Numerical Analysis of Equivalence Ratio Fluctuations in a Partially Premixed Gas Turbine Combustor Using Large Eddy Simulations

2018 ◽  
Vol 141 (4) ◽  
Author(s):  
Ping Wang ◽  
Qian Yu ◽  
Prashant Shrotriya ◽  
Mingmin Chen
Keyword(s):  
Reaction Mechanism ◽  
Equivalence Ratio ◽  
Flame Temperature ◽  
Premixed Flames ◽  
Large Eddy Simulations ◽  
Combustion Model ◽  
Inlet Channel ◽  
Large Eddy ◽  
Partially Premixed Flames ◽  
Partially Premixed

In the present work, the fluctuations of equivalence ratio in the PRECCINSTA combustor are investigated via large eddy simulations (LES). Four isothermal flow cases with different combinations of global equivalence ratios (0.7 or 0.83) and grids (1.2 or 1.8 million cells) are simulated to study the mixing process of air with methane, which is injected into the inlet channel through small holes. It is shown that the fluctuations of equivalence ratio are very large, and their ranges are [0.4, 1.3] and [0.3, 1.2] for cases 0.83 and 0.7, respectively. For simulating turbulent partially premixed flames in this burner with the well-known dynamically thickened flame (DTF) combustion model, a suitable multistep reaction mechanism should be chosen aforehand. To do that, laminar premixed flames of 15 different equivalence ratios are calculated using three different methane/air reaction mechanisms: 2S_CH4_BFER, 2sCM2 reduced mechanisms and GRI-Mech 3.0 detailed reaction mechanism. The variations of flame temperature, flame speed and thickness of the laminar flames with the equivalence ratios are compared in detail. It is demonstrated that the applicative equivalence ratio range for the 2S_CH4_BFER mechanism is [0.5, 1.3], which is larger than that of the 2sCM2 mechanism [0.5, 1.2]. Therefore, it is recommended to use the 2S_CH4_BFER scheme to simulate the partially premixed flames in the PRECCINSTA combustion chamber.

Blowout Characteristics of Partially Premixed Flames of Prevaporized Blends of Biofuels and Petroleum Fuels

2017 ◽  
Author(s):  
Tonci Maleta ◽  
Ramkumar N. Parthasarathy ◽  
Subramanya R. Gollahalli
Keyword(s):  
Laminar Flame ◽  
Flame Temperature ◽  
Premixed Flames ◽  
Temperature Profiles ◽  
Flame Velocity ◽  
Gas Phase Reactions ◽  
Partially Premixed Flames ◽  
Inner Diameter ◽  
Partially Premixed ◽  
Petroleum Fuels

The laminar partially premixed flames of prevaporized Jet-A, canola methyl ester (CME) and blend flames of Jet-A and CME were studied over a range of equivalence ratios of 0.6–0.8 with and without heated coflow. Measurements of blowout velocities and flame temperature profiles were made. The injector was designed to produce a uniform inner flow and had an inner diameter of 12.7 mm. The flames were laminar and blue in color (dominated by homogeneous gas-phase reactions). The temperature profiles in all the flames were similar, with a peak temperature of 1680 K. The blowout velocity increased with equivalence ratio for all the flames; the blowout velocity of pure CME flames was higher than that of pure Jet-A flames with no coflow present. The blowout velocity of the blend flames ranged around the values for the pure fuel flames. A Damkohler number (based on the velocity gradient at the jet boundary and chemical reaction time scale estimated from laminar flame velocity) of unity characterizes the blowout velocity. As the coflow velocity was increased, the blowout velocity was increased, and the differences between the values for the various flames became smaller.

Aspect Ratio Effects on Partially Premixed Flames From Elliptic Burners in Coflow

2006 ◽  
Author(s):  
P. Hariharan ◽  
C. Periasamy ◽  
S. R. Gollahalli
Keyword(s):  
Flame Structure ◽  
Flame Temperature ◽  
Premixed Flames ◽  
Combustion Products ◽  
Jet Flame ◽  
Aspect Ratios ◽  
Partially Premixed Flames ◽  
Partially Premixed ◽  
Comparison Measurements ◽  
Good Agreement

In this paper, partially premixed flames of propane-hydrogen blends from elliptic burner geometries in coflow environment have been experimentally studied. Two different elliptic burner geometries with aspect ratios (AR) of 3:1 and 4:1 were used. A circular burner with the same discharge area as that of the elliptic burner was employed for comparison. Measurements were taken at stoichiometric and three other equivalence ratios. Global flame characteristics such as visible height, emission indices, and flame radiation were measured. Flame structure data such as transverse profiles of inflame concentrations of combustion products and local flame temperature were also measured at three axial locations in the flame. Results indicate that elliptic burner flames were shorter, more radiating, and produced lower NO and CO emissions than the corresponding circular burner flames. Results from the inflame measurements of NO and CO were in good agreement with the corresponding global data. Further, the 4:1 AR elliptic burners exhibited a twin-jet flame structure at fuel-rich conditions. The twin-flame structure was evident from the inflame measurements of temperature and combustion species. This study suggests that the combination of elliptic burner geometry and coflow reduces NO and CO emissions from combustion systems, which could potentially lead to cleaner environment.

