The effect of oxygen content on the turbulent flame speed of ammonia/oxygen/nitrogen expanding flames under elevated pressures

This paper reports flashback limits and turbulent flame local displacement speed measurements in flames stabilized by a low swirl injector operated at elevated pressures and inlet temperatures with hydrogen and methane blended fuels. The goal of this study is to understand the physics that relate turbulent flame speed to flashback events at conditions relevant to gas turbine engines. Testing was conducted in an optically accessible single nozzle combustor rig at pressures ranging from 1 to 8 atm, inlet temperatures from 290 to 600 K, and inlet bulk velocities between 20 and 60 m/s for natural gas and a 90%/10% (by volume) hydrogen/methane blend. The propensity of flashback is dependent upon the proximity of the lifted flame to the nozzle that is itself dependent upon pressure, inlet temperature, and bulk velocity. Flashback occurs when the leading edge of the flame in the core of the flow ingresses within the nozzle, even in cases when the flame is attached to the burner rim. In general the adiabatic flame temperature at flashback is proportional to the bulk velocity and inlet temperature and inversely proportional to the pressure. The unburned reactant velocity field approaching the flame was measured using a laser Doppler velocimeter with water seeding. Turbulent displacement flame speeds were found to be linearly proportional to the root mean square of the velocity fluctuations about the mean velocity. For identical inlet conditions, high-hydrogen flames had a turbulent flame local displacement speed roughly twice that of natural gas flames. Pressure, inlet temperature, and flame temperature had surprisingly little effect on the local displacement turbulent flame speed. However, the flow field is affected by changes in inlet conditions and is the link between turbulent flame speed, flame position, and flashback propensity.

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A Comparison of Turbulent Flame Speed Correlations for Hydrocarbon Fuels at Elevated Pressures

Volume 4B: Combustion, Fuels and Emissions ◽

10.1115/gt2016-57804 ◽

2016 ◽

Cited By ~ 3

Author(s):

Eoin M. Burke ◽

Felix Güthe ◽

Rory F. D. Monaghan

Keyword(s):

Experimental Data ◽

Laminar Flame ◽

State Of The Art ◽

Turbulent Flame ◽

Flame Speed ◽

Percentage Error ◽

Continue Development ◽

Turbulent Flame Speed ◽

Elevated Pressures ◽

Insight Into

The aim of this work is to provide insight into the state-of-the-art turbulent flame speed (ST) correlations and to determine the most appropriate correlations to use under different turbulent premixed combustion conditions. The accuracies of 16 correlations for ST are determined using a large volume of data over a range of conditions. Accuracy is based on a mean absolute percentage error (MAPE). The comparison is completed once using the original authors’ adjustable parameters and a second time using parameters proposed by the current work that minimize MAPE for four different groups of data. Based on the results of the analysis using the newly-suggested parameters, the five most accurate correlations are then further examined to evaluate their respective abilities to predict trends under various turbulent conditions. While many correlations perform well over the range of data (MAPE < 33%), no single correlation can predict all experimentally-observed trends for methane flames under these conditions. Further issues are found when predicting trends for larger hydrocarbons; ethane and propane. Although low errors are again found (MAPE < 25%), correlations are not generally able to replicate the observed trends of experimental data for C2H6 and C3H8. While it is commonly accepted that no single correlation can accurately predict ST, this work has shown that the correlation derived by Muppala provides the closest overall agreement to the data examined. However it cannot be defined as a general correlation. For this reason the authors have proposed to continue development of an ST modeling tool based on a modified version of the Cantera 1D freely propagating laminar flame speed (SL) code. Greater cooperation in the ST research community to expand the range of available experimental data and better enable direct comparison of data and correlations from different experiments is also recommended.

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

Fluids ◽

10.3390/fluids4030146 ◽

2019 ◽

Vol 4 (3) ◽

pp. 146 ◽

Cited By ~ 2

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.

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Experimental study of laminar and turbulent flame speed of a spherical flame in a fan-stirred closed vessel for hydrogen safety application

Nuclear Engineering and Design ◽

10.1016/j.nucengdes.2016.07.007 ◽

2017 ◽

Vol 312 ◽

pp. 214-227 ◽

Cited By ~ 14

Author(s):

J. Goulier ◽

N. Chaumeix ◽

F. Halter ◽

N. Meynet ◽

A. Bentaïb

Keyword(s):

Experimental Study ◽

Turbulent Flame ◽

Flame Speed ◽

Closed Vessel ◽

Spherical Flame ◽

Turbulent Flame Speed ◽

Safety Application ◽

Hydrogen Safety

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Application of a New Turbulent Flame Speed Combustion Model on Burn Rate Simulation of Spark Ignition Engines

10.4271/2016-01-0588 ◽

2016 ◽

Cited By ~ 3

Author(s):

Shiyou Yang ◽

Hemanth Kolla ◽

Nedunchezhian Swaminathan

Keyword(s):

Turbulent Flame ◽

Spark Ignition ◽

Flame Speed ◽

Combustion Model ◽

Spark Ignition Engines ◽

Turbulent Flame Speed ◽

Burn Rate

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

Combustion and Flame ◽

10.1016/j.combustflame.2012.10.006 ◽

2013 ◽

Vol 160 (2) ◽

pp. 351-365 ◽

Cited By ~ 5

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

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

Volume 2: Turbo Expo 2005 ◽

10.1115/gt2005-68565 ◽

2005 ◽

Cited By ~ 9

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.

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

Volume 2: Coal, Biomass and Alternative Fuels; Combustion and Fuels; Oil and Gas Applications; Cycle Innovations ◽

10.1115/97-gt-395 ◽

1997 ◽

Cited By ~ 8

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.

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