The term “pressure thrust” refers to the component of thrust generated by the pressure differential across the nozzle of a propulsion system, such as a ramjet engine. It is a result of the higher pressure at the nozzle exit compared to the lower ambient pressure at the engine’s inlet. Pressure thrust is a significant factor in the overall thrust produced by jet engines, especially in cases where the exhaust pressure at the nozzle exit is substantially higher than the ambient pressure.
The formula for calculating the pressure thrust of a ramjet engine is as follows:
Pressure Thrust (F_pressure) = (P_exit – P_ambient) * A_exit
Where:
- F_pressure is the pressure thrust in newtons (N).
- P_exit is the pressure at the nozzle exit in pascals (Pa).
- P_ambient is the ambient pressure outside the engine in pascals (Pa).
- A_exit is the area of the nozzle exit in square meters (m²).
In this formula:
- “P_exit” represents the pressure of the exhaust gases at the nozzle exit.
- “P_ambient” represents the ambient air pressure outside the engine.
- “A_exit” is the cross-sectional area of the nozzle exit.
The pressure thrust is directly proportional to the pressure differential (P_exit – P_ambient) and the area of the nozzle exit. A higher pressure at the nozzle exit relative to the ambient pressure results in greater pressure thrust. This can be achieved by various means, such as efficient combustion and nozzle design.
In ramjet engines, the pressure thrust can be an important contributor to the net thrust, especially when the exhaust pressure is significantly greater than ambient pressure. It works in conjunction with the momentum thrust (generated by the high-velocity exhaust gases) to provide the overall thrust necessary to propel the vehicle forward.