PREDICTION OF LEAN BLOWOUT LIMITS FOR BLUFF BODY STABILIZED FLAME USING A GRADIENT METHOD OF DAMKÖHLER NUMBER AND TEMPERATURE

The prediction of the lean blowout for bluff body stabilized flame is of great significance for the design of a combustion chamber. In this paper, a lean blowout experiment was conducted on the bluff body stabilizer, and the CH* chemiluminescence was used to illustrate the impact of different equivalence ratios on the flame structure. The realizable k-ε turbulence model and flamelet generated manifolds combustion model were used to simulate the non-premixed bluff body stabilized flame. The characteristic region was determined based on the CO mass fraction, and the relative change rate of the average Damköhler number and temperature relative to the global equivalence ratio within the characteristic region was used as indicators for predicting lean blowout. The results show that as the equivalence ratio decreases, the flame intensity in the recirculation zone decreases, however, the flame intensity within the shear layer remains almost constant. When the equivalence ratio decreases to near blowout, there is a significant decrease in the flame intensity within the shear layer. CO is an important product in combustion and is directly related to the amount of heat released by combustion. The variation pattern of the characteristic region determined based on CO mass fraction with equivalence ratio is consistent with the actual flame variation. The relative rate of change of Damköhler number and temperature within the characteristic region is used to predict lean blowout. The lean blowout limits predicted by these two indicators are compared with experimental results and showed good consistency at different airflow rates and temperature. In general, within the range of examined parameters, the lean blowout limits predicted by Damköhler number are more accurate than the one based on temperature.