To optimise the operation of gas turbine combustors with respect to emission, cycle efficiency and components lifetime, increased attention has to be attributed to diagnostic techniques and more flexible control schemes. Chemiluminescence is an obvious choice and a relatively easy and low cost option for such a diagnostic tool. Application examples include spectral analysis and light intensity scaling, temporal analysis studying flame dynamic effects and imaging techniques resolving spatial distribution of heat release zones, as well as combinations of the methods like phase matched imaging and tracking of ignition kernels using high speed imaging. Further fundamental work should be triggered on the nature for the excited species and their formation pathways as well as their connection to heat release and the NO x formation processes.

This paper deals with a detailed thermoacoustic assessment of an annular reheat combustor. Extensive tests have been conducted in the GT26 Test Power Plant in Switzerland. To this end, the combustion chamber has been instrumented with advanced pulsation sensors, an optical probe, strain gauges and accelerometers. A large number of dynamic pressure sensors recorded the acoustic pressure wave propagations in the axial and circumferential directions over a very large frequency range. A modal analysis technique has been developed to extract the acoustic mode shapes from the experimental data. This technique allows for decomposition in standing and traveling waves, hence revealing the nature of the acoustic field. The extracted mode shapes showed a very good agreement with results from 3-d finite element calculations. Combustion stability has been quantified by a methodology that extracts pulsation growth rates from experimental data. This novel method relies on advanced statistic processing of the instantaneous pulsation amplitudes. It has the advantage that it is insensitive to probe location, which is of particular advantage for high frequencies (higher than 1 kHz).

The capability to switch online from a main to a back-up fuel is a necessity for dual fuel gas turbines. The switching procedure is itself challenging; fuel gas, fuel oil and supporting systems need to be operated in parallel, with the safe start-up and shut-down of each system having to be ensured. Additionally, the requirements of gas turbine and combined cycle have to be considered; with the target to provide fast reliable fuel switching, without a major effect on the power output. Alstom’s GT26/GT24 High Load Fuel Switchover (HLFSW) fulfils these requirements. HLFSW is a concept which allows switching back and forth between fuel gas and fuel oil in the load range of base load down to 60 % relative GT load. A key feature of the HLFSW is the stable load during the complete duration of the fuel switchover process, ensuring nearly constant power output in combined cycle mode from the moment the fuel switchover is triggered until standard operation is achieved on the secondary fuel. In this paper the integration of the HLFSW into the engine operation concept is presented. It is shown, how the sequential combustion of the Alstom GT26/GT24 is transferred from primary to secondary fuel by sequential fuel switchover. The focus is on how the high load fuel switchover concept is embedded into the gas turbine’s engine operation concept, allowing a smooth transfer between the fuel gas standard operation concept and the fuel oil standard operation concept and vice-versa, resulting in a fuel switchover concept without any significant disturbances to the heat recovery steam generator (HRSG).