Method of monitoring a gas turbine engine
Operation of gas turbine engines and in particular gas turbine engines utilised for aircraft, in an efficient manner is a desired objective. Thus engine efficiency is typically determined through use of an engine performance parameter. One such engine performance parameter is with regard to specific fuel consumption. However, such parameters may vary as a result of inherent deterioration with regard to the engine. By utilising a computational model to determine variations in the performance parameter such as the specific fuel consumption changes as a result of such inherent engine degradation can be accommodate. Thus, such degradation may not swamp actual changes in fuel consumption or the engine performance parameter which are indicative of changes of engine efficiency. Generally and initially, computational results are utilised in order to provide a value with regard to degradation changes in the performance parameter, but such changes may be augmented by practical test results in order to tune the off-set constants a, b for an individual engine.
1. A method of monitoring a gas turbine engine performance parameter at a predetermined power setting for the engine as a determinant of engine efficiency, the method characterized in that a value for the engine performance parameter is adjusted for operational deterioration in the performance parameter, the value for the change in the parameter is given by a relationship:
S=(a×change in the parameter at core constant pressure ratio)+(b×change in the parameter at by-pass pressure ratio);
whereby a and b are constants determined for a specific engine type by analysis through a computer model of the specific engine with the steps of:
a) Determination of engine performance parameter values using a computer model with deterioration assumed only in the low pressure system for the engine to provide a low data set;
b) Determination of engine performance parameter values using a computer model with deterioration assumed only in the core pressure system for the engine to provide a core data set;
c) Determination of engine performance parameter values using a computer model with deterioration assumed in all pressure systems for the engine to provide a combined data set;
d) Scaling the low data set, the core data set and the combined data set to an equivalent of a predetermined value of deterioration in the value of S and plotting a relational variation for the relative changes in parameters due to the low pressure system and the core pressure system; and
e) Comparing the relative changes in the parameters due to the low pressure system and the core pressure system as solutions for the constants a, b in the relationship above through use of simultaneous equation analysis and solution of the respective relational variations;
thereby determining engine deterioration and subsequently improving the engine's operational efficiency.
2. A method as claimed in claim 1 wherein the core system further comprises a high pressure system and, where present, an intermediate pressure system of a gas turbine engine.
3. A method as claimed in claim 1 wherein the respective pressure systems include fan and turbine combinations in the gas turbine engine.
4. A method as claimed in any of claim 1 wherein the predetermined value of deterioration is above 0.1%.
5. A method as claimed in claim 1 wherein the low, core and combination data sets are determined by the same computational model or an aggregate of results from a plurality of computational models for each data set.
6. A method as claimed in claim 1 wherein the data sets are combined with test results for determination of engine performance parameters with regard to the engine.
7. A method as claimed in claim 6 wherein the data sets are augmented with in-service operational test results for the engine performance parameters.
8. A method as claimed in claim 1 wherein the engine performance parameter is any one of specific fuel consumption, pressure, temperature and shaft speed.