Effect of excitation on gas centered swirl coaxial injectors

Abstract

Studies on combustion instability in liquid rocket engines are important in improving combustion efficiency andpreventing combustion chamber losses. To prevent combustion instability, methods such as baffles and cavities are used. The injector is located in the middle of the perturbation-propagation process in the rocket engine, so it is important to study the suppression of combustion instability using the design of the injector. Much research has been focused on the study of liquid excitation in a single injector; however, the actual injector used in a liquid rocket engine is a coaxial injector. In this study, the dynamic characteristics of a gas-centred swirl coaxial injector were investigated by varying the gap thickness and momentum-flux ratio. Spray photographs were captured by synchronizing a stroboscope and digital camera, and a high-speed camera and Xenon lamp were also used. To measure the liquid film, a measurement system was implemented using the electrical conductance method. For excitation of the gas, an acoustic speaker was used to impart a frequency to the gas. The gGas velocity and effect of excitation were measured by hot-wire anemometry. A mechanical pulsator was used for liquid flow excitation. Liquid fluctuation was measured by a dynamic pressure sensor. In both gas and liquid excitation cases, the gain increased as the gap thickness decreased and the momentum-flux ratio increased. From these results, it can be concluded that gap thickness and momentum-flux ratio are major factors in suppressing combustioninstability. DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4653