Fuel Influence on Targeted Gas Turbine Combustion Properties: Part I — Detailed Diagnostics

The threshold combustion performance of different fuel formulations under simulated altitude relight conditions were investigated in the altitude relight test facility located at the Rolls-Royce plc. Strategic Research Centre in Derby, UK. The combustor employed was a twin-sector representation of an RQL gas turbine combustor. Eight fuels including conventional crude-derived Jet A-1 kerosene, synthetic paraffinic kerosenes (SPKs), linear paraffinic solvents, aromatic solvents and pure compounds were tested. The combustor was operated at sub-atmospheric air pressure of 41 kPa and air temperature of 265 K. The temperature of all fuels was regulated to 288 K. The combustor operating conditions corresponded to a low stratospheric flight altitude near 9 kilometres. The experimental work at the Rolls-Royce (RR) test-rig consisted of classical relight envelope ignition and extinction tests, and ancillary optical measurements: Simultaneous high-speed imaging of the OH* chemiluminescence and of the soot luminosity was used to visualize both the transient combustion phenomena and the combustion behaviour of the steady burning flames. Flame luminosity spectra were also simultaneously recorded with a spectrometer to obtain information about the different combustion intermediates and about the thermal soot radiation curve. This paper presents first results from the analysis of the weak extinction measurements. Further detailed test fuel results are the subject of a separate complementary paper [1]. It was found in general that the determined weak extinction parameters were not strongly dependent on the fuels investigated, however at the leading edge of the OH* chemiluminescence intensity development in the pre-flame region fuel-related differences were observed.

Modelling of Thermoacoustic Combustion Instabilities Phenomena: Application to an Experimental Rig for Testing Full Scale Burners

This paper concerns the acoustic analysis of self–sustained thermoacoustic pressure oscillations that occur in a test rig equipped with full scale lean premixed burner. The experimental work is conducted by Ansaldo Energia and CCA (Centro Combustione Ambiente) at the Ansaldo Caldaie facility in Gioia del Colle (Italy), in cooperation with Politecnico di Bari. The test rig is characterized by a longitudinal development with two acoustic volumes, plenum and combustion chamber, coupled by the burner. The length of both chambers can be varied with continuity in order to obtain instability at different frequencies. A previously developed three dimensional finite element code has been applied to carry out the linear stability analysis of the system, modelling the thermoacoustic combustion instabilities through the Helmholtz equation under the hypothesis of low Mach approximation. The heat release fluctuations are modelled according to the κ-τ approach. The burner, characterized by two conduits for primary and secondary air, is simulated by means of both a FEM analysis and a Burner Transfer Matrix (BTM) method in order to examine the influence of details of its actual geometry. Different operating conditions, in which self–sustained pressure oscillations have been observed, are examined. Frequencies and growth rates of unstable modes are identified, with good agreement with experimental data in terms of frequencies and acoustics pressure wave profiles.

Broadband Combustion Noise Prediction With the Fast Random Particle Method

A new highly efficient, hybrid CFD/CAA approach for broadband combustion noise modeling is introduced. The inherent sound source generation mechanism is based on turbulent flow field statistics, which are determined from reacting RANS calculations. The generated sources form the right-hand side of the linearized Euler equations for the calculation of sound fields. The stochastic time-domain source reconstruction algorithm is briefly described with emphasis on two different ways of spatial discretization, RPM (Random Particle Method) and the newly developed FRPM (Fast RPM). The application of mainly the latter technique to combustion noise (CN) prediction and several methodical progressions are presented in the paper. (F)RPM-CN is verified in terms of its ability to accurately reproduce prescribed turbulence-induced one- and two-point statistics for a generic test and the DLR-A jet flame validation case. Former works on RPM-CN have been revised and as a consequence methodical improvements are introduced along with the progression to FRPM-CN: A canonical CAA setup for the applications DLR-A, -B and H3 flame is used. Furthermore, a second order Langevin decorrelation model is introduced for FRPM-CN, to avoid spurious high frequency noise. A new calibration parameter set for reacting jet noise prediction with (F)RPM-CN is proposed. The analysis shows the universality of the data set for 2D jet flame applications and furthermore the method’s accountance for Reynolds scalability. In this context, a Mach number scaling law is used to conserve Strouhal similarity of the jet flame spectra. Finally, the numerical results are compared to suitable similarity spectra.

Analysis of Turbulent Swirling Flow in an Isothermal Gas Turbine Combustor Model

Isothermal turbulent swirling flow in a model combustor is computationally and experimentally investigated. The main purpose was the validation of turbulence models for this flow type. The experiments were carried out at the German Aerospace Centre (DLR), Stuttgart. For the modeling, the validation of the LES approach, applying the Smagorinsky subgrid-scale model, using wall-functions, takes a central role in the present study. URANS calculations based on SST and RSM were also performed. An analysis for LES showed that a sufficient resolution is indeed obtained for grid index values proposed in the literature. It was also observed that coarser grids can still deliver useful results. LES results were observed to be quite accurate, except the swirl velocity in the outer parts of the jet, which was under-predicted. URANS results were not that good, whereas the RSM performed better than the SST, especially in predicting the swirl velocity in the outer parts. An investigation performed on different domain sizes indicated that the outlet boundary formulation has some influence on the prediction of the upstream flow. The influence of the differencing scheme on LES was also investigated.

