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FP7

AEROPZT Report Summary

Project ID: 632604
Funded under: FP7-JTI
Country: United Kingdom

Final Report Summary - AEROPZT (Development of materials, processes, and means to enable the application of Piezoelectric materials in aero engine controls)

Executive Summary:
A Consortium of organisations from across Europe, TWI Ltd (United Kingdom), Noliac A/S (Denmark), Cedrat Technologies SA (France) and Politecnico di Torino (Italy), was formed to develop materials, processes and means to enable the application of piezoelectric materials in aero engine controls.

The project was divided into five main stages. The first, definition of the optimum performance requirements and the environmental specifications for operation in aero engine controls was performed through collaboration between the Consortium and a possible future user of the technology. The project focused on the development of a piezoelectric actuator with an encapsulation to enable operation in aero engine fuel staging valves.

The second stage of the project involved the research and development of materials and designs for the piezoelectric stacks, actuator assembly and encapsulation. Two piezoelectric materials, two actuator designs, and two distinct encapsulation approaches (stack encapsulation and actuator encapsulation) were designed and manufactured. All the variables were presented in the form of Breadboard Models (BBMs).

The third stage of the project involved the empirical evaluation of the BBM devices through a series of laboratory tests at extreme environmental conditions defined during the first stage. The objective was to evaluate the materials and designs selected for subsequent optimisation of performance. The outcome was the selection of the actuator, piezoelectric component and encapsulation materials and designs to be further developed. The materials and designs were optimised through modelling and presented in the form of Engineering Qualification Models (EQMs).

In the fourth stage of the project, EQM devices were manufactured. The EQMs were then subjected to a series of accelerated environmental tests to evaluate performance and behaviour of materials and designs at the conditions set in stage one. The results indicated that the EQM was able to comply with the pressure, fluid exposure and mechanical cycling requirements; however the behaviour at extreme thermal conditions was limited.

The fifth stage of the project involved a series of evaluations to determine the impacts on the materials and designs tested during stage four, particularly aimed at identifying the weak features. From the analysis it was concluded that all the materials selected successfully performed under the tested conditions, and that the assembly design of both piezoelectric stacks and encapsulation system were limited when exposed to elevated temperatures.

In conclusion, novel materials and processes complying with most of the optimum environmental and performance requirements were developed. The actuator stroke and high temperature requirements were limited, however the optimisation required to fulfil the requirements was identified. Immediate exploitable products were achieved with possible future applications in the aero engine control and instant application in the vibration tool holder market.

Project Context and Objectives:
Project Context

ACARE (the Advisory Council for Aviation Research and Innovation in Europe) has set guidelines for the environmental impact of aerospace that target significant reductions in aircraft emissions. The ACARE targets for civil aircraft include NOx and CO2 emissions reductions of 80% and 50% respectively by 2020. Although airframes make a significant contribution, most of the balance (especially NOx) will be contributed by the engines. These contributions are expected to be achieved by lean burn, increased propulsive efficiency and increments in cycle efficiency via reduced component losses. Augmenting performance can be achieved by introducing new active controls to reduce off-design component efficiency loss, improve surge margin and lean-blow out margin. Unfortunately, current implementations are limited by the characteristics of existing electromechanical and hydraulic actuation devices (i.e. frequency response and cyclic life) and the high temperature, pressure and possibly liquid wetted operating conditions. Piezoelectric ceramics can overcome some of these limitations and offer the potential to make highly reliable actuation devices partially because the strain is developed without wear or friction.

The project work was centred on the specific requirements of the SAGE 6 initiative; however the results will have much wider applicability. The objective of SAGE 6 is to demonstrate lean-burn as a whole engine system to a TRL6 maturity level. It is expected that the main focus of test activity for the integrated system will be concentrated on a new demonstrator vehicle based around and Rolls-Royce Trent 1000 engine suitable for installation on a flying test bed. Future builds of existing demonstrator engines such as the EFE and E3E and potentially experimental industrial platforms that use similar staging methodology will also be included into the programme.

Project Objectives

AEROPZT has addressed the challenge of developing more capable piezoelectric ceramics, protective encapsulation systems and actuator designs, targeting fluid flow control challenges (e.g. lean-burn combustion fuel staging). In this application the aim is to maintain precise control of flow between pilot-mains fuel streams to enable combustion processes that reduce NOx emissions. Additional active control elements include management of lean-combustion thermoacoustic instability and lean-blow out. The technologies developed within this project will have a wide range of device applications, such as direct clearance control actuation, air flow manipulation for boundary layer control and sensor devices.

The specific objectives of the AEROPZT project were:

1. Development and manufacture of piezoelectric materials capable of operating over the temperature range -40°C to 180°C, whilst maintaining sufficient margin from the Curie temperature to prevent depolarisation in use.
2. Development of an encapsulation methodology and processing methods to enable the piezo elements to operate reliably in a fuel-wetted environment.
3. Design of a piezo element stack which is capable of delivering the force and stroke required for a typical fuel staging valve.
4. Design of the complete actuator assembly for the fuel staging valve assembly.
5. Determination of cyclic life requirements for the fuel staging application and demonstration that this performance can be delivered by the piezo stack and complete actuator assembly.
6. Accelerated environmental testing to determine possible failure modes.
7. To gain knowledge of the degradation processes both on a macro level (in terms of the performance as a valve element) and any changes in the material micro-structure as a result of the degradation processes.

