Injectors

After some weeks thinking about the best type of injector configuration, I've decided to use a swirl injector as it will atomize efficiently the methanol. 

Gaseous oxygen will be delivered to the injector directly from the top, the oxygen stream will flow from the pressurized supply into an 8mm tube that will collide with the methanol cone. This cone pattern is produced by the momentum of the tangentially injected methanol from two orifices at both sides of the injector. 

Above is shown a 3D model concept of the swirl injector. It will be made out of copper as all the engine.

I also thought about using doublet impinging jets but really small orifices will be required and I personally consider that kind of injector plate more complex for small chambers because it will need more piping, machining and more copper than a single swirl injector.

To design an injector we have to determine the injection area of the oxidizer and the fuel. This can be done with equation 1.1. 

1.1

Where mx is the mass flow rate, Cd is the discharge coefficient, rho is the fluid density and delta p is the pressure drop and A is the injection area.

To calculate the diameter of every injection orifice, first the area given by equation 1.1 is divided by the number of orifices of the injector plate and then, equation 1.2 is used to determine the diameters.

1.2

In the case of doublet injectors, is necessary to determine the resultant momentum of the two streams of propellant. The resultant stream should be axial as it is important to keep the combustion off the chamber wall.

Figure 1-1 Resulting momentum of two impinging propellant streams. Sourece: Rocket Propulsion Elements, George P. Sutton and Oscar Biblarz

1.3