scholarly journals Turbulent flame speed and reaction layer thickening in premixed jet flames at constant Karlovitz and increasing Reynolds numbers

2020 ◽  
Author(s):  
Antonio Attili ◽  
Stefano Luca ◽  
Dominik Denker ◽  
Fabrizio Bisetti ◽  
Heinz Pitsch
Keyword(s):  
Reaction Layer ◽  
Turbulent Flame ◽  
Reynolds Numbers ◽  
Flame Speed ◽  
Jet Flames ◽  
Turbulent Flame Speed

An Efficient Computational Model for Premixed Turbulent Combustion at High Reynolds Numbers Based on a Turbulent Flame Speed Closure

1997 ◽  
Author(s):  
Vladimir Zimont ◽  
Wolfgang Polifke ◽  
Marco Bettelini ◽  
Wolfgang Weisenstein
Keyword(s):  
Computational Model ◽  
Transport Equation ◽  
Turbulent Combustion ◽  
Turbulent Flame ◽  
Reynolds Numbers ◽  
Flame Speed ◽  
Closed Form Expression ◽  
Turbulent Length Scale ◽  
Premixed Turbulent Combustion ◽  
Turbulent Flame Speed

Theoretical background, details of implementation and validation results of a computational model for turbulent premixed gaseous combustion at high turbulent Reynolds numbers are presented. The model describes the combustion process in terms of a single transport equation for a progress variable; closure of the progress variable’s source term is based on a model for the turbulent flame speed. The latter is identified as a parameter of prime significance in premixed turbulent combustion and is determined from theoretical considerations and scaling arguments, taking into account physico-chemical properties of the combustible mixture and local turbulent parameters. Specifically, phenomena like thickening, wrinkling and straining of the flame front by the turbulent velocity field are considered, yielding a closed form expression for the turbulent flame speed that involves, e.g., speed, thickness and critical gradient of a laminar flame, local turbulent length scale and fluctuation intensity. This closure approach is very efficient and elegant, as it requires only one transport equation more than the non-reacting flow case, and there is no need for costly evaluation of chemical source terms or integration over probability density functions. The model was implemented in a finite-volume based computational fluid dynamics code and validated against detailed experimental data taken from a large scale atmospheric gas turbine burner test stand. The predictions of the model compare well with the available experimental results. It has been observed that the model is significantly more robust and computationally efficient than other combustion models. This attribute makes the model particularly interesting for applications to large 3D problems in complicated geometries.

Boundary Layer Flashback Prediction for Turbulent Premixed Jet Flames: Comparison of Two Models

2019 ◽  
Author(s):  
Alireza Kalantari ◽  
Nicolas Auwaijan ◽  
Vincent McDonell
Keyword(s):  
Boundary Layer ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Operating Conditions ◽  
Pollutant Emissions ◽  
Jet Flames ◽  
Turbulent Flame Speed ◽  
Turbulent Premixed

Abstract Lean-premixed combustion is commonly used in gas turbines to achieve low pollutant emissions, in particular nitrogen oxides. But use of hydrogen-rich fuels in premixed systems can potentially lead to flashback. Adding significant amounts of hydrogen to fuel mixtures substantially impacts the operating range of the combustor. Hence, to incorporate high hydrogen content fuels into gas turbine power generation systems, flashback limits need to be determined at relevant conditions. The present work compares two boundary layer flashback prediction methods developed for turbulent premixed jet flames. The Damköhler model was developed at University of California Irvine (UCI) and evaluated against flashback data from literature including actual engines. The second model was developed at Paul Scherrer Institut (PSI) using data obtained at gas turbine premixer conditions and is based on turbulent flame speed. Despite different overall approaches used, both models characterize flashback in terms of similar parameters. The Damköhler model takes into account the effect of thermal coupling and predicts flashback limits within a reasonable range. But the turbulent flame speed model provides a good agreement for a cooled burner, but shows less agreement for uncooled burner conditions. The impact of hydrogen addition (0 to 100% by volume) to methane or carbon monoxide is also investigated at different operating conditions and flashback prediction trends are consistent with the existing data at atmospheric pressure.

An Efficient Computational Model for Premixed Turbulent Combustion at High Reynolds Numbers Based on a Turbulent Flame Speed Closure

1998 ◽  
Vol 120 (3) ◽  
pp. 526-532 ◽  
Author(s):  
V. Zimont ◽  
W. Polifke ◽  
M. Bettelini ◽  
W. Weisenstein
Keyword(s):  
Computational Model ◽  
Transport Equation ◽  
Turbulent Combustion ◽  
Turbulent Flame ◽  
Reynolds Numbers ◽  
Flame Speed ◽  
Closed Form Expression ◽  
Turbulent Length Scale ◽  
Premixed Turbulent Combustion ◽  
Turbulent Flame Speed

Theoretical background, details of implementation, and validation results for a computational model for turbulent premixed gaseous combustion at high turbulent Reynolds numbers are presented. The model describes the combustion process in terms of a single transport equation for a progress variable; turbulent closure of the progress variable’s source term is based on a model for the turbulent flame speed. The latter is identified as a parameter of prime significance in premixed turbulent combustion and determined from theoretical considerations and scaling arguments, taking into account physico-chemical properties and local turbulent parameters of the combustible mixture. Specifically, phenomena like thickening, wrinkling, and straining of the flame front by the turbulent velocity field are considered, yielding a closed form expression for the turbulent flame speed that involves, e.g., speed, thickness, and critical gradient of a laminar flame, local turbulent length scale, and fluctuation intensity. This closure approach is very efficient and elegant, as it requires only one transport equation more than the non reacting flow case, and there is no need for costly evaluation of chemical source terms or integration over probability density functions. The model was implemented in a finite-volume-based computational fluid dynamics code and validated against detailed experimental data taken from a large-scale atmospheric gas turbine burner test stand. The predictions of the model compare well with the available experimental results. It has been observed that the model is significantly more robust and computationally efficient than other combustion models. This attribute makes the model particularly interesting for applications to large three-dimensional problems in complicated geometries.

