The thermal stability of Eyjafjallajökull ash versus turbine ingestion test sands

Ulrich Kueppers,Kai-Uwe Hess,Corrado Cimarelli,Fabian B Wadsworth,Jacopo Taddeucci,Donald B Dingwell

doi:10.1186/2191-5040-3-4

Abstract

The 2010 eruption of Eyjafjallajökull (Iceland) and the 2011 eruptions of Grimsvötn (Iceland), Cordon Caulle (Chile) and Nabro (Ethiopia) have drastically heightened the level of awareness in the general population of how volcanic activity can affect everyday life by disrupting air travel. The ingestion of airborne volcanic matter into jet turbines may cause harm by (1) abrasion of engine parts, (2) destabilisation of the fuel/air mix and its dynamics and (3) by melting and sintering ash onto engine parts. To investigate the behaviour of volcanic ash upon reheating, we have performed experiments at ten temperature steps between 700 and 1600°C on (1) fresh volcanic ash from the final explosive phase of the 2010 Eyjafjallajökull (EYJA) eruption and (2) two standard materials used in ingestion tests in the history of turbine testing (MIL E 5007C test sand, MIL; Arizona Test Dust, ATD). We confirm expected large differences in the samples’ response to thermal treatment. We quantify the physical basis for these differences using thermogravimetry and differential scanning calorimetry. Glassy volcanic ash softens at temperatures that are considerably lower than those required for crystalline silicates to start to melt. We find that volcanic ash starts softening at temperatures as low as 600°C and that complete sintering takes place at temperatures as low as 1050°C. Accordingly, the ingestion of volcanic ash in the hot zone of turbines will rather efficiently transform the angular volcanic particles into sticky droplets with a high potential of adhering to surfaces. These experiments demonstrate both a large variability in the material properties of ash from Eyjafjallajökull volcano and a strong contrast to the behaviour of the test sands. In light of these differences, the application in volcanic crises of models of the impact of ash on operability of passenger jet turbines that have been based on test sand calibrations must be re-evaluated. We stress as well that ingestion tests should not only investigate the turbine’s response to ash concentration (g/m3) but also to ash dosage.

Highlights

IntroductionThe civil aviation authorities have primarily been concerned with localised ash plumes (Guffanti et al 2010)
For many years, the civil aviation authorities have primarily been concerned with localised ash plumes (Guffanti et al 2010)
Constraining the impact of volcanic ash on the operational reliability of passenger turbines is difficult because many important parameters are highly variable due to natural and/or engineering reasons: 1) Volcanic ash composition, 2) glass fraction (Kennedy and Russell 2012), 3) interstitial melt/bulk rock composition, 4) ash concentration, 5) grainsize distribution at turbine inlet, 6) air flow speed inside a turbine, 7) temperature inside a turbine, 8) maximum pressure inside a turbine, 9) degree of grainsize reduction inside the turbine and 10) dominant grainsize in the hot zone of the turbine

Summary

Introduction

The civil aviation authorities have primarily been concerned with localised ash plumes (Guffanti et al 2010). Eyjafjallajökull eruption, the combination of eruption duration, meteorological situation and area of airspace closure lead to substantial economic loss, which was not restricted to airline and airport companies (Budd et al 2011) and affected industrial activities and goods production. The increasing duration of airspace closure and the consequent magnitude of economic loss and logistical problems created an increasing reticence towards the imposed flight ban on the part of the airline and cargo companies. While in-flight ash detection is still a complicated task (Prata and Tupper 2009), airspace contamination by volcanic ash at the time of the Eyjafjallajökull eruption was confirmed for large areas of Europe by direct sampling (Schumann et al 2011) or LIDAR measurements (Wiegner et al 2012). The apparent problem of visual detection of volcanic ash (Weinzierl et al 2012) stimulated a change in terminology and was implemented in the latest ICAO (2013) working paper (IAVWOPSG/7-WP/17)

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Conclusion