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How does Spacex Raptor engine Work?
SpaceX's Raptor engine is one of the most powerful rocket engines in the world. With 350 bars, it holds the record for the highest chamber pressure among all rocket engines, playing a crucial role in the success of Starship. So, how does SpaceX's Raptor engine work?
It employs the full-flow staged combustion cycle to generate thrust. A schematic of the cycle is provided here to enhance understanding of the engine's working principle.
The fuel is depicted in red within the diagram. It exits the tank and enters the fuel pump directly, where the fluid's pressure is increased. Subsequently, the flow divides into two paths. The larger volumetric flow goes directly into the fuel-rich preburner, where most of the fuel is burned with a small portion of oxidizer. The other portion of the main flow enters the oxidizer-rich preburner.
After the fuel is burned within the fuel-rich preburner, the hot gas enters the turbine. The turbine shares the same shaft as the pump and consequently drives the pump. Behind the turbine, the gases are directed into the combustion chamber, where all the fuel is burned with the oxidizer.
The assembly is symmetrical; thus, the oxidizer follows the same components as the fuel. It first enters the pump, then splits into two flows, with the smaller portion going to the fuel-rich preburner and the larger portion going to the oxidizer-rich preburner. Once again, the hot gases from the preburner drive the turbine, which shares the same shaft as the pump. Finally the oxidizer is flows into the combustion chamber.
Let's see how this works in reality. Here is a picture of the Raptor engine. The most important components are above the nozzle, so let's take a closer look. The most visible part of the engine is the fuel turbopump, which is located on the side of the engine and marked in white. Here, we can identify most of the components we have already seen in theory.
The fuel inlet is located on top of the turbopump. The next red circle marks where the actual centrifugal pumps are positioned. The Raptor engine utilizes a two-stage centrifugal pump to increase the pressure of the fuel more efficiently. On the left, you can see the pump exit pipe marked with red arrows. The flow out of the centrifugal pump first goes through the main fuel valve and then further down to cool the combustion chamber, throat, and nozzle walls.
After the fuel has cooled the walls of the engine, the fuel itself attains a higher temperature. The fuel is then collected in two ports and flows through pipes to the fuel-rich preburner, marked here with an orange circle. There, the fuel is burned with a small portion of the oxidizer. You can see the pipe through which the oxidizer flows to the preburner on the left side, marked with blue arrows. To regulate the amount of oxidizer burned in the preburner, a second recirculation pipe is visible.
After the fuel is burned, the hot gases enter the fuel-rich gas turbine, located above the preburner. Here, the power to drive the centrifugal pump is generated. The hot gases exit the turbine on the right side. The exit pipe leads to the injector head where both the fuel and oxidizer are injected into the combustion chamber.
After identifying most components of the fuel turbopump, let's now focus on the oxidizer turbopump. Positioned directly above the injector head and combustion chamber along the engine's center axis, the oxidizer turbopump is often challenging to discern in pictures due to the presence of secondary equipment. In the image selected here, the oxidizer turbopump is at least partly visible within the white circle.
The large pipe situated atop the engine serves as the oxidizer inlet. Directly below the inlet are the first and second stages of the oxidizer centrifugal pump, distinguished by their dark grey-colored casing marked with a dark blue circle.
In contrast to the fuel turbopump, the pressurized oxidizer from the centrifugal pump here enters the oxidizer-rich preburner directly. The casing of the preburner shares the dark grey color and is indicated by the blue circle. Following the preburner is the oxidizer-rich turbine, identified by its light grey-colored casing marked in light blue.
Given the complexity of the assembly, understanding the setup can be challenging with all the components in view. To aid comprehension, I've overlaid the picture with a schematic representation illustrating the potential internal configuration of the turbopump.
The outcome of this process is visible here. Once again, the oxidizer enters the turbopump at the top, with the first and second-stage centrifugal pumps following in sequence. Subsequently, the oxidizer passes through the preburner before flowing through the turbine. I trust that this image enhances the clarity of some of the explanations.
Now that we've identified the more intricate components of the engine, let's turn our attention to the commonplace parts situated below the oxidizer turbopump. These components include the injector, combustion chamber, throat, and nozzle, as indicated by the configuration marked with a white circle.
At the outset, we discussed the necessity for fuel to pass through the engine walls for cooling purposes. In this image, four circuits, marked in black, can be observed circulating around the engine walls. The primary functions of these circuits are to supply a greater volume of cooling flow to the most critical parts of the engine walls and to collect the fuel for the backflow to the preburner.
As mentioned earlier, the injection head is positioned directly beneath the oxidizer-rich turbine and, in this picture, to the left of the fuel-rich turbine. The location is highlighted with a white circle. The engine layout also allows for the identification of the contours of the combustion chamber, the throat, and, of course, the nozzle.
