Method for the monitoring of a degree of coking at seals by a gas generator shaft

1. A method for monitoring a degree of coking at dynamic seals of a turbine engine comprising:

a gas generator comprising a rotary shaft and an injection wheel mounted on said rotary shaft, the injection wheel being adapted for spraying fuel by centrifugation, and

an injection manifold, adapted for conveying fuel as far as the injection wheel,

the dynamic seals adapted for ensuring a seal between the injection wheel and the injection manifold,

wherein the method comprises the steps of:

measuring, during a self-rotation phase of the turbine engine, a speed of rotation of the rotary shaft,

determining, from the time-dependent change of the thereby measured speed of rotation, a degree of coking at the dynamic seals, and

selectively performing maintenance on the turbine engine based on the determined degree of coking at the dynamic seals.

2. The monitoring method according to claim 1 , wherein the step for determining the degree of coking at the dynamic seals comprises a measurement of deceleration of the rotary shaft between two speeds of rotation of the rotary shaft.

3. The monitoring method according to claim 2 , wherein the measurement of deceleration is conducted between a first speed between 1,000 and 2,500 revolutions per minute, and a second speed between 500 and 1,000 revolutions per minute.

4. The monitoring method according to claim 2 , wherein the determination of the degree of coking at the dynamic seals comprises one of the steps from among the following group:

comparing the deceleration of the rotary shaft with a predetermined threshold,

determining a difference between the deceleration and an initial deceleration of the turbine engine between the two speeds of rotation of the rotary shaft, and comparing the difference with a predetermined threshold, and

determining a change rate associated with said deceleration depending on the use of the turbine engine, and comparing said change rate with a predetermined threshold.

5. The monitoring method according to claim 1 , applied in a turbine engine further comprising a starter, the method further comprising the steps:

measuring during a phase for initiating a rotation of the rotary shaft by the starter upon starting the turbine engine, a current flowing through the starter and a voltage on terminals of the starter,

determining, from the measured current and voltage, a representative datum of a resistive torque of the rotary shaft of the gas generator.

6. The monitoring method according to claim 5 , wherein the step for determining the degree of coking at the dynamic seals is achieved from the time-dependent change in the speed of rotation of the rotary shaft of the gas generator and from a value of the representative datum or time-dependent change in the representative datum of a resistive torque of the rotary shaft depending on the use of the turbine engine.

7. A system for monitoring a coking condition at the dynamic seals of the turbine engine comprising:

the gas generator, comprising the rotary shaft and the injection wheel mounted on said rotary shaft, the wheel being adapted for spraying fuel by centrifugation,

the injection manifold, adapted for conveying fuel as far as the injection wheel, and

the dynamic seals, adapted for ensuring the seal between the injection wheel and the injection manifold,

the monitoring system being adapted for applying the method according to claim 1 and comprising:

at least one sensor for the speed of rotation of the rotary shaft of the gas generator, adapted for carrying out acquisitions at a frequency greater than or equal to 2 Hz, and

a processing unit, including a memory and processing means adapted for processing the acquisitions of the speed of rotation in order to determine the degree of coking at the dynamic seals.

8. The monitoring system according to claim 7 , wherein the turbine engine further comprises a starter, the monitoring system further comprising at least one device for measuring a voltage on terminals of the starter and the current flowing through the starter, said at least one device being adapted for acquiring voltage and current measurements at a frequency greater than or equal to 10 Hz.

9. The turbine engine, comprising:

the gas generator, comprising the rotary shaft and

the injection wheel mounted on said shaft, the wheel being adapted for spraying fuel by centrifugation,

the injection manifold, adapted for conveying fuel as far as the injection wheel, and

the dynamic seals, adapted for ensuring the seal between the injection wheel and the injection manifold, wherein the turbine engine further comprises the monitoring system according to claim 7 .