In liquid rocket engine, the study on throttling have been conducted since 1930’s. The throttleable rocket engine enables the operational possibilities, for example docking of spacecraft, maneuvering in certain orbit and landing on a surface of planet, attitude control, entrance to atmosphereless of planet and etc. To achieve throttling in liquid rocket engine, methods are classified by target variable, such as high pressure drop, change in discharge coefficient, various density, and change in nozzle area
Meanwhile, as rocket engine employed bi-propellant instead of mono-propellant, mixing efficiency became a major criteria in engine design stage. In order to mix fuel and propellant, impinging type injector, coaxial type injector, etc. were developed. For a coaxial type injector, the injector, such as shear coaxial injector and swirl coaxial injector, could be classified by injection type. And liquid centered injector and gas centered could be classified by injection position.
To investigate the characteristics of injector, lots of method have been studied. In liquid rocket engine, rocket engine do not employed a single injector, but tens or hundreds of injector are installed in injector plate. So, interference between spray from injector could be occurred. To avoid the interference, prediction of spray angle is important variable in characteristics of liquid rocket injector. Also the diameter of droplets is considered in design stage since it could influence on combustion instability.
In this study, dual manifold, one of controlling discharge coefficient, was used to control the thrust in liquid phase. And liquid centered coaxial injector was employed to mix liquid and gas simulant. To investigate variation of mixture ratio F/O ratio increased 0, 1/10, 1/8, and 1/6 in the experience. In order to comparative study between dual manifold injector and single manifold injector, the spray angle, mass flow rate, diameters of droplets, and mean diameter of droplets which are representative characteristics in spray, were investigated.