Method for monitoring a starting sequence of a turbomachine and monitoring system implementing said method

A method for monitoring a starting sequence of a turbomachine comprising a compressor provided with a rotor, a starter capable of rotating the rotor and a combustion chamber wherein a mixture of air and fuel is ignited by an ignition device, the method comprising:

• acquiring a measurement signal of an engine speed of the rotor during the starting sequence;
• determining a bracketing of a time zone during which an ignition instant takes place, the bracketing being defined by a lower limit corresponding to a first event necessarily taking place before an ignition instant and an upper limit corresponding to a second event necessarily taking place after the ignition instant;
• and
• determining, between the lower limit and the upper limit, a break point in a variation with time of the measurement signal, said break point corresponding to the ignition instant of the air-fuel mixture in the combustion chamber,
• determining a break point in the variation with time of the measurement signal comprising:
• a) determining a sliding window which is displaced between the lower limit and the upper limit,
• b) dividing the sliding window into a first half-window and a second half-window, each one of the first half-window and the second half-window containing a portion of the measurement signal corresponding to a curve portion,
• c) approximating each curve portion by a separate polynomial and determining a dominant coefficient of each one of the curve portions,
• d) comparing the dominant coefficient of the curve portion of the first half-window with the dominant coefficient of the curve portion of the second half-window, and
• e) reiterating steps b)-d) until the sliding window has slid over an entire length of the time zone, and then identifying a half-window from the first and second half-windows of which the two dominant coefficients are the most different, said half-window containing the break point in the variation with time of the measurement signal.