Premixed flame response to equivalence ratio perturbations

Shreekrishna,; Hemchandra, Santosh; Lieuwen, Tim

doi:10.1080/13647830.2010.502247

Cited by 68 publications

(46 citation statements)

References 51 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Previous theoretical and numerical studies suggest that fluctuations of the local flame speed due to equivalence-ratio stratification provide a mechanism for wrinkling the flame, described as a differential propagation [2]. Whether the differential propagation mechanism has a significant impact on the turbulent flame speed depends on the magnitude of the flame speed fluctuations ′ ̅ ⁄ [2] and the length scale of the equivalence ratio fluctuations [3,4]: it has been suggested that differential propagation can be significant for ′~′ [2] at stratification length scales between the integral scale and the scale where scalar dissipation timescale competes with the flame propagation timescale [5,6]. However flame surface density-based modelling approaches have been assessed in equivalence-ratio stratified flames and have achieved moderate success without considering effects of differential propagation [7,8].…”

Section: Introductionmentioning

confidence: 99%

Analysis of turbulent flame propagation in equivalence ratio-stratified flow

Richardson

Chen

2017

Proceedings of the Combustion Institute

View full text Add to dashboard Cite

Effects of equivalence ratio stratification on turbulent combustion processes are investigated using Direct Numerical Simulation. The simulation results are analysed in terms of flame surface area and the burning intensity. The local effects of stratification are then investigated further by examining statistics of the displacement speed conditioned on the flame-normal equivalence ratio gradient. The local burning intensity is found to depend on the orientation of the stratification with respect to the flame front, so that burning intensity is enhanced when the flame speed in the products is faster than in the reactants. The flame surface area is also influenced by equivalence ratio stratification and this may be explained by differences in the surface averaged consumption speed and differential propagation effects due to flame speed variations associated with equivalence ratio fluctuations.

show abstract

Section: Introductionmentioning

confidence: 99%

Analysis of turbulent flame propagation in equivalence ratio-stratified flow

Richardson

Chen

2017

Proceedings of the Combustion Institute

View full text Add to dashboard Cite

show abstract

“…In most real systems, combustion is not fully premixed and even in laboratories, very few swirled flames are truly fully premixed. The effects of equivalence ratio fluctuations on flame stability in combustors have been known for a long time [7,8]: changes in air inlet velocity induce variations of the flow rate through the flame but may also induce mixing fluctuations and the introduction into the combustion zone of nonconstant equivalence ratio pockets. These pockets create unsteady combustion and can generate instabilities.…”

Section: Introductionmentioning

confidence: 99%

Large Eddy Simulation of combustion instabilities in a lean partially premixed swirled flame

Franzelli

Riber

Gicquel

et al. 2012

Combustion and Flame

275

162

View full text Add to dashboard Cite

a b s t r a c tThis paper investigates one issue related to Large Eddy Simulation (LES) of self-excited combustion instabilities in gas-fueled swirled burners: the effects of incomplete mixing between fuel and air at the combustion chamber inlet. Perfect premixing of the gases entering the combustion chamber is rarely achieved in practical applications and this study investigates its impact by comparing LES assuming perfect premixing and LES where the fuel jets are resolved so that fuel/air mixing is explicitely computed. This work demonstrates that the perfect premixing assumption is reasonable for stable flows but is not acceptable to predict self-excited unstable cases. This is shown by comparing LES and experimental fields in terms of mean and RMS fields of temperature, species, velocities as well as mixture fraction pdfs and unsteady activity for two regimes: a stable one at equivalence ratio 0.83 and an unstable one at 0.7. IntroductionThe instabilities of swirled turbulent flows have been the subject of intense research in the last ten years. One important issue has been to identify the possibilities offered by simulation and especially Large Eddy Simulation (LES) to predict self-excited combustion oscillations. The specific example of swirled combustors where flames couple with acoustic modes has received significant attention [1-4] because such oscillations are often found in real gas turbines [5,6]. An important question in swirled unstable flames is the effect of mixing on stability. In most real systems, combustion is not fully premixed and even in laboratories, very few swirled flames are truly fully premixed. The effects of equivalence ratio fluctuations on flame stability in combustors have been known for a long time [7,8]: changes in air inlet velocity induce variations of the flow rate through the flame but may also induce mixing fluctuations and the introduction into the combustion zone of nonconstant equivalence ratio pockets. These pockets create unsteady combustion and can generate instabilities.In many experiments, LES is performed assuming perfect mixing mainly because the computational work is simpler: there is no need to mesh the fuel injection holes or to resolve the zone where these jets mix with air. However, this assumption totally eliminates fluctuations of equivalence ratio as a mechanism of instability, thereby limiting the validity of the LES. One specific example of such limitations is reported in the experiment of [9][10][11] which has been computed by multiple groups [12][13][14][15][16]. This methane/air swirled combustor was especially built to study combustion instabilities in such systems and for all computations up to now, perfect mixing has been assumed by LES experts because methane was injected in the swirler, far upstream of the combustor, suggesting that perfect mixing is achieved before the combustion zone. Interestingly, all computations performed with perfect mixing assumptions have failed to predict the unstable modes observed in the experiments. Moreover, recent...

show abstract

“…The heat of reaction is very much sensitive to the changes in the equivalence ratios for lean mixtures. For near-stoichiometric or rich mixtures, the heat of reaction is almost insensitive to the changes in the equivalence ratio [10]. In Fig.…”

Section: Flame Oscillationsmentioning

confidence: 94%

“…Researchers also investigated the unsteady premixed flame dynamics in order to understand flow-combustion interactions and combustion instability problems observed in gas turbine combustors. In some cases the flow perturbations have been achieved by vibrating wire in the flow field [4][5][6], in other cases the perturbations are achieved by the acoustic excitations in the flow path [7][8][9][10][11][12][13][14][15][16][17]. These studies also investigated the heat release fluctuations, flame kinematics and flame deformation due to external perturbations.…”

Section: Introductionmentioning

confidence: 99%

“…Shreekrishna et al [10] studied the heat release response of premixed flame subjected to equivalence ratio perturbations. They showed that the response of rich flames to equivalence ratio oscillations is fundamentally different from that of lean flames as the heat release rate depends on the equivalence ratio in the case of lean flames while the heat release rate is independent of equivalence ratio for rich flames.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effect of Low Frequency Burner Vibrations on the Characteristics of Premixed Flames

Kanthasamy

Raghavan

Srinivasan

2012

International Journal of Spray and Combustion Dynamics

View full text Add to dashboard Cite

Mechanical vibrations in a burner are found to affect the characteristics of premixed flames. In the present experimental investigation, the effects of axial vibrations of a tubular burner on the characteristics of laminar premixed methane-air flames are investigated. The effect of the frequency and amplitude of the burner vibrations on the flame height oscillations are studied. At a low frequency of around 10 Hz, no effect of vibrations on flame characteristics is observed. At frequencies higher than 10 Hz, the amplitude of flame height oscillations is found to increase with increase in both frequency and amplitude of burner vibrations for the range of frequencies and amplitudes considered.

show abstract

Premixed flame response to equivalence ratio perturbations

Cited by 68 publications

References 51 publications

Analysis of turbulent flame propagation in equivalence ratio-stratified flow

Analysis of turbulent flame propagation in equivalence ratio-stratified flow

Large Eddy Simulation of combustion instabilities in a lean partially premixed swirled flame

Effect of Low Frequency Burner Vibrations on the Characteristics of Premixed Flames

Contact Info

Product

Resources

About