By Alexandra Branscombe

WASHINGTON, DC –Thousands of airplane passengers were stranded in airports across Europe in 2010 when Iceland’s Eyjafjallajökull volcano spewed billions of cubic feet of volcanic ash into the sky. The large cloud of ash – enough to fill at least two football stadiums – threatened to clog jet engines and cause airline accidents.

But it is not just large volumes of volcanic ash that can cause problems for jet engines. Volcanic ash can melt when it gets inside the hot engine and even small amounts of the melted ash can do harm by sticking to the interior of turbines, interacting with protective coatings, or clogging parts that cool the engine.

The Eyjafjallajökull volcano in Iceland erupted in April 2010, sending up into the sky an enormous ash cloud that halted air travel across Europe for several days. A new study published in Geophysical Research Letters looks at the harm that even small amounts of melted ash can do to jet engines.
Credit: Gunnlaugur Þór Briem/Flickr creative commons

A new laboratory experiment has measured the temperature at which the ash from a particular volcano in Guatemala turns molten, sticks to metal and begins to flow. The findings suggest that, if some of this ash got into a jet engine that was hotter than this critical temperature, the ash could stick and thereby place the engine at risk of malfunctioning, said Donald Dingwell of Ludwig Maximilian University (LMU) in Munich, Germany, who oversaw the research.

He and his colleagues described their experiment in a paper published last month in Geophysical Research Letters, a journal of the American Geophysical Union.

“This is the first study that experimentally analyses these fusion characteristics of volcanic ash using a high precision apparatus at high temperature,” said Wenjia Song, also of LMU, who is lead author of the study. The researchers suggested that their measurements could provide the basis for further research examining the melting and sticking behavior of hundreds of different types of volcanic ash that could come into contact with jet engines.

The findings should inform decision-making by aviation authorities when ruling whether or not it is safe to fly an airplane through a cloud of volcanic ash, said LMU’s David Damby, also a co-author. The improved “understanding of the interaction between ash and jet engines could also provide a feedback to engineers and manufacturers when assessing their current production,” he said.

When volcanic ash is heated, it turns from a powder into a liquid bead, which can then stick to solid surfaces like the inside of a jet engine. The beginning of this process is called sintering.

Ashes from different volcanoes do not all undergo this process in the same way, Dingwell said . The chemical properties of ash can vary from volcano to volcano, and can cause sintering to occur at different temperatures for different types of ash, he said.

As part of the new study, the researchers set out to describe how the chemical makeup of volcanic ash affects the way it undergoes the sintering process. For the new study, the team heated a small pile of ash from the Santiaguito volcano in Guatemala to 1,400 degrees Celsius (2,552 degrees Fahrenheit) on a ceramic mold. As the ash was heated, they observed the powder turning into liquid, which bubbled and melted as the temperature rose.

The researchers discovered that the ash from the Santiaguito volcano did not stick to the mold at temperatures below 1,256 degrees Celsius (2,112 degrees Fahrenheit). But at higher temperatures, the ash began to stick to the mold’s surface and then flow as a liquid. If components inside a jet engine were hotter than this critical temperature, there is the possibility that ash will stick to these regions, potentially putting the engine in jeopardy, explained Damby.

The researchers said the technique outlined in the new study could be used to determine the sintering behavior of other types of ash. They plan to use this method to build a database of the chemical composition and sintering behavior of the hundreds of different types of ash emitted by volcanoes worldwide.

“Throwing buckets of ash into fully operational jet turbines every time a volcano erupts isn’t practical, Damby noted. “So, we use studies like this to understand the fundamental behaviour of ash at high temperatures and to generalize the results of a few expensive ash-ingestion tests.”

 – Alexandra Branscombe is a science writing intern in AGU’s Public Information department

**This post was updated to include additional comments by the researchers. The text of the original post is posted below.

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Volcanic ash creates sticky situations for jet engines

Thousands of airplane passengers were stranded in airports across Europe in 2010 when Iceland’s Eyjafjallajökull volcano spewed billions of cubic feet of volcanic ash into the sky. The large cloud of ash – enough to fill at least two football stadiums – threatened to clog jet engines and cause airline accidents.

But it is not just large volumes of volcanic ash that can cause problems for jet engines. Volcanic ash can melt when it gets inside the hot engine and even small amounts of the melted ash can do harm by coating the interior of turbines, interacting with protective coatings, or sticking to parts that cool the engine.

A new laboratory experiment has measured the temperature at which the ash from a particular volcano in Guatemala turns molten, sticks to metal and begins to flow. The findings suggest that, if some of this ash got into a jet engine that was hotter than this critical temperature, the engine could be at risk of overheating or even stalling, said one of the experimenters David Damby of Ludwig Maximilians University in Munich, Germany.

Damby and his colleagues described their experiment in a paper published last month in Geophysical Research Letters, a journal of the American Geophysical Union. The researchers said the measurement could provide the basis for further research examining the melting and sticking behavior of hundreds of different types of volcanic ash that could come into contact with jet engines.

This information could help airplane manufacturers design engines that can withstand some types of ash and help pilots determine when it is not safe to fly an airplane through a cloud of volcanic ash, said Damby. “Understanding the interaction between ash and jet engines will help engineers and manufacturers assess their current production,” he noted. “Ultimately [this research] will help get people to their destinations safely.”

When volcanic ash is heated, it turns from a powder into a liquid bead, which can then stick to solid surfaces like the inside of a jet engine. This process is called sintering.

Ashes from different volcanoes do not undergo this process in the same way, said Donald Dingwell, also of Ludwig Maximilians and a co-author of the new paper. The chemical properties of ash can vary from volcano to volcano, and can cause sintering to occur at different temperatures for different types of ash, he said.

As part of the new study, the researchers set out to describe how the chemical makeup of volcanic ash affects the way it undergoes the sintering process. For the new study, the team heated a small pile of ash from the Santiaguito volcano in Guatemala to 1,400 degrees Celsius (2,552 degrees Fahrenheit) on a metal mold. As the ash was heated, they observed the powder turning into liquid, which bubbled and melted as the temperature rose.

The researchers discovered that the ash from the Santiaguito volcano did not stick to the mold at temperatures below 1,256 degrees Celsius (2,112 degrees Fahrenheit). But at higher temperatures, the ash began to stick to the mold’s surface and then flow as a liquid.

This information shows that an airplane could safely fly through an ash cloud from the Santiaguito volcano if the engine temperature remained below 1,240 degrees Celsius. But, if regions inside a jet engine were hotter than that critical temperature, the aircraft could be in jeopardy, explained Damby.

The researchers said the technique outlined in the new study could be used to determine the sintering behavior of other types of ash. They plan to use this method to build a database of the chemical composition and sintering behavior of the hundreds of different types of ash emitted by volcanoes worldwide.

“Throwing buckets of ash into fully operational jet turbines every time a volcano erupts isn’t practical, so we use studies like this to understand the fundamental behaviour of ash at high temperatures,” said Damby.