scholarly journals Stabilization Mechanisms of Swirling Premixed Flames With an Axial-Plus-Tangential Swirler

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Paul Jourdaine ◽  
Clément Mirat ◽  
Jean Caudal ◽  
Thierry Schuller
Keyword(s):  
Velocity Field ◽  
Flow Velocity ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Flame Temperature ◽  
Premixed Flames ◽  
Axial Flow ◽  
Operating Conditions ◽  
Fluorescence Measurements ◽  
Flame Shape

The stabilization of premixed flames within a swirling flow produced by an axial-plus-tangential swirler is investigated in an atmospheric test rig. In this system, flames are stabilized aerodynamically away from the solid components of the combustor without the help of any solid anchoring device. Experiments are reported for lean CH4/air mixtures, eventually also diluted with N2, with injection Reynolds numbers varying from 8500 to 25,000. Changes of the flame shape are examined with OH* chemiluminescence and OH laser-induced fluorescence measurements as a function of the operating conditions. Particle image velocimetry (PIV) measurements are used to reveal the structure of the velocity field in nonreacting and reacting conditions. It is shown that the axial-plus-tangential swirler allows to easily control the flame shape and the position of the flame leading edge with respect to the injector outlet. The ratio of the bulk injection velocity over the laminar burning velocity Ub/SL, the adiabatic flame temperature Tad, and the swirl number S0 are shown to control the flame shape and its position inside the combustion chamber. It is then shown that the axial velocity field produced by the axial-plus-tangential swirler is different from those produced by purely axial or radial devices. It takes here a W-shape profile with three local maxima and two minima. The mean turbulent flame front also takes this W-shape in an axial plane, with two lower positions located slightly off-axis and corresponding to the positions where the axial flow velocity is the lowest. It is finally shown that these positions can be inferred from axial flow velocity profiles under nonreacting conditions.

Stabilization Mechanisms of Swirling Premixed Flames With an Axial-Plus-Tangential Swirler

2017 ◽  
Author(s):  
Paul Jourdaine ◽  
Clément Mirat ◽  
Jean Caudal ◽  
Thierry Schuller
Keyword(s):  
Flow Velocity ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Flame Temperature ◽  
Premixed Flames ◽  
Axial Flow ◽  
Operating Conditions ◽  
Injection Velocity ◽  
Fluorescence Measurements ◽  
Flame Shape

The stabilization of premixed flames within swirling flows produced by an axial-plus-tangential swirler is investigated in an atmospheric test rig. In this system, flames are stabilized aerodynamically away from the solid elements of the combustor without help of any solid anchoring device. Experiments are reported for lean CH4/air mixtures, eventually also diluted with N2, with injection Reynolds numbers varying from 8 500 to 25 000. Changes of the flame shape are examined with OH* chemiluminescence and OH laser induced fluorescence measurements as a function of the operating conditions. Particle image velocimetry measurements are used to reveal the structure of the velocity field in non-reacting and reacting conditions. It is shown that the axial-plus-tangential swirler allows controlling the flame shape and the position of the flame leading edge with respect to the injector outlet. The ratio of the bulk injection velocity over the laminar burning velocity Ub/SL, the adiabatic flame temperature Tad and the swirl number S0 are shown to control the flame shape and its position. It is then shown that the axial flow field produced by the axial-plus-tangential swirler is different from those produced by axial or radial swirlers. It takes here a W-shape profile with three local maxima and two minima. The mean turbulent flame front also takes this W-shape in an axial plane, with two lower positions located slightly off-axis and corresponding to the positions where the axial flow velocity is minimum. It is finally shown that these positions can be inferred from axial flow velocity profiles under non-reacting conditions.

A predictive combustion model for one-dimensional gasoline engine simulation

2020 ◽  
pp. 146808742094590
Author(s):  
Yoshihiro Nomura ◽  
Seiji Yamamoto ◽  
Makoto Nagaoka ◽  
Stephan Diel ◽  
Kenta Kurihara ◽  
...  
Keyword(s):  
Gasoline Engine ◽  
Early Stage ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Operating Conditions ◽  
Combustion Model ◽  
One Dimensional ◽  
Turbulent Reynolds Number ◽  
Proposed Model ◽  
Wide Range

