Optimization of oxygen-kerosene gas generator mixing processes

The study presents optimization results aimed at improving fuel–oxidizer mixing while preserving the operational characteristics of a liquid rocket engine combustion chamber. Traditional chamber design methods described in classic textbooks are based on semi-empirical procedures intended primarily for high-thrust engines delivering several tens of tons of thrust. There is now a growing demand for commercial launch vehicles of the light and ultralight classes. Given the tight size, mass, and energy budgets of small liquid engines, particular attention is paid to the compactness and reliability of injector assemblies. The work addresses the design and optimization of the injector head to achieve optimal mixing at a standoff from the injector faceplate sufficient to minimize its thermal load. Computational fluid dynamics is applied with combustion, heat transfer, species transport, and radiation. To account for the liquid phases of oxygen and kerosene and to represent their velocities in the injectors correctly, a pseudo-gas equation of state is used. Injector throttling characteristics are computed in ANSYS. Global parametric optimization (particle swarm method) is performed over injector angles, diameters, and layout. “NASA CEA” equilibrium calculations are used to validate output parameters. The developed optimization technique reduces combustion chamber dimensions by nearly a factor of two. Combining computational fluid dynamics of mixing and combustion with optimization algorithms enables preliminary design optimization before prototype fabrication, thereby lowering development and manufacturing costs. Compared with common approaches — parametric sweeps, gradient optimization based on simplified correlations, design of experiments, and manual tuning through test campaigns — the method relies on coupled flow and heat-transfer calculations with a fast pseudo-gas model and automatic selection of injector geometry by criteria of mixture uniformity and combustion stability. This reduces the number of physical iterations, improves spray uniformity, and lowers thermal stresses on components. Application areas of the suggested method: injector heads for small- and medium-thrust liquid engines, gas generators, and ignition chambers of test stands. Prospects of the method: accounting for unsteady oscillations and acoustics, optimization under uncertainties, integration of additive manufacturing constraints, and automated channel synthesis.

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