POWERPLANT - QUIZ 2 Reviewer

Primary Function of compressor

Primary Function of compressor

Supply sufficient air for combustion burners.

Secondary Function of compressor

Supply bleed air for various engine and aircraft purposes, such as:
- Air conditioning/pressurization
- Wing/nacelle anti-icing
- Pressurization of potable water and hydraulic tanks
- Cargo compartment heating
- Pneumatic drive units
- Engine starting
- Thrust reverser center drive unit

Centrifugal Flow Compressor

- Also known as radial outflow compressor.
- Early design, still used in smaller engines and APUs.
- Typically limited to two stages due to efficiency concerns.
Advantages:
Simple manufacturing.
Low cost and weight.
Low starting power requirements.
Efficient across a wide range of rotational speeds.
High pressure rise per stage (~8:1).

Impeller

Takes air in and accelerates it outward via centrifugal force.

Single-stage

One impeller.

Double-stage

Two impellers, back-to-back (double-sided impeller).

Diffuser

Divergent duct slowing air to increase static pressure; directs flow to manifold.

Manifold

Smoothly distributes air to the combustion section, ensuring even division to each combustion chamber.

Axial Flow Compressor

- Consists of rotor and stator elements.
- Achieves high pressure ratios by adding multiple stages.

Pressure ratio per stage

1.25:1

Single spool

Compressor and turbine on a single shaft.

Dual-spool

Divided into low-pressure (N1) and high-pressure (N2) compressors.

N1

driven by a two-stage turbine.

N2

driven by a single-stage turbine.

Rotor Blades

- Airfoil shape, twisted for velocity variation.
- Fixed loosely for vibration damping.
- Materials: Stainless steel (early stages), titanium (later stages).

Stator Blades

- Stationary, airfoil-shaped.
- Direct air to the next stage, reducing swirl.
- Fixed or variable angles.
- Secured via dovetail arrangement, often shrouded at tips to minimize vibration.

Combustion Chamber

- A combustion section is typically located directly between the compressor section and turbine section.
All combustion sections contain the same basic elements:
- One or more combustion chambers (combustors)
- A fuel injection system
- An ignition source
- A fuel drainage system

Combustion chamber

or combustor in a turbine engine is where the fuel and air are mixed and burned.

Fuel Injection System

- Meters the appropriate amount of fuel through the fuel nozzles into the combustors.
- Fuel nozzles are located in the combustion chamber case or in the compressor outlet elbows.

Ignition Source:
Typical ignition source is the high-energy capacitor discharge system, consisting of:
- An exciter unit
- Two high-tension cables
- Two spark igniters
- Produces 60 to 100 sparks per minute, creating a ball of fire at the igniter electrodes.
- Safety precaution: Care must be taken to avoid lethal shocks during maintenance tests.

Fuel Drainage System

- Drains unburned fuel after engine shutdown to:
- Reduce the possibility of exceeding tailpipe or turbine inlet temperature limits.
- Prevent gum deposits in the fuel manifold, nozzles, and combustion chambers caused by fuel residue.

Diffuser/Stator

Decelerates the air and raises its static pressure.

Fuel Supply

Fuel is supplied to the airstream by two distinct methods:
- Injection of a fine atomized spray into the recirculating airstream through spray nozzles.
- Pre-vaporization of the fuel before it enters the combustion zone.

Can Type

- Typical for turboshaft and APUs.

Components:
Outer case or housing
Perforated stainless steel combustion chamber liner (inner liner)

Features:
Well-suited to centrifugal compressor engines due to equal air division at the diffuser.
Multiple-can combustion chamber consists of individual combustor cans acting as separate burner units.

Flame Propagation:
Individual combustors are interconnected by small flame propagation tubes.
Combustion starts in cans equipped with igniter plugs; flame travels through tubes to ignite other cans.
Inner tubes carry the flame; outer tubes carry airflow for cooling and insulation.
Typical multiple-can combustion section contains 8-10 cans.
Cans are numbered clockwise when viewed from the engine rear.

Annular Type

- Consists of a single, annular flame tube contained in an inner and outer casing.
- Open at the front to the compressor and at the rear to the turbine nozzles.

Advantages:
Most efficient in terms of thermal efficiency, weight, and physical size.

Airflow:
Air enters at the front and exits at the rear, with primary and secondary airflow similar to multiple-can design.
Maintenance:
Entire unit must be removed for repair or replacement, often requiring engine separation at a major flange.

850-1700 Celsius

Maximum temperature is limited withing this range from which the turbine blades and nozzles are made

650-1150 Celsius

temperature rise requirement from the combustion process

Between 200 and 550 Celsius

temperature just before entering the combustion chamber

500ft/s

velocity of air from the engine compressor to the combustion chamber

Can-Annular Type

Combines features of multiple-can and annular combustors.
Invented by Pratt & Whitney.

Structure
Removable steel shroud encircles the combustion section.
Flame tubes inside a common air casing.
Flame propagation tubes connect individual liners.

Advantages:
Ease of overhaul and testing of multiple-can arrangement.
Compactness of annular combustor design.

Maintenance:
Individual can and liner can be removed and replaced as one unit.