Flashback and Turbulent Flame Speed Measurements in Hydrogen/Methane Flames Stabilized by a Low-Swirl Injector at Elevated Pressures and Temperatures

2013 ◽  
Vol 136 (3) ◽  
Author(s):  
David Beerer ◽  
Vincent McDonell ◽  
Peter Therkelsen ◽  
Robert K. Cheng
Keyword(s):  
Turbulent Flame ◽  
Flame Temperature ◽  
Flame Speed ◽  
Inlet Temperature ◽  
Local Displacement ◽  
Turbulent Flame Speed ◽  
Elevated Pressures ◽  
Swirl Injector ◽  
Inlet Conditions ◽  
Displacement Speed

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.

Modeling of Inhomogeneously Premixed Combustion With an Extended TFC Model

2000 ◽  
Vol 124 (1) ◽  
pp. 58-65 ◽  
Author(s):  
W. Polifke ◽  
P. Flohr ◽  
M. Brandt
Keyword(s):  
Laminar Flame ◽  
Mixture Fraction ◽  
Turbulent Flame ◽  
Flame Temperature ◽  
Flame Speed ◽  
Premixed Combustion ◽  
Combustion Stability ◽  
Model Parameters ◽  
Turbulent Flame Speed ◽  
Functional Relationships

In many practical applications, so-called premixed burners do not achieve perfect premixing of fuel and air. Instead, fuel injection pressure is limited, the permissible burner pressure drop is small and mixing lengths are curtailed to reduce the danger of flashback. Furthermore, internal or external piloting is frequently employed to improve combustion stability, while part-load operation often requires burner staging, where neighboring burners operate with unequal fuel/air equivalence ratios. In this report, an extension of the turbulent flame speed closure (TFC) model for highly turbulent premixed combustion is presented, which allows application of the model to the case of inhomogeneously premixed combustion. The extension is quite straightforward, i.e., the dependence of model parameters on mixture fraction is accounted for by providing appropriate lookup tables or functional relationships to the model. The model parameters determined in this way are adiabatic flame temperature, laminar flame speed and critical gradient. The model has been validated against a test case from the open literature and applied to an externally piloted industrial gas turbine burner with good success.

Modeling of Inhomogeneously Premixed Combustion With an Extended TFC Model

2000 ◽  
Author(s):  
Wolfgang Polifke ◽  
Peter Flohr ◽  
Martin Brandt
Keyword(s):  
Laminar Flame ◽  
Mixture Fraction ◽  
Turbulent Flame ◽  
Flame Temperature ◽  
Flame Speed ◽  
Premixed Combustion ◽  
Combustion Stability ◽  
Model Parameters ◽  
Turbulent Flame Speed ◽  
Functional Relationships

In many practical applications, so-called premixed burners do not achieve perfect premixing of fuel and air. Instead, fuel injection pressure is limited, the permissible burner pressure drop is small and mixing lengths are curtailed to reduce the danger of flashback. Furthermore, internal or external piloting is frequently employed to improve combustion stability, while part-load operation often requires burner staging, where neighboring burners operate with unequal fuel/air equivalence ratios. In this report, an extension of the Turbulent Flame speed Closure (TFC) model for highly turbulent premixed combustion is presented, which allows application of the model to the case of inhomogeneously premixed combustion. The extension is quite straightforward, i.e. the dependence of model parameters on mixture fraction is accounted for by providing appropriate lookup tables or functional relationships to the model. The model parameters determined in this way are adiabatic flame temperature, laminar flame speed and critical gradient. The model has been validated against a test case from the open literature and applied to an externally piloted industrial gas turbine burner with good success.

Flame Front Characteristic and Turbulent Flame Speed of Lean Premixed Syngas Combustion at Gas Turbine Relevant Conditions

2009 ◽  
Author(s):  
S. Daniele ◽  
P. Jansohn ◽  
K. Boulouchos
Keyword(s):  
Flame Front ◽  
Gas Turbine ◽  
Turbulent Flame ◽  
Front Surface ◽  
Flame Speed ◽  
Inlet Temperature ◽  
Oh Radicals ◽  
High Hydrogen ◽  
Turbulent Flame Speed ◽  
Front Detection

