The swirl injector is used in combustion engines such as aircraft engine, liquid rocket engine, and ramjet. It supplies the propellant to the combustion chamber. In swirl injector, the spray characteristics changed according to the injector geometry. There are many kinds of injectors, but the swirl injector has good atomization quality and uniform droplet distribution.
After the propellant enters the tangential inlet, it rotates inside of the swirl chamber. And then, water sprayed in the form of a thin liquid film at the end of the orifice, and the liquid sheet was in the form of a hollow cone shape. For this reason, an air-core is formed inside the injector, and the discharge coefficient is reduced due to the formation of the air-core. The atomization of droplets in the injector directly affects the combustion efficiency. The propellant is uniformly distributed, and the atomization performance is judged by how small it is divided. The better the atomization performance, the higher the combustion efficiency. Spray characteristics include the liquid film thickness, spray angle, breakup length, and discharge coefficient. Since these characteristics affect combustion process, so it is essential that research is carried out.
In the case of the single swirl injector, an experiment can be performed by fabricating an injector with a translucent material such as acrylic. This allows us to observe the flow inside the injector. However, there is a disadvantage of carrying out experiments at low pressure. In addition, when the electrode is mounted to measure the thickness of the liquid film, the injector is not completely sealed and liquid leaks out. Even if the bi-swirl coaxial injector is manufactured with a transparent material, it is difficult to visualize the inside of the injector because two single injectors are combined. In order to overcome the limitations of these experiments, numerical simulation was performed.
The computational analysis was performed on the bi-swirl coaxial injector for the combustion chamber. And the spray characteristics according to the recess length were investigated. It was confirmed that the spray angle did not change according to the flow rate in single injection. Also, it was confirmed that the spray angle decreases as the recess length increases. The change of spray angle was observed at external mixing conditions in the bi-injection. In the experimental studies, the spray angle was changed as the MR increased. Through the analysis, it was found that the discharge coefficient was changed at the tip mixing and internal mixing condition in bi-injection. This is because the water sprayed from the inner injector collides on the outer injector and interferes with the flow of water sprayed from the outer injector.
In the bi-swirl coaxial injector using moon exploration, the analysis was carried out by using property values as the actual propellant. The designed injector differential pressure was satisfied to be 5 bar. As a result of the simulation, the closed-closed type injector has an error of 10% in the spray angle, but it has a larger error in the open-open type injector. This assumes that the geometry constant of the injector changes because of the grid, and this result come out. As a result of checking the injector differential pressure through two types of injector analysis, the result is similar to that of the design point considering the pressure loss.