Video: Ash in a jet engine
The passengers on board a 1982 British Airways flight from London to Auckland, New Zealand, know that volcanic ash and jet engines are a dangerous mix. All four of BA flight 009’s engines failed simultaneously after it flew through an ash cloud. But mysteriously, they all kicked into life before disaster could strike. Now we might finally be able to say why.
Although 100,000 flights were cancelled earlier this year following the eruption of the Eyjafjallajökull volcano in Iceland, little is known about the effects of ash on jet engines. One reason for this is the reluctance of engine makers to destructively test many different types of engine, each costing in the region of $12 million.
So Thorsteinn Sigfusson at the University of Iceland in Reyjavijk and his team decided to mimic in the lab what happens when a jet engine flies through ash. They built a ceramic crucible and placed turbine vanes from used jet engines inside, before heating it to 1150 ºC – the typical in-flight temperature.
Next, they sieved volcanic ash collected from farmland near Eyjafjallajökull and kept those particles that were 57 micrometres in diameter or less. These are the particles that reached aircraft cruising altitudes, above 9 kilometres, in European skies during the eruption. They then loaded the ash into a sandblaster and fired it at the hot blades.
The red-hot vanes became coated in a glassy film as the ash melted, so much so that a real jet engine would clog up and fail. But when the team dropped the temperature to 720 ºC – a temperature an engine will cool to after failing – the ash began jumping off the vanes until most of it had gone (see video, above).
The glass, says Sigfusson, had reached a transition temperature and changed into a crystal structure that could not stick to the alloy.
“With the BA plane in 1982, the natural transition in the basaltic glass somehow cleaned the deposits from the blades so they could restart the engines. I think we are seeing that same glass transition,” says Sigfusson.
“My vision would be that we can look at ways to somehow de-ash an engine that has passed a volcano with this knowledge,” he says. “It shows that cooling the engine can cause self-removal of the trouble.”
The finding will be submitted to the Icelandic Civil Aviation Administration. It will be seized upon by engineers, says Fred Prata at the Norwegian Institute for Air Research in Kjeller. “I have never seen ash actually melting on a turbine blade or other hot engine part before,” he says. Analysis of the video could be “helpful and fascinating”, he adds.
More on these topics: