Журнал - The Engine Yearbook 2005

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ENGINE YEARBOOK 2005

incident by DS&S’ health monitoring

systems and the relevant technical

data was made available to support a

rapid decision on the necessary

course of action.

A technical variance was

subsequently issued to waive the

borescope requirements (no defects

were found when the engine was

inspected four days later) and the

necessary people, information and

approvals were all in place to meet

the aircraft on its arrival.

Consequently, thanks to the fast and

effective decision-making enabled by

the EHM system, the aircraft was

immediately able to turn around and

continue on its return journey.

Realising the benefits

Thanks to its advanced knowledge

management, modelling and

computational intelligence

techniques, DS&S’ EHM system has

been proven to deliver a wide range

of operational and administrative

benefits, including:

Engineering

● more accurate diagnosis of

problems;

● real-time alerting; access to data

24/7;

● easier maintenance contract

administration;

● rapid identification of performance

and reliability issues;

● improved maintenance planning;

and

● reduced unplanned removal rates.

Customer service

● increased customer service levels;

and

● increased revenue opportunities.

Flight operations

● enhanced safety;

● improved dispatch reliability; and

● improved crew and aircraft

utilisation.

Management

● reduced operating and support

costs; and

● accurate planning and forecasting.

In fact, DS&S continuously

monitors the value of EHM services

provided to its customer, and these

have been shown to routinely deliver

a return on investment of between

300 and1,000 per cent.

... and things can only get better

In the quest to deliver even greater

benefits in the future, DS&S is

actively involved in the distributed

aircraft maintenance environment

(DAME) project

, a ‘grid’-based

diagnosis and prognosis system for

aero-engine data (see figure 3). Grid

computing utilises the free resources

of a large number of high-bandwidth

network-connected computers to

tackle difficult computational

problems in a fraction of the time

that would be needed for a single

computer, at a much lower cost than

a dedicated multi-processor super-

computer.

This £3m ($5m) project, which is

co-sponsored by Rolls-Royce and

Cybula Ltd is expected to finalise in

2005 and has already developed a

complete pattern storage and search

system, based on existing AURA

search technology. To facilitate the

use of this distributed system, an

application specific, portal-based

data browser and search interface has

been developed called the signal data

explorer.

The problems solved in developing

a demonstration of this technology

have many applications outside of the

specific remit of the project and DS&S

is leading the efforts to apply the

technologies developed under DAME

to all aspects of aero-engine

monitoring, in both grid and non-grid

environments, so its customers will

continue to benefit from access to the

world’s most advanced EHM

solutions. ■

1 The details of the complete DAME

project can be found in Chapter 5 of

Grid 2: Blueprint for a New Computing

Architecture (Second Edition); I Foster

& C Kesselman (Ed), published by

Elsevier/Morgan Kaufmann, 2004.

In the quest to deliver even

greater benefits in the future,

DS&S is actively involved in the

distributed aircraft maintenance

environment (DAME) project,a

‘grid’-based diagnosis and

prognosis system for aero-engine

data.

EYB2005_2 7/9/04 11:16 am Page 59

ENGINE YEARBOOK 2005

Filtration technology for gas turbine

engine fuel and lubrication systems

The filtration of fuels and

lubricants is critical to aircraft

gas turbine engines in

minimising fluid-system

component wear and

subsequent engine damage.

Puliyur Madhavan of the

scientific and laboratory

services department of Pall

Corporation reviews the

state-of-the-art in gas

turbine filtration technology.

ecent developments in filtration

technology have addressed

contamination control issues in fuel

and lubrication systems in aircraft gas

turbine engines It is now possible to alert

operators in advance of impending fluid-

system problems, reducing costly in-flight

engine shutdowns. This article discusses

‘best filtration practices’ for OEMs,

operators, and maintenance and engine

test personnel.

In-system filtration — lubricants

Since turbofan-engine main-shaft

bearings often operate in the elasto-

hydrodynamic or partial elasto-

hydrodynamic lubrication regime, with

lubricant film thickness of ~ 0.1µm or less,

the presence of particulate contamination

in the lubricant can lead to the initiation of

bearing damage. Based on the examination

of approximately 200 incidents in current

aircraft gas-turbine main-shaft bearings,

involving engines in the field, Averbach

concluded that, in most cases damage to

bearings was initiated at the surface.

