Features of lean premixed flame stabilized on a bluff-body with different temperature magnitude

The bluff-body is widely employed to improve the performance of the lean premixed combustion LPC which has advantages of high efficiency and low pollutant emissions. To further improve the LPC performance stabilized on the bluff-body, the effect of the bluff-body temperature on the lean premixed flame LPF feature near the flammability limit is studied here. The bluff-body temperature is controlled by the electrically heated rod or cooling water, and its values are set as ∼300 K (CB), naturally heat-conducting condition (NHB), 600 K (HB-600), and 900 K (HB-900), respectively. The experimental results show that the flammability limits and LPF behaviors in the case of CB and NHB are nearly the same because of the insignificant difference in the bluff-body temperature magnitude between them. The flammability limit can be significantly extended when the bluff-body temperature is heated to 900 K. Unexpectedly, the stable residual flame appears at the near-limit condition in the case of HB-900. It is the first time to observe the stable residual flame in the case of the fuel of Lewis number Le≈1.0. Then, the flame structures in the case of NHB, HB-600, and HB-900 are revealed numerically. It is found that the fresh reactant arrives at the flame primarily via diffusion rather than convection. The pre-heating effect on the fresh reactants and heat-loss effect to the bluff-body are also evaluated quantitatively. In the case of NHB, the flame can be classified to the adiabatic zone and mixed zone. By contrast, in the case of HB-600 and HB-900, the flame can be classified to the adiabatic zone, excess reaction zone, and weak reaction zone. This study expands our understanding on improving the LPC performance via controlling the bluff-body temperature.