Jet engines have been the successful drivers of aircraft for nearly a century. Today we will explain the technology behind the jet engine in a logical bit-by-bit manner. A jet engine keeps an aircraft moving forward using a very simple principle the same that makes an airfield balloon move. You are correct if you guessed “newton’s third law of motion”.
Just like the reaction force generated 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 yielding a high-speed jet at the exit. Higher the speed of the jet the greater the thrust force that makes an aircraft move forward.
The engine we have discussed so far is more specifically called a turbojet engine. Turbojet engines tend to produce high levels of noise. And then – one fine day – a revolutionary improvement was made to this engine. By fitting a large fan with the low-pressure spool such engines are called turbofan engines.
Almost every commercial aircraft run on them!!!
Such high-speed exhaust is achieved by a permutation of techniques; if you can heat the incoming air to a high temperature it will expand tremendously and will produce the high-velocity jet. For this objective, a combustion chamber is run down. An atomized form of the fuel is burnt in the combustion chamber effective combustion entails 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 tally up the 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.
At this point, we can observe 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, and 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 aircraft use a slightly improved compressor turbine arrangement called a spool*. Here two independent turbine compressor stages have 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 slower 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 blades life some modern aircraft even use a 3 spool engine.
The turbofan engine bypasses a huge amount of air the ever-narrowing bypass 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 enhances airflow 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 impressively highly fuel economical.
The noise produced by a jet engine is prominently 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 less noisy exhaust and better fuel economy the turbofan engines continue to lead aircraft propulsion systems.
Hope this portrayed a fine introduction to the working of jet engines.
Note: A spool is engineering shorthand for the combination of an engine compressor and high-pressure turbine that drives it using a connecting drive shaft. In a single-spool engine, the high-pressure turbine drives the entire compressor.