OCR Text |
Show 13 axis, 2V/R shows the critical velocity gradient and also the overall chemical reaction rate. To express the overall chemical reaction of propane by the Arrhenius form, we must know the flame temperature. In the present study, we assumed the flame temperatures as the adiabatic flame temperatures shown in Figure 9. This assumption is reasonable, because the flame is very thin and the flame sheet assumption is indeed appropriate. Even though the surrounding temperature increases from 300 K to 1000 K, 2550 | 1 | 1 1 1 *: " • - " CD 3 CC i_ CD n E CD r- CD E CO L_ O •*-> (IS .CaO TJ < 2500 2450 2400 2350 2300 2250 200 400 600 800 1000 1200 Preheating Temperature (K) Figure 9. Preheating and Adiabatic Temperatures. the adiabatic flame temperature increases about 300 K. At high temperature, the dissociation reactions, which are endothermic, are predominant. Therefore, the adiabatic temperature is not affected considerably by the surrounding temperature change. To make the Arrhenius plot, we must know the reaction rate as a function of temperature. As mentioned before, the critical velocity gradient is the measure of the overall reaction rate of propane. Figure 10 shows the Arrhenius plot of the data obtained in the present study. The vertical axis ln(2V/R) corresponds to the overall reaction rate and vertical axis shows the inverse of the adiabatic temperature. The slope is surprisingly linear which in turn proved that the overall reaction of propane can |