Gas-centered swirl coaxial injectors have become an important subject of study for staged combustion rocket engines with hydrocarbon fuels. While these injectors are employed successfully in rocket engines, it is very rare to find the related research results as applicable to design data. An experimental study on spray characteristics of gas-centered swirl coaxial injectors has been performed. The effects of momentum flux ratio and recess length on the spray characteristics have been investigated by cold flow tests with a photographic technique. The liquid intact length L, which profoundly affects the global spray characteristics, decreases as the momentum flux ratio M increases. The critical momentum flux ratio Mc is introduced to identify the flow patterns as internal or external mixing in the injectors. Concerning the effect of the recess length lR, it is shown that the spray cone angle and the drop size decrease as lR increases.

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