The Structure of Two-Stage Counterflow n-Heptane-Air Flames

2000 ◽  
Author(s):  
S. K. Aggarwal ◽  
H. S. Xue
Keyword(s):  
Strain Rate ◽  
Reaction Zone ◽  
Equivalence Ratio ◽  
Flame Structure ◽  
Premixed Combustion ◽  
Premixed Flame ◽  
Partially Premixed Combustion ◽  
Reaction Zones ◽  
Partially Premixed ◽  
Partially Premixed Flame

Partially premixed flames are formed by mixing air (in less than stoichiometric amounts) into the fuel stream prior to the reaction zone, where additional air is available for complete combustion. Such flames can occur in both laboratory and practical combustion systems. In advanced gas turbine combustor designs, such as a lean direct injection (LDI) combustor, partially premixed combustion represents an impotent mode of burning. Spray combustion often involves partially premixed combustion due to the locally fuel vapor-rich regions. In the present study, the detailed structure of n-heptane/air partially premixed flame in a counterflow configuration is investigated. The flame is computed by employing the Oppdif code and a detailed reaction mechanism consisting of 275 elementary reactions and 41 species. The partially premixed flame structure is characterized by two-stage burning or two distinct but synergistically coupled reaction zones, a rich premixed zone on the fuel side and a ‘nonpremixed zone on the air side. The fuel is completely consumed in the premixed zone with ethylene and acetylene being the major intermediate species. The reactions involving the consumption of these species are found to be the key rate-limiting reactions that characterize interactions between the two reaction zones, and determine the overall fuel consumption rate. The flame response to the variations in equivalence ratio and strain rate is examined. Increasing equivalence ratio and/or strain rate to a critical value leads to merging of the two reaction zones. The equivalence ratio variation affects the rich premixed reaction zone, while the variation in strain rate predominantly affects the nonpremixed reaction zone. The flame structure is also characterized in terms of a modified mixture fraction (conserved scalar), and laminar flamelet profiles are provided.

A Study on Flame Structures in CH4 Counterflow Partially Premixed Flame

2014 ◽  
Vol 694 ◽  
pp. 474-477
Author(s):  
Jing Luo ◽  
Lian Sheng Liu ◽  
Zi Zhong Chen
Keyword(s):  
Reaction Zone ◽  
Equivalence Ratio ◽  
Flame Structure ◽  
Premixed Flame ◽  
Counterflow Flame ◽  
Partially Premixed ◽  
Flame Structures ◽  
The Rich ◽  
Partially Premixed Flame ◽  
Two Temperature

An experimental and simulation work had been conducted to study a one-dimensional partially premixed methane/air counterflow flame in this paper. Flame images are obtained through experiments and computations using GRIMech 3.00 chemistry were performed for the flames studied. The partially premixing effects upon the flame were revealed by comparing the flame structures and emissions with premixed flames at the same equivalence ratio. The results show the premixed flame only has a single flame structure. However, PPF has distinct double flame structures at present equivalence ratio. Temperature is relatively high in the whole combustion zone for premixed flame, while, for PPF, there are two temperature peaks in a rich premixed reaction zone on the fuel side and a nonpremixed reaction zone on the oxidizer side respectively. For PPF, NO concentration in the nonpremixed zone is much higher compared to that in the rich premixed zone because of higher OH concentration in the nonpremixed zone.

H2/CO/air premixed and partially premixed flame structure at different pressures based on reaction limit analysis

2018 ◽  
Vol 63 (19) ◽  
pp. 1260-1266 ◽  
Author(s):  
Zaigang Liu ◽  
Wenjun Kong ◽  
Jean-Louis Consalvi ◽  
Wenhu Han
Keyword(s):  
Limit Analysis ◽  
Flame Structure ◽  
Premixed Flame ◽  
Partially Premixed ◽  
Partially Premixed Flame

A numerical investigation of the flame structure of an unsteady inverse partially premixed flame

1997 ◽  
Vol 111 (4) ◽  
pp. 296-311 ◽  
Author(s):  
Zhuang Shu ◽  
Suresh K. Aggarwal ◽  
Viswanath R. Katta ◽  
Ishwar K. Puri
Keyword(s):  
Numerical Investigation ◽  
Flame Structure ◽  
Premixed Flame ◽  
Partially Premixed ◽  
Partially Premixed Flame

Combustion Structures in Lifted Ethanol Spray Flames

2004 ◽  
Vol 126 (2) ◽  
pp. 254-257 ◽  
Author(s):  
Stephen K. Marley ◽  
Eric J. Welle ◽  
Kevin M. Lyons
Keyword(s):  
Reaction Zone ◽  
Flame Structure ◽  
Leading Edge ◽  
Laser Induced Fluorescence ◽  
Premixed Combustion ◽  
Diffusion Mode ◽  
Spray Flames ◽  
Partially Premixed Combustion ◽  
Planar Laser ◽  
Single Reaction

The development of a double flame structure in lifted ethanol spray flames is visualized using OH planar laser-induced fluorescence (PLIF). While the OH images indicate a single reaction zone exists without co-flow, the addition of low-speed co-flow facilitates the formation of a double flame structure that consists of two diverging flame fronts originating at the leading edge of the reaction zone. The outer reaction zone burns steadily in a diffusion mode, and the strained inner flame structure is characterized by both diffusion and partially premixed combustion exhibiting local extinction and re-ignition events.

Relative Effects of Velocity- and Mixture-Coupling in a Thermoacoustically Unstable, Partially-Premixed Flame

2021 ◽  
Author(s):  
Ashwini Karmarker ◽  
Jacqueline O’Connor ◽  
Isaac Boxx
Keyword(s):  
Gas Turbine ◽  
Equivalence Ratio ◽  
Premixed Flame ◽  
Turbine Engines ◽  
Gas Turbine Engines ◽  
Real Gas ◽  
Planar Laser ◽  
Partially Premixed ◽  
Partially Premixed Flame ◽  
The Impact

Abstract Combustion instability, which is the result of a coupling between combustor acoustic modes and unsteady flame heat release rate, is a severely limiting factor in the operability and performance of modern gas turbine engines. This coupling can occur through different coupling pathways, such as flow field fluctuations or equivalence ratio fluctuations. In realistic combustor systems, there are complex hydrodynamic and thermo-chemical processes involved, which can lead to multiple coupling pathways. In order to understand and predict the mechanisms that govern the onset of combustion instability in real gas turbine engines, we consider the influences that each of these coupling pathways can have on the stability and dynamics of a partially-premixed, swirl-stabilized flame. In this study, we use a model gas turbine combustor with two concentric swirling nozzles of air, separated by a ring of fuel injectors, operating at an elevated pressure of 5 bar. The flow split between the two streams is systematically varied to observe the impact on the flow and flame dynamics. High-speed stereoscopic particle image velocimetry, OH planar laser-induced fluorescence, and acetone planar laser-induced fluorescence are used to obtain information about the velocity field, flame, and fuel-flow behavior, respectively. Depending on the flow conditions, a thermoacoustic oscillation mode or a hydrodynamic mode, identified as the precessing vortex core, is present. The focus of this study is to characterize the mixture coupling processes in this partially-premixed flame as well as the impact that the velocity oscillations have on mixture coupling. Our results show that, for this combustor system, changing the flow split between the two concentric nozzles can alter the dominant harmonic oscillation modes in the system, which can significantly impact the dispersion of fuel into air, thereby modulating the local equivalence ratio of the flame. This insight can be used to design instability control mechanisms in real gas turbine engines.

Multi-Dimensional Flamelet Manifolds for Laminar Partially Premixed Flame

2015 ◽  
Vol 1092-1093 ◽  
pp. 520-524
Author(s):  
Chang Min Cao ◽  
Tao Hong Ye ◽  
Yu Xin Wu ◽  
Wei Wei
Keyword(s):  
Flame Structure ◽  
Direct Calculation ◽  
Premixed Flame ◽  
Dimensional Manifold ◽  
Flamelet Model ◽  
Partially Premixed ◽  
Partially Premixed Flame ◽  
Low Dimensional ◽  
Low Dimensional Manifold ◽  
Chemistry Tabulation

The aim of this paper is to evaluate the performance of thermo-chemistry tabulation approaches for numerical simulation of laminar partially premixed flame by comparing with the results of detail chemistry. Two thermo-chemistry tabulation approaches are considered: the multidimensional flamelet manifolds (MFM) method and Flame Prolongation of Intrinsic low-dimensional manifold (FPI) method. The fuel streams with different equivalence ratios (ΦF=1.8,ΦF=2.464) are analyzed. In both of the equivalence ratios the results obtained from MFM method are in closer agreement with the direct calculation than FPI method. It is concluded that multi-dimensional flamelet manifolds can capture more precisely partially premixed characteristic of the multi-regime flame structure, comparing to single-dimensional flamelet model FPI.

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