scholarly journals The Effects of CO2 Additional on Flame Characteristics in the CH4/N2/O2 Counterflow Diffusion Flame

Molecules ◽  
2021 ◽  
Vol 26 (10) ◽  
pp. 2905
Author(s):  
Ying Chen ◽  
Jingfu Wang ◽  
Xiaolei Zhang ◽  
Conghao Li
Keyword(s):  
Thermal Properties ◽  
Heat Release ◽  
Flame Front ◽  
Release Rate ◽  
Diffusion Flame ◽  
Flame Temperature ◽  
Radiative Properties ◽  
One Dimensional ◽  
Negative Effect ◽  
Counterflow Diffusion Flame

The effects (chemical, thermal, transport, and radiative) of CO2 added to the fuel side and oxidizer side on the flame temperature and the position of the flame front in a one-dimensional laminar counterflow diffusion flame of methane/N2/O2 were studied. Overall CO2 resulted in a decrease in flame temperature whether on the fuel side or on the oxidizer side, with the negative effect being more obvious on the latter side. The prominent effects of CO2 on the flame temperature were derived from its thermal properties on the fuel side and its radiative properties on the oxidizer side. The results also highlighted the differences in the four effects of CO2 on the position of the flame front on different sides. In addition, an analysis of OH and H radicals and the heat release rate of the main reactions illustrated how CO2 affects the flame temperature.

scholarly journals Quantification of the Local Heat Release Rate During Flame-Vortex Interactions at Different Lewis Numbers and Equivalence Ratios

2014 ◽  
Vol 16 (2-3) ◽  
pp. 195
Author(s):  
J.A. Denev ◽  
I. Naydenova ◽  
H. Bockhorn
Keyword(s):  
Heat Release ◽  
Flame Front ◽  
Heat Release Rate ◽  
Release Rate ◽  
Lewis Number ◽  
Local Heat ◽  
Flame Extinction ◽  
Single Vortex ◽  
Vortex Interactions ◽  
Polarisation Effect

<p>The present work aims at the detailed understanding of the local processes in premixed combustion of hydrogen, methane and propane flames at unsteady conditions. The methodology consists of the analysis of simulations of two-dimensional flame-vortex interactions as well as statistical data obtained from threedimensional Direct Numerical Simulations (DNS) of the flame front interacting with a set of vortexes. Special attention is given to the relationship between the Lewis number (<em>Le</em>) of the fuel and the flame front stretch in terms of both curvature and strain rate. A large single vortex bends the flame front thus creating both positive and negative curvatures, which in turn enhance the heat release rate in some locations of the flame front and decrease it in others. The resulting effect is called “polarisation effect”. The occurrence and the strength of the polarisation effect of curvature are tightly bound up with the Lewis number of the fuel. The polarisation effect is quantified by the ratio of maximum to minimum heat release rates along the flame front, which defines the Polarisation Effect Number (PEN). The more the Lewis number of a fuel deviates from unity, the stronger the polarisation effect is. Strong polarisation effects lead finally to local flame extinction. This is demonstrated for hydrogen flames with<em> Le</em> = 0.29 (lean) and Le = 2.2 (rich) as well as for artificially designed cases with <em>Le</em> = 0.1 and <em>Le</em> = 10.0. Therefore, flame extinction can occur for both thermodiffusively stable and unstable flames. It is shown that choosing an appropriate mixture of real fuels with different Lewis numbers, the homogeneity of the heat release rate along the flame front could be considerably enhanced. This relatively uniform heat release rate is not sensitive to curvature, which consequently decreases the occurrence of local extinction.</p><p> </p>

scholarly journals Non-Premixed Filtered Tabulated Chemistry: Filtered Flame Modeling of Diffusion Flames

Fuels ◽  
2021 ◽  
Vol 2 (2) ◽  
pp. 87-107
Author(s):  
Pedro Javier Obando Vega ◽  
Axel Coussement ◽  
Amsini Sadiki ◽  
Alessandro Parente
Keyword(s):  
Flame Front ◽  
Diffusion Flame ◽  
Diffusion Flames ◽  
Premixed Combustion ◽  
One Dimensional ◽  
Counterflow Flame ◽  
Tabulated Chemistry ◽  
Laminar Diffusion ◽  
Lift Off ◽  
The One

The flame front filtering is a well-known strategy in turbulent premixed combustion. An extension of this approach for the non-premixed combustion context has been proposed by means of directly filtering counterflow diffusion flamelets. Promising results were obtained for the non-premixed filtered tabulated chemistry formalism on 1-D and 2-D unresolved counterflow flame configurations. The present paper demonstrates the soundness of this approach on a 3-D real laminar non-premixed coflow flame. The model results are compared against the direct filtering of the fully resolved laminar diffusion flame showing that the formalism adequately describes the underlying physics. The study reveals the importance of the one-dimensional counterflow flamelet hypothesis, so that the model activation under this condition is ensured by means of a flame sensor. The consistent coupling between the model and the flame sensor adequately retrieves the flame lift-off and satisfactorily predicts the profile extension due to the filtering process.

scholarly journals Effects of an Organic-Inorganic Hybrid Containing Allyl Benzoxazine and POSS on Thermal Properties and Flame Retardancy of Epoxy Resin

Polymers ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 770 ◽  
Author(s):  
Benben Liu ◽  
Huiling Wang ◽  
Xiaoyan Guo ◽  
Rongjie Yang ◽  
Xiangmei Li
Keyword(s):  
Thermal Properties ◽  
Heat Release ◽  
Flame Retardant ◽  
Epoxy Resin ◽  
Heat Release Rate ◽  
Flame Retardancy ◽  
Release Rate ◽  
Cone Calorimeter ◽  
Inorganic Hybrid ◽  
X Ray

A novel organic-inorganic hybrid containing allyl benzoxazine and polyhedral oligomeric silsesquioxane (POSS) was synthesized by the thiol-ene (click) reaction. The benzoxazine (BOZ)-containing POSS (SPOSS-BOZ) copolymerized with benzoxazine/epoxy resin was used to prepare composites of SPOSS-PBZ-E nanocomposites(NPs). The polymerization behavior was monitored by FