Experimental investigation of partially premixed,highly-diluted dimethyl ether flames at low temperatures

Atmospheric-pressure highly-diluted laminar dimethyl ether (DME)–oxygen flames with temperatures below 1500 K were stabilized for the first time on a specially designed burner which allows preheating of the gas streams of fuel and oxidizer. With regard to the partially premixed structure of these flames which contain up to 90% argon in the unburnt gases, molecular-beam mass spectrometry (MBMS) with electron ionization (EI) was used to investigate chemical species profiles of reactants, intermediates, and products at a series of lateral positions and as function of distance from the burner. The flame structure reveals a near one-dimensional behavior at the flame front and beyond, towards the burnt gas. In a systematic approach, combustion parameters including stoichiometry, dilution, and gas preheating temperature were varied. The partial premixing effects upon the flame were revealed by comparing the distribution of flame species in a full two-dimensional concentration field above the burner, which is a starting point to model such flames in further studies. Formaldehyde and the methyl radical as two prominent species in the combustion process of DME were used to discuss characteristics of both high- and low-temperature kinetics.