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Jet engines have been the successful drivers of aircrafts for nearly a century now. In this video, we will explain the technology behind the jet engine in a logical, step by step manner. A jet engine keeps an aircraft moving forward using a very simple principle, the same that makes an air filled balloon move. Yes, Newton’s third law of motion. Just like the reaction force produced by the air moves the balloon, the reaction force produced by the high speed jet at the tail of the jet engine makes it move forward.
So the working of a jet engine is all about producing a high speed jet at the exit. The higher the speed of the jet, the greater the thrust force. The thrust force makes an aircraft move forward.
Such high speed exhaust is achieved by a combination of techniques. If you can heat the incoming air to a high temperature, it will expand tremendously and will create the high velocity jet. For this purpose a combustion chamber is used. An atomized form of the fuel is burnt in the combustion chamber. Effective combustion requires air to be at moderately high temperature and pressure.
To bring the air to this condition, a set of compressor stages are used. The rotating blades of the compressor add energy to the fluid and its temperature and pressure rise to a level, suitable to sustain combustion.
The compressor receives the energy for the rotation from a turbine, which is placed right after the combustion chamber. The compressor and turbine are attached to the same shaft. The high energy fluid that leaves the chamber makes the turbine blades turn. You can see that, the turbine blades have a special airfoil shape, which creates lift force and make them turn. As the turbine absorbs energy from the fluid, its pressure drops.
Through these steps, we have achieved our objective; a really hot and high speed air emitted from the exit of the engine. The engine case becomes narrower towards the outlet, which results in even greater jet velocity.
So the working of a jet engine is all about producing a high speed jet at the exit. The higher the speed of the jet, the greater the thrust force. The thrust force makes an aircraft move forward.
Such high speed exhaust is achieved by a combination of techniques. If you can heat the incoming air to a high temperature, it will expand tremendously and will create the high velocity jet. For this purpose a combustion chamber is used. An atomized form of the fuel is burnt in the combustion chamber. Effective combustion requires air to be at moderately high temperature and pressure.
To bring the air to this condition, a set of compressor stages are used. The rotating blades of the compressor add energy to the fluid and its temperature and pressure rise to a level, suitable to sustain combustion.
The compressor receives the energy for the rotation from a turbine, which is placed right after the combustion chamber. The compressor and turbine are attached to the same shaft. The high energy fluid that leaves the chamber makes the turbine blades turn. You can see that, the turbine blades have a special airfoil shape, which creates lift force and make them turn. As the turbine absorbs energy from the fluid, its pressure drops.
Through these steps, we have achieved our objective; a really hot and high speed air emitted from the exit of the engine. The engine case becomes narrower towards the outlet, which results in even greater jet velocity.
In short, the synchronized operation of the compressor, combustion chamber and turbine makes the aircraft move forward.
Modern aircrafts use a slightly improved compressor-turbine arrangement called a two spool. Here 2 independent turbine-compressor stages are used. The shaft of the outer compressor-turbine passes concentrically through the inner one. The outer turbine is subjected to a low energy fluid and will run at a lower speed than the inner turbine. Low pressure blades are longer; this low speed helps to reduce centrifugal stress induced at the root, thus improving the blade’s life. Some modern aircrafts even use a 3 spool engine.
The engine we have discussed so far is more specifically called as Turbo jet engine. Turbojet engines tend to produce high levels of noise. A revolutionary improvement was made to this engine by fitting a large fan with the low pressure spool. Such engines are called Turbofan engines, and almost every commercial aircraft run on them.
A turbofan engine bypasses a huge amount of air. The ever narrowing by pass duct provides a good jet velocity to the bypassed air. In a turbofan engine the majority of the thrust force comes from the fan’s reaction force. Further, the fan greatly improves air flow in the system by sucking in more air. Thus it helps to improve the thrust. This means, high thrust creation with an expense of slightly more fuel. This is the reason why Turbofan engines are highly fuel economical.
The noise produced by a jet engine is highly dependent on the exit jet velocity. Since in a turbofan, the bypassed cold air gets mixed with the hot air, it is possible to keep the outlet velocity within a limit. Thus it overcomes the noise problem.
With quieter exhaust and better fuel economy, the turbofan engines continue to dominate aircraft propulsion systems. We hope this video provided a nice introduction to the working of jet engines.
Modern aircrafts use a slightly improved compressor-turbine arrangement called a two spool. Here 2 independent turbine-compressor stages are used. The shaft of the outer compressor-turbine passes concentrically through the inner one. The outer turbine is subjected to a low energy fluid and will run at a lower speed than the inner turbine. Low pressure blades are longer; this low speed helps to reduce centrifugal stress induced at the root, thus improving the blade’s life. Some modern aircrafts even use a 3 spool engine.
The engine we have discussed so far is more specifically called as Turbo jet engine. Turbojet engines tend to produce high levels of noise. A revolutionary improvement was made to this engine by fitting a large fan with the low pressure spool. Such engines are called Turbofan engines, and almost every commercial aircraft run on them.
A turbofan engine bypasses a huge amount of air. The ever narrowing by pass duct provides a good jet velocity to the bypassed air. In a turbofan engine the majority of the thrust force comes from the fan’s reaction force. Further, the fan greatly improves air flow in the system by sucking in more air. Thus it helps to improve the thrust. This means, high thrust creation with an expense of slightly more fuel. This is the reason why Turbofan engines are highly fuel economical.
The noise produced by a jet engine is highly dependent on the exit jet velocity. Since in a turbofan, the bypassed cold air gets mixed with the hot air, it is possible to keep the outlet velocity within a limit. Thus it overcomes the noise problem.
With quieter exhaust and better fuel economy, the turbofan engines continue to dominate aircraft propulsion systems. We hope this video provided a nice introduction to the working of jet engines.