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.
AEROPZT addressed the challenge of developing piezoelectric ceramics, encapsulation and actuator designs primarily for staged combustion fuel staging in the context of the SAGE6 project. In this application the aim was to enable pilot-main fuel staging without significant un-commanded thrust transients and reductions in surge margin (so called bumpless transfer). Another important application in the field of combustion was the control of thermoacoustic instability and lean blow out. It was expected that the materials and technologies developed will have a wide range of other applications for active control within the engine such as active surge control, boundary layer control and active clearance control.
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.