Project Results:
• In collaboration with a leader in the aero engine industry, the Consortium was able to produce a list of device optimum requirements and environmental specifications for operation of a piezoelectric actuator as a fuel staging valve in aero engine control. The main performance and environment specifications are as follows:

Parameter Required actuator performance
Stroke (μm) 2000
Operating frequency (Hz) 5
Blocked force (N) 89
Volume (mm) 100x100x80
Operating temperature (ºC) -40 to 180
Survival temperature (ºC) -80 to 250
Environment maximum pressure (Bar) 168
Life and Reliability 30,000 hours or >4000 flight cycles, equivalent to approximately 1x108 operating cycles
Fluid exposure 5% NaCl solution

• Research and development of materials and designs for piezoelectric components, actuator and encapsulation was complete through a series of modelling exercises and empirical characterisation tests. As a result, the following materials and designs were selected and produced:

o Two piezoelectric materials (HT-S and HT-H).
o Two actuator designs (Amplified Piezoelectric Actuator (APA) and Parallel Pre-stressed Actuator (PPA)).
o Two distinct encapsulation approaches (stack encapsulation and actuator encapsulation).
o All the variables were presented in the form of four Breadboard Models (BBMs).

• The BBM devices were subjected to empirical evaluation through a series of laboratory tests at extreme environmental conditions as per the projects requirements, which led to the selection of materials and designs for subsequent optimisation of performance. The tests performed included:

o Thermal stability test.
o Thermal shock test.
o Soak and cycle test.
o Fatigue test.

• The outcome of the initial test was the selection of the following for further development:

o APA actuator design.
o HT-H piezoelectric material.
o Actuator encapsulation design.

• The materials and designs were optimised through modelling and presented in the form of Engineering Qualification Models (EQMs).

• The optimised EQMs formed of APA actuators, HT-H piezoelectric stacks and an actuator encapsulation system, were designed and manufactured.

• The EQMs were subsequently subjected to a series of accelerated environmental tests to evaluate performance and behaviour of materials and designs as per the project requirements. The testing programme included:

o Thermal testing:
▪ - Thermal stability.
▪ - Thermal cycling.
o Pressure testing
▪ - Including thermal and fluid exposure.
o Fluid exposure testing:
▪ - Including actuator mechanical cyclic testing.
o Mechanical cyclic testing
▪ - Piezoelectric stack ageing tests.
▪ - Actuator operational cycling.

• The results indicated that the EQM was able to comply with the pressure, fluid exposure and mechanical cycling requirements; however the behaviour at extreme high thermal conditions was limited.
• A series of NDT evaluations before, during and after the tests was completed to determine the impacts on the materials and designs tested, particularly aimed at determining the possible failure modes.
• From the post-test NDT evaluations it was concluded that:
o The piezoelectric material selected complied with the overall project environmental requirements, including the operational temperature requirements.
o The performance limitations identified were solvable by redesign of the piezoelectric stack and encapsulation assemblies.

• Comparison of the project optimum requirements for fuel staging valves in engine control and those achieved in the project is presented in Table 1.

Table 1. Actuator required and achieved performances
Parameter Required actuator performance Achieved actuator performance
Stroke (μm) 2000 1020
Operating frequency (Hz) 5 5
Blocked force (N) 89 134
Volume (mm) 100x100x80 159x30x20
Operating temperature (ºC) -40 to 180 -39 to 180
Environment maximum pressure (Bar) 168 168
Life and Reliability 1x108 cycles 1x108 cycles
Fluid exposure (immersion) NaCl solution NaCl solution

• The novel piezoelectric materials complied with the environmental requirements.
• Designs complying with most of the optimum environmental and performance requirements were developed.
• The actuator volume, stroke and high temperature performance was limited; however the optimisation required to fully accomplish the requirements was identified.
• Immediate exploitable piezoelectric, actuator and encapsulation products were achieved with possible future applications in aero engine controls.
• Instant exploitable application of the products developed was identified for the vibration tool holder market.

Potential Impact:
Potential Impacts

The final results of the AEROPZT project comprise:

1. A piezoelectric material capable of operation over a temperature range of -39°C to 180°C.
2. A piezoelectric actuator capable of operation over a temperature range of -39°C to 100°C.
3. Encapsulation capable of enabling operation in a pressurised and fluid immersed environment.
4. A piezoelectric actuator with encapsulation capable of producing the force required for a fuel staging valve.
5. An amplified stroke piezoelectric actuator with characteristics suitable for fuel staging and directly applicable in vibration tools holders.
6. Data validating the cyclic and environmental performance of the piezoelectric stack element design for the fuel staging valve application.

