Readings on Specific Gas Turbine Flame Behaviours Using an Industrial Combustion Monitoring System

The new energy mix places greater demands on power gas turbine operation; precision combustion monitoring, therefore has become a major issue. Unforeseen events such as combustion instabilities can occur and represent a danger to the integrity of the hot parts and also lead to a limitation of the output power. This is usually accompanied by an increase in maintenance costs. The enlarged off-design operating envelope of gas turbines to adapt to a fast-changing grid has made this issue even more acute, necessitating an expansion of the operating envelope into areas that were — for many engines — not foreseen in the original combustor design process. A good understanding of what happens within the gas turbine combustor is crucial. Complex and costly full-field measurements such as laboratory optical instrumentation in precision combustion diagnostics are not suitable for permanent fleet deployment. For practical and financial reasons, the monitoring should ideally be achieved with a limited amount of discrete sensors. If installed and interpreted correctly, fast response measurement chains could lead to a better gas turbine combustion management, possibly yielding considerable savings in terms of operating and maintenance costs. The firm Meggitt Sensing System (MSS), assisted by Combustion Bay One (CBOne), initiated an applied research programme dedicated to this topic — with MSS providing the instrumentation and CBOne providing the facility and test conditions. The objective was to investigate realistic combustion phenomena in a precisely controlled and reproducible way and to document the individual readings of the heat-resistant fast pressure transducers mounted on the combustor casing, as well as the accelerometers mounted on the outer surface of the machine. Particular attention was paid to the correlation between these two types of sensor readings. This paper reports on the monitoring of the flame using piezoelectric dynamic pressure sensors and accelerometers in a number of different situations that are relevant to the safe and efficient operation of gas turbines. Discussed are single events such as flame ignition, lean blow-out and flash-back, as well as longer test sequences observing the effect of warming-up or the presence of flame instability. The measurement chains and processing techniques are discussed in detail. The atmospheric test rig used for this purpose and the different testing configurations required for each of these situations are also illustrated in detail. The results and recommendations for their implementation in an industrial context conclude this paper.