Among the important factors contributing

to surface damage were surface defects,

scores and dents caused by hard abrasive

particulate contamination. Based on

theoretical studies and field experience, a

substantial improvement in bearing fatigue

life is predicted along with improved

lubricant fluid cleanliness. Filtration rated

at 3-6µm would be optimal for gas turbine

engine-lubrication systems, although

service-life considerations may require

coarser filtration in some instances.

In-system filtration — fuel

In comparison, the filtration rating of

engine main-fuel filters range from about

20µm to 100+µm; the finer filtration

rating is often employed in fuel-hydraulic

systems. Historically, coarser filtration

ratings have been specified, primarily

based on service-life considerations and

overall fuel-system performance.

However, fuel-control systems

(mechanical and electrical) can be sensitive

to contamination and therefore require

finer filtration. In such cases a tangential

flow filter, sometimes referred to as a

‘wash flow’ filter, is employed in some

applications. Figure 1 depicts a tangential

flow filter. The direction of the majority of

the flow is tangential to the filtration

surface rather than normal to the filtration

surface. A small percentage of the flow

proceeds normally and is filtered, this

percentage being regulated by the

adjustment of line pressures. Since the

main velocity component is tangential to

the filtration surface, a significant

proportion of the particulates that are

smaller than the passageways within the

filtration medium follow the main flow

stream so that the filtration rating of the

filter is effectively finer than would be

expected from the mean size of the

passageways in the filtration medium. In

addition, the tangential flow of the

majority of the fluid stream serves to clean

the filtration surface so that in proper

operation, the filtration passageways will

not plug up with contaminant, resulting

in a very long filter service life.

Recent advances in laser-drilling

technology now permit the manufacture

of tangential-flow filters fabricated from

a single piece of material with laser-

drilled holes which has a high void

volume and uniform distribution of

passages (Figure 1.).

Design

The proper functioning of fuel and

lubricant filter elements is dependent

on many factors. Filter performance

parameters such as filtration efficiency,

EYB2005_3 7/9/04 1:58 pm Page 60

ENGINE YEARBOOK 2005

remove debris effectively on a ‘single-

pass’ basis and prevent recirculation of

damaging debris through the fluid

system. They are characterised by high

particle-removal efficiencies: 99.5 per

cent to 99.9 per cent for particles in the

1-3µm (and larger) size ranges. They

also exhibit significant particle removal

efficiencies in the smaller size ranges,

including sub-micron size ranges, for

removal of hard, abrasive contamination

(polishing compounds).

‘Green run’ filter elements can be

configured to replace the service-filter

element during ‘green-run’ testing or as

a separate remote filter depending on

the ‘green-run’ test-facility

requirements.

A valuable option is the use of a Dirt

Alert(r) ‘green-run’ filter element which

incorporates a ‘pull-out’ diagnostic

layer that permits the examination of

debris captured on the layer during

‘green-run’ testing. It is discussed in

detail later in this article.

Two-stage filter system

Most commercial operators establish

filter-element service intervals based on

their field experience and the

filter-element service life and filter

integrity can be adversely affected by

harsh operational and environmental

conditions. These can include the

extreme low temperatures and pressures

encountered during cold starting and

soak-back, as well as the products of oil

degradation in lubrication systems.

A number of laboratory procedures

have been developed to simulate

extreme operating conditions

encountered during service. The

generic term for these procedures is

‘conditioning’ and they are carried out

on filter elements prior to engine-

performance testing. Industry standards

recommend ‘conditioning’ as part of the

performance specification of gas-turbine

engine-fuel and lubricant filters and

such work is necessary to determine

whether filter element performance will

degrade during actual service.

‘Green run’ testing

The various processes involved

during maintenance, overhaul and final

assembly can result in the generation of

contaminant debris. This includes built-

in debris in new components,

machining chips, residual grinding

debris, fine polishing compounds and

debris generated from the making and

breaking of fittings. It can also include

airborne environmental contaminants,

such as silica sand, and other mineral

compounds and contaminants

introduced from the fluids, such as

cleaning solvents and the contamination

of improperly-filtered service fluids.

Built-in debris can cause catastrophic

component failure and/or the initiation of

component damage such as the denting of

bearing surfaces. Unless built-in debris is

filtered out of the fluid, it can rapidly

plug filter elements during engine

service, resulting in abnormally low filter-

element service life. This is of significance

for engine-fuel-filter elements subsequent

to the maintenance of aircraft fuel tanks.

