Evolution of Condition Monitoring Sensors for Aero …...closed position results in failure of filter and loss of particle retention. c) Filter placement in scavenge line results in

Evolution of Condition Monitoring Sensors for Aero Engine Components

O c t o b e r 2 0 1 1

Evolution of Condition Monitoring Sensors for Aero Engine Components | October 2011

© 2011, HCL Technologies. Reproduction Prohibited. This document is protected under Copyright by the Author, all rights reserved.

TABLE OF CONTENTS

Abstract ............................................................................................. 3

Abbreviations .................................................................................... 4

Market trend ...................................................................................... 5

Solution ............................................................................................. 6

Best Practices ................................................................................. 12

Common Issues .............................................................................. 13

Conclusion....................................................................................... 14

Reference ........................................................................................ 15



3

Abstract

Aero engine is a complex equipment operating under extreme conditions like very cold to very hot temperatures, fast rotating components, high and low pressure, and disturbances in the inlet pressures due the environmental or maneuvers and coordination of different systems based on throttle position and altitude.

One of the most widely used technique of rotating components is fluid monitoring, as fluid is the medium passing all over the stressed parts it is more likely that it carries evidence of faults from all the parts it comes in contact with. This necessitated the development of various condition monitoring technologies to monitor highly rotating stressed parts.

The paper presents an overview of wear debris condition monitoring

equipment developed over a period of time from the end user

perspective i.e. pilot and the maintenance communities.



4

Abbreviations

Sl. No. Acronyms Full form

1 ECD Electric Chip Detector

2 MCD Magnetic Chip Detector

3 FDR Flight Data Recorder



5

Market trend

Aircraft engines have failures like non-recoverable in-flight shutdowns leading to crash, or emergency landings and incidents resulting in unscheduled maintenance leading to inventory and dispatch delays. The rotating components contribute significantly to the total faults or failures. Wear is associated with all rotating and sliding surfaces, it involves material removal at different rates and often in different particle sizes.The objective of monitoring is prompt detection of failure modes which are even in rapid progression. Aero engine have closed re-circulatory Lubrication System to reduce friction, carry away heat and debris from rotating components back to the debris monitors or bottom of the oil tank. It has physical interaction with Fuel, Secondary Air System compoenents. Hence the reliable operation of the gas turbine engine depends on the proper functioning of the Lubrication System. Majority of fleet down times are due to the problems like oil leaks, high oil consumption, high oil temperature and debris in oil and filter clogging.The system schematic is shown at fig.1

Fig.1 Schematic of engine lubrication system



6

Solution

Oil debris monitoring is one practical way of monitoring the condition of rotating components as the lubrication system is a closed re-circulatory. This is evident from the number of technologies developed over a period of time.

1) Mechanical

In early days filter was installed in-line to oil scavenge and delivery lines to protect the rotating assemblies. The particles captured here were used for wear trend monitoring.The same is still used as a additional tooling during testing of new developmental or manufactured engines.

Advantages:

a) Simple in construction b) Good particle capture efficiency as total flow, flows across

it.

Limitations: a) Fully clogged filter leads to opening of bypass valve and

further generated debris become abrasives resulting in secondary damages and chances are that all the damages may happen without any prior indication to pilot.

b) Over pressure in system due to jamming of relief valves in closed position results in failure of filter and loss of particle retention.

c) Filter placement in scavenge line results in pressure drop, so placing filter only in oil delivery line does not reveal the true quantity of particles generatedas the there is change that particles generated may settle down in tank.

2) Magnetic chip collectors

Which are placed in one or all scavenge/return line i.e. downstream of bearings to collect and retain all ferrous particles.



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Advantages:

a) Easy to attend without much oil loss, does not result in appreciable pressure drop.

b) The ferrous particles are retained for further examination.

Limitations: a) No prior indication to maintenance technician or pilot about

the debris collection.

3) Electro mechanical sensors

This sensor address the problem of online indication with the collection of particles and subsequent closure of electrical switch

Advantages:

a) The particles are available for wear trending b) Online condition monitoring and Signal to pilot/FDR c) Metallic as well as non metallic particles can be detected.

Limitations:

a) Moving parts may lead to seizure due to temperature, debris

b) Signal is generated due to wear products as well oil sludge causing concern to pilot

c) Does not distinguish size of particles leading to same signal to pilot for very powdery particles or big chunk of mass.

4) Electric (Mesh/disc)

Electrically conductive particle detectors these are screen type/stacked discs when the particle fills the pores/stack indication is provided.



8

Advantages:

a) Electrically conductive particles can be detected. b) Signal is provided to pilot.

Limitations:

a) Robustness of the mesh in the system. b) Placement of this in system to have good capture efficiency.

As most of the stressed rotating parts are made of ferromagnetic material and all the other damages like rubbing of casings are secondary. This resulted in focus on technologies detecting accurately the ferrous particles.

