OF DIETHYL-ETHER

An experimental and numerical study of the oscillatory cool flames of a C2H5OC2H5 + O2 + N2 mixture has been performed in a jet-stirred flow reactor at reactant pressures up to 300 mmHg. The mean residence time was 4 +/- 2 s. Reaction was detected by a very fine thermocouple in the vessel. The primary objective was to study the low-temperature oxidation of diethyl ether and to establish the kinetic origins of this reactivity. The dialkyl ethers appear to be the most reactive class of organic compounds as far as cool flame and ignition phenomena are concerned, the lowest temperature at which oscillatory cool flames were observed in the present experiments being 430 K. The highest temperature for their existence was 590 K. No ignitions were detected in these experiments but complex oscillatory-cool-flame modes were obtained. The p-T(a) regions for the existence of the different kinds of reactions were mapped. Numerical analysis was based on a 92 reaction scheme developed from that used to study the cool flame and ignition phenomena of acetaldehyde. Particular attention was paid to the processes involving alkylperoxy and alkyldiperoxy species. Oscillatory cool flames were obtained in the modelling at vessel temperatures considerably below those corresponding to the cool flames of acetaldehyde. The low-temperature reactivity of diethyl ether oxidation appears to be associated with the primary hydroperoxide CH3CH(OOH)OC2H5. Dihydroperoxides seem not to play any part in the chain branching associated with this oxidation. Aperiodic non-isothermal phenomena were also obtained in the simulations, the kinetic origins of which appear to be related to reactions of the CH3CO radical, as also found in acetaldehyde oxidation.