Many aircraft OEMs prescribe a sequence

for fuel-filter element replacements after

significant fuel-tank maintenance,

starting with a short replacement interval

and gradually increasing to the ‘normal’

fuel-filter replacement interval.

High efficiency, fine filter elements,

are currently available for ‘green-run’,

engine-flushing, applications that

requirements of the MRB. However,

accelerated loading of the filter-element

due to abnormally high contaminant

ingress or component wear can result in

filter element bypass in-flight and

hence, unfiltered fluid circulating

through the system. Consequently,

several engine manufacturers require in-

flight shutdown of an engine when the

filter element differential-pressure

switch is activated.

Costs associated with an in-flight

shutdown have been estimated to be as

high as $500,000. In addition, in-flight

shutdowns can also have an adverse

impact on airline ETOPS ratings. The

two-stage filter system is designed to

address such concerns and is shown in

schematic form in Figure 2. It combines

a primary filter element with a coarser,

secondary filter element configured in

series, typically nested within the

primary filter element for compactness.

Under normal operating conditions,

flow proceeds through the primary

and secondary element to system

components. The particulate

contamination is effectively removed

by the finer, primary and secondary

filter element so that there is minimal

Figure 2

EYB2005_3 7/9/04 1:59 pm Page 61

accumulation of contaminant particles

in the coarser, secondary filter

element. Bypass of the primary filter

element due to plugging, or during

transient cold-start conditions in

lubrication systems, results in the

fluid being shunted to the secondary

filter element. This is designed to

provide an acceptable level of

filtration, as determined by the

engine manufacturer, for short

periods of engine operation.

A secondary filter element bypass

valve is provided in order to maintain

fluid flow through the system in the

unlikely event that the secondary filter

element plugs up also. It should be

noted that the two-stage filter system

also minimises unnecessary in-flight

engine shutdowns associated with

faulty differential-pressure indicator

actuations (Figure 1b).

Diagnostic filter elements

The monitoring of debris present in

the fluid provides valuable

information about the condition of

fluid-wetted components. When

gathered and sequentially logged, this

information provides the possibility

of preventive maintenance prior to

component malfunction and/or in-

flight failure. The ‘full-flow’

characteristics of filter elements are

ideal for efficiently capturing metallic

wear debris as well as non-metallic

debris, such as contaminants from the

environment, material from seals, and

lubricant-degradation products such

as coke.

The Dirt Alert® diagnostic filter

element has a removable diagnostic

layer (Figure 4), which is pleated

upstream of the filter support mesh

and filter medium. It can easily be

removed to allow visual inspection of

the collected contaminants and more

sophisticated laboratory analysis,

such as the determination of the

chemical composition of the

contaminant via x-ray fluorescence

spectroscopy (XRF).

The three principal areas of

application of Dirt Alert filter elements

of interest to engine operators are:

‘green-run’ testing of engine lubrication

systems; the evaluation of

contamination in the fuel filter elements

after significant aircraft fuel-tank

maintenance; and regular flight

operation.

Examination of the debris on the

diagnostic layer can provide

information about the debris built into

or being generated by an engine. Once

a baseline has been established by the

operator, the debris collected on the

diagnostic layer can pinpoint ‘abnormal’

engines, allowing corrective action to

take place prior to engine installation.

In the case of fuel filters, it can be used

to determine the nature of the material

introduced into the engine from aircraft

fuel tanks subsequent to aircraft

maintenance.

The wear debris collected on the

diagnostic layer can also provide

valuable information about

lubrication or fuel-system component

wear during regular flight operation.

It can augment information gleaned

from on-board magnetic/metallic

debris detector inspection,

particularly when trying to

distinguish between ‘nuisance

warnings’ and more significant wear

debris.

Recent advances

A recent unique development is the

Ultipleat® filter element (Figure 2).

The pleats of these elements are

curved to support one another over

the entire pleat length. This results in

additional filter area but, more

importantly, significantly improves

performance. This is due to the fact

that, unlike traditional fan-pleat filter

elements, the flow is evenly

distributed over the entire surface

area of the element and the pleats are

supported against ‘grouping’ during

cold-start (‘grouping’ is a distortion

of a fan-pleat element whereby pleat

spacing becomes non-uniform and

can adversely affect performance).

The larger filter area, combined with

a more uniform flow distribution

results in a filter element with higher

dirt-holding capacity than a

traditional filter element (Figure 2).