5) Electro Magnetic

Sensor works on the principle of closure of the circuit due the particle accumulation between the poles

Advantages:

a) All ferrous particles are retained for wear trending. b) Online signal is given to pilot.

Limitations:

a) Signal is same irrespective of the particle size i.e. same signal for big and small particles, leading to pilot attention even for small particles.

This resulted in development of capacitor based Chip detectors.

6) Chip detector with capacitor

Chip detector with inbuilt or separate capactor aka Zapper® is

developed to to distinguish the small or big particles.



9

Works on the principle of closure of the circuit due to bridging of particles between the poles, as the circuit closes the capacitor discharges the predetermined amount of energy to break the bridge. If the circuit opens the event is recorded in FDR and the particles are considered as nuisance one/ insignificant. If the circuit is close the signal is fed to pilot. Various logics are implemented to monitor the electrical circuitry.

Advantages:

a) The signal is generated to only significantly large debris not for nuisance once.

b) Also possible to monitor the electrical circuit.

Limitations:

a) Robustness over a period of time. b) The burnt out bridge may also have big particles. And the

number of particles and size of each is unknown.

Maintenance philosophy has changed from reactive to preventive to prognostics to address queries like will the engine completes the next flight, does it need to be changed/replaced in next two weeks, who many spares needed for next month, i.e. planning and provisioning by commercial or military head quarter.

Sensor technology has changed in tune with the change in maintenance requirements of the engineers, pilots, planners.

7) Electro Magnetic induction sensors

Quantitative Debris Monitor® uses the permanent magnet based

electromagnetic induction principle to quantify the number of particles and the size of each particle.



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Advantages:

a) Particle size and no of particle will be known b) Signal can be given to pilot based on size and count.

Limitations:

a) Voltage induction will be less as the no of particles accumulated on pole piece increase beyond a limit.

b) Can detect only ferrous debris. c) Signal depends on flux disturbance, signal is not same for

particles of different forms and same volume.

8) Electromagnetism

The induction sensors also detects both ferrous and non ferrous debris with the changes in phase of the signal, however they cannot be used for analysis as the particles are not retained with the sensor.

As the aerospace demands improvements in specific thrust and thrust to weight ratio of aero engines, various material technologies and surface engineering methods are developed. Hence obviating the development of sensors to detect the non metallic materials like ceramics as they are being used in gears and bearings.

9) Electrostatic

Sensor is basically developed to detect the debris present in the gas path of the engine, is adopted to detect the charged particles in the lubrication system due to wear.

Advantages:

a) Metallic, non metallic debris can also be detected.

Limitations:

a) Depend on time the particles generated and the charge on it.

The challenges are quantifying the size of the paricles i.e distinguishing the flakes/chips and spheres. The technologies under development are LASER, ultrasonic imaging, to detect the size and shape of the particles in the system. Overview of the technologies products used in aerospace is given in below table.



11

Product Company In line/ On line

Technology used

Particle Size Range

Ferrous Non Ferrous

Smart Zapper Eaton In Line-On Line

Magnetic 100 µm NA

Quantitative Debris Monitor Eaton In Line Electro Magnetic induction

50 µm NA

Tech Alert 20 Macom Technologies On Line Inductive 1 µm NA

Tech Alert 10 Macom Technologies On Line

Inductance of coil Eddy current

50µm 150µm

Metal Scan Gas TOPS Ltd. On Line Inductive 100 µm 400 µm

Oil line sensor Smith aerospace In line Electro static

20 µm NA

Chip collector Chip detector Pulsed chip detectors

Eaton Vibrometers Allen aircraft products

In line Magnetic >100 µm

NA



12

Best Practices

This new sensor development involves in-depth knowledge of

materials, conditions inside engine, types of failures, along with the

extensive use of electromagnetic,electrical circuit analysis and

Matlab tools is helping the time to market along with the prototype

testing and realtime testing on engine is essential.



13

Common Issues

Challenge in condition monitoring is to detect the size and shape

the particles, quantity of debris irrespective of material during flight

generated due to new and already used components and

integration on engine.



14

Conclusion

The initial sensors developed to understand the type of failure or safe guard the other components from this debris becoming abrasive went through lot of technological changes primarily based on the changes of maintenance philosophies and also on the developments in materials for the rotating components.

The challenge is to integrate the new technologies on the engine so

that they can be utilized to monitor the system online and corrective

actions can be planned by maintenance crew present on ground.



15

Reference

www.eaton.com

www.vibrometer.com

Author Info

Mr.Naidu Nallasani has 8 years of experience in

lubrication, fuel system of Aero engine design

improvement, troubleshooting and 3 years

experience in lubrication system sensor

development.

http://www.eaton.com/

http://www.vibrometer.com/

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Evolution of Condition Monitoring Sensors for Aero …...closed position results in failure of filter and loss of particle retention. c) Filter placement in scavenge line results in