A new predictive combustion model for a one-dimensional computational fluid dynamics tool in the multibody dynamics processes of gasoline engines was developed and validated. The model consists of (1) a turbulent burning velocity model featuring a flame radius–based transitional function, steady burning velocity that considers local quenching using the Karlovitz number and laminarization by turbulent Reynolds number, as well as turbulent flame thickness and its quenching model near the liner wall, and (2) a knock model featuring auto-ignition by the Livengood–Wu integration and ignition delay time obtained using a full-kinetic model. The proposed model and previous models were verified under a wide range of operating conditions using engines with widely different specifications. Good agreement was only obtained for combustion characteristics by the proposed model without requiring individual calibration of model constants. The model was also evaluated for utilization after prototyping. Improved accuracy, especially of ignition timing, was obtained after further calibration using a small amount of engine data. It was confirmed that the proposed model is highly accurate at the early stage of the engine development process, and is also applicable for engine calibration models that require higher accuracy.

scholarly journals Dynamic-Stability Characteristics of Premixed Methane Oxy-Combustion

2011 ◽  
Author(s):  
Andrew P. Shroll ◽  
Santosh J. Shanbhogue ◽  
Ahmed F. Ghoniem
Keyword(s):  
Dynamic Stability ◽  
High Speed ◽  
Vortex Breakdown ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Flame Temperature ◽  
Wave Mode ◽  
Oxygen Mixture ◽  
Quarter Wave ◽  
Fuel Mixtures

This work explores the dynamic stability characteristics of premixed CH4/O2/CO2 mixtures in a 50kW swirl stabilized combustor. In all cases, the methane-oxygen mixture is stoichiometric, with different fractions of carbon dioxide used to control the flame temperature (Tad). For the highest Tad’s, the combustor is unstable at the five-quarter wave mode. As the temperature is reduced, the combustor jumps to the three quarter mode and then to the quarter wave before eventually reaching blowoff. Similar to the case of CH4/air mixtures, the transition from one mode to another is predominantly a function of the Tad of the reactive mixture, despite significant differences in laminar burning velocity and/or strained flame consumption speed between air and oxy-fuel mixtures for a given Tad. High speed images support this finding by revealing similar vortex breakdown modes and thus similar turbulent flame geometries that change as a function of flame temperature.

Using CFD for Time-Delay Modeling of Premix Flames

2001 ◽  
Author(s):  
Peter Flohr ◽  
Christian Oliver Paschereit ◽  
Bart van Roon ◽  
Bruno Schuermans
Keyword(s):  
Time Delay ◽  
Heat Release ◽  
Time Delays ◽  
Flame Temperature ◽  
Model Fitting ◽  
Operating Conditions ◽  
Fuel Injector ◽  
Fuel Injectors ◽  
Flame Shape ◽  
Good Agreement

This paper presents a refined model of the transfer function of a premix burner, compares the model with experiments, and discusses how the model can be used to map stability characteristics of a combustion system. The model is based on the assumption that acoustic velocity fluctuations cause modulations of fuel concentration at the fuel injector which, after a time delay, result in fluctuating heat release rates at the flame. Here, the time delay is modeled as a multitude of single time delays. The distribution of these time delays can be found either from model fitting to experimental data, or can be obtained directly from numerical simulations of the burner. The effect of distributed time delays is caused by axially distributed fuel injectors, turbulent diffusion, and a non-planar flame shape. As a consequence, heat release fluctuations at higher frequencies cancel, an effect which is also observed experimentally. It is found that the model is generally in good agreement with experiments. It is also demonstrated that the model can be used to map the burner stability charactistics for various operating conditions, e.g. for variations in power and flame temperature. A stability analysis is performed by incorporating the flame model into a combustor network model.

An Analysis of Local Quantities of Turbulent Premixed Flames Using DNS Databases

2007 ◽  
Author(s):  
Kazuya Tsuboi ◽  
Shinnosuke Nishiki ◽  
Tatsuya Hasegawa
Keyword(s):  
Reaction Rate ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Premixed Flames ◽  
Three Dimensional ◽  
Flame Surface ◽  
Turbulent Premixed Flames ◽  
Density Ratios ◽  
Turbulent Burning Velocity ◽  
Turbulent Premixed

An analysis of local flame area was performed using DNS (Direct Numerical Simulation) databases of turbulent premixed flames with different density ratios and with different Lewis numbers. Firstly, a local flame surface at a prescribed progress variable was identified as a local three-dimensional polygon. And then the polygon was divided into some triangles and local flame area was evaluated. The turbulent burning velocity was evaluated using the ratio of the area of turbulent flame to that of planar flame and compared with the turbulent burning velocity obtained by the reaction rate.

