A turbojet engine is a type of gas turbine engine that generates thrust by expelling a high-velocity jet of hot gases from its exhaust. These engines are widely used in aviation, particularly for high-speed aircraft like military fighter jets. This process involves a continuous flow of air undergoing significant changes in pressure, temperature, and velocity as it moves through the engine.
How a Turbojet Works: A Pressure Journey
Air enters a turbojet engine through the inlet, where its speed is initially slowed down, leading to a slight increase in static pressure. This incoming air then flows into the compressor section, a series of rotating blades and stationary vanes that progressively squeeze the air into a smaller volume. As the air is compressed, its pressure and temperature rise considerably. After compression, the highly pressurized air enters the combustion chamber.
In the combustion chamber, fuel is injected and ignited, leading to a continuous burning process. This combustion primarily causes a dramatic increase in the gas’s temperature and volume, though the pressure remains relatively constant or experiences only a minor drop due to friction. The hot, high-energy gases then expand through the turbine section, which is connected by a shaft to the compressor. As the gases pass through the turbine, they transfer a portion of their energy to spin the turbine blades, which in turn drives the compressor. Finally, the gases exit through the exhaust nozzle, accelerating to a very high velocity to produce thrust.
The Point of Maximum Pressure
The highest gas pressure within a turbojet engine is achieved at the outlet of the compressor, precisely before the air enters the combustion chamber. The compressor’s design is specifically engineered to maximize this pressure. It consists of multiple stages, each contributing incrementally to the overall pressure rise. For instance, in an axial-flow compressor, rotating blades accelerate the air, and stationary vanes then convert this velocity into increased pressure.
Modern turbojet compressors can increase the air’s pressure by 10 to 40 times its initial atmospheric pressure. This intense compression significantly increases the air’s density and temperature, preparing it for efficient combustion. Maintaining this high pressure is important for the engine’s thermodynamic efficiency, as it allows for a greater expansion of gases later in the cycle to generate power. The structural integrity of the compressor is essential to withstand these extreme pressure conditions.
From Pressure to Thrust
As the gases expand through the turbine, their pressure and temperature decrease because energy is extracted. The remaining hot, high-pressure gases then enter the exhaust nozzle. The nozzle is shaped to accelerate these gases to supersonic velocities. As the gases rapidly expand and exit the nozzle at high speed, they create a reactive force. This force, known as thrust, propels the aircraft forward, converting the internal energy of the gas into kinetic energy for propulsion.