WORKING CYCLE AND AIRFLOW

CDA –Materiales Aeronáuticos

Ivan Solis A00803014

Introduction

The gas turbine engine is essentially a heat engine using air as a working fluid to provide thrust.

Working cycle

Is similar to that of the four-stroke piston engine.

In the gas turbine engine, combustion occurs at a constant pressure, whereas in the piston engine it occurs at a constant volume.

Each instance there is induction, compression, combustion and exhaust

The relations between pressure,volume and temperature

There are three main conditions in the engine working

cycle during which these changes occur. During

compression, when work is done to increase the pressure

and decrease the volume of the air, there is a

corresponding rise in the temperature. During combustion,

when fuel is added to the air and burnt to increase the

temperature, there is a corresponding increase in volume

whilst the pressure remains almost constant. During

expansion, when work is taken from the gas stream by the

turbine assembly, there is a decrease in temperature and

pressure with a corresponding increase in volume.

Changes in the temperature and pressure of the air can be traced through an engine by using the airflow diagram in fig. 2-5. With the airflow being continuous, volume changes are shown up as changes in velocity.

Changes in velocityand pressure

During the passage of the air through the engine, aerodynamic and energy requirements demand changes in its velocity and pressure.

Where supersonic speeds are encountered, such as in the propelling nozzle of the rocket, athodyd and some jet engines (Part 6), a convergent-divergent nozzle or venturi (fig. 2-4) is used to obtain the maximum conversion of the energy in the combustion gases to kinetic energy.

Airflow

A straight-through flow system is the basic design, as it provides for an engine with a relatively small frontal area and is also suitable for use of the by-pass principle.