Starov A.V.   Гольдфельд М.А.  

Hydrogen Injection Scheme Influence on Flow Structure in Supersonic Combustor of Constant Cross-Section

Reporter: Starov A.V.

At supersonic velocities in the combustor channel, special efforts to ensure ignition and flame stabilization are necessary. In these conditions, it is required to ensure the presence of gas-dynamic sources of self-ignition. As such a source, slot channels located on the upper and lower walls of the main combustor channel were proposed. High static flow parameters in these slot channels ensured self-ignition of hydrogen. The exhaust jet from the nozzle of the slot channels to the main channel promoted to the ignition and combustion of fuel in the main channel. At the same time, such a stabilization scheme proved to be sensitive to the hydrogen mixing efficiency. Since there was no fuel supply in the slot channels and the local excess of hydrogen in them (affecting ignition and combustion) was determined by the flow structure on the part between the combustor entrance and the slot channels.
A replaceable block of flat profiled nozzles with an exit area of 50mm x 100мм provided a discrete change of the Mach number. The combustor model consisted of an injector insertion, a section with a constant cross section of 100mmx100мм with a length of 365 mm, and an expanding section of 390 mm long, so that the cross-sectional area of combustor exit increases by 3.6 times with respect to the exit of the nozzle. Slot channels of 145 mm length were installed at a distance of 65 mm from the back step at the combustor entrance. Parallel fuel injection was carried out from vertical pylons at combustor entrance and had the ability to change the distribution of hydrogen along the height of the pylons. Each pylon had four interchangeable nozzles. In the experiments, two variants of hydrogen injection were used: one injector 2.5 mm of diameter on each pylon in the core of the flow (undistributed injection) and four nozzles with a diameter of 1.3 mm on each pylon (distributed injection). The tests were carried out in the hot-shot wind tunnel IT-302M ITAM SB RAS in the attached pipe-line mode with the following parameters at the combustor entrance: M = 2-6, P0 = 27-270 bar and T0 = 1900-2900K and hydrogen-air ratio from 0.6 to 1.1.
As a result, it was established that at Mach numbers 2-3, the combustion intensity with distributed injection is higher than when applying undistributed injection. This is explained by the fact that in this range of Mach numbers with undistributed injection the concentration of hydrogen in the slot channels is significantly lower than the stoichiometric value until its complete absence. With the increase of the Mach number, the effect on the combustion efficiency of the distributed injection version is reduced. At Mach numbers 4-6, the hydrogen concentration in the slot channels is close to the stoichiometric ratio when using undistributed injection.

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