Reconstruction and Analysis of the Acoustic Transfer Matrix of a Reheat Flame From Large-Eddy Simulations

2017 ◽  
Author(s):  
Mirko Bothien ◽  
Demian Lauper ◽  
Yang Yang ◽  
Alessandro Scarpato
Keyword(s):  
Transfer Matrix ◽  
Equivalence Ratio ◽  
Premixed Flames ◽  
Temperature Fluctuations ◽  
Large Eddy Simulations ◽  
Lean Premixed Flames ◽  
Single Output ◽  
Auto Ignition ◽  
Large Eddy ◽  
Flame Response

Lean premix technology is widely spread in gas turbine combustion systems, allowing modern power plants to fulfill very stringent emission targets. These systems are, however, also prone to thermoacoustic instabilities, which can limit the engine operating window. The thermoacoustic analysis of a combustor is thus a key element in its development process. An important ingredient of this analysis is the characterization of the flame response to acoustic fluctuations, which is straightforward for lean-premixed flames that are propagation stabilized, since it can be measured atmospherically. Ansaldo Energia’s GT26 and GT36 reheat combustion systems feature a unique technology where fuel is injected into a hot gas stream from a first combustor, which is propagation stabilized, and auto-ignites in a sequential combustion chamber. The present study deals with the flame response of mainly auto-ignition stabilized flames to acoustic and temperature fluctuations for which a CFD system identification approach is chosen. The current paper builds on recent works, which detail and validate a methodology to analyze the dynamic response of an auto-ignition flame to extract the Flame Transfer Function (FTF) using unsteady Large-Eddy Simulations (LES). In these studies, the flame is assumed to behave as a Single-Input Single-Output (SISO) or Multi-Input Single-Output (MISO) system. The analysis conducted in GT2015-42622 qualitatively highlights the important role of temperature and equivalence ratio fluctuations, but these effects are not separated from velocity fluctuations. Hence, this topic is addressed in GT2016-57699, where the flame is treated as a multi-parameter system and compressible LES are conducted to extract the frequency-dependent FTF to describe the effects of axial velocity, temperature, equivalence ratio and pressure fluctuations on the flame response. For lean-premixed flames, a common approach followed in the literature assumes that the acoustic pressure is constant across the flame and that the flame dynamics are governed by the response to velocity perturbations only, i.e., the FTF. However this is not necessarily the case for reheat flames that are mainly auto-ignition stabilized. Therefore, in this paper we present the full 2 × 2 transfer matrix of a predominantly auto-ignition stabilized flame and hence describe the flame as a Multi-Input Multi-Output (MIMO) system. In addition to this, it is highlighted that in presence of temperature fluctuations the 2 × 2 matrix can be extended to a 3 × 3 matrix relating the primitive acoustic variables as well as the temperature fluctuations across the flame. It is shown that only taking the FTF is insufficient to fully describe the dynamic behavior of reheat flames.

Reconstruction and Analysis of the Acoustic Transfer Matrix of a Reheat Flame From Large-Eddy Simulations

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Mirko Bothien ◽  
Demian Lauper ◽  
Yang Yang ◽  
Alessandro Scarpato
Keyword(s):  
Transfer Matrix ◽  
Equivalence Ratio ◽  
Premixed Flames ◽  
Temperature Fluctuations ◽  
Large Eddy Simulations ◽  
Lean Premixed Flames ◽  
Single Output ◽  
Auto Ignition ◽  
Large Eddy ◽  
Flame Response

Lean premix technology is widely spread in gas turbine combustion systems, allowing modern power plants to fulfill very stringent emission targets. These systems are, however, also prone to thermoacoustic instabilities, which can limit the engine operating window. The thermoacoustic analysis of a combustor is thus a key element in its development process. An important ingredient of this analysis is the characterization of the flame response to acoustic fluctuations, which is straightforward for lean-premixed flames that are propagation stabilized, since it can be measured atmospherically. Ansaldo Energia's GT26 and GT36 reheat combustion systems feature a unique technology where fuel is injected into a hot gas stream from a first combustor, which is propagation stabilized, and auto-ignites in a sequential combustion chamber. The present study deals with the flame response of mainly auto-ignition stabilized flames to acoustic and temperature fluctuations for which a computational fluid dynamics system identification (SI) approach is chosen. The current paper builds on recent works, which detail and validate a methodology to analyze the dynamic response of an auto-ignition flame to extract the flame transfer function (FTF) using unsteady large-Eddy simulations (LES). In these studies, the flame is assumed to behave as a single-input single-output (SISO) or a multi-input single-output (MISO) system. The analysis conducted in GT2015-42622 qualitatively highlights the important role of temperature and equivalence ratio fluctuations, but these effects are not separated from velocity fluctuations. Hence, this topic is addressed in GT2016-57699, where the flame is treated as a multiparameter system and compressible LES are conducted to extract the frequency-dependent FTF to describe the effects of axial velocity, temperature, equivalence ratio, and pressure fluctuations on the flame response. For lean-premixed flames, a common approach followed in the literature assumes that the acoustic pressure is constant across the flame and that the flame dynamics are governed by the response to velocity perturbations only, i.e., the FTF. However, this is not necessarily the case for reheat flames that are mainly auto-ignition stabilized. Therefore, in this paper, we present the full 2 × 2 transfer matrix of a predominantly auto-ignition stabilized flame, and hence, describe the flame as a multi-input multi-output (MIMO) system. In addition to this, it is highlighted that in the presence of temperature fluctuations, the 2 × 2 matrix can be extended to a 3 × 3 matrix relating the primitive acoustic variables as well as the temperature fluctuations across the flame. It is shown that only taking the FTF is insufficient to fully describe the dynamic behavior of reheat flames.

Probing the equivalence ratio in partially premixed flames by combining optical techniques and modeling results

2018 ◽  
Vol 190 (8) ◽  
pp. 1442-1454
Author(s):  
Laura Merotto ◽  
Mariano Sirignano ◽  
Mario Commodo ◽  
Andrea D’Anna ◽  
Francesca Migliorini ◽  
...  
Keyword(s):  
Equivalence Ratio ◽  
Premixed Flames ◽  
Optical Techniques ◽  
Partially Premixed Flames ◽  
Partially Premixed
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