Turbofan Engine

Introduction

Hello readers, in last post we discussed about turbojet engine. Today we are going learn turbofan engine which is much similar to turbojet engine. As this is connected to turbojet engine one should first understand Turbojet engine (have look to my previous post) in order to understand turbofan quickly.

Turbofan engine similar to turbojet engine but have greater efficiency at lower speed. Main difference in construction of turbofan engine is that it contains bypass line addition to arrangement of turbojet engine and front of turbofan engine has fan at inlet of engine.

This construction can be shown as below.

Working

The fan in front of engine is driven by the turbine of engine. It uses two separate shaft to maintain speed of fan lower than the speed of turbine. Surrounding of fan is known as cowl which is used to guide air. Some part of air enters to turbine while rest of part is bypassed through bypass line. The air entered in main line is compressed and used to support combustion of fuel in combustion chamber where high pressure gas is generated. This gas is used to drive turbine.

An important term bypass ratio is often used while categorizing this engine. Bypass ratio is the ratio of the mass flow rate of the bypass stream to the mass flow rate entering the core. This ratio is also used to determine efficiency of engine. 

According to amount of air bypasses the engine this engine can be categorized as low bypass ratio engine and high bypass ratio engine.

Today most of jet airlines are powered by high bypass ratio because of good fuel economy and less noise. However modern combat aircraft uses low bypass ratio engine.

Application

Many commercial airline company uses this engine to propel air craft. Air India Boeing 787 GE is example of aircraft which uses such engine.

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