OCR Text |
Show 5 chamber. The concentration of nitric oxides was measured by a chemilumi-nescence analyzer. Carbon dioxide was also injected instead of the fuel to simulate the mixing process of the fuel with air or burned gases in noncombusting conditions, although the air was preheated as was in combusting conditions. The concentration of carbon dioxide was measured with a gas chromatograph. Local fluctuating temperature in the flame was measured with a fine thermocouple of 25pm (Pt/Pt-Rhl3%) coated with Si02, whose time constant of frequency response was electrically compensated. Chemiluminescence emitted by the exited intermediate species in flames just after their reaction can be the index of the overall reaction process. For example, O H is one of the major species at high temperatures, C H is an indicator of local heat release rate and C2 radicals are produced at the initial stage of hydrocarbon oxidation [11]. Further, it was reported that the intensity ratio of CH to C2 varies with the equivalence ratio under a specified condition [12]. Therefore, we tried to apply C2/CH measurement to the flames interested using a new optical receiver called Multi-color Integrated Cassegrain Receiving Optic (MICRO) which was designed to detect spatially resolved optical signals [13]. The wavelength of 516.5 n m was selected among C2 band emissions and 431.5 n m for C H band. Results and discussion Autoignition temperature Imagine a gaseous fuel at ambient temperature is injected into an air stream. When the fuel mixes with combustion air, some heat is necessary to initiate combustion, and a recirculating flow of combustion products behind a flame holder or a pilot flame is frequently utilized for stabilizing flames in furnaces. However, if combustion air is sufficiently heated above the autoignition temperature of the fuel prior to mixing, combustion somewhere in the furnace definitely follows the mixing of two reactants, even if the flame in the near field of the fuel jet is blown off by a strong sheer motion. |