This results in some interesting

options: longer service life; smaller

size and weight at equivalent service

life; or the ability to use a higher

efficiency filter element without

jeopardising service life.

Additionally, the polymeric support

mesh used on these filters reduces filter-

element weight by as much as 50 per

cent compared with traditional metal

mesh-supported elements, and does not

interfere with analysis techniques, such

as XRF, used to analyze the chemical-

elemental composition of the

contaminant captured in a filter

element.

Since an Ultipleat filter element is

supported both upstream and

downstream, it can accept flows in

either the normal, outside-to-in, or

the reverse, inside-to-out, flow

direction. Reverse-flow filters capture

ENGINE YEARBOOK 2005

Recent advances in laser-drilling

technology now permit the

manufacture of tangential-flow

filters fabricated from a single

piece of material with laser-

drilled holes which has a high

void volume and uniform

distribution of passages.

Figure 3

Figure 4

EYB2005_3 7/9/04 2:01 pm Page 62

ENGINE YEARBOOK 2005

Lynch, C. W., and Cooper, R. B., ‘The

Development of a Three-Micron Absolute

Main Oil Filter for the T53 Gas Turbine’,

Journal of Lubrication Technology, Vol.

93( No. 3), pp. 430-436, (1971).

Bachu, R., Sayles, R., Macpherson, P.

B., ‘The Influence of Filtration on Rolling

Element Bearing Life’, Proceedings of

33rd MFPG meeting, Gaithersburg, MD,

April 21-23, pp. 326-347, (1981).

Needelman, W. M., and Zaretsky, E.

V., ‘New Equations Show Oil Filtration

Effects on Bearing Life’, Power

Transmission Design, Volume 33( # 8),

pp. 65-68, (1991).

Ioannides, E, Beghini, E., Jacobsen,

B., Bergling, G., and Goodall

Wuttkowski, J., ‘Cleanliness and its

Importance to Bearing Performance’,

Lubrication Engineering, Vol. 49( No.

9), pp. 657-663, (1993).

Losche, T., Weigand, M., and

Heurich, G., ‘Refined life calculation of

rolling bearings reveals reserve

capacities’, FAG Technical Information

No. WL 40-43 E, April (1994).

‘Application of the New ISO 281

Standard for Bearing Life Prediction’,

ABMA Symposium for presentation of

the ASME Design Guide for Life

Ratings for Modern Rolling Bearings,

Baltimore, MD, March 7-8, 2002

Aerospace Information Report

AIR1666A, ‘Performance Testing of

Lubricant Filter Elements Utilised in

Aircraft Power and Propulsion

Lubrication Systems’, SAE, (2002).

Hovey, R.. M., ‘Operational Experience

With High Bypass Turbofan Engines -

Reflections for Future Designs’,

presented at the Canadian Aeronautics

& Space Institute Annual General

Meeting; Propulsion Division, May

1990, Toronto, Canada.

Humphrey, G. R., Little, D., Godin,

R., Whitlock, R., ‘Energy Dispersive X-

Ray Fluorescence Evaluation of Debris

from F-18 Engine Oil Filters’,

Proceedings of JOAP International

Condition Monitoring Conference, 1998

JOAP Technology Showcase, Mobile,

AL, April 20-24, 1998.

Humphrey, G. R.,, ‘Joint Strike Fighter

- Analysis of Filter Debris by Energy

Dispersive X-Ray Fluorescence’, JOAP

International Condition Monitoring

Conference, Technology Showcase 2000,

Mobile, AL, April 3-6, 2000.

all contaminants inside the filter

element, making filter change out

easier. Also, the all-polymeric support

meshes allow for increased disposal

options to meet ISO 14001 objectives.

Filter element differential-pressure

monitoring:

Differential-pressure indicators can

either be mechanical indicators or

electronic switches and are currently

utilised to provide an indication when

the filter-element differential pressure

exceeds the indicator actuation setting.

However, continuous monitoring of the

filter-element differential pressure, in

conjunction with the fluid temperature

and flow rate, can provide information

concerning contaminant loading of the

filter element and permit the

identification of ‘abnormal’ contaminant

loading conditions, once a baseline

trend has been established.

An electronic differential-

pressure/temperature sensor comprised

of a differential-pressure transducer and

a precision resistance temperature

detector (RTD) that could replace

conventional indicators is currently

undergoing final development testing.

