Numerical simulation of fuel droplets evaporation and combustion regimes in the combustion chambers of liquid rocket engines

Аuthors

Sidlerov D. A.^*, Ponomarev A. A.^**

Keldysh Research Centre, 8, Onezhskaya str., Moscow, 125438, Russia

*e-mail: sidlerov@rambler.ru
**e-mail: ponomar_aa@mail.ru

Abstract

In this article a physical-mathematical model, which gives the possibility to compute features of individual and group regimes of evaporation and combustion of dense turbulent sprays, consisting of fuel droplets, is considered. Investigation results of operational process peculiarities inside combustion chambers by varying the regimes of evaporation and combustion of fuel droplets are presented.

Working process development inside liquid rocket engine combustion chamber is in a significant extent determined by an interaction of liquid sprayed flows of fuel and oxidizer. Combustion of propellant droplet arrays can be profoundly affected by the collective interaction between droplets that impedes large scale intermixing of fuel and oxidizer vapor thus forming oxidizer or fuel reach regions with unflammable conditions inside sprays. Additionally, the presence of large number of comparatively cold liquid droplets tends to decrease the temperature inside spray.

Three spray combustion regimes can be proposed: 1) individual regime of combustion, typical for sparse sprays, when every droplet is surrounded by an individual combustion front; 2) regime, when droplets in internal regions of the spray have no individual combustion fronts, and at the same time in the outer regions of spray individual droplet combustion regime takes place; 3) regime, when droplets inside the spray only evaporate, and combustion front surrounds all the spray on the outside.

The mathematical model includes equations of the Navier-Stokes type and the k — ε turbulence model. The combustion rate is defined by the model of turbulent vortex dissipation and from the generalized equation of chemical kinetics of the Arrhenius type. Calculation of motion, warming up, evaporation and breaking of droplets is conducted in the Lagrange approach. Thereat, the interchange with mass, momentum and energy between phases of gas and droplets with regard to turbulent flow characteristics are taken into account. The equations are digitized with the control-volume method and solved with an algorithm of the SIMPLER type.

Additional relations, which give the possibility to identify realization of individual or group spray combustion regimes, are being proposed.

This technique is widely used at Keldysh Research Centre for numerical modeling of the working process in subscale and full-scale combustion chambers and gas generators that operate with a variety of injectors and using different propellants.

Possibilities of the method have been demonstrated by an investigation of features of the working process inside a combustion chamber with coaxial jet injectors under different regimes of fuel spray combustion.

Keywords:

evaporation and combustion of fuel droplets, combustion chamber, numerical simulation

References

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