Experimental study on combustion and flow resistance characteristics of an afterburner with air-cooled bluff-body flameholder

In the afterburner assembled with an air-cooled bluff-body flameholder, cooling air is directly injected into the recirculation zone behind the bluff-body, which can reduce the local temperature and increase the oxygen concentration of the gas mixture in the wake of the bluff-body, thereby affecting the total pressure loss and combustion characteristics. To better understand the flow and combustion process of the system, the exhaust gas temperature, cold and hot total pressure losses in a rectangular premixed combustor are investigated under different cooling air jet conditions. Experimental results show that the added cooling air could improve the combustion efficiency and widen the blowout limit, whereas it could also give rise to an extra total pressure loss. However, when the cooling air flow rate was higher than a critical value, i.e., after the blowing ratio reached 2.5, the recirculation zone could be blown away, resulting in a failed ignition in the afterburner. Notably, the decreased temperature difference between the mainstream and the cooling air could improve the combustion efficiency and reduce the thermal resistance loss but enlarge the cold flow loss and hot total pressure loss. Moreover, since the oxygen content declined and autoignition appeared after the mainstream temperature reached 1100 K, the exhaust gas temperature and combustion efficiency declined rapidly, and the hot total pressure loss also decreased. In addition, with the fuel-gas ratio increasing, the combustion efficiency significantly dropped, the exhaust gas temperature and thermal resistance loss firstly increased to a peak value (at the equivalence ratio of 1.14) and then decreased for excessively fuel-rich combustion.