Quantifying the impact of heat loss, stretch and preferential diffusion effects to the anchoring of bluff body stabilized premixed flames

As emission legislation becomes more stringent, the modelling of turbulent lean premixed combustion is becoming an essential tool for designing efficient and environmentally friendly combustion systems. However, to predict emissions, reliable predictive models are required. Among the promising methods capable of predicting pollutant emissions with a long chemical time scale, such as nitrogen oxides (NOx), is conditional moment closure (CMC). However, the practical application of this method to turbulent premixed flames depends on the precision of the conditional scalar dissipation rate,. In this study, an alternative closure for this term is implemented in the RANS-CMC method. The method is validated against the velocity, temperature, and gas composition measurements of lean premixed flames close to blow-off, within the limit of computational fluid dynamic (CFD) capability. Acceptable agreement is achieved between the predicted and measured values near the burner, with an average error of 15%. The model reproduces the flame characteristics; some discrepancies are found within the recirculation region due to significant turbulence intensity.

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Characteristics of Flame Bases for V-Gutters Stabilized Premixed Flames

Volume 8A: Heat Transfer and Thermal Engineering ◽

10.1115/imece2013-63196 ◽

2013 ◽

Author(s):

Fan Gong ◽

Yong Huang

Keyword(s):

Thermal Conductivity ◽

Temperature Gradient ◽

Equivalence Ratio ◽

Premixed Flames ◽

Flame Stabilization ◽

Operating Conditions ◽

Inlet Temperature ◽

Heat Conducting ◽

Inlet Velocity ◽

The Impact

The objective of this work is to investigate the flame stabilization mechanism and the impact of the operating conditions on the characteristics of the steady, lean premixed flames. It’s well known that the flame base is very important to the existence of a flame, such as the flame after a V-gutter, which is typically used in ramjet and turbojet or turbofan afterburners and laboratory experiments. We performed two-dimensional simulations of turbulent premixed flames anchored downstream of the heat-conducting V-gutters in a confined passage for kerosene-air combustion. The flame bases are symmetrically located in the shear layers of the recirculation zone immediately after the V-gutter’s trailing edge. The effects of equivalence ratio of inlet mixture, inlet temperature, V-gutter’s thermal conductivity and inlet velocity on the flame base movements are investigated. When the equivalence ratio is raised, the flame base moves upstream slightly and the temperature gradient dT/dx near the flame base increases, so the flame base is strengthened. When the inlet temperature is raised, the flame base moves upstream very slightly, and near the flame base dT/dx increases and dT/dy decreases, so the flame base is strengthened. As the V-gutter’s thermal conductivity increases, the flame base moves downstream, and the temperature gradient dT/dx near the flame base decreases, so the flame base is weakened. When the inlet velocity is raised, the flame base moves upstream, and the convection heat loss with inlet mixture increases, so the flame base is weakened.

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Experimental investigation of isothermal and reacting flow characteristics downstream of axisymmetric bluff body stabilizers under stratified or fully premixed inlet mixture conditions

10.12681/eadd/48856 ◽

2020 ◽

Author(s):

Γεώργιος Πατεράκης

Keyword(s):

Experimental Investigation ◽

Turbulent Flow ◽

Bluff Body ◽

Operating Conditions ◽

Reacting Flow ◽

Wide Range ◽

Flow Features ◽

Air Mixing ◽

The Impact ◽

Stratified Flames

The current work describes an experimental investigation of isothermal and turbulent reacting flow field characteristics downstream of axisymmetric bluff body stabilizers under a variety of inlet mixture conditions. Fully premixed and stratified flames established downstream of this double cavity premixer/burner configuration were measured and assessed under lean and ultra-lean operating conditions. The aim of this thesis was to further comprehend the impact of stratifying the inlet fuelair mixture on the reacting wake characteristics for a range of practical stabilizers under a variety of inlet fuel-air settings. In the first part of this thesis, the isothermal mean and turbulent flow features downstream of a variety of axisymmetric baffles was initially examined. The effect of different shapes, (cone or disk), blockage ratios, (0.23 and 0.48), and rim thicknesses of these baffles was assessed. The variations of the recirculation zones, back flow velocity magnitude, annular jet ejection angles, wake development, entrainment efficiency, as well as several turbulent flow features were obtained, evaluated and appraised. Next, a comparative examination of the counterpart turbulent cold fuel-air mixing performance and characteristics of stratified against fully-premixed operation was performed for a wide range of baffle geometries and inlet mixture conditions. Scalar mixing and entrainment properties were investigated at the exit plane, at the bluff body annular shear layer, at the reattachment region and along the developing wake were investigated. These isothermal studies provided the necessary background information for clarifying the combustion properties and interpreting the trends in the counterpart turbulent reacting fields. Subsequently, for selected bluff bodies, flame structures and behavior for operation with a variety of reacting conditions were demonstrated. The effect of inlet fuel-air mixture settings, fuel type and bluff body geometry on wake development, flame shape, anchoring and structure, temperatures and combustion efficiencies, over lean and close to blow-off conditions, was presented and analyzed. For the obtained measurements infrared radiation, particle image velocimetry, laser doppler velocimetry, chemiluminescence imaging set-ups, together with Fouriertransform infrared spectroscopy, thermocouples and global emission analyzer instrumentation was employed. This helped to delineate a number of factors that affectcold flow fuel-air mixing, flame anchoring topologies, wake structure development and overall burner performance. The presented data will also significantly assist the validation of computational methodologies for combusting flows and the development of turbulence-chemistry interaction models.

