How does TurboJet Engine Works?

HOW DOES TURDOFAN ENGINE WORK

∆ HOW DO TURBOFAN ENGINES WORK?

∆  Turbofan Engines

 A closer look at how modern jet engine

then manufacturing juggernauts like Boeing or Airbus usually launch a new aircraft type, the headline figure is almost always how fuel efficient the new plane is compared to its predecessor. More often than not, nearly all of the fuel savings can be traced back to improvements in the engines. 

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∆ The Basics Principal

Before we get into the complex engineering of a modern turbofan engine, let’s understand the basics of how planes fly. Speaking very broadly, aircraft need two things to take to the skies: lift and thrust. Lift is the upward force generated by the wings, while thrust can be defined as forward momentum that comes from an airplane’s engines.

While traveling, passengers can only see a large fan at the front and a relatively small exhaust pipe at the back of a jet engine, but there’s a lot more going on between these two components. The main components of a turbofan engine include the fan blade, a compressor section, the combustion chamber, turbines, and the exhaust.

 

A turbofan engine works in four simple steps: suck, squeeze, bang, and blow, much like internal combustion engines in road vehicles. Up front, air is sucked into the engine through the massive fan. The high-velocity air then enters the second stage, where it is compressed using low-pressure and high-pressure compressor blades, in that order.

By this time, the air is up to 40 times denser than normal, with temperatures reaching a few hundred degrees. The compressed air will then enter the combustion chamber, where fuel will be sprayed in an attempt to mix the two. The mixture is then ignited, which results in the rapid expansion of the gases, which are ultimately coughed out from the exhaust nozzles.

Newton’s third law of motion states that every action has an equal and opposite reaction. In this case, exhaust gases leaving the engine at high velocity will propel the aircraft forward with an equal and opposite force, otherwise known as 

∆ Bypass ratio

While you now know the basic workings of a turbofan engine, there is one crucial detail left to understand. When air enters the engine through the large inlet fan, all of it doesn’t go to the engine core. A large chunk of incoming air travels between the engine cowling and the outer layer of the core. This air is known as bypass air as it exits out the back but does not go through the engine core. However, it is worth noting that bypass air also generates thrust. In fact, it produces more than half of the total engine thrust.

In simple terms, the higher the bypass ratio of an engine, the more efficient it will be, as the core is only responsible for generating a small part of the total engine thrust. It can even be said that the core's main function is to power the inlet fan in order to keep the bypass air flowing at capacity. This is what makes a modern turbofan engine significantly more efficient than older turbojet engines that are now predominantly used in fighter planes.

The amount of air distributed between the bypass path and the engine core is known as bypass air and is usually identified by the bypass ratio. A bypass ratio of 12:1 means that for every 12 units of air passing through the bypass duct, one unit is supplied to the engine core.

Since the bypass air is still passing through the engine inlet fan, it will have a slightly higher velocity compared to the outside. As a result, some thrust is also generated when bypass air exits the engine.

∆ How do the inlet fan and compressor turbines work?

The large inlet fan present at the front of the engine is powered by the engine itself. When the air-fuel mixture is combusted, the resulting hot gases are passed through a set of turbines that are concentrically connected to the inlet fan. In this way, a small part of the power generated by the engine is spent on keeping the fan running.

The compressor turbines in the "squeeze" stage are also powered in a similar way. Most modern turbofan engines have two concentric shafts running through the center, one for the inlet fan and another for the compressor turbines.

BY - TANISHQ TEJAS DESHMUKH

12 August 2022