The Graben:. Injectors

The third parameter that should be considered is the droplet size. Everything mentioned above will influence the degree of atomization. Typically atomization is caused by the liquid being broken up due to the collapse of unstable fluid sheets, jets or ligaments, or by the shearing action of air. There are a number of ways commonly used to atomize a liquid such as pressure atomization, air atomization, centrifugal atomization, electrostatic atomization, and ultrasonic atomization.

Pressure atomization or airless atomization occurs when high pressures force a fluid through a small orifice. As the liquid flows through the nozzle, the energy from the fluid pressure is converted into momentum and as soon as the liquid emerges from the nozzle, the friction between the atmosphere and liquid causes the liquid to separate into droplets. The atmospheric friction must provide enough resistance to overcome the liquid's surface tension, viscosity, and density for atomization to occur. Also, for this atomization scheme the orifice diameter, atmosphere, and relative velocity between the liquid and atmosphere all have an effect on the droplet size and quality of atomization.

In air atomization the fluid flows through a nozzle at a lower velocity than that required for pressure atomization. At the nozzle tip, high velocity air is injected into the liquid stream to disrupt and accelerate the liquid. The pressure of the air provides the energy required to atomize the liquid. As with pressure atomization, the relative velocity between the fluid and air causes atomization.

Centrifugal atomization requires a nozzle that has a spinning disc. The centrifugal acceleration created by the rotating disc forces the liquid to the edge of the disc where it forms ligaments or sheets of liquid. These ligaments and sheets then break apart into droplets due to the friction between the liquid and atmosphere. The rotational speed of the disc and the flow rate of the liquid affect the droplet size and quality of atomization.

Electrostatic atomization exposes a liquid to an intense electric field where the atomizer is charged and the target object being sprayed is grounded. The electric field is used to charge the liquid, once the liquid has the same charge as the atomizer the repulsive forces cause the liquid to tear from the atomizer and flow toward the grounded object. So, in this scheme the electric field strength, liquid flow rate, and the liquid's physical and electrical properties all affect the droplet size and quality of atomization.

The last atomization process is ultrasonic atomization. This process uses an electromechanical device that vibrates at a high frequency. As the liquid passes over the vibrating surface it breaks up into droplets. This scheme is not typically used because it is only effective for low viscosity newtonian fluids.

For this design, and most other rocket designs, pressure atomization is the primary process used in the injector system. Of course, all the processes mentioned above can be used to produce a broad range of droplet sizes which are typically split into the following categories: