One of the most destructive and dangerous materials a commercial or military jet engine can ingest is volcanic ash and one of the least would be crayons and cereal.
But those two substances were a key part of testing NASA has been conducting on smart engine sensors that could detect and help pilots avoid a volcanic plume. The new sensors are expected to detect the degradation caused by the volcanic ash, quantify the significance of the event, and aid in identifying which components might require maintenance, NASA stated.
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NASA said the sensors also would measure emissions and combustion and can detect the effect of the ash on the engine in real time and research the prognostic capabilities that could predict how long it will take for an issue to emerge. The sensors include one that evolved from one that was used for the space shuttle main engines, high-temperature fiber optics, high-temperature thin film sensors and acoustic microphone arrays. Also included is a microwave tip clearance sensor developed through the Small Business Innovative Research program that measures the complex gap from the outer wall of the turbine to the tips of the blades, NASA said.
"The primary issue is that volcanic ash forms glass in the hot sections of some engines," said John Lekki, NASA Vehicle Integrated Propulsion Research (VIPR) Principal Investigator in a statement. "This clogs cooling holes and chokes off flow within the engine which can eventually lead to an engine power loss. It is very erosive, which causes damage to compressor blades and other parts in the engine."
NASA pointed to a U.S. Geological Survey that found more than 80 commercial aircraft encountered potentially hazardous volcanic ash in flight and at airports from 1993-2008. That was before the big 2010 volcanic eruption of Eyjafjallajökull in Iceland which disrupted hundreds of flight in Europe and the lives of about 10 million airline passengers over six days.
So where do the crayons come in? NASA used a cereal and crayons combination to blow into the test engines at the beginning of VIPR project test cycle to establish the sensors could detect tiny bits of debris and set a baseline for the sensitivity of the devices.
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For the test program, which began in 2012, NASA partnered with Federal Aviation Administration, the U.S. Air Force Research Laboratory, Pratt & Whitney, Rolls Royce Liberty Works, General Electric Aviation and Boeing Research & Technology, to conduct the series of VIPR engine tests.
The VIPR tests used an Air Force C-17 cargo transport and two overhauled F117 engines. The F117 engine is a military version of a commercial Pratt & Whitney engine that is used on the Boeing 757.
"One of the things we found out was that the original volcanic ash distribution rig we were using to introduce the ash into the engine ate itself,' said Paul Krasa, VIPR project manager, based at NASA's Langley Research Center in Hampton, Virginia. "Volcanic ash literally has such an erosive characteristic to it that it was able to cut through fittings, so we had to go though a redesign."
Preliminary observations after the volcanic ash was introduced found glass accumulating around hotter parts of the engine, NASA stated. "There was erosion in the compressor and 'glassification' in the turbine," NASA said.
The VIPR test results should be publicly released in summer, 2016.
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