Stagnation Plate Research Articles

Extinction mechanism of lean methanes/air turbulent premixed flame in a stagnation point flow

Effects of flame stretch, flame curvature and heat loss to the solid wall on the extinction of turbulent premixed flames formed in a stagnation point flow have been studied experimentally. Lean methane/air mixture, whose Lewis number is less than unity, was used. Bulk stretch rate was varied from 15 s −1 to 60 s −1 , while the turbulent intensitys of velocity fluctuation in the approach flow was varied from laminar condition to 0.6 m/s. The flame stretch due to flow divergence was estimated by measuring the mean centerline velocity profile with LDV and the flame curvature and flame location were measured by using laser tomographic technique. The total stretch rate is defined as a sum of flame stretch due to flow divergence and that due to flame curvature. The lean methane/air flame is intensified by a Lewis number effect and the flame can locate close to the wall. As a result, the heat loss to the stagnation plate affects the flame and finally the flame is extinguished under the influences of both heat loss and the total flame stretch. On the other hand, the flame of premixed gas with Le>1 (e.g. lean propane/air flame) is extinguished due to total flame stretch. From these results, it can be concluded that the extinction mechanism of wrinkled laminar flame is supposed to be fundamentally the same as that of laminar flame when the flame stretch is reasonably estimated by taking into account the effect of flame curvature.

The application of single-pulse CARS for temperature measurements in a turbulent stagnation flame

N2Q-branch CARS spectra have been recorded and evaluated for temperature determination in a turbulent, premixed CH4/air stagnation flame with a burner of 40 mm diameter and 22 kW thermal load. Temperature histograms on the flame axis at different distances from the stagnation plate have been measured. Problems of practical applicability are addressed, including those arising from the limited spatial resolution of the BOXCARS geometry, from an insufficient dynamic range of the diode array detector, and from a memory effect of the detector in the case of measurements in highly turbulent flame areas with strong intermittency. Some information is given on the computerized acquisition and on the evaluation of the large amounts of data that are necessary for extensive investigations in large combustion systems.

Structure and propagation of turbulent premixed flames astabilized in a stagnation flow

Turbulence statistics in premixed methane/air flames stabilized by a stagnation plate have been measured using the two-component laser Doppler velocimetry technique. Experimental conditions cover equivalence ratios of 0.67 to 1.16, incident turbulence intensities of 0.1 to 0.7 m/s, and global stretch rates of 100 to 230 sec−1. Results on turbulence statistics show that in crossing the flame the increase in fluctuation is more pronounced in the normal component while the Reynolds stress remains almost zero, and that the velocity joint probability density function is bimodal for rich flames and mono-modal for lean flames. It is also demonstrated that the present stagnation flame configuration can be usefully applied for the determination, of the turbulent flame speed ST. Values of ST determined as functions of the equivalence ratio and turbulence intensity agree well with those in the literture. It is suggested that the stagnation flame offers potential as a viable configuration for the study of planar, turbulent premixed flames uncomplicated by fluctuations generated by the stabilization regions associated with the conventional conical Bunsen flames and V-flames