Reducing aero-engine operational costs
Challenge
Responding to the international drive for improved fuel-efficiency, leading aircraft engine manufacturers are designing smaller, lighter engines, operating at higher temperatures and pressures than those
currently in service. Such engines also ‘bleed’ hot, high-pressure air to support other important aircraft systems, typically extracted at over 200 °C.
In these harsh environments, multiple onboard sensing devices, including air pressure sensors, are relied on to maintain safe and efficient flight operations. For engine manufactures, the more precisely they can specify air pressure measurements, the more fuel-efficient they can specify their engines designs. Another operational cost requirement is optimising periods between sensor re-calibrations, ideally synchronised with routine maintenance downtimes.
Therefore, sensor manufacturers would offer a competitive advantage if they could demonstrate long-term reliability, with no significant measurement drift, at such temperatures over the 12 to 18 months targeted by the aviation industry.
Solid-state pressure sensors already reached similar levels of measurement accuracy to existing primary standards, as product development outpaced that of calibration methods. Existing calibration methods remained susceptible to variations in ambient conditions so could not offer measurement certainty. Therefore, evolving demands of the aviation sector could not be satisfied by calibration laboratories.
Solution
The EMPIR project Industrial standards in the intermediate pressure-to-vacuum range developed new primary standards based on liquid column manometry and force-balanced piston gauges.
The project established the means to provide calibration services using such state-of-the-art pressure measurement instrumentation. Among several metrology institutes, LNE implemented a calibration service using metrology-grade piston gauges and force-balanced piston gauges.
Impact
Druck Ltd, part of the energy technology company Baker Hughes, manufactures Micro-Electro-Mechanical System sensors for flight control and air data measurement applications. By combining silicon-based microelectronics with micro-machining, the technology offers ten times the performance of standard silicon sensors. To suit harsher environments, Baker Hughes repackaged the technology, as Trench Etched Resonant Pressure Sensors (TERPS).
For a future engine platform, GE Aviation commissioned development of a high-temperature TERPS sensor, specified to 150 parts per million (ppm) accuracy over 12 months at 200 °C, a temperate above the operating range of existing Druck sensors.
Baker Hughes developed a test rig at its Leicester, UK facility, to automatically test for long-term reliability, or absence of measurement drift. The rig incorporated a modified version of its PACE 1000 TERPS instrument as a reference pressure indicator for the prototype high-temperature TERPS sensor under test. Demonstrating the target sensor accuracy required long-term 15 ppm accuracy for the reference device, a level of performance that could not be demonstrated by any commercial calibration laboratory.
The company, therefore, contacted LNE, that tested two PACE 1000 devices, before and after Baker Hughes’s 18-month test. In July 2019 it certified that pressure readings over this timescale were within the target limits for calibration equipment.
Importantly for Baker Hughes, this established the stability of its reference standard and the reliability of the prototype hightemperature sensor, that was duly delivered to its client at a technology readiness level above its initial expectations.
Many steps lie ahead before production readiness. If, as Baker Hughes hopes, the new TERPS technology is employed in production engines, the new calibration service will have helped enhance the cost-effectiveness of aviation operations and supported EU policies designed to reduce aviation emissions.
- Category
- EMPIR,
- Industry,