A Liquid Rocket Combustor CFD analysis is the most important step in designing powerful engines for space travel. In a liquid rocket engine, fuel and oxidizer must mix and burn instantly to create massive thrust. This process is very complex and dangerous to test in real life. Therefore, engineers rely on Liquid Rocket Combustor CFD simulation to predict what happens inside the chamber. This allows us to see the flame and heat without building expensive prototypes.

In this report, we use Liquid Rocket Combustor ANSYS Fluent to model the turbulent burning process. We specifically use the Non-premixed combustion ANSYS Fluent method. This method is perfect for rockets because the fuel and oxidizer enter the chamber separately. We also use the PDF Fluent model (Probability Density Function). This tool helps us calculate the complex chemistry and temperature changes very accurately. By using this Rocket Combustion Fluent approach, we can verify if the engine design is safe and efficient before it is manufactured. For more details on simulating fire and flames, please check our Combustion tutorials: https://cfdland.com/product-category/engineering/combustion-cfd-simulation/

Figure 1: A comparison diagram showing the difference between solid and liquid-fuel rocket engine concepts.

Simulation Process: Non-Premixed Modeling in ANSYS Fluent

The simulation process for this Liquid Rocket Combustor CFD project began with designing a 2D geometry. Because rocket engines are round, we used an axisymmetric setup in ANSYS Fluent. This smart choice saves computer time while keeping the results very accurate. To track the chemicals, we activated the Species Transport model. This allows the software to calculate how the fuel and oxidizer move and mix.

The most critical part of the setup was the Non-premixed combustion ANSYS Fluent model. In this method, we do not mix the fuel before it enters. We selected the “Non-adiabatic” option because heat loss to the rocket walls is a major design factor. We also used the “Chemical Equilibrium” assumption. This means the Liquid Rocket Combustor ANSYS Fluent solver assumes the fuel burns instantly as soon as it touches the oxidizer. To solve this efficiently, we generated a PDF Fluent table. This table pre-calculates the temperature and chemical species for every possible mixture. This technique allows us to simulate the extreme conditions of a rocket engine quickly and reliably.

Figure 2:  The Mean Temperature PDF table generated in ANSYS Fluent, used to calculate reaction rates based on mixture fraction.

Post-processing: Thermal Analysis and Flame Stability Assessment

The post-processing analysis provides deep insight into the engine’s performance. We must analyze the contours carefully to help the manufacturer improve the design. First, we look at the Temperature contour (Figure 3). The simulation reveals that the flame is not a simple ball of fire. Instead, it forms a distinct cone shape. The most important finding is the maximum temperature of 3017 K. This extreme heat is located in the “shear layer,” which is the boundary where the fuel stream meets the oxidizer stream. For a designer, this is critical information. It confirms that the mixing is efficient, but it also warns that the injector face must be cooled to survive this heat.

Next, we analyze the flow dynamics using the Velocity contour (Figure 4). A rocket engine must push gas out fast to create thrust. The Liquid Rocket Combustor CFD simulation shows that the gas velocity at the inlet nozzles reaches 1601 m/s. This is a very high speed. The contour shows that the flow slows down slightly as it expands into the main chamber, which helps stabilize the flame. If the velocity was too high everywhere, the flame might “blow out.”

Figure 3: Temperature contour from the Liquid Rocket Combustor CFD study, revealing a peak flame temperature of 3017 K..

Figure 4: Velocity contour showing the high-speed injection jets accelerating to 1601 m/s.

Finally, we evaluate the combustion chemistry using the Mass Fraction contours. The O Mass Fraction (Figure 6) shows a bright yellow loop. This loop marks the zone of intense reaction. It proves that the oxygen is being consumed exactly where we want it to be. The H2O2 contour (Figure 5) shows intermediate chemicals in the mixing layer. The fact that these reaction zones are stable and symmetrical confirms that the flame is anchored properly. This Rocket Combustion Fluent analysis assures the manufacturer that the engine will burn smoothly without dangerous instabilities or unburned fuel exiting the nozzle.

Figure 5: H2O2 Mass Fraction contour highlighting the chemical mixing layers where intermediate species are formed.

Figure 6: O Mass Fraction contour indicating the exact zone of intense chemical reaction in the rocket combustor.