Aerodynamic Quenching and Burning Velocity of Turbulent Premixed Methane-Air Flames

2015 ◽  
Author(s):  
Girish V. Nivarti ◽  
R. Stewart Cant
Keyword(s):  
Turbulence Intensity ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Premixed Flames ◽  
Experimental Studies ◽  
Flame Speed ◽  
Flame Surface ◽  
Turbulent Flame Speed ◽  
Combustion Models ◽  
Turbulent Premixed

Industry-relevant turbulent premixed combustion models continue to rely on empirical expressions for turbulent flame speed in closure modelling for the mean turbulent reaction rate. To date, an accurate sub-model for turbulent flame speed has not been proposed for flows with high turbulence intensities. Experimental studies in the pertinent combustion regime, known as the Thin Reaction Zones (TRZ) regime, are limited by the existing techniques of turbulence generation whereas, until recently, the high computational expense involved in solving such problems has restricted theoretical studies. We investigate the behaviour of premixed flames in the TRZ regime by conducting a parametric 3D Direct Numerical Simulation (DNS) study of stoichiometric methane-air mixtures using single-step chemistry in an inflow-outflow configuration. Inflow turbulence intensity is varied while keeping the integral length scale constant across six separate simulations which span altogether a significant portion of the TRZ regime. The resulting variation of turbulent flame speed with turbulence intensity demonstrates the well-known bending phenomenon and conforms with recent experimental observations of freely-propagating premixed flames in this regime. As turbulence intensity is increased, the calculated flame surface exhibits an increasing degree of wrinkling and pocket-formation. In addition, the internal thermo-chemical structure of the flame is greatly affected when the turbulence intensity is more than an order of magnitude higher than the laminar flame speed. These qualitative observations establish the present DNS framework as a powerful tool for capturing turbulence-chemistry interactions that influence the bending phenomenon. Hence, this work forms the basis for further analysis using a detailed chemical description to investigate these interactions and, thereby, improve combustion models of industrial relevance.

scholarly journals Dynamic-Stability Characteristics of Premixed Methane Oxy-Combustion

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Andrew P. Shroll ◽  
Santosh J. Shanbhogue ◽  
Ahmed F. Ghoniem
Keyword(s):  
Natural Frequency ◽  
Dynamic Stability ◽  
High Speed ◽  
Vortex Breakdown ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Flame Temperature ◽  
Low Frequency ◽  
Oxygen Mixture ◽  
Fuel Mixtures

This work explores the dynamic stability characteristics of premixed CH4/O2/CO2 mixtures in a 50 kW swirl stabilized combustor. In all cases, the methane-oxygen mixture is stoichiometric, with different dilution levels of carbon dioxide used to control the flame temperature (Tad). For the highest Tad’s, the combustor is unstable at the first harmonic of the combustor’s natural frequency. As the temperature is reduced, the combustor jumps to fundamental mode and then to a low-frequency mode whose value is well below the combustor’s natural frequency, before eventually reaching blowoff. Similar to the case of CH4/air mixtures, the transition from one mode to another is predominantly a function of the Tad of the reactive mixture, despite significant differences in laminar burning velocity and/or strained flame consumption speed between air and oxy-fuel mixtures for a given Tad. High speed images support this finding by revealing similar vortex breakdown modes and thus similar turbulent flame geometries that change as a function of flame temperature.

Fundamental Combustion Characteristics of Lean and Stoichiometric Hydrogen Laminar Premixed Flames Diluted With Nitrogen or Carbon Dioxide

2016 ◽  
Vol 138 (11) ◽  
Author(s):  
Hong-Meng Li ◽  
Guo-Xiu Li ◽  
Zuo-Yu Sun ◽  
Zi-Hang Zhou ◽  
Yuan Li ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Equivalence Ratio ◽  
Burning Velocity ◽  
Flame Temperature ◽  
Premixed Flames ◽  
Combustion Characteristics ◽  
Inert Gas ◽  
Chemical Effect ◽  
Laminar Burning Velocity ◽  
Suppression Effect

