Description

A propulsion system that creates thrust by compressing ram air is known as a solid fuel ramjet (SFRJ) engine. Simply put, it is an air-breathing engine that burns solid fuel using oxygen from the atmosphere instead of a fuel oxidizer carried inside the engine. The structure of an engine is typically made up of an air inlet, a combustion chamber where solid fuel is burned, and a nozzle from which exhaust gases are released to generate thrust. According to the ram effect theory, a solid fuel ramjet's (SFRJ) forward motion compresses entering air before combustion. Here is a detailed explanation of how it operates:

- Air Intake: The ram action causes air to be driven into the intake as the SFRJ advances.

- Compression: The incoming air is compressed as the engine moves ahead.

- Combustion: In the combustion chamber, where the solid fuel is present, the compressed air enters. The fuel burns due to the compressed air's heat igniting it.

- Thrust Production: When fuel is burned, hot gases are created that expand and are expelled from the engine's back nozzle. This force causes the engine to move forward.

Due to their high efficiency and speed, SFRJs are mostly used in the aerospace and defense industries.

In a Solid Fuel Ramjet (SFRJ), the fuel flow might be either slower or faster than the speed of sound, which is determined by the Mach number at the entry point.

When the mixture of fuel and oxidizer in the combustion chamber travels at a speed lower than the sound speed, it is called Subsonic Flow (Mach number < 1). This allows pressure changes or information to move against the flow, implying that downstream changes can influence the upstream flow. In terms of an SFRJ, this could impact the combustion efficiency and the thrust produced.

The 2D model is created in design modeler and meshed in ANSYS Meshing software 35,224 elements.

Methodology

In this project, we simulated an SFRJ with Hydroxyl-terminated polybutadiene, HTPB, as the solid fuel, and the inlet air is considered subsonic flow because the Mach number is 0.9. the model has two inlets, one entering the air and the other entering the fuel. Also, the cone half angle of the diffuser is 20 degrees. To calculate the inlet velocity of air based on Mach number, we used the following formula :

V inlet=M×√(γ×R×T)

In which the γ presents (Cp/Cv) that equals 1.4 for air, the R represents the specific gas constant that is 287 for air, and the T presents absolute temperature. This way, the air velocity inlet is computed as 311.5[m/s], which equals 0.94 [kg/s] as the mass flow inlet.

The air comes in through the diffuser inlet, and the HTPB comes in via the fuel inlet to the chamber, and the combustion happens via the reaction below:

The species transport model defines the reaction and models the combustion in the chamber. It should be noted that volumetric and dissipation rates are activated in the species model.
The turbulence of the flow is simulated with the Realizable K-ε model, which is suitable for this problem.

Conclusion

Today, SFRJ can have a chamber temperature of up to 2900 K. Our simulation shows that the maximum temperature of the combustion occurring in the chamber reaches 1485 K, which is desirable T as a result.

The temperature and velocity contours of the processes in the simulated SFRJ are presented. Also, the oxygen and CO2 mass fraction contours are presented to show how the reactants and products are distributed via this reaction and simulation process.