Alstom’s combustion development on the EV burner concept has taken another step forward with the introduction of a staged premix system, which allows even lower NOx values also at lower part load values compared to the pilot/premix EV burner. The development target was achieved by introducing one fuel stage over the conventional EV fuel lance, while other fuel stage is realized with a gas hole injection pattern over the EV air slots, similar to the conventional EV burner system. Due to this no major design modifications for the EV burner system were required, and the new system is fully retrofittable to the existing GT26 gas turbine engines including the existing fuel distribution system. The final design is a result of a step-by-step development. In a first step, variants defined in a feasibility study by CFD calculations indicated that a staged fuel gas injection over the fuel lance could substitute a part of the conventional premix gas injection. The water tunnel tests results performed with the LIF measurement technique demonstrated the improved mixing properties of the staged EV burner in the burner flow field. With a single burner test facility under atmospheric pressure conditions the broad operating range of the staged EV burner system could be confirmed. The single burner tests allowed investigation of the low NOx operating range for the burner system also with respect to flame generated instabilities. Finally the burner system was validated with gas turbine engine tests at the Alstom GT Test Power Plant in Birr, Switzerland, which demonstrated the excellent combustion performance of the staged EV burner system derived by the development procedure.

The ALSTOM low emission swirl-induced premix EV-burner is investigated by OH-planar laser induced fluorescence (PLIF) and OH*-chemiluminescence (CL) imaging on a full-scale industrial burner test rig. Three different burner variants have been compared by their flame shape and position as well as emission and pulsation behavior. The flame images have been used to enable comparison and validation of thermoacoustic and computational fluid dynamics (CFD) models. The flame movement upstream inside the burner can be related to emissions and pulsation. Depending on the burner two different mechanisms dominate the acoustic pulsations: One is based on equivalence ratio fluctuations coupled to a sudden displacement of flame anchoring point into the burner. Another mechanism seems to be related to turbulence intensity fluctuations. The experimental images were compared with the results of Reynolds-averaged Navier-Stokes (RANS) CFD simulations for varying parameters for validation. The turbulence treatment in time-averaged RANS models is not sufficient to describe the flame movement properly and encourages to apply a more sophisticated treatment like LES, which is capable of describing bi stable behavior.

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We report on specific heat determinations of 99.9999% pure gallium applying an optical A.C. method. Data were taken with a temperature resolution, relative to the melting point T,, of 2 mK, starting from 1.5 K below T, and proceeding across the melting transition. The specific heat which was derived from amplitude and phase measurements, increases below the nominal melting point. The implication of these findings is discussed.

Gaseous unburned hydrocarbons (UHC) are investigated in an atmospheric pressure combustor with premixing and prevaporization. The rectangular combustion chamber is equipped with silica quartz windows allowing laser-based investigations in the UV regime. A new double shell concept is employed to atomize the fuel (n-heptane) and to stabilize the flame. For the detection of UHC, a tuneable ArF (λ ≈ 193 nm) or KrF (λ ≈ 248 nm) excimer laser is used. The results show that this imaging technique is feasible in an atmospheric pressure, liquid fuelled combustor. Liquid and gaseous fuel is detected inside the vortices induced by the double shell, where the main combustion processes occur. Furthermore, droplets and UHC can be found along the symmetry line of the double shell. Comparing the two approaches used for the visualization of UHC, it turns out that the application of a KrF laser seems to be more suitable.