Wall chemical effect of metal surfaces on DME/air cool flame in a micro flow reactor

Wall chemical effect on DME/air weak flames (U _in =1.5cm/s, φ=0.85) was investigated using a micro flow reactor with a streamwise temperature gradient experimentally. The quartz channel used in this study has a rectangular cross-section of 1.5×5mm, which offers a good optical access for the planar laser-induced fluorescence (PLIF) measurement. The walls can be replaced for examining wall chemical effects of different wall materials. Wall surface materials, quartz, SiC, type 321 stainless steel (SUS321), iron, nickel and chromium, were employed. For SiC, SUS321 and metals, a 150-nm-thick film is deposited on the inner surface of the quartz channel to achieve different wall chemical boundary with identical thermal boundary condition. Streamwise distributions of DME, CO and CO ₂ in the weak flame were measured with the gas chromatography (GC), and HCHO and OH distributions were measured through PLIF. It is found that species distributions in both the low- and high-temperature oxidation zones of the weak flame are significantly altered for different wall surface materials. Comparing with that in the quartz and SiC-coated channel, DME in the SUS321-coated channel has a much higher concentration in the negative temperature coefficient (NTC) region, while CO and HCHO have lower concentrations. The peak of OH is shifted downstream, and so as the rising of CO ₂ . According to the results of the pure metal-coated channels, iron and nickel in the SUS321 should be responsible for the changes. These results suggest that the wall chemical effect of metal may exert strong influence on the low-temperature oxidation, which changes the species pool in the cool flame and leads to a modification of the hot flame region downstream.