Assessment and Characterization of Volcanic Ash Threat to Gas Turbine Engine Performance

Abstract

Multiple volcanoes erupt yearly propelling volcanic ash into the atmosphere and creating an aviation hazard. The plinian eruption type is most likely to create a significant aviation hazard. Plinian eruptions can eject large quantities of fine ash up to an altitude of 50,000 m (164,000 ft). While large airborne particles rapidly fall, smaller particles at reduced concentrations drift for days to weeks as they gradually descend and deposit on the ground. Very small particles, less than 1 μm, can remain aloft for years. An average of three aircraft encounters with volcanic ash was reported every year between 1973 and 2003. Of these, eight resulted in some loss of engine power, including a complete shutdown of all four engines on a Boeing 747. However, no crashes have been attributed to volcanic ash. The major forms of engine damage caused by volcanic ash are: (1) deposition of ash on turbine nozzles and blades due to glassification (2) erosion of compressor and turbine blades (3) carbon deposits on fuel nozzles. The combination of these effects can push the engine to surge and flame out. If a flame out occurs, engine restart may be possible. Less serious engine damage can also occur. In most cases the major damage will require an engine overhaul long before the minor damage becomes an operational issue, but under some conditions no sign of volcanic ash is evident and the turbine cooling system blockage could go unnoticed until an engine inspection is performed. Several organizations provide aircrew procedures to respond to encounters with a volcanic ash cloud. If a volcanic ash encounter is suspected, then an engine inspection, including borescope, should be performed with particular attention given to the turbine cooling system.

Adhesion of Volcanic Ash Particles under Controlled Conditions and Implications for Their Deposition in Gas Turbines

“…Such particles may melt, or at least soften, in flight, making it more likely that, if they strike solid surfaces within the turbine, they will adhere to them on impact. Ongoing increases in turbine entry temperature clearly raise the danger of this happening and there is particular concern about volcanic ash [1][2][3][4][5][6], which often has a relatively low softening temperature [4,7,8].…”

Assessing the magnitude of volcanic risk to global shipping

“…This can result in erosion of blades and other engine components, deposition of glass which restricts airflow, and the deposition of carbon on the fuel nozzles (Davison and Rutke 2014). These all result in outcomes ranging from changes in engine efficiency, to a requirement for maintenance or complete overhaul, through to engine shutdown (Chen and Zhao 2015; Wylie et al 2017;Vogel et al 2019).…”

High-Temperature Solid Particle Erosion of Aerospace Components: Its Mitigation Using Advanced Nanostructured Coating Technologies

“…In particular, Plinian eruptions can release large quantities of fine ash particles up to an altitude of 164,000 ft. Even though the large particles reach the ground rapidly due to gravity, the smaller particles stay and drift for days to weeks before reaching the ground [50]. Unlike sand, volcanic ash is usually composed of small, sharp pieces of rocks, minerals, and glass with a size in the range of 0.001 to 2 mm in diameter.…”

“…Acids such as HCl and HF dissolve in water and result in acid rain, whereas maximum SO 2 gradually converts into sulphuric acid (H 2 SO 4 ) aerosols. These aerosol droplets can be absorbed by the volcanic ash particle surfaces, which are hard, extremely abrasive, and mildly corrosive [7,[50][51][52]. When volcanic ash enters the aircraft engine, two phenomena simultaneously occur in the cold and hot sections of the engine.…”