Compressor Stall

From Wikipedia, the free encyclopedia

A compressor stall is a situation of abnormal airflow through the compressor stage of a jet engine, causing a stall of the vanes of the compressor rotor.

All compressor stalls result in a loss of engine power. This power failure may only be momentary (occurring so quickly it is barely registered on engine instruments), or may shut the engine down completely (that is, causing a flameout). When a compressor stall affects the airflow through the entire engine it is also known as a compressor surge (although definitions differ, and often the terms are used interchangeably).


Types

There are two general types of compressor stall.
The first, the "axis-symmetric stall", is a straightforward expulsion of air out the intake due to the compressor's inability to maintain pressure on the combustion chamber.
In the second, "rotational stall", the air flow disruption of the stall causes standing pockets of air to rotate within the compressor without moving along the axis. Without fresh air from the intake passing over the stalled compressor vanes they overheat, causing accelerated engine wear and possible damage.


Causes

Compressor stalls are aerodynamic stalls in which the airfoils in the compressor lose their lifting capability. This often results in a sudden change in the pressure differential between the intake and combustion chamber. Jet aircraft pilots must take this into account when dropping airspeed or increasing throttle.

The following factors can induce compressor stall:

Engine thrust too high for the operating altitude

Engine operation outside specified design parameters

Turbulent or disrupted airflow to the engine intake

Contaminated or damaged engine components (such as damaged or wrongly positioned guide vanes)

Abrupt increases in engine thrust

Use of reverse thrust at insufficient forward speed, resulting in reingestion of turbulent airflow

One of the most common causes of first stage compressor stalls in commercial aviation aircraft is a bird strike. On take-off, while maneuvering on the ground or while on approach to landing, planes operate in proximity to birds. It is not uncommon for birds to be sucked into the intake of the engine and often can cause a first-stage compressor stall. Because birds are combustible material, a fire or flames described as "shooting" out of the engine are common reports during this type of compressor stall.

In the case of an axi-symmetric stall, an entire stage of airfoils stall. This may cause an increase in rotor speed due to the large reduction in work done by the stalled rotor stage, which results in other stages stalling and creating a domino effect in which the remainder of the compressor stages stalling. The result of this is the loss of the compressor's capability to maintain a pressure ratio and the subsequent backflow from the combustor section.

In the case of a rotating stall, a single airfoil stalls. This stall creates the aforementioned pocket of stagnant air, which then passes to the next airfoil on the rotor. The pocket of stagnant air causes this airfoil to stall, thus propagating the stall.


Effects

Compressor stalls can result in one or more extremely loud bangs emanating from the engine as the combustion process "backfires". This may be accompanied by an increased exhaust gas temperature, and yawing of the aircraft in the direction of the affected engine.
The effects of a stall can vary. A minor stall may create an alarming noise but have little other effect. On the other hand, a violent compressor surge might completely destroy the engine and set it on fire.
The appropriate response to compressor stalls varies according the engine type and situation — but usually consists of immediately and steadily decreasing thrust on the affected engine.


Trivia

The Lockheed SR-71 Blackbird, a supersonic reconnaissance aircraft developed in the United States, employed special jet engines that were known for their tendency to “unstart,” that is, their tendency to produce spectacular compressor stalls, often violent enough to throw the pilot's head against the canopy of the aircraft. The stalls occurred when shockwaves over the jet intakes moved out of their proper location during high-speed supersonic flight. The stalls produced a very dramatic loss of thrust and a violent yaw moment, and required quick action by the crew to avoid compromise of the mission or airframe. Unstarts were the bane of SR-71 pilots until computer controls on the engines later in the SR-71 program significantly reduced their incidence and simplified recovery.

Retrieved from "http://en.wikipedia.org/wiki/Compressor_stall"

CFM56 Remains Engine of Choice for Single-Aisle Aircraft; Logs $4.1 Billion in Firm Engine Orders in 2004

Press Release

CFM56 Remains Engine of Choice for Single-Aisle Aircraft; Logs $4.1 Billion in Firm Engine Orders in 2004
February 09, 2005 -- EVENDALE, Ohio - CFM International continued to be the world's leading aircraft engine supplier in 2004, logging orders for 683 commercial and military engines at a value of approximately $4.1 billion. In addition, the company received orders for a total of 118 CFM56-3 and CFM56-5C/P upgrade kits.

CFM International (CFM) is a 50/50 joint company between Snecma Moteurs of France and General Electric Company. Since the company's formation in 1974, it has delivered more than 14,550 engines to 400 commercial and military customers worldwide. In 2004, the company delivered 728 new CFM56 engines.

In September, CFM formally launched the next generation of upgrades with the CFM56-5B/-7B Tech Insertion program, which incorporates technologies developed as part of Project TECH56. The package includes improvements to the high-pressure compressor, the combustor, and the high- and low-pressure turbines. It will help customers to lower overall operating costs through lower maintenance costs, longer time on wing, lower fuel consumption, and reduced NOx (nitrogen oxides) emissions.

The CFM56-5B was selected to power 57 percent of the Airbus A320 family aircraft ordered in 2004. As the only engine that can power each A320 model with the same bill of materials, the CFM56-5B is the engine of choice for major airlines, low-cost carriers, and leasing companies worldwide.

Major CFM56-5B orders include: U.S.-based low-cost startup carrier Virgin America, with an order for 18 firm, 72 option CFM56-5B-powered A319/A320 aircraft; long-time CFM customer China Southern Airlines, with an order for CFM56-5B engines to power 21 A320 family aircraft; Cebu Pacific Air ordered 12 A319s; and in December, airline partners Air Berlin and NIKI Luftfahrt chose the CFM56-5B to power 70 firm, 40 option A320s.

The CFM56-7B is the sole powerplant for Boeing Next-Generation 737 aircraft. Major 2004 orders include: Brazilian low-cost carrier Gol Transportes Aereos, with a firm order for 17 737-800 aircraft, in addition to taking purchase options on 28 additional aircraft; THY ordered 15 CFM56-7-powered 737s; GE Capital Aviation Services order 12 additional 737s; and Southwest Airlines firmed options on 12 additional 737s.

About CFM

CFM combines the resources, engineering expertise and services of two major aircraft engine manufacturers: Snecma Moteurs of France, and GE Transportation - Aircraft Engines in the U.S.A.

Underlying CFM's rapid and hard-earned success is the excellence of its product and the competence of its organization: designers, engineers, technical representatives, product support managers and sales personnel throughout the world. CFM's goal is to maintain the trust of airlines and airframers by providing superior engines, as well as the outstanding and dedicated services that contribute to the operational and the financial success of our customers.

CFM is not an acronym. The company (CFM), and product line (CFM56), got their names by a combination of the two parent companies' commercial engine designations: GE's CF6 and Snecma's M56.

Source: http://www.geae.com/engines/commercial/cfm56/