This paper focuses on the description of the turbulent flame speed, at gas turbine like conditions, for different syngas mixtures, selected in order to simulate syngas compositions typically derived from gasification of coal, oil, biomass, and used for power generation in integrated gasification combined cycle (IGCC) processes. In this paper the turbulent flame speed is reported as global consumption rate and calculated based on a mass continuity approach applied to the combustor inlet area and the flame front surface, which was detected experimentally. Flame front detection was done by means of planar laser induced fluorescence technique taking OH radicals as seeding dyes. An in-house developed flame front detection software tool has been further improved and utilized in this work in order to better fit ultra-lean H2-rich flames. Experiments were carried out in a High Pressure Test Rig for operating pressures up to 15 bar. Data provided in this paper will focus on a pressure level of 5 bar, adiabatic flame temperatures up to 1900 K, inlet velocities from 40 to 80 m/s, and inlet temperature of 672 and 772 K. As expected, the results highlight the strongly elevated values of turbulent flame speed for high hydrogen containing fuel gas mixtures. Compared with flame speed data for pure CH4 the ratio (STSyn/STCH4) takes up values of 7 to 8. In absolute terms values go up even beyond 10 m/s. With increased H2 content in the mixture the burning velocity raises, due to the faster chemical kinetics characteristic of this compound and due to physical properties of H2 (Le<1) which enhance flame front corrugation (i.e. flame front surface). Inlet velocity and pressure variations showed to have weak effect on the average flame front position whereas this last parameter is strongly affected by the mixture composition, the equivalence ratio and inlet temperature.

Flashback, Blow Out, Emissions, and Turbulent Displacement Flame Speed Measurements in a Hydrogen and Methane Fired Low-Swirl Injector at Elevated Pressures and Temperatures

2012 ◽  
Author(s):  
David Beerer ◽  
Vincent McDonell ◽  
Peter Therkelsen ◽  
Robert K. Cheng
Keyword(s):  
Natural Gas ◽  
Atmospheric Pressure ◽  
Turbulent Flame ◽  
Turbine Engines ◽  
Inlet Temperature ◽  
Gas Turbine Engines ◽  
Pressure Data ◽  
High Hydrogen ◽  
Elevated Pressures ◽  
Swirl Injector

This paper reports on a work in progress study measuring flashback, blow out, emissions and turbulent displacement flame speeds in a low swirl injector operated at elevated pressures and inlet temperatures with hydrogen and methane based fuels in an optically accessible combustor rig. The goal is to extend the knowledge of low-swirl flames at conditions relevant to gas turbine engines. Testing was conducted at pressures ranging from 3 to 6 atm, inlet temperatures from 290 to 600K, and inlet bulk velocities from 20 to 60 m/s for natural gas and a 90%/10% by volume hydrogen/methane blend. Blow out limits for natural gas were found to be independent of pressure and inlet temperature but weakly dependent on velocity. Flashback limits for hydrogen were found to be independent of inlet temperature but strongly dependent on velocity and pressure. Local displacement turbulent flame speeds for methane were measured and appear to coincide with atmospheric pressure data in the literature. NOx emissions for both fuels were found to be exponentially dependent upon firing temperature, but emissions for the high hydrogen content flames were consistently higher than natural gas flames.

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

2016 ◽  
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.

Correlations for Turbulent Flame Speed of Different Syngas Mixtures at High Pressure and Temperature

2012 ◽  
Author(s):  
S. Daniele ◽  
P. Jansohn
Keyword(s):  
High Pressure ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Fuel Mixture ◽  
Turbulent Flames ◽  
Flame Speed ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Turbulent Flame Speed ◽  
Combustion Properties

There is an obvious lack of data and understanding of the behavior of turbulent flames at high temperature and high pressure, especially concerning hydrogen containing fuels. Among the many relevant parameters, the turbulent flame speed “ST” is one of the most interesting for scientists and engineers. This paper reports an experimental investigation of premixed syngas combustion at gas-turbine like conditions, with emphasis on the determination of ST/SL derived as global fuel consumption per unit time. Experiments at pressures up to 2.00 MPa, inlet temperatures and velocities up to 773K and 150 m/s respectively, u′/SL greater than 100 are presented. Comparison between different syngas mixtures and methane clearly show much higher ST/SL for the former fuel. It is shown that ST/SL is strongly dependent on preferential diffusive-thermal (PDT) effects, co-acting with hydrodynamic effects, even for very high u′/SL. ST/SL increases with rising hydrogen content in the fuel mixture and with pressure. A correlation for ST/SL valid for all investigated fuel mixtures, including methane, is proposed in terms of turbulence properties (turbulence intensity and integral length scale), combustion properties (laminar flame speed and laminar flame thickness) and operating conditions (pressure and inlet temperature). The correlation captures effects of preferential diffusive-thermal and hydrodynamic instabilities.

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.

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