The pintle injector is a promising candidate of the propellant injection systems for a rocket engine with deep throttling capability which is essential for future space transportation missions. However, studies focusing on combustion phenomena in a rocket engine with a pintle injector is rather limited. In this study, optical measurements inside an ethanol/liquid oxygen rocket engine combustor with a planar pintle injector are conducted to clarify spray and flame structures in the pintle injector. Combustion tests where the chamber pressure is 0.36 to 0.40MPa and O/F is 1.15 to 1.40 are conducted. Effects of the injection configuration on spray structures are also evaluated. High speed imaging techniques are used to observe the flame and spray structures under hot fire conditions. Strong chemiluminescence of CH is observed in the vicinity of the impinging point of two propellants. Luminous flame is observed intermittently in the vicinity of the faceplate and the upper wall of the combustor with the direct observation of the flame. Characteristic exhaust velocity efficiency with oxidizer-centered configuration is lower than fuel-centered configuration due to the large amount of propellant impinging on the upper wall of the combustor. Periodical phenomena with the frequency of approximately 300Hz which can be related to atomization processes are also observed.
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