scholarly journals Numerical Investigation of Pressure Influence on the Confined Turbulent Boundary Layer Flashback Process

Fluids ◽  
2019 ◽  
Vol 4 (3) ◽  
pp. 146 ◽  
Author(s):  
Aaron Endres ◽  
Thomas Sattelmayer
Keyword(s):  
Boundary Layer ◽  
Gas Turbines ◽  
Separation Zone ◽  
Turbulent Flame ◽  
Pressure Rise ◽  
Flame Speed ◽  
Zone Size ◽  
Detailed Chemical Kinetics ◽  
Turbulent Flame Speed ◽  
Quenching Distance

Boundary layer flashback from the combustion chamber into the premixing section is a threat associated with the premixed combustion of hydrogen-containing fuels in gas turbines. In this study, the effect of pressure on the confined flashback behaviour of hydrogen-air flames was investigated numerically. This was done by means of large eddy simulations with finite rate chemistry as well as detailed chemical kinetics and diffusion models at pressures between 0 . 5 and 3 . It was found that the flashback propensity increases with increasing pressure. The separation zone size and the turbulent flame speed at flashback conditions decrease with increasing pressure, which decreases flashback propensity. At the same time the quenching distance decreases with increasing pressure, which increases flashback propensity. It is not possible to predict the occurrence of boundary layer flashback based on the turbulent flame speed or the ratio of separation zone size to quenching distance alone. Instead the interaction of all effects has to be accounted for when modelling boundary layer flashback. It was further found that the pressure rise ahead of the flame cannot be approximated by one-dimensional analyses and that the assumptions of the boundary layer theory are not satisfied during confined boundary layer flashback.

scholarly journals Extension of the turbulent flame speed closure model to ignition in multiphase flows

2013 ◽  
Vol 160 (2) ◽  
pp. 351-365 ◽  
Author(s):  
Jan M. Boyde ◽  
Patrick C. Le Clercq ◽  
Massimiliano Di Domenico ◽  
Manfred Aigner
Keyword(s):  
Multiphase Flows ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Closure Model ◽  
Turbulent Flame Speed

Flame Characteristics and Turbulent Flame Speeds of Turbulent, High-Pressure, Lean Premixed Methane/Air Flames

2005 ◽  
Author(s):  
P. Griebel ◽  
R. Bombach ◽  
A. Inauen ◽  
R. Scha¨ren ◽  
S. Schenker ◽  
...  
Keyword(s):  
Flame Front ◽  
Gas Turbines ◽  
Equivalence Ratio ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Operating Conditions ◽  
Turbulent Flame Speed ◽  
Front Position ◽  
Preheating Temperature ◽  
Lean Premixed

The present experimental study focuses on flame characteristics and turbulent flame speeds of lean premixed flames typical for stationary gas turbines. Measurements were performed in a generic combustor at a preheating temperature of 673 K, pressures up to 14.4 bars (absolute), a bulk velocity of 40 m/s, and an equivalence ratio in the range of 0.43–0.56. Turbulence intensities and integral length scales were measured in an isothermal flow field with Particle Image Velocimetry (PIV). The turbulence intensity (u′) and the integral length scale (LT) at the combustor inlet were varied using turbulence grids with different blockage ratios and different hole diameters. The position, shape, and fluctuation of the flame front were characterized by a statistical analysis of Planar Laser Induced Fluorescence images of the OH radical (OH-PLIF). Turbulent flame speeds were calculated and their dependence on operating conditions (p, φ) and turbulence quantities (u′, LT) are discussed and compared to correlations from literature. No influence of pressure on the most probable flame front position or on the turbulent flame speed was observed. As expected, the equivalence ratio had a strong influence on the most probable flame front position, the spatial flame front fluctuation, and the turbulent flame speed. Decreasing the equivalence ratio results in a shift of the flame front position farther downstream due to the lower fuel concentration and the lower adiabatic flame temperature and subsequently lower turbulent flame speed. Flames operated at leaner equivalence ratios show a broader spatial fluctuation as the lean blow-out limit is approached and therefore are more susceptible to flow disturbances. In addition, because of a lower turbulent flame speed these flames stabilize farther downstream in a region with higher velocity fluctuations. This increases the fluctuation of the flame front. Flames with higher turbulence quantities (u′, LT) in the vicinity of the combustor inlet exhibited a shorter length and a higher calculated flame speed. An enhanced turbulent heat and mass transport from the recirculation zone to the flame root location due to an intensified mixing which might increase the preheating temperature or the radical concentration is believed to be the reason for that.

An Optimized Correlation for Turbulent Flame Speed for C1-C3 Fuels at Engines-Relevant Conditions

2021 ◽  
Author(s):  
Sajjad Yousefian ◽  
Eoin M. Burke ◽  
Felix Guthe ◽  
Rory f.d. Monaghan
Keyword(s):  
Turbulent Flame ◽  
Flame Speed ◽  
Turbulent Flame Speed
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