The sensor provides continuous

differential pressure and temperature

output signals (analogue or digital) and

can be interfaced with the engine-

control system (ECU, FADEC). In

conjunction with fluid-flow rate

information, the sensor allows the

monitoring of the filter element

differential-pressure build-up rate due

to contaminant loading.

The measurement of the temperature

along with the differential pressure

eliminates the need for ‘thermal-

lockout’ provisions common in

conventional filter-element differential-

pressure indicators. In addition to

identifying ‘abnormal’ contaminant

loading conditions, the sensor can also

assist operators in optimising filter-

element service life. ■

References

Averbach, B. L., and Bamberger, E.

N., ‘Analysis of Bearing Incidents in

Aircraft Gas Turbine, Mainshaft

Bearings’, Tribology Transactions, Vol.

34, pp. 241-247, (1991).

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EYB2005_3 13/9/04 1:41 pm Page 63

ENGINE YEARBOOK 2005

Economic aspects of maintaining

engine efficiency

Reduced fuel consumption,

maintenance costs, pollution

and risk of engine failure are

all benefits of keeping gas

turbine gas paths clean. The

actual size of these benefits

depends on the type of

engine and the environment

in which it is operated, as

well as operational factors

such as the actual rating and

type of operation. Gas

Turbine Efficiency (GTE)

explains.

odern gas turbine engine

compressor airfoils are far

more efficient than older

types of airfoils. In a JT8D-219, the

average pressure increase per

compressor stage is 1.33 compared with

2.8 in the CFM56-5C4. However, as the

efficiency increases per compressor

stage, the sensitivity to disturbance also

increases. The benefits of a clean

engine/compressor section are even

more significant with these highly

efficient profiles. A comparison can be

made between the very efficient airfoils

of high performance gliders, where a

glide ratio of 60:1 is not uncommon,

compared with an MD-80, which has a

glide ratio of 28:1. The glider profile is

highly efficient and tailored for its task

without the constraints of an airliner:

fuel storage, housing of landing gear,

speed, range etc. The glider profile is,

however, very susceptible to

disturbance and needs to be kept in an

absolutely clean condition.

Engine efficiency

Disturbances caused by different

types of contamination on stationary

as well as rotating compressor airfoils

cause loss of efficiency in the

compressor section, just as on a wing.

To compensate for the loss of

compressor efficiency so that the

same level of thrust is generated, the

compressor rotors have to be operated

at a higher rotational speed. Also,

more fuel must be used to achieve the

same amount of air compression in

the compressor sections. This

increased fuel-burn lowers overall

operational efficiency and increases

the load on the engine. In the hot

section, increased fuel-burn causes

operation at a higher overall

temperature and engine speed,

resulting in an engine that is more

susceptible to surge as well as hot-

section and, to some extent,

compressor failure.

Pollution and adhesive fluids

The rate at which a gas path is

contaminated depends on the

quantity of particles and vapour in

the air that flows through the engine.

The main causes of compressor

contamination are usually general air

pollution and operations at airports

where the level of contamination,

particular during taxi operations, is

very high. The level of contamination

may also be affected by other

operational conditions such as de-

icing and anti-icing procedures.

When de- or anti-icing is being

conducted with the engines running,

larger amounts of de- or anti-icing

fluid are ingested into the engines.

The amount of ingestion, particularly

for aircraft types with engines

mounted on the wing, is substantial

during the de- or anti-ice procedure.

For aft-mounted engines the ingestion

during aircraft rotation is significant,

as a large amount of anti-icing fluid

departs wing trailing edges.

Several operators have taken

account of the effects of ingestion of

de- or anti-icing fluid into the

compressor sections and require

engine run-ups after de- or anti-icing

with the engines running, to prevent

build-up of cabin smoke from fluid

residue during the takeoff roll. De-

icing and, in particular, anti-icing

fluids are adhesive by nature. This

quality is exaggerated when the fluids

are heated in the compressor section.

The level of compressor

Washing of Airbus A319 engines.

EYB2005_3 7/9/04 2:02 pm Page 64

ENGINE YEARBOOK 2005

contamination depends on the fluid

type as well as the application

method; remote de- or anti-icing with

engines running versus at the gate

prior to engine-start. It also depends

on the level of contamination of the

air that is being compressed after the

de- or anti-icing procedure.

