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Show 12 thermocouple. At first, the temperature profiles were measured along the stagnation streamline and then the N 0 X concentration corresponding to the temperature was measured. Thus these figures were constructed on the NOx-Tf plane. It is interesting that these two curves are similar with each other. It is of importance that the N 0 X concentration decreases with the strain rates. This observation agrees with the numerical calculation by Drake and Blint [9]. As mentioned above, the residence time decreases with the strain rate. As the result, incomplete combustion occurs and the amount of N 0 X formed in the flame and diffusive layer is small. However, as the combustion reaction proceed to the equilibrium state, N 0 X formation is enhanced by the Zel'dovich mechanism downstream of the flame. Within the range of the flame temperature from 1300 K to 1625 K, N0X is nearly constant. Namely, the N 0 X concentration is independent of the flame temperature. This small temperature dependency is inherent in the prompt NO mechanism. Therefore, within this low temperature range, N 0 X originating from the prompt NO mechanism is predominant. In the temperature range above 1625 K (this is very close to the lowest temperature that sustains the combustion, when the surrounding is the room temperature), N 0 X increases with the flame temperature. This is caused by the fact that the N 0 X originating from Zel'dovich thermal mechanism which depends strongly on the temperature. 3.5 Arrhenius Plot of N0X against the Inverse of Adiabatic Flame Temperature As shown in Fig. 4, the critical extinction limit is increased exponentially with the temperature of the preheated airflow. This fact suggests that global chemical reaction rate can be expressed by the exponential function of temperature. The flame extinction occurs when the chemical reaction rate is slower than the rate of transport of reactants by diffusion. For the cylindrical burner case, the rate of transport of reactant by diffusion is expressed by velocity gradient 2V/R. Therefore, the vertical |