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Three-dimensional cellular premixed flames generated by hydrodynamic and diffusive-thermal instabilities (Effects of unburned-gas temperature and heat loss)

Transactions of the JSME (in Japanese) ◽

10.1299/transjsme.19-00274 ◽

2019 ◽

Vol 85 (879) ◽

pp. 19-00274-19-00274

Author(s):

Satoshi KADOWAKI ◽

Masato NOGAMI ◽

Thwe Thwe Aung ◽

Toshiyuki KATSUMI ◽

Wataru YAMAZAKI ◽

...

Keyword(s):

Heat Loss ◽

Premixed Flames ◽

Three Dimensional ◽

Gas Temperature

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A Two-Stage Method to Determine Optimal Product Sampling considering Dynamic Potential Market

The Scientific World JOURNAL ◽

10.1155/2015/167481 ◽

2015 ◽

Vol 2015 ◽

pp. 1-9 ◽

Cited By ~ 1

Author(s):

Zhineng Hu ◽

Wei Lu ◽

Bing Han

Keyword(s):

Impact Analysis ◽

Negative Influence ◽

Key Factors ◽

Two Stage ◽

Logistic Analysis ◽

Potential Market ◽

Dynamic Potential ◽

Diffusion Effects ◽

The Impact ◽

Changing Rate

This paper develops an optimization model for the diffusion effects of free samples under dynamic changes in potential market based on the characteristics of independent product and presents a two-stage method to figure out the sampling level. The impact analysis of the key factors on the sampling level shows that the increase of the external coefficient or internal coefficient has a negative influence on the sampling level. And the changing rate of the potential market has no significant influence on the sampling level whereas the repeat purchase has a positive one. Using logistic analysis and regression analysis, the global sensitivity analysis gives a whole analysis of the interaction of all parameters, which provides a two-stage method to estimate the impact of the relevant parameters in the case of inaccuracy of the parameters and to be able to construct a 95% confidence interval for the predicted sampling level. Finally, the paper provides the operational steps to improve the accuracy of the parameter estimation and an innovational way to estimate the sampling level.

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Preferential diffusion effects in opposed-flow diffusion flame with blended fuels of CH4CH4 and H2H2

International Journal of Hydrogen Energy ◽

10.1016/j.ijhydene.2007.10.004 ◽

2008 ◽

Vol 33 (2) ◽

pp. 842-850 ◽

Cited By ~ 10

Author(s):

J SOOKIM

Keyword(s):

Diffusion Flame ◽

Opposed Flow ◽

Preferential Diffusion ◽

Diffusion Effects ◽

Blended Fuels

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Extinction Limits of Nonadiabatic, Catalyst-Assisted Flames in Stagnation-Point Flow

10.1115/imece2001/htd-24259 ◽

2001 ◽

Author(s):

Stephen B. Margolis ◽

Timothy J. Gardner

Keyword(s):

Stagnation Point ◽

Heat Loss ◽

Heat Production ◽

Fuel Efficiency ◽

Premixed Flames ◽

Stagnation Point Flow ◽

Pollutant Formation ◽

Flow Geometry ◽

Parameter Ranges

Abstract Because combustion is essentially an Arrhenius process, premixed flames generally can only exist within certain parameter ranges, or extinction limits, that correspond to a rate of heat production that is sufficient to sustain the reaction in a given flow geometry. Nonetheless, it is frequently desirable to extend these limits, often for the purpose of increasing fuel efficiency and/or reducing the rate of formation of pollutant species. Another emerging motivation is to allow combustion to be sustained in relatively small volumes, which are characterized by larger surface-to-volume ratios, that would otherwise lead to extinguishing levels of heat loss. Surface catalysts are widely used to achieve such enhancements with respect to efficiency and pollutant formation, and we wish to now consider the role catalysts might play with respect to nonadiabatic flames.

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