Using acoustic waves to push aviation safety further
In recent years, the aviation industry has identified a new threat to flight safety – the existence of high concentrations of ice particles at high altitudes. In an aircraft engine under "perfect storm" conditions (certain temperature, flow, geometry and ice crystal concentrations), ice can accumulate very quickly. This dangerous build-up can choke an engine within minutes, reducing it to idle, or if the ice sheds, can damage engine components or result in a flame-out. Currently, no reliable sensor system exists that can provide pilots with early indications of ice crystal accretion, but National Research Council of Canada (NRC) is addressing this technology gap with the development of an Ultrasound Ice Accretion Sensor.
The Ultrasound Ice Accretion Sensor is a very small, thin, lightweight non-intrusive device that has low power requirements – features that are extremely attractive to the aerospace industry. Using ultrasound, it acts as both a microphone and a speaker, sending out an acoustic wave that is reflected back, and providing data about conditions on the other side of the 'skin.' The reflected acoustic signal is analyzed using methods developed at NRC.
The most innovative aspect is that, contrary to most other sensors, the ultrasound sensor does not have to be placed within the environment being measured. It is applied to the non-exposed surface of an engine or aircraft component, eliminating the risk of it going through the engine or becoming damaged by ice and debris.
"Knowing where icing is likely to occur in an engine can be narrowed down – NRC's Reducing Aviation Icing Risk research program has done years of work on that," explains Dan Fuleki, Icing Group Project Manager at NRC. "So when we positioned this sensor in the right locations on the other side of the wall from the flow, we were able to determine that ice accretion was happening."
Over three years, the sensor was put through rigorous testing at NRC's world-class facilities for ice crystal icing investigation. Modifications to enhance the technology included improving performance and durability through changes to materials, cabling and fabrication, and the development and testing of installation procedures. Finally, the sensor was ready to move to a definitive high altitude ice crystal icing engine test.
That test came in November 2015. Through NRC's Memorandum of Understanding (MOU) with NASA to collaboratively advance icing research and improve flight safety, the sensor was tested at the NASA Propulsion Systems Laboratory. In partnership with Honeywell Engines and the Ice Crystal Consortium, which provided a test engine known to roll back to idle in certain icing conditions, the sensor was tested at 30,000 feet in a real icing environment.
"The test gave us a valuable opportunity to evaluate the technology and the initial results are very positive," said Fuleki. "We have been able to detect ice accretion in an actual engine icing environment, and have also seen that this sensor has sufficient sensitivity to distinguish between severe and light accretions and in effect, to measure the accretion intensity." A major aircraft company present during the testing showed great interest in including the sensor as part of their future icing tests for classical icing detection.
Now developed to technology readiness level (TRL) 6, there are already some well-suited industry users for this technology. Incorporating the sensor into aircraft, along with other probes and radar technology, could help pilots avoid situations where they would have to contend with engine ice crystal icing. The impact of this tiny but powerful sensor will be profound as the aerospace industry realizes financial benefits and most critically, flight safety advantages.
The Ultrasound Ice Accretion Sensor project is supported through NRC's Reducing Aviation Icing Risk research program.