INDEX

Introduction

Objectives

Classification of Gas Turbine

Applications of Gas turbine

Methods to improve the thermal efficiency of gas turbine

Jet-propulsion

Types of jet engines

Rocket engine

INTRODUCTION

A gas turbine is a machine delivering mechanical power or thrust. It does this using a gaseous working fluid. The mechanical power generated can be used by, for example, an industrial device. The outgoing gaseous fluid can be used to generate thrust. In the gas turbine, there is a continuous flow of the working fluid.

Cont…

This working fluid is initially compressed in the compressor. It is then heated in the combustion chamber. Finally, it goes through the turbine.

The turbine converts the energy of the gas into mechanical work. Part of this work is used to drive the compressor. The remaining part is known as the net work of the gas turbine.

Objectives

After this lesson students should be able to: – Define what a jet engine is

– Describe how Newton’s laws apply to jet or rocket engines

– List examples of jet engine applications

– List some key points in the history of jet propulsion

– List advantages and disadvantages of jet engines

Classification of Gas Turbine

Constant pressure type

Constant Volume type

According to thermodynamic cycle

a) Brayton cycle

b) Atkinson cycle (Constant volume)

c) Ericsson cycle(Intercooler and repeaters)

Applications of Gas turbine

For supercharging of I.C. engines

Ship propulsion i.e. Marine engines

Industrial applications. Like Crude oil pumping, Refining processes.

Air craft engines.

Electric power generation.

For the turbojet and turbo propeller engines.

Fig. Open Cycle gas turbine

Open Cycle gas turbine

9

Closed gas cycle turbine

Fig. T-S & P-V Diagrams of closed cycle gas turbine

Basic Components

Basic Components

Basic Components • Compressor

• Draws in air & compresses it

• Combustion Chamber • Fuel pumped in and ignited to burn with

compressed air

• Turbine • Hot gases converted to work

• Can drive compressor & external load

Basic Components • Compressor

• Draws in air & compresses it

• Combustion Chamber • Fuel pumped in and ignited to burn with

compressed air

• Turbine • Hot gases converted to work

• Can drive compressor & external load

Basic Components • Compressor

• Draws in air & compresses it

• Combustion Chamber • Fuel pumped in and ignited to burn with

compressed air

• Turbine • Hot gases converted to work

• Can drive compressor & external load

Constant volume Gas turbine

To stack

Boiler

Exhaust Gas

Valve V1

Air

Compressor

Steam turbine

Motor

Valve V2

Valve V3

Load

Feed Water

Exhaust Fuel Tank

16

GAS TURBINE WITH REGENERATION CYCLE

A gas-turbine engine with regenerator. T-s diagram of a Brayton cycle with regeneration.

The thermal efficiency of the Brayton cycle increases as a result of regeneration since less fuel is used for the same work output.

17

T-s diagram of a Brayton cycle with regeneration.

Effectiveness of regenerator

Effectiveness under cold-air standard assumptions

Under cold-air standard assumptions

GAS TURBINE WITH INTERCOOLING CYCLE

GAS TURBINE WITH REHEATING CYCLE

20

Brayton cycle with intercooling, reheating, and regeneration

A gas-turbine engine with two-stage compression with intercooling, two-stage expansion with reheating, and regeneration and its T-s diagram.

For minimizing work input to compressor and maximizing work output from turbine:

An engine that burns fuel and uses the expanding exhaust gases to turn a turbine and/or produce thrust

The concept of thrust is based on the principle of Newton’s Third Law

21

Jet-propulsion

In jet engines, the high-temperature and high-

pressure gases leaving the turbine are accelerated in a

nozzle to provide thrust.

4.4.1 Principles of jet propulsion

It is based on Newton's first and third law of motion.

A jet engine is an engine that discharges a fast moving

jet of fluid to generate thrust in accordance with

Newton's third law of motion.

An engine that burns fuel and uses the expanding

exhaust gases to turn a turbine and/or produce thrust

Types Of Jet engines

•Turbo jets

•Turbo fans

•Ramjets

•Rockets

Jet Engine

Jet Engine

Working principle jet engines are also called as gas turbines. The engine sucks air in at the front with a fan. A compressor raises the pressure of the air. The compressed air is then sprayed with fuel and an electric spark lights the mixture. The burning gases expand and blast out through the nozzle, at the back of the engine. As the jets of gas shoot backward, the engine and the aircraft are thrust forward.

Turbo jet engines

Turboprop engine

Approximately 80 to 90% of the thrust is produced by the propeller and 10 to 20% of thrust is produced by jet exit of the exhaust gases

Turboprop engine

Ram jet engine

Rocket Principles

• Rocket thrust is the reaction force produced by expelling particles at high velocity from a nozzle opening.

• High pressure/temperature/velocity exhaust gases

provided through combustion and expansion through

nozzle of suitable fuel and oxidizer mixture.

• A rocket carries both the fuel and oxidizer onboard

the vehicle whereas an air-breather engine takes in

its oxygen supply from the atmosphere.

Solid propellant rocket engine

In the solid-chemical rocket, the fuel and oxidizer are intimately mixed together and cast into a solid mass, called a grain, in the combustion

The propellant grain is firmly cemented to the inside of the metal or plastic case, and is usually cast with a hole down the center. This hole, called the perforation, may be shaped in various ways, as star, gear, or other more unusual outlines, The perforation shape and dimension affects the burning rate or number of pounds of gas generated per second and, thereby, the thrust of the engine.

After being ignited by a pyrotechnic device, which is usually triggered by an electrical impulse, the propellant grain burns on the entire inside surface of the perforation. The hot combustion gases pass down the grain and are ejected through the nozzle to produce thrust.

Types of solid propellant

a) Restricted burning

a) Restricted burning

A restricted-burning charge is usually in the shape of a

solid cylinder.

It completely falls the combustion chamber and burns

only on its end.

The thrust developed is proportional to the cross-sectional

area of the charge

The restricted-burning charge provides a low thrust and

long burning time.

It is essentially free to burn on all surfaces at the

same time

The restricted burning propellant delivers a small

trust for a relatively long period while unrestricted

type delivers relatively large thrust for short period.

It’s application is in aircraft rockets, antiaircraft

rockets and boosters etc.

Types of solid propellant

b) Unrestricted burning

Liquid propellant rocket engine

• The common liquid rocket is bipropellant;

it uses two separate propellants, a liquid fuel and liquid oxidizer

• These are contained in separate tanks and are mixed only upon injection into the combustion chamber

• They may be fed to the combustion chamber by pumps or by pressure in the tanks

Liquid propellant rocket engine