This was RIT Launch Initiative's first attempt to build a liquid rocket engine. We gained valuable experience with engine design, manufacturing, and testing. The knowledge gained through this project has led to a better understanding of rocket engines, and the continuation of liquid development within the club.
Combustion Chamber and Cooling Shell
The combustion chamber is where the propellants will mix and chemically react, which causes a rapid increase in temperature and pressure which pushes the gases towards the nozzle. The nozzle is comprised of a converging section, which accelerates the flow velocity to Mach 1, and a diverging section, which allows the gases to reach supersonic speeds. Through conservation of momentum, the flow of the gases produces a force in the opposite direction of the flow, called thrust. The combustion chamber will be machined out of 6061 aluminum, chosen for its easy machinability, low cost, and availability. Computer-aided manufacturing techniques will likely be applied to ensure precise geometry. The flame temperature of the chosen propellants will likely exceed 5000°F, so the combustion chamber must be cooled in some way to withstand these temperatures. This will be done by transferring heat through the chamber walls to cool water flowing through an outer shell. The water will enter the cooling shell near the throat of the combustion chamber, where most of the heat will be concentrated, absorb much of this heat, and then exit near the top of the chamber. This system is vital to the success and safety of the entire project, so much of our effort is directed at ensuring this design is robust. 1020 drawn-over-mandrel steel tube was selected for the cooling shell.
The primary purpose of the injector is to properly mix the fuel and oxidizer to achieve even and consistent combustion. This is done by breaking up the liquids into very small particles, a process known as atomization. In this case, only the fuel needs to be atomized, since the oxidizer is already in a gaseous state. Oxygen enters at the top of the injector and flows through a straight tube into the combustion chamber. Fuel enters at the side of the injector into an inner reservoir, then flows through six small orifices that lead into the combustion chamber. When both propellants are flowing simultaneously, the oxygen will expand out from the center orifice and collide with the methanol, causing atomization. This design is also convenient because oxygen is extremely corrosive at high temperatures, but since it will be surrounded by methanol, there should be minimal contact between the combustion chamber walls and the oxygen. The injector will be connected to a load cell via the steel disc suspended by threaded rods. This will be one of two methods for measuring the thrust produced by the engine.
The test stand will provide surfaces for mounting all of the necessary components for the feed system and data acquisition systems. The engine is mounted vertically to the engine interface, which protrudes from the steel shield. Strain gauges attached to the engine interface will measure the thrust produced by the engine. For redundancy, a load cell will connect the injector to the engine interface. The steel shield protects the fuel and oxidizer tanks from the unlikely event of a catastrophic failure of the engine. The plywood on the back of the test stand ensures easy mounting of instruments, tanks, and other feed system components.
The feed system is responsible for delivering the propellants from their respective storage tanks to the engine. On the oxygen side, a manual valve must first be opened, which allows the oxygen from the high pressure tank to pass through a regulator to lower the pressure. Once the test engineers have retreated to a safe distance, a solenoid valve will be remotely opened to allow the oxygen to flow to the engine. A check valve prevents any backflow. Since the fuel is liquid, nitrogen is used to create the pressure that will force the methanol through the system. The nitrogen passes through another regulator to obtain the correct pressure and then through a check valve and into the fuel tank. The fuel then flows through a regulator and another remotely controlled solenoid valve. The fuel line also contains a manual valve and finally a check valve. You will also notice a nitrogen line that splits off before the fuel tank and bypasses the solenoid valve. This is a "purge" line that will be used to clear out any residual propellants at the conclusion of the test fire, and can also be used in the event of a failure that requires the test to be aborted.
In collaboration and under the guidance of Rochester Propulsion Lab, the liquid sub-team was able to successfully test RL-36 engine. The culmination of 3 years of work led to a simplified version of the initial design, with plenty of compromises to get to the test stand. However, these setback where all useful lessons and experiences for members, demonstrating the difficulty and reality of bringing a design to reality as an engineer.
Preliminary Design Review:
Critical Design Reviews: