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Experimental and Numerical Research of the Ignition and Flame Propagation Process in the Supersonic Flows

Author: GongCheng
Tutor: LiangJianHan
School: National University of Defense Science and Technology
Course: Aeronautical and Astronautical Science and Technology
Keywords: scramjet supersonic combustion ignition LES
CLC: V231.2
Type: Master's thesis
Year: 2011
Downloads: 72
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Abstract

The ignition processes of the ignition in a scramjet combustor with cavities were studied in this paper. The attention was focused on the formation and propagation of the initial flame.Numerical simulations of ignition in the pre-mixed flow show that: when the flame was initialed by a spark igniter, the initial flame format near the igniter which in the cavity and propagate into the cavity shear layer. Then the initial flame spreads along the cavity shear layer and ignites downstream gas very quickly by the convection of the shear layer. When the total temperature of the flow is high enough to auto-ignite, the initial flame format in the rump of the cavity. The expansion by the burning gas in the cavity is important for the spreading of the combustion in the main flow. To the combustor with single cavity, when the initial gas in the cavity is exhausted, the combustion in the main flow couldn’t be maintained, while to the combustor with several cavities, when the shock waves meet on the flame front, a detonation may generate and spread to the upstream.Numerical and experimental investigations on the ignition of fuel transverse Jet into Supersonic flow show that, for the forced ignition, the spark generates near the igniter, and grows to form flame in the cavity. The initial flame spreads along the cavity shear layer and ignites the fuel distributed downstream very quickly. With the pressure downstream rises up, the pre-combustion shock and the flame go against the stream and finally the whole fuel jet flame is ignited and stabilized. For the auto-ignition, the initial flame generate in tail of the shear layer, then the flame ignite the gas downstream the cavity on one way, and spread opposite the shear layer on the other way. When the whole shear layer is burning, the process of the flame spread is similar to the one of forced ignition.Two different flame spread mechanisms were discussed based the numerical and experimental data. One called the the sustaining auto-igniting mechanism consider that the cavity establish a feedback between the tail and head of the shear layer, while there is a another feedback between heat release from combustion and the upstream shock train. The other one is called the turbulent flame propagating mechanism, which consider that a banding zone in which the turbulent flame speed is higher than the gas velocity may extent in the shear layer. These two mechanism types have a competition-relation on the ignition.

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