OCR Text |
Show 13 Chemiluminescence of radicals Since C2 radicals are produced at the initial stage of hydrocarbon oxidation, the wide distribution of C2 indicates the dispersed combustion reaction. Adding that, since C H is an indicator of local heat release rate, the wide distribution of C H also indicates the dispersed combustion reaction. The distributions of local intensity ratio of C2 to CH are shown in Fig.8. The lower values of the ratio prevail the combustion chamber for the case of nozzle 2, but the relatively high values were observed for the case of nozzle 4. Comparing with the previous observation of nitric oxide emissions and temperatures, the higher value of C2/CH prevails the combustion chamber, the lower flame temperature is generated, hence the lower nitric oxide. As previously mentioned, nitric oxide emission varies widely depending on the mixing process in the combustion chamber although other operating conditions are kept constant, we need any measure to evaluate the degree of mixing favorable for low nitric oxide. The intensity ratio C2/CH is reported to increase with the preheated temperature of combustion air between 973 K and 1373 K as well as the decrease of oxygen content from 2 1 % to 5 % in the preheated combustion air [15]. Accordingly, the intensity ratio C2/CH can be used as an indicator for the combustion regime of high thermal efficiency and low nitric oxide emission. Xmm Xmm Xmm Xmm (a) Nozzle 1 (b) Nozzle 2 (c) Nozzle 3 (d) Nozzle 4 Fig. 8 Distributions of intensity ratio of C2 to CH band luminescence |