Performance of Multiple-Injection Dry Low-NOx Combustor on Hydrogen-Rich Syngas Fuel in an IGCC Pilot Plant

Successful development of oxygen-blown integrated coal gasification combined cycle (IGCC) technology requires gas turbines capable of achieving dry low-nitrogen oxides (NOx) combustion of hydrogen-rich syngas for low emissions and high plant efficiency. The authors have been developing a “multiple-injection burner” to achieve the dry low-NOx combustion of hydrogen-rich syngas. The purposes of this paper are to present test results of the multi-can combustor equipped with multiple-injection burners in an IGCC pilot plant and to evaluate the combustor performance focusing on effects of flame shapes. The syngas fuel produced in the plant contained approximately 50% carbon monoxide, 20% hydrogen, and 20% nitrogen by volume. In the tests, the combustor that produced slenderer flames achieved lower NOx emissions of 10.9 ppm (at 15% oxygen), reduced combustor liner and burner plate metal temperatures, and lowered the combustion efficiency at the maximum load. The test results showed that the slenderer flames were more effective in reducing NOx emissions and liner and burner metal temperatures. These findings demonstrated that the multiple-injection combustor achieved dry low-NOx combustion of the syngas fuel in the plant.

Prometheus: A Geometry-Centric Optimization System for Combustor Design

The following paper presents an overview of the Prometheus design system and its applications to gas turbine combustor design. Unlike a traditional “optimizer-centric” method, Prometheus aims to reduce both the level of workflow complexity and rework by taking a more “geometry-centric” approach to design optimization by shifting the control of script generation away from the optimization program to the computer aided design (CAD) package. Prometheus therefore enables significant geometry changes to be automatically reflected in all subsequent scripts necessary for the analysis of a combustor. Prometheus’ current capabilities include automatic fluid volume generation and aero-thermal and thermo-acoustic network generation as well as automatic mesh and computational fluid dynamics (CFD) script generation.

A Comparison of RANS and LES of an Industrial Lean Premixed Burner

LES and RANS simulations of a Siemens scaled combustor are compared against comprehensive experimental data. The steady RANS simulation modeled one quarter of the geometry with 8M polyhedral cells using the SST-k-ω model. Unsteady LES simulations were performed on the quarter geometry (90°, 8M cells) as well as the full geometry (360°, 32M cells) using the WALE sub-grid model and dynamic evaluation of model coefficients. Aside from the turbulence model, all other models are identical for the RANS and LES. Combustion was modeled with the Flamelet Generated Manifold (FGM) model, which represents the thermo-chemistry by mixture fraction and reaction progress. RANS simulations are performed using Zimont and Peters turbulent flame speed (TFS) expressions with default model constants, as well as the kinetic rate from the FGM. The flame speed stalls near the wall with the TFS models, predicting a flame brush that extends to the combustor outlet, which is inconsistent with measurements. The FGM kinetic source model shows improved flame position predictions. The LES predictions of mean and rms axial velocity, mixture fraction and temperature do not show improvement over the RANS. All three simulations over-predict the turbulent mixing in the inner recirculation zone, causing flatter profiles than measurements. This over-mixing is exacerbated in the 900 case. The experiments show evidence of heat loss and the adiabatic simulations presented here might be improved by including wall heat-loss and radiation effects.

Combustion System Development and Testing for MAN’s New Industrial Gas Turbines MGT 6100 and MGT 6200

This paper describes the development and test results of the low emission combustion system for the new industrial gas turbines in the 6–7 MW class from MAN Diesel & Turbo. The design of a robust combustion system and the achievement of very low emission targets were the most important design goals of the combustor development. During the design phase, the analysis of the combustor (i.e. burner design, air distribution, liner cooling design) was supported with different CFD tools. This advanced Dry Low Emission can combustion system (ACC) consists of 6 cans mounted externally on the gas turbine. The behavior and performance of a single can sector was tested over a wide load range and with different boundary conditions; first on an atmospheric test rig and later on a high pressure test rig with extensive instrumentation to ensure an efficient test campaign and accurate data. The atmospheric tests showed a very good performance for all combustor parts and promising results. The high pressure tests demonstrated very stable behavior at all operation modes and very low emissions to satisfy stringent environmental requirements. The whole operation concept of the combustion system was tested first on the single-can high pressure test bed and later on twin and single shaft gas turbines at MAN’s gas turbine test facility. During the engine tests, the can combustors demonstrated the expected combustion performance under real operation conditions. All emissions and performance targets were fully achieved. On the single shaft engine, the combustors were running with single digit ppm NOx levels between 50% and 100% load. The validation phase and further optimization of the gas turbines and the engine components are ongoing. The highlights of the development process and results of the combustor and engine tests will be presented and discussed within this paper.

Effects of Air Jets Through Combustor Liner Holes on Emissions of Lean Staged Combustor

In JAXA, combustion technologies have been developed with a target that is an 80% NOx reduction of the CAEP/4 standard. A lean staged fuel nozzle with a pilot mixer and a main one in a coaxial arrangement has been developed by single-sector combustor tests under LTO cycle conditions of the target engine with a total pressure ratio of 25.8. In this study, effects of air jets through combustion liner holes on combustion characteristics was investigated. Combustion tests were conducted by using four single-sector combustor liners with different air holes, no air holes, six air holes with short distance from the fuel nozzle, six air holes with long distance from the fuel nozzle, and one air flow path with three swirlers. From these results, air jets affect NOx emissions and combustion efficiency. Numerical analyses are also conducted by using a commercial large eddy simulation code, Front Flow Red. Quench of high temperature of pilot burned gas and NOx generation by air jets are captured by numerical simulations.