Cost reduction

A shorthaul aircraft will generally

conduct more takeoffs and landings

per day than a longhaul aircraft; 12

or more cycles per day is not

uncommon for a shorthaul aircraft. A

longhaul aircraft will generally

conduct two or three takeoffs and

landings per day, usually at high

rating. The overall usage in terms of

block hours is normally higher for

longhaul aircraft than for shorthaul

aircraft. Although longhaul aircraft

engines are exposed to fewer

contaminant particles per cubic

metre of air, contamination of the

compressor sections influences cost,

safety and environment.

A reduction in fuel burn has a large

impact on cost, as longhaul aircraft

are normally operated with a high

number of block hours per day. Fuel-

burn is also a concern on several

routes affecting payload and

revenues. If the Association of

European Airlines’ (AEA) total fleet

lowered its fuel consumption by one

per cent — not unrealistic if efficient

engine cleaning was used —

hundreds of thousands of tons of fuel

could be saved every year.

Maintaining compressor efficiency

is highly important to keep hot-

section temperatures down, thereby

reducing maintenance costs and the

risk of failure. Hot-sections of today’s

high bypass engines are rather

advanced and costly to repair. The

lowering of the overall hot section

temperature enables longer life in on-

condition/ trend monitoring

The rate at which a gas path is

contaminated depends on the

quantity of particles and

vapour in the air that flows

through the engine.

Note the total gas path penetration.

EYB2005_3 9/9/04 11:55 am Page 65

maintenance programmes and parts

cost when on fixed time programs.

Shorthaul aircraft will in general

have a faster degradation of

compressor efficiency due to

contamination as they are operated in

an environment with higher air

contamination levels.

Bird strikes

Air traffic has increased rapidly over

the past years, with the exception of a

small stagnation as a result of the

September 11th disaster. With an

increasing number of aircraft flying,

the number of bird strikes has

increased as well. The number of bird

ENGINE YEARBOOK 2005

strikes to civil aircraft in the United

States has increased every year from

1990 to 2000, doubling from 2,880 in

1996 to 5,761 in 2000. Based on these

figures, it is clear that an airline must

anticipate a number of bird strikes

each year and have good routines to

handle them. If a bird hits a turbine

engine, it is necessary to inspect the

engine to ensure that no damage has

occurred. Inspection after a bird strike

can, in many cases, be made easier and

quicker if proper cleaning can be

accomplished while the engines is still

installed. It is also important to

remove all blood as soon as possible

since it increases the probability

engine parts corrosion.

Environmental impact

The increasing contribution of air

traffic to the greenhouse effect and to

air pollution as a whole is a growing

concern. The European Commission,

among others, has stated that decisions

have to be made regarding the long-term

sustainability of aviation. In the

Commission’s publication “European

Aeronautics: A Vision for 2020”, the

goal for 2020 is “a 50 per cent cut in

emissions per passenger kilometre

(which means a 50 per cent cut in fuel

consumption in new aircraft) and an 80

per cent cut in nitrogen oxide

emissions.” Many actions have to be

taken to meet this objective, and one

important thing to do is keep the

engines clean and thereby maintain high

efficiency. Voluntary agreements such as

the British Airways commitment to

reduce CO

emissions by 125,000 tons

per annum by 2006 in return for £6.5

million in state incentives are expected

to grow more common.

The GTE solution

Compressor-efficiency deterioration

cannot be eliminated but it can be

limited. Keeping the gas path clean is

the best way to ensure that fuel is

used in an optimum way. How then

can this benefit your business? And

how can the numbers be validated?

The value for any particular business

depends on the type of operation and

the environment in which operations are

conducted. GTE can assist by creating an

analytical model of operations which

computes the benefits that can be

expected. Validating the analytical

model is easier in some areas than others.

The direct operational cost reduction

and the reduction in fuel-burn can be

measured by various engine tests or they

can be compared with past performance

over a period of time. The value of back-

to-back testing in engine cells does not

give the full picture, however, as the

comparison is made on an engine with a

contaminated compressor before and

after cleaning. If washing is performed

too late or irregularly, the compressor

section can be allowed to deteriorate

beyond a redeemable level and it cannot

be returned to the state it could have

been in if cleaning had been done at

optimum intervals.