In this work, the laminar combustion characteristics of H2/N2/air (H2/CO2/air) were systematically investigated under different hydrogen ratios (40–100%) and equivalence ratios (0.4–1.0) in a closed combustion vessel using the spherical expanding flame method associated with Schlieren technology. The unstretched laminar burning velocities were compared with data from previous study, and the result indicates that excellent agreements are obtained. Numerical simulations were also conducted using GRI3.0 and USC II mechanisms to compare with the present experimental results. The Markstein length for H2/inert gas can be decreased by decreasing the equivalence ratio and hydrogen ratio. The results indicate that the H2/inert gas premixed flames tend to be more unstable with the decrease of equivalence ratio and hydrogen ratio. For H2/N2 mixture, the suppression effect on laminar burning velocity is caused by modified specific heat of mixtures and decreased heat release, which result in a decreased flame temperature. For H2/CO2 mixture, the carbon dioxide has stronger dilution effect than nitrogen in reducing laminar burning velocity owing to both thermal effect and chemical effect.

scholarly journals Combustion Characteristics for Turbulent Prevaporized Premixed Flame Using Commercial Light Diesel and Kerosene Fuels

2014 ◽  
Vol 2014 ◽  
pp. 1-17
Author(s):  
Mohamed S. Shehata ◽  
Mohamed M. ElKotb ◽  
Hindawi Salem
Keyword(s):  
Reynolds Number ◽  
Flow Velocity ◽  
Equivalence Ratio ◽  
Gas Flow ◽  
Flame Temperature ◽  
Combustion Process ◽  
Perforated Plate ◽  
Operating Conditions ◽  
Fuel Type ◽  
Gas Flow Velocity

Experimental study has been carried out for investigating fuel type, fuel blends, equivalence ratio, Reynolds number, inlet mixture temperature, and holes diameter of perforated plate affecting combustion process for turbulent prevaporized premixed air flames for different operating conditions. CO2, CO, H2, N2, C3H8, C2H6, C2H4, flame temperature, and gas flow velocity are measured along flame axis for different operating conditions. Gas chromatographic (GC) and CO/CO2infrared gas analyzer are used for measuring different species. Temperature is measured using thermocouple technique. Gas flow velocity is measured using pitot tube technique. The effect of kerosene percentage on concentration, flame temperature, and gas flow velocity is not linearly dependent. Correlations for adiabatic flame temperature for diesel and kerosene-air flames are obtained as function of mixture strength, fuel type, and inlet mixture temperature. Effect of equivalence ratio on combustion process for light diesel-air flame is greater than for kerosene-air flame. Flame temperature increases with increased Reynolds number for different operating conditions. Effect of Reynolds number on combustion process for light diesel flame is greater than for kerosene flame and also for rich flame is greater than for lean flame. The present work contributes to design and development of lean prevaporized premixed (LPP) gas turbine combustors.

scholarly journals Laser Velocimeter Measurements in the Pump of an Automotive Torque Converter: Part II — Unsteady Measurements

1994 ◽  
Author(s):  
K. Brun ◽  
R. D. Flack ◽  
J. K. Gruver
Keyword(s):  
Velocity Field ◽  
Flow Field ◽  
Flow Velocity ◽  
Angular Position ◽  
Torque Converter ◽  
Operating Conditions ◽  
Plane Flow ◽  
Through Flow ◽  
Periodic Fluctuations ◽  
Pump Inlet

The unsteady velocity field found in the pump of an automotive torque converter was measured using laser velocimetry. Velocities in the inlet, mid-, and exit planes of the pump were investigated at two significantly different operating conditions: turbine/pump rotational speed ratios of 0.065, and 0.800. A data organization method was developed to visualize the three dimensional, periodic unsteady velocity field in the rotating frame. For this method, the acquired data is assumed to be periodic at synchronous and blade interaction frequencies. Two shaft encoders were employed to obtain the instantaneous angular position of the torque converter pump and turbine at the instant of laser velocimeter data acquisition. By proper “registration” of the data visualizing the transient interaction effects between the stator and the pump, and the pump and the turbine was possible. Results showed strong cyclic velocity fluctuations in the pump inlet plane as a function of the relative stator-pump position. Typical percent periodic fluctuations in the through flow velocity were 70% of the average through flow velocity. The upstream propagation influence of the turbine on the pump exit plane flow field was seen to he smaller. Percent periodic fluctuations of the through flow velocity were typically 30%. The effect of the stator and turbine on the mid-plane flow field was seen to be negligible. The incidence angle at the pump inlet fluctuated by 27° and 14° for the 0.065 and 0.800 speed ratios, respectively. Typical slip factors at the exit were 0.965 and fluctuated by less than 1%.

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