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Gas Turbine combustion diagnostics system

Why combustion diagnostics?

Gas turbine performance is very sensitive to turbine entry temperature (TET). Every endeavour is made by gas turbine manufacturers to increase TET because it improves engine performance. However turbine life is also sensitive to TET. For example - running a gas turbine operating at peak conditions results in a significant loss in creep life, typically half the base rating creep life. Poor combustion can give rise to an uneven radial temperature spread resulting in hot spots. Such damage can seriously damage the hot end components of an engine, resulting in unscheduled down time and increased maintenance costs. Clogged or loose fuel nozzles are the main causes of combustion problems and can give rise to severe burning problems in the hot end components.

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The above illustrates the damage to Nozzle Guide Vanes due to combustion problems

Detection of combustion problems

Monitoring the Exhaust Gas Temperature spread (EGT Spread) is a good means of detecting combustion problems. However most system do not give alarms or display expected EGT spread profiles and often miss the onset of damage resulting from combustion problems.

Means of overcoming the problem using the XCOMB program

XCOMB achieves this by not only plotting the spread but also displaying the deviation from the mean value, raising alarms when the EGT spread exceeds an alarm limit for deviation (typically ± 50 degrees from the mean EGT value). In addition, the expected spread is also plotted enabling the user to detect the onset of combustion problems by comparing the expected EGT spread with the actual EGT spread


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