Aircraft Combustion Section and Chamber

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Questions and Answers

What is the primary function of the combustion section in a gas turbine engine?

To compress air for combustion

To add heat energy to the flowing gases (correct)

To cool the engine components

To generate electricity

What is the result of adding fuel heat in the combustion process?

A decrease in gas volume

No change in gas volume

An increase in gas volume (correct)

A change in gas pressure only

What is the purpose of the fuel drainage system in the combustion section?

To ignite the fuel in the combustors

To cool the engine components

To drain unburned fuel after engine shutdown (correct)

To inject fuel into the combustors

What type of system is typically used as an ignition source in the combustion section?

High-energy capacitor discharge system Signup and view all the answers

What is the primary goal of a combustion chamber in a gas turbine engine?

To burn the fuel/air mixture as efficiently and quickly as possible Signup and view all the answers

What is the effect of the perforations in the inner liner of the combustion chamber?

They increase the flame propagation Signup and view all the answers

What is the process referred to when fuel heat is added and the volume of the gas increases, causing an acceleration of gases to occur?

Combustion at constant pressure Signup and view all the answers

What is a major consideration when designing a combustion chamber?

Accomplishing the task with the minimum loss in pressure and maximum heat release Signup and view all the answers

How many basic types of combustion chambers are currently used?

Three Signup and view all the answers

What is a characteristic of the multiple-can type combustion chamber?

It is well suited to centrifugal compressor engines Signup and view all the answers

What is a benefit of the inner liner in a multiple-can combustor?

It is highly heat resistant and easily removed for inspection Signup and view all the answers

What is a disadvantage of the multiple-can type combustion chamber?

It is inefficient in terms of the amount of space required and adds weight Signup and view all the answers

What is the primary function of the reverse-flow annular combustor?

To allow for a shorter and lighter engine design Signup and view all the answers

What percentage of the incoming air is designated as primary in a combustor?

20%–30% Signup and view all the answers

What is the purpose of the swirl vanes in the primary combustion air?

To give the air a radial motion and slow down its axial velocity Signup and view all the answers

What is the result of the airflow passing through the swirl vanes?

The air is slowed down to 5–6 ft/s Signup and view all the answers

What is the purpose of the primary combustion air?

To support the combustion process Signup and view all the answers

What is the advantage of the reverse-flow combustor design?

Simplified engine design Signup and view all the answers

What is the purpose of the toroidal vortex in the combustion section?

To provide the turbulence required to mix the fuel and air Signup and view all the answers

What is the approximate percentage of primary airflow in relation to total airflow?

25% Signup and view all the answers

What is the result of a lean air-fuel mixture in the combustion process?

Incomplete combustion with a lower flame temperature Signup and view all the answers

What is the purpose of the secondary airflow in the combustion section?

To mix with the burned gases and cool the air Signup and view all the answers

What is the term for a perfectly balanced air-fuel mixture?

Stoichiometric mixture Signup and view all the answers

What is the range of combustible air-fuel ratios?

8:1 to 22:1 Signup and view all the answers

What is an advantage of the can-annular combustor design?

It is designed for ease of on-the-wing maintenance Signup and view all the answers

What is a characteristic of the annular combustor?

It has a single unit that encircles the outside of the turbine shaft housing Signup and view all the answers

What is a benefit of the annular combustor design?

For the same power output, the length of the chamber can be 75% or less of that of a multiple-can system Signup and view all the answers

How many spark igniters are typically used in an annular combustor?

Two spark igniters Signup and view all the answers

What is a disadvantage of the annular combustor design?

It must be removed as a single unit for repair or replacement Signup and view all the answers

What is the airflow path in an annular combustor?

Airflow enters at the front and is discharged at the rear Signup and view all the answers

Study Notes

Combustion Section

Located between the compressor diffuser and turbine section
Contains: combustion chambers (combustors or cans), fuel injection system, ignition source, and fuel drainage system

Combustion Chamber

Where fuel and air are mixed and burned
Fuel injection system supplies fuel through fuel nozzles
Ignition source: high-energy capacitor discharge system
Fuel drainage system: drains unburned fuel after engine shutdown
Function: adds heat energy to flowing gases, expanding and accelerating them into the turbine section

Combustion Process

When fuel heat is added, gas volume increases, causing acceleration of gases
Process referred to as combustion at constant pressure
To efficiently burn fuel/air mixture, combustion chamber must:
- Mix fuel and air effectively in the best ratio for good combustion
- Burn the mixture efficiently and quickly
- Cool hot combustion gases to a temperature the turbine blades can tolerate
- Distribute hot gases evenly to the turbine section

Types of Combustion Chambers

Multiple-can
Can/annular
Annular
Functionally the same, but design and construction differ

Multiple-Can Combustor

Consists of a series of individual combustor cans
Well suited for centrifugal compressor engines
Each can has a perforated stainless steel liner inside the outer case
Inner liner is highly heat resistant and easily removable for inspection
Advantages: easy on-the-wing maintenance, uniform temperature at the turbine

Can-Annular Combustion Chamber

Components: housing, perforated inner liner, and shroud
Can be shaped to contain one or more concentric baskets
Ignition source: two spark igniters

Annular Combustor

Most efficient, with a shorter length than multiple-can systems for the same power output
Consists of a housing and a perforated inner liner
Liner is a single unit that encircles the outside of the turbine shaft housing

Reverse-Flow Annular Combustor

Airflow can reverse direction
Combustion gases flow in the opposite direction of the normal airflow through the engine
Turbine wheels are inside the combustor area rather than downstream
Advantages: shorter and lighter engine

Combustion Airflow

Divided into primary and secondary paths
Primary combustion air: 20%–30% of incoming air, directed inside the liner in the front end of a combustor
Secondary airflow: 70%–80% of incoming air, flows at a velocity of several hundred feet per second around the combustor's periphery

Primary Combustion Air

Passes through swirl vanes, giving the air a radial motion and slowing down its axial velocity to 5–6 ft/s
Toroidal vortex created in the flame area provides turbulence to mix fuel and air
Combustion process is complete in the first third of a combustor

Secondary Airflow

Forms a cooling air blanket on both sides of the liner and centers the combustion flames
Some secondary air is slowed and metered into the combustor through perforations in the liner
Ensures combustion of any remaining unburned fuel
Mixes with burned gases and cools the air to evenly distribute energy to the turbine nozzle

Combustion Air / Fuel Ratio

Liquid fuels must be converted from liquid to vapor before they will burn
Stoichiometric mixture: 15 parts air to one part fuel by weight
Combustible air-fuel ratios: 8:1 to 22:1
Often expressed as 60:1, which refers to total airflow rather than primary combustor airflow

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Description

Learn about the combustion section in an aircraft engine, its components, and the combustion chamber's function in adding heat energy to the flowing gas.