Turbojet

The turbojet engine consists of four sections: compressor, combustion chamber, turbine section, and exhaust. The compressor section passes inlet air at a high rate of speed to the combustion chamber

The combustion chamber contains the fuel inlet and igniter for combustion

The expanding air drives a turbine, which is connected by a shaft to the compressor, sustaining engine operation

The accelerated exhaust gases from the engine provide thrust

This is a basic application of compressing air, igniting the fuel-air mixture, producing power to self-sustain the engine operation, and exhaust for propulsion

Turbojet engines are limited in range and endurance

They are also slow to respond to throttle applications at slow compressor speeds

• Turboprop

A turboprop engine is a turbine engine that drives a propeller through a reduction gear.

The exhaust gases drive a power turbine connected by a shaft that drives the reduction gear assembly

Reduction gearing is necessary in turboprop engines because optimum propeller performance is achieved at much slower speeds than the engine' operating rpm

Turboprop engines are a compromise between turbojet engines and reciprocating power plants

Turboprop engines are most efficient at speeds between 250 and 400 mph and altitudes between 18,000 and 30,000'

They also perform well at the slow airspeeds required for takeoff and landing, and are fuel efficient

The minimum specific fuel consumption of the turboprop engine is normally available in the altitude range of 25,000' to the tropopause.

Turbofans were developed to combine some of the best features of the turbojet and the turboprop.

Turbofan engines are designed to create additional thrust by diverting a secondary airflow around the combustion chamber.

The turbofan bypass air generates increased thrust, cools the engine, and aids in exhaust noise suppression.

This provides turbojet-type cruise speed and lower fuel consumption.

The inlet air that passes through a turbofan engine is usually divided into two separate streams of air.

One stream passes through the engine core, while a second stream bypasses the engine core.

It is this bypass stream of air that is responsible for the term "bypass engine".

A turbofan's bypass ratio refers to the ratio of the mass airflow that passes through the fan divided by the mass airflow that passes through the engine core.

The fourth common type of jet engine is the turboshaft

It delivers power to a shaft that drives something other than a propeller

The biggest difference between a turbojet and turboshaft engine is that on a turboshaft engine, most of the energy produced by the expanding gases is used to drive a turbine rather than produce thrust

Many helicopters use a turboshaft gas turbine engine

In addition, turboshaft engines are widely used as auxiliary power units on large aircraft