The best way to validate the analytical

modelling is to measure the results over

time. Several operators have chosen this

alternative and continue using GTE

equipment. Validation of reduced

maintenance costs can be conducted

through modelling of the achieved hot

section temperature reduction, as well as

over time based on the on-condition

times achieved or actual parts cost. The

environmental impact of optimising

As gas-turbine technology has

developed, with high blade

loadings and ever-increasing

temperatures, more efficient and

effective cleaning methods are

necessary.

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ENGINE YEARBOOK 2005

compressor performance can be

validated as a factor of the achieved

reduction in fuel-burn.

The most difficult factor to assess is

the contribution to flight safety. It is

very difficult to measure for example, if

a surge-margin increase of one per cent

has been achieved during operation.

The increased flight safety of operating

with an optimised compressor section

tends to be notional since:

■ it is advantageous to have margin to

surge; and

■ it is advantageous to operate the

engine at the lowest possible

temperatures and rotational speeds

Several airline operators have

overlooked gas turbine cleaning for

many years. In the past, the amount of

engineering time invested in cleaning

equipment did not represent value for

money. Moreover, neither the cleaning

efficiency nor the man-hours required

to use the equipment measured up to

the demands of the market.

Furthermore, as gas-turbine

technology has developed, with high

blade loadings and ever-increasing

temperatures, more efficient and

effective cleaning methods are necessary.

The GTE concept is to give the gas

turbine world highly engineered,

environmentally adapted and cost-

effective methods for gas-turbine

cleaning, making life easier for engine

manufacturers and end-users — in other

words, the best deal for our customers.

Today, GTE produces a wide range

of patented high-pressure cleaning

equipment, which is marketed

globally. GTE’s expertise and

experience provides the technical

support required to achieve the most

cost-effective cleaning solutions for

gas turbines. Have you ever heard

of a royally-awarded cleaning

concept for gas turbines? Well, GTE

has one. ■

Fuel Burn 1999 2000

Aircraft Block Hours 7,455,500 7,884,100

Flown (source: AEA)

Average fuel [kg/h] 2,798 2,798

Fuel [ton] 20,859,674 22,058,849

1% of fuel [ton] 208,597 220,588

Yearly fuel burn, calculated on the AEA

member airlines’ fleet.The average fuel

consumption is an approximation for cruise

level calculated from CFMU information and

the BADA aircraft database.

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ENGINE YEARBOOK 2005

Advanced repair and

coating technologies

New engine repair and

thermal barrier-coating

technologies are helping

airlines and other aircraft

operators reduce their total

cost of ownership and keep

engines and critical engine

components working longer

and performing better.

Honeywell, a company

renowned for its

manufacturing capabilities,

describes its expansive

engine-repair capabilities.

perators are increasingly turning

to service providers with the

resources to develop and

maintain state-of-the-art maintenance,

repair and overhaul (MRO) capabilities.

The name of one of the top innovators

in the field of third-party MRO will

come as a surprise to many aerospace

industry insiders: Honeywell.

Mention the name ‘Honeywell’ and

most people think of a technology and

manufacturing company. It is well known

for developing and producing gas-

turbine engines for business aircraft and

helicopters; integrated avionics and flight

safety systems; auxiliary power units;

and aircraft landing and braking systems.

It is also widely known for its engine

MRO capabilities, which include a global

network of service resources that has

been primarily dedicated to meeting the

needs of owners and operators of

Honeywell-equipped aircraft. Only

recently has it made the strategic

decision to develop and offer repair and

overhaul services for non-Honeywell

engines and engine components.

A new view of engine repair

“Honeywell has developed advanced

technologies and techniques that are

changing the way that people think about

aircraft engine repair,” says Bernd Kessler,

vice president and general manager of

Aviation Aftermarket Services for

Honeywell. “Today, we’re able to repair

worn and damaged engine parts that

would have been scrapped just a few years

ago. Thanks to recent advances, some

customers are telling us that our

refurbished parts are as good as new parts.

In fact, they say that repaired parts

sometimes outperform new parts that come

fresh off the assembly line.”

According to Kessler, Honeywell has

invested heavily in developing new repair

and coating capabilities at a time when

many OEMs and third-party MRO

providers have cut back. “The downturn

in commercial aviation has caused many

"Since repairing a part costs

significantly less than replacing it,

operators can see a significant

positive impact on their

operating costs and their bottom

lines over the life of an engine."

—Bill Metera, director of sales

and marketing for Honeywell’s

newly formed advanced-repair

technology business.

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