The piezoelectric solution has the potential to contribute in a highly significant way to attain the following impacts:

1. Fuel valves with improved frequency response capable of performing the bumpless transfer function under feedback control.
2. Improved engine surge margin during transient manoeuvres.
3. Reduced thrust perturbations due to fuelling transients.
4. Improved safety of lean-burn staged combustion systems.
5. Proven application of piezoelectric materials in a safety critical environment.
6. Improved durability and reduced cost of the fuel staging system due to the piezo actuator having fewer moving and wearing parts.

In addition to the direct benefit from the project for the fuel staging application, a number of other applications were also identified. For example it is well known that lean combustion is prone to thermo-acoustic instability. High frequency valves could be used for secondary fuel injection, as part of a feedback control system to damp and eliminate the instability. A sensor would detect changes in pressure or heat release (via chemiluminescence possibly of OH) and then the secondary injector device would deliver fuel with the correct phase relationship to damp the instability. Such thermo-acoustic instabilities can cause both physical damage to the engine and / or lean blow out, potentially endangering the aircraft. Such a system may also widen the envelope of safe operation.

Other potential applications for piezoelectric actuators within an engine have been identified, including active surge control, active clearance control and active boundary layer control. All of these technologies could improve the efficiency of the engine, enabling fuel savings as well as emission reduction. If all of the technologies were implemented the savings would be highly significant.

External factors likely to influence the successful attainment of the aforementioned impact includes the fact that lean-burn itself may not be accepted by civil airlines. There is no doubt that introducing extra complexity will incur a cost penalty that will be resisted by operators. Potentially thermal management of the injector could be used to eliminate some of the need for purging and priming, thus simplifying the fuel staging and lessening the need for an improved valve technology.

Significant potential impacts may also result from the following secondary applications:

1. Extended product range of long-stroke APA actuators.
2. Encapsulation of actuators.
3. Piezoelectric actuator meeting the requirements for a Vibration Tool Holder (VTH) system, in terms of encapsulation, piezoelectric ceramic protection and heat management.
4. High temperature piezoelectric ceramics.

Dissemination activities

The main dissemination activities of the project included:

1. Establishment of the project website with both confidential and publically accessible areas
(www.aeropzt.eu).
2. Production of dissemination material in the form of leaflets, presentations, posters/exhibition material and a project logo.
3. Presentations at industrial and academic conferences.
4. Publication of articles in print and on-line journals.
5. Development of appropriate training material.
6. One-to-one interactions with key aviation sector organisations.

The following list summarises the conference/exhibition/event presentations made to promote the AEROPZT project:

• Investigation of large signal properties of quasi-static PZT actuators at elevated temperature, Piezo 2015 Electroceramics for End-users VIII, 25-28 January 2015, Maribor, Slovenian.
• Extreme performances of piezo system: high stroke, high frequency, high temperature, SMART2015 7th ECCOMAS Thematic Conference on Smart Structures and Materials, 3-6 June 2015, Ponta Delgada, Azores.
• Temperature dependence of soft/hard PZT material properties and impact on the design choice, The 12th International Workshop on Piezoelectric Materials and Applications in Actuators (IWPMA 2015), 29 June - 1 July 2015, Vilnius, Lithuania.
• Advantages of large piezoelectric actuators and high power drivers for fatigue and fretting test, 4th International Conference on Fracture Fatigue and Wear (FFW 2015), 27-28 August 2015, Ghent, Belgium.
• Full characterisation of PZT actuators in quasi-static, large signal operation at elevated temperature, Actuator 2016, 13-15 June 2016, Bremen, Germany.
• Encapsulated piezo actuators for use at high power levels and/or within harsh environmental conditions, Actuator 2016 trade show & conference, 13-15 June 2016, Bremen, Germany.
• New developments in piezo actuators: long stroke actuators and high power electronics, SGE 2016 symposium, 7-9 June 2016, Grenoble, France.

The following three journal articles were also produced:

• Investigation of large signal properties of quasi-static lead zirconate titanate actuators at elevated temperature, Advances in Applied Ceramics journal, Volume 115, Issue 2, 2016, p72-76.
• Temperature dependence of soft-doped / hard-doped PZT material properties under large signal excitation and impact on the design choice, Vibroengineering Journal, Vol. 18, Issue 3, 2016, p1555-1562.
• Numerical analysis of piezoceramic actuators for high temperature applications, Composite Structures Journal, Vol. 151, 2016, p36-46.

List of Websites:
www.aeropzt.eu

Relevant Contact Details:
Dr Hugo Marques
TWI Limited
Granta Park, Great Abington,
Cambridge, CB21 6AL, UK
TEL: +44 (0) 1223 899 000
WEB: www.twi-global.com
Email: hugo.marques@twi.co.uk

Related information

Contact

Daniel Moss, (Commercial Officer)
Tel.: +44 1223 89 9440
E-mail
Record Number: 191844 / Last updated on: 2016-11-15
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