| 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.
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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Gas Turbine
combustion diagnostics system 
