Experimental and numerical study on thermodynamic performance in a designate pilot-ignition structure: Step

Abstract

Reliable ignition and stable flame spreading were extremely important especially for the increasing expansion of flight envelope. A new pilot-ignition structure- step- was put forward with low resistance and developed to meet more critical challenges. To optimize structure parameters, thermodynamic performance with various step heights (30 mm, 40 mm, 50 mm, and 60 mm) was investigated in premixed combustion, such as ignition and blow-off loop measured by intelligent metal tube flowmeter, and flame development recorded by high-speed camera. Additionally, numerical simulation of flow field was performed to analyse the influence of flow pattern on thermodynamic characteristics. It was found that flow pattern occurred transition with the increase of step height, namely, couple-vortex recirculation in 30 mm-height step structure and single-vortex recirculation in the other three. Additionally, the four kinds of steps realised successful ignition and stability loop. Specially, ignition and blow-off performance of 30 mm-height step structure with particular couple-vortex recirculation was sensitive to temperature, and improved with the growing temperature; also its ignition limits were increasing with the growing velocity, especially up to 200 m/s, ignition limits were almost lower than the others. Once ignited, flame development rate had a convex-function relation to temperature and optimized temperature existed at an extreme point (at 800 K), it decreased progressively with growing velocity. Moreover, flame spreading height up to core flow increased first and then decreased with growing temperature, and it was monotone decreasing with the growing inlet velocity. The step structure conducted in this work was validated for its reliable ignition and broad stability loop. Low-resistance pilot ignition design was developed and employed for turbojet/ramjet.