Studying jets injection into the combustion chamber method effect on air-fuel mixture mixing efficiency
Thermal engines, electric propulsion and power plants for flying vehicles
Keldysh Research Centre, 8, Onezhskaya str., Moscow, 125438, Russia
The advantage of the combined air-jet engine structure, with gas generator placed in its loop, consists in work process better stability due to relative independence of the processes in gas generator and main combustion chamber. Gasification and partial fuel decomposition (with a small quantity of oxidizer) occur in the gas generator due to pyrolysis and/or burning reaction. The derived gas is mixed with the air and reheated in the main combustion chamber. Gas generator jet high temperature must ensure self-ignition and flame stabilization. The important problem consists in providing efficient mixing of the two-phase gas generator gas flow with the main flow. It is necessary to calculate the injected get propagation in cross-flow to determine optimal injection angle, since the fuel and oxidizer pattern and mixing behavior over chamber cross-sections affects significantly the combustion chamber work process.
Various versions of axial gas generator nozzle with co-current injection unit were studied, and an optimal (from the combustion efficiency viewpoint) was sel ected. With the use of a gas generator nozzle cluster with multiple jets, mixing intensifies. The supersonic flow is further decelerated by the oblique shocks, occurring due to jets injection at the angle of chamber axis. It all leads to combustion efficiency increase for the structure with four circular jets and a central one.
The injection angle dependence of the mixing efficiency was studied for the case of jet injection fr om the combustion chamber wall. The results were compared with empirical formulas for the jet trajectory in a cross flow. Most uniform distribution of the injected gas was obtained at an angle α = 135°.
The necessity of the accounting for the condensed particles spectrum was demonstrated for two-phase gas-generator gas.
Keywords:flame stabilization system by jets, gas generator, mixing efficiency, condensed particles
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