GE Oil&Gas has recently launched a new heavy-duty gas turbine, the MS5002E, which underwent an extensive theoretical and experimental study on fuel flexibility. Today, fuel flexibility is one of the most challenging requirements in the Oil&Gas market. The fuel flexible operation demands a wide variety of assessments, ranging from rig tests of the combustor to theoretical consolidation of the results. The present paper describes the used methodology to increase the capabilities of burning diverse gaseous fuels, at fixed geometry. It analyzes all factors affecting the operation of the combustor with the goal to identify and extend the boundaries. Such boundaries are a result of multiple variables, like resistance to flashback and autoignition, emissions, pressure pulsations and capability of igniting. Flashback is when the reaction velocity overtakes the flow velocity and the flame moves back to the fuel injection points, threatening the integrity of the hardware. The resistance of the MS5002E to flashback and flame holding was evaluated by performing extensive experiments on a single fuel nozzle. Flame holding test results were then used to develop a transfer function for the prediction of the flame holding behavior of different mixtures. Another variable of interest is the resistance to autoignition: MS5002E took advantage of previously defined transfer functions from GE Energy that estimate the temperature above which a given mixture is likely to autoignite, at fixed pressure. Since the MS5002E is a DLN machine, it was also necessary to exclude the possibility of lean-blow-out in the whole operating range: dedicated tests on a single-can basis were used for this scope. Emissions and pressure pulsations were extensively measured on a single-can basis, since these parameters are fundamental for a lean premixed combustor. For particular mixtures, like those with high content of inert gases, the capability of igniting repeatably and reliably is an additional requirement that needs experimental validation. The combination of all the aforementioned variables determines the composition limit of the fuel mixture that the machine can tolerate. As a result of all the assessment, it was possible to achieve an increase in the maximum allowable concentrations for the following constituents: propane (up to 20%), nitrogen (up to 20% with no modifications to the control algorithms; up to 25% with minor modifications to the control algorithms) and hydrogen (up to 5%). Future tests will deliver increased capabilities also for ethane and butane.

Pratt & Whitney is developing a 107 kN (24,000 pound) thrust PW6000 engine for the 100-seat aircraft market. The combustor for this engine has been designed by combining the TALON emissions concept demonstrated on the PW4000 engine family with an advanced CFD-based analysis system to optimize the combustor exit temperature distribution. The design objective is to provide a low cost highly reliable engine, which produces low emissions. This paper is the second of two parts, which describe an advanced CFD-based analysis system used to optimize the combustor exit temperature distribution for turbine life. The analysis system applied the identical Allstar solver, which is described and validated in part I, to the PW6000 combustor. All calculations in this paper were completely predictive in nature. The effect of dilution hole pattern changes on the exit temperature profile was determined by solving the flowfield from the prediffuser inlet to the combustor exit. Results from the study were used to understand the physical processes taking place inside the prediffuser and combustor that impact the exit temperature profile and from this understanding a hole pattern configuration was identified. Full annular rig measurements of the pressure drop and airflow distribution throughout the model along with exit temperature profile measurements agreed very well with CFD predictions. A second target exit temperature profile was defined based upon engine testing and the analysis tool demonstrated the ability to define a second dilution hole pattern that met the target profile to optimize turbine life. An annular rig test again confirmed the CFD predictions. Parametric studies were also performed on the prediffuser inlet pressure profile to predict how the turbine inlet temperature profile would change. These studies were used to desensitize the combustor temperature profile to prediffuser inlet profile changes that may occur over the life of the engine. The predictive capability of this CFD-based analysis tool has significantly reduced experimental development costs and has optimized the combustor exit temperature profile to meet PW6000 design objectives.

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Due to the substantial increase in sources of gas, natural gas interchangeability is a key subject in the industry today. The extensive pipeline network means that natural gas arriving at appliances, boilers, burners and power plant turbines could come from anywhere. Fuel compositions vary from one source to another. Moreover, most recently, Liquefied Natural Gas has emerged as a major source and the composition of gas derived from LNG substantially differs from the natural gas one. In Dry Low NOx (DLN) systems, those changes in fuel composition can cause dangerous increase in combustion dynamics and can also affect the NOx emissions of the machine. Therefore, in order to meet the growing market demand for gas turbine combustors able to tolerate significant alterations in fuel composition, a system capable of burning gases with differing and variable over time Wobbe Indexes was developed. This innovative system does not involve any combustion hardware modifications. It allows the use of a premixed combustion system that complies with emissions, reliability, and safety, even when burning a fuel that is distinctly different from the original design gas. In particular, the system was developed in order to meet the requirements of a customer for burning any continuously and slowly varying mixture of two fuel gases, whose Wobbe Indexes difference is up to 25%. Since the burner is designed for 100% of the gas with lower Wobbe Index, the gas that has a higher WI needs to be heated, in order to achieve a target Modified Wobbe Index; the same happens for any mixture of the two gases. The system is based on a closed loop control on the Modified Wobbe Index of the fuel. Two turbine control gas chromatographs, located upstream the combustor inlet, measure the gas characteristics (LHV, specific gravity and temperature) and calculates the MWI. If it is different from the target one, it is corrected by modifying the temperature set point of a heat exchanger. The hardware is completed with one more plant gas chromatograph, located upstream the heat exchanger, for evaluating the fast and complete switch from one gas to the other one. In addition to the normal operation, that is with the 100% Lower Wobbe Index gas (L) or 100% Higher Wobbe Index gas (H) or any continuously and slowly varying mixture of these two gases, the system allows both the black and the normal start, the complete switch back and forth between 100% L gas and 100% H gas and load sheds and rejection. Moreover the two gases can be burned in diffusion combustion mode, as available, without requiring any increase in temperature, with no limitation from firing to full load. The capability of the system to adjust to all of the previously described events, potentially dangerous and damaging for the Gas Turbine combustion system, makes it suitable for applications that burn different lots of gases coming from different LNG sources, since it allows the turbine to accommodate the differences in Wobbe Index, due to various gas lots on a pipe line.

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