Understanding Axial Flow Compressors and Combustion Chambers

Axial Flow Compressor

Most popular type of turbine engine.

Components of an axial flow compressor

Rotor and stator.

Rotor

Blades that are stainless steel, are loose when cool and will click when engine rotates, present at a specific angle, contoured like thin propeller blades, forces the air backward.

How does the rotor accelerate the air?

Each rotor and stator stage speeds up the air more and more due to the rotor pushing the air backwards.

Stator

Slows the air and raises the air pressure, functioning like a diffuser.

Stage

A combination of a rotor and stator.

Inlet Guide Vanes

The front ones don't move but the second ones do; air comes in to redirect it.

Spool

Each independent system in multiple compressors used in different engines.

N1

Lower pressure section of the engine.

N2

High pressure section of the engine.

Effect of sinking N1

Makes us happy.

Effect of sinking N2

Makes the pax happy.

Advantages of Axial Flow Compressor

High peak efficiencies, small frontal area, straight through flow for high ram efficiency, can increase pressure by increasing stages.

Disadvantages of an Axial Flow Compressor

Efficient at narrow rotational speeds, difficult to manufacture at high cost, high weight, high starting power required, susceptible to FOD damage.

Compressor Stalls From a Pilot's Perspective

An incipient stall is not really noticeable; as it progresses, a low pulsating sound occurs, increasing in intensity and can lead to the sound of explosion or backfire.

Causes of a Compressor Stall

Blade failure, too lean of mixture, severe pitch up or down disrupting the normal airflow, excess fuel flow, engine speed too high or too slow for operations, damage to turbine blades.

Proper fuel-air mixture burning

Mix the fuel air per the ambient conditions, cool the gases within operating temperature of the turbine, channel the gases to the turbine to maximize rotation.

Types of Chambers

Three types of chambers are referenced but not specified.

Can

A type of combustion chamber.

Can annular

A type of combustion chamber that is annular in shape.

Outer casting

The external structure of the combustion chamber.

Perforated inner liner

An inner layer of the combustion chamber that has perforations.

Fuel injection system

A system that injects fuel into the combustion chamber.

Ignition system

A system that ignites the fuel in the combustion chamber.

Fuel drainage system

A system that drains excess fuel from the combustion chamber.

Can Combustion Chamber

Can be used with axial flow but work better with centrifugal flow.

Airflow in the (Can) Combustion Chamber

Air entering the can is separated into two airflows.

Annular Combustion Chamber

Has an undivided shape going the entire circumference.

Ignition System of Annular

A system much different than reciprocating engines.

Turbojet Ignition System

Comprised of exciter units, intermediate voltage lead, transformer, and high tension leads.

Turbojet ignition must

Provide powerful high heat spark and large spark over the gap.

Electronic Ignition System

Sets up the voltage and charges up capacitors.

Igniter Plugs

Long reach igniters that provide spark directly to fuel air flow.

Turbines Purpose

Convert kinetic energy of exhaust to mechanical energy.

The Stator

The first thing the exhaust reaches, called turbine guide vanes.

Two Purposes of Stator

Accelerate the air to the rotor for peak rotation and have the air striking the rotor at the most effective angle.

Fixed Shaft Turbine

Goes between the turbine and the compressor.

Advantages of a fixed shaft turbine

Quick response to throttle inputs and controlled descent.

T1 drives/turns N2

Indicates that T1 is responsible for driving N2.

Free Turbine

Has two separate turbine sections driving two compressors.

First Turbine is considered the high pressure turbine

The first turbine drives the compressor section.

Free Turbine Advantages

Better control of prop speed and easier engine start.

Main Bearings Advantages

Low cost, low friction, precision alignment, and high speeds.

Main Bearings Disadvantages

Foreign matter damage and fail without warning.