RuAviation

More than a thousand active volcanoes are registered on our planet, which, in the event of an eruption, pose a serious threat to air transport. Volcanic ash emissions into the atmosphere create vast clouds that affect aircraft, damaging their fuselages and aerodynamic surfaces. Furthermore, the ingestion of ash into engines is a significant risk factor. The accumulation of ash particles on the turbine nozzle guide vanes can lead to a critical reduction in the volume of air entering the turbine, and consequently to compressor surge, followed by engine shutdown.

Numerical modelling of the processes occurring inside an engine when volcanic ash is ingested is being carried out by specialists at JSC UEC-Aviadvigatel in conjunction with Perm National Research Polytechnic University. As part of the research, assessments have been made of the volumes of high-temperature zones where ash particles can transition to a liquid phase, posing the greatest danger. The data obtained provides a better understanding of the mechanisms of ash impact on the operational capability of aero engines. Such research contributes to enhanced flight safety.

“The accumulation of vitreous ash deposits on the nozzle guide vanes leads to a reduction in the flow passage area, which contributes to the occurrence of compressor surge, which is not a normal operating mode for the engine. In 1989, a Boeing 747 encountered an ash cloud from the Redoubt volcano, which led to the shutdown of all four engines due to the accumulation of ash particles. It was only thanks to the professionalism of the pilots that disaster was averted. Such events make the study of this issue extremely relevant,” the Polytechnic stated.

When ash particles enter the engine’s combustion chamber, they are exposed to high temperatures, reaching 1400 °C, causing them to melt. The ash then cools and crystallises on the nozzle guide vanes, forming deposits that reduce the clearances between the blades. The reduction in the flow passage area leads to a loss of gas-dynamic stability of the compressor, and subsequently to engine failure. These physical and mechanical processes require a thorough study of the impact of volcanic ash on the various engine operating modes.

According to Diana Popova, an engineer at JSC UEC-Aviadvigatel and a postgraduate student at the Aviation Engines department of Perm Polytechnic, numerical modelling of thermophysical processes in the combustion chamber of the PD-14 engine, conducted at three operating conditions – cruise, rated, and idle – showed different volumes of ash melting zones.

“The volume of high-temperature zones in cruise mode exceeds 54%, in rated mode it exceeds 81%, and in idle mode it does not exceed 25.3%. This indicates the need to reduce the engine operating mode when encountering volcanic ash clouds to minimise the impact,” commented Diana Popova.

The research findings confirm the ICAO recommendations on the need to reduce engine thrust to idle power when encountering volcanic ash clouds and the need to leave the ash cloud by reversing course. The use of rated power to fly over a cloud is unacceptable due to the high risk of engine failure.

In 2021, CIAM carried out tests on the PD-14 engine’s gas generator with volcanic ash. In accordance with the test program, the flight conditions of an aircraft in cruise mode for one hour were simulated. Ash from the Kamchatka Shiveluch volcano was used for the tests. One hour of the PD-14 being in the aggressive environment did not lead to any changes in its characteristics. The power plant, developed by Perm’s UEC-Aviadvigatel, confirmed its safety when flying through an ash cloud.

“Ash was fed into the gas generator and the engine’s behaviour was observed. After this, the engine was completely disassembled and the impact of volcanic deposits on the components was assessed. The ash did not have a significant impact on the elements of the flow path,” CIAM stated at the time about the progress of the tests.