Experimental and numerical study on thermodynamic characteristics in a Z-shaped evaporating pilot-flameholder

Reliable ignition and flame stability are crucial, particularly for the increasing expansion of flight envelopes. Herein, a novel Z-shaped evaporating pilot-flameholder is put forward to overcome critical challenges; further, the flameholder's ignition, blowout, and fully-developed flame characteristics under the operating conditions of turbine-based combined cycle combustors are experimentally investigated with the numerical flow field. The dynamic ignition process and the equivalence ratio of flame are acquired using a high-speed color camera and processed using an image-processing algorithm. The experimental results confirm the high ignition and blowout performance of the Z-shaped evaporating flameholder resulting from the superiority of its evaporating atomizer and Z-shaped structure. The ignition process of the Z-shaped flameholder simultaneously generates the diffusion and premixed flame types. The ignition performance of Z-shaped flameholder is significantly affected by the premixed degree of the pilot flame, which is a comprehensive index of the fuel atomization, evaporation, and turbulent mixing. The reflux rate and the premixed degree after ignition are little affected by the operating conditions, and the blowout performance is mainly influenced by the flow residence time and temperature. Further, the local equivalence ratio of the flame is acquired by calibrating the green/blue and equivalence ratios. Changing the equivalence ratio alters the double-reaction-zone feature in the Z-shaped evaporating flameholder. Under low fuel-lean conditions, flame stability is mainly contributed by the secondary reaction zone.