One of the most crucial problems in aviation is related to the stall and surge processes in engines. These irregular nonlinear variations of the pressure in an engine compressor often lead to its complete destruction, fire and aircraft damage. The pressure sensors' signals from an aircraft engine were analyzed by the wavelet methods developed by this group. For the first time, the precursors of the stall and subsequent surge processes were found. Their time separation from the stall onset is long enough (about 1 sec or more) to apply them in engine control systems, which would prevent possible engine damage (for both in-flight and on-earth conditions). The work was performed in collaboration with Central Institute for Aviation Motors. The same method is also effective for engines of other types, e.g., pumps, automotors, hydroturbines etc.

The complicated red curve describes pressure variation in the compressor. The dispersion of wavelet coefficients at the fifth level (green dotted line) shows a remarkable drop about 2 sec prior to the surge. For purely statistical fluctuations, no precursor appears as shown by the blue dotted line.

Precursor figure.