| OCR Text |
Show 8 the preheating temperature was increased, flame strength was also increased. Here, we must note that the extinction temperature gradient almost increases linearly up to the spontaneous ignition temperature. Then extinction strain rate goes up nearly exponentially. At the upper extreme, the velocity gradient at extinction becomes infinity. This fact suggests that there should be a critical preheating temperature beyond which the flame is always stabilized. Figure 5 shows the extinction temperature of the flame as a function of strain rate. When the strain rate is increased with the increase of the airflow rate, the flame temperature at extinction increases slightly except for the extremely high strain rate. The transport of the reactants is enhanced by strain rate. The chemical reaction should be enhanced farther to consume the reactants, which leads to the higher temperature to maintain the flame. At the higher extreme of the strain rate, flame temperature at the state of extinction seems to decrease again. At extremely high strain rate condition, the flame is pushed to the cylinder surface, and the heat loss to the cylinder cannot be negligible. Therefore, the flame temperature at the extinction 1600 1200 u ° 800 H 400 0 0 4000 8000 12000 2V/R 1/s Figure 5. Effect of Strain Rate on the Extinction Temperature. |
