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How Jet Engines Operate To Power Airplane

Jet Engine

 

Jet engines have come a long way and have become the central aspect of modern aviation engines. It is now the main power source of modern Airplanes. Before its invention, the aviation industry has been relying on internal combustion engines for a power source.

In this post, we shall be discussing Jet Engine and how they came into the world of aviation.

What is a Jet Engine?

A jet engine is a special type of engine with a unique design and working principle which has become the main power source for modern airplanes. However, the application of jet engines is not limited to the Aviation industry rather it has found useful applications to the power plant station for the generation of power. Due to the above reasons, the Jet Engine is also known as Gas Turbine.

In other words, the Jet Engine can be used to turn the propeller of a power generating plant which is another popular application besides the powering of airplanes.

 

Design and Working Principle of Jet Engine

The design of the jet engines is unique and completely different from those of rocket engines and reciprocating engines. Consider jet engine design has an axial acting mechanism that executes its operations axially.

It has lines of operations along its length. The Fan, the compressor, the Combustor, the turbine, and the exhaust (Nozzle).

Consider the diagram below as a simple illustration of Jet Engine design:

Jet Engine Design

At the front is Fan made up of Fan blades that suck cool air into the engine. The cool air will be forced to pass through the front openings of the engine due to the sucking fan blade attached to the shaft of the engine.

Behind the Fan, blades are sets of impellers arranged very close to each other for the purpose of multi-stage air compression. The work of the impellers is to compress the cool air that entered into the engine and force the air to pass through its tiny openings with high pressure coming from the rotating impellers. The high pressure impacted on the air will raise its temperature to over 900 degrees Celsius a temperature that is hot enough to ignite any aviation fuel (kerosene).

Just behind the compressor (multistage impellers) is a combustor. The combustor is similar to the combustion cylinder of internal combustion engines in terms of function however, it has a different design s its wall is reinforced with refractory concrete to withstand the great heat coming from the combustion f aviation fuel.

As the compressed hot air is forced into the combustor with very high pressure, there will be pressure and temperature buildup on the combustor while an injector sprays a specific volume of aviation fuel into the combustor leading to spontaneous explosion and combustion (burning) of the fuel this action will create a great thrust to counter the reaction from the explosion as the burnt gas escapes out of the combustor to meet another set of wind-turbine-like impellers.

The Wind turbine impellers are arranged closely to each other just behind the combustor and act as the turbine of the engine. The action of this unit is where the engine got its name as a gas turbine. The hot exhaust gas from the combustor will move with high pressure and temperature into the wind turbine impellers and force the impellers to start rotating. As the turbine impellers rotate they drive its shaft that holds other components.

The shaft that holds the wind turbine impellers is the same shaft that holds the compressor impellers and the fan blade of the engine. The entire length of the shaft has different sets and types of bearings to enable each unit to operate effectively.

The rotation of the shaft will repeat the entire process and help to keep the combustion continuous. The exhaust gas after leaving the turbine impellers to impact its kinetic energy will lose significant energy in the form of reduced temperature and pressure. To raise the temperature and pressure again, the gas will be forced to pass through a tapered nozzle such that it produces thrust that makes the gas exit the nozzle with pressure and temperature several times higher than when it entered into the engine thereby producing another thrust that helps to keep the airplane moving forward.

 

Types of Jet Engines

There are about six main types of jet engines used in modern aviation and power plant applications. Let us discuss these jet engines and their areas of application:

 

Turbojet

The turbojet engine is the original jet engine that powers airplanes using the gas turbine principles. It is the basic design of a jet engine that acts as a rocket to modern airplanes.

The powering unit of the turbojet is centered on the nozzle. The thrust from exhaust leaving the engine is a result of the speed of the hot air leaving the nozzle. In this type, the jet engine turbine channels most of its energy to drive the compressor to get high-pressure gas. In other words, the turbine takes away little energy from the exhaust gas.

This type of jet engine is a general-purpose type that is suitable for small and low-speed airplanes because it produces steady amounts of power all the time.

Jet Engine Design

Turboprop

A turboprop is a jet engine that drives a propeller for the purpose of propelling air. This type of jet engine can be found in most modern propeller aircraft. The turbine extracts most of the exhaust gas energy and uses it to rotate its shaft which has the propeller blades fixed on it at the outer front of the engine. Because it offers less air resistance this type of jet engine is mostly used in workhorse cargo planes and other smaller light aircraft.

The working principle of Turboprop is the same as Turboshaft the only difference is that the Turboshaft shaft is mounted vertically while the turboprop propeller is mounted axially in the direction of airflow.

 

 

Turbofan (low-bypass)

Turbofan jet engine was developed to overcome some of the lapses of other existing jet engines and one of such lapses high air resistance. This type of jet engine exert more energy on the main shaft carrying its turbine and use its rotation to carry the inner fan and outer bypass which has little space between them.

The outer bypass is a fan that stays at the outer front with space created between the larger sizes of the engine to the inner fan in the engine. The dragged air is forced into the inner fan while some volumes of the air escape to the surrounding of the engine which helps in cooling the engine as well as reducing its noise.  It is a typical jet engine used in most passenger airplanes.

Turbofans (low bypass) jet engine

 

 

Turbofan (high-bypass)

This is similar to the low-bypass. The only difference is the space between the inner fan and the outer fan bypass. Instead of a small gap, it has a large gap that allows more cool air to travel along the outer walls of the engine for effective engine cooling and noise reduction.

Turbofan jet Engine (High bypass)

 

 

Turboshaft

Turboshaft is a special type of jet engine used to drive the shaft of helicopters as well as most power plants.it has its main energy centered on the shaft. In other words, the turbine extracts high energy from the exhaust gas and uses it to drive its shaft which is connected to a vertically connected shaft via a gear mechanism such that the axial rotation of the shaft can be transmitted to the radial rotation of the vertical shaft.

A good example of the Turboshaft jet engine is the one used in powering most of the helicopters. The blades of the helicopter rotate due to the rotation of the vertical shaft connected to the main shaft of the turbine.

The exhaust gas of the engine has little thrust on the engine because most of the energy has been exhausted in the turbine which is used mainly for shaft rotation. It is the same turbine that is mostly used in power plants.

 

 

Ramjet and Scramjets

Ramjet is another type of jet engine that seems to have a different dimension of design and working principle. This is the engine behind most of the hypersonic and supersonic jets. It has few working parts and is closely related to a rocket engine but work on the principle of a jet engine.

Instead of fans that drag cool air into the engine, it has a tapered opening that forces incoming is to enter the engine and be compressed by the action of the forward movement of the airplane. The compressed air is trapped in a combustion chamber while the injectors spray the fuel which leads to combustion and exhaust of high temperature and pressure gas. The flame holder helps to balance and add more thrust to the gas by making it pass through a nozzle. The end power is a high thrust that pushes the airplane forward.

The below diagram is a simple illustration of Ramjet’s design.

RAMJET ENGINE

 

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