Flame structure interactions and state relationships in an unsteady partially premixed flame

AIAA Journal ◽  
1998 ◽  
Vol 36 ◽  
pp. 1190-1199
Author(s):  
Suresh K. Aggarwal ◽  
Ishwar K. Puri
Keyword(s):  
Flame Structure ◽  
Premixed Flame ◽  
Partially Premixed ◽  
Partially Premixed Flame

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

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 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

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.

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.

Effect of Acoustic Feedback on Lagrangian Coherent Structures in a Backward Facing Step Combustor With a Partially Premixed Flame

2017 ◽  
Author(s):  
Ramgopal Sampath ◽  
S. R. Chakravarthy
Keyword(s):  
Coherent Structures ◽  
Large Scale ◽  
Pressure Oscillation ◽  
Velocity Fields ◽  
Premixed Flame ◽  
Time Resolved ◽  
Acoustic Feedback ◽  
Acoustic Characterization ◽  
Partially Premixed ◽  
Partially Premixed Flame

The thermoacoustic oscillations of a partially premixed flame stabilized in a backward facing step combustor are studied at a constant equivalence ratio in long and short combustor configurations corresponding to with and without acoustic feedback respectively. We perform simultaneous time-resolved particle image velocimetry (TR-PIV) and chemiluminescence for selected flow conditions based on the acoustic characterization in the long combustor. The acoustic characterization shows a transition in the dominant pressure amplitudes from low to high magnitudes with an increase in the inlet flow Reynolds number. This is accompanied by a shift in the dominant frequencies. For the intermittent pressure oscillations in the long combustor, the wavelet analysis indicates a switch between the acoustic and vortex modes with silent zones of relatively low-pressure amplitudes. The short combustor configuration indicates the presence of the vortex shedding frequency and an additional band comprising the Kelvin Helmholtz mode. Next, we apply the method of finite-time Lyapunov exponent (FTLE) to the time-resolved velocity fields to extract features of the Lagrangian coherent structures (LCS) of the flow. In the long combustor post transition with the time instants with dominant acoustic mode, a large-scale modulation of the FTLE boundaries over one cycle of pressure oscillation is evident. Further, the FTLEs and the flame boundaries align each other for all phases of the pressure oscillation. In the short combustor, the FTLEs indicate the presence of small wavelength waviness that overrides the large-scale vortex structure, which corresponds to the vortex shedding mode. This behaviour contrasts with the premixed flame in the short combustor reported earlier in which such large scales were found to be seldom present. The presence of the large-scale structures even in the absence of acoustic feedback in a partially premixed flame signifies its inherent unstable nature leading to large pressure amplitudes during acoustic feedback. Lastly, the FTLE boundaries provide the frequency information of the identified coherent structure and also acts as the surrogate flame boundaries that are estimated from just the velocity fields.

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