The effects of volcanic ash – Q&A

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The effects of volcanic ash – Q&A

The eruption of the Icelandic volcano Eyjafjallajokul is still disturbing air travel in Europe. Safran’s technical experts are participating in current deliberations by government authorities (DGAC in France, Civil Aviation Authority in the U.K.). Jacques Renvier, from Snecma’s Engineering and R&T division, provides further details on this ash cloud that continues to ground aircraft.

What makes up a cloud of volcanic ash?

Volcanic ash comprises tiny particles of lava, ranging in size from just a few microns to about a tenth of a millimeter. These particles contain at least 80% silica, a highly abrasive material, and sulfur compounds. The small particles are suspended in the atmosphere at altitudes corresponding to the operating altitudes of aircraft, and may travel thousands of kilometers. In terms of prevention, clouds of volcanic ash cannot always be easily seen by the naked eye or by radar.

What effect does this volcanic ash have on aircraft and their engines?

Based on all the analyses of flights carried out in these clouds, the main impact on engines can be summarized in three points:

Erosion of the compressor guide vanes, leading to a significant loss in engine operability.
Melting of particles going through the combustor, followed by resolidification of the silica on the high-pressure turbine nozzle guide vanes, thus degrading throughput and thermal resistance over time. Furthermore, obstructing this section raises the surge line of the HP compressor, affecting its operability.
Contamination by these particles of bleed air, which is directed to engine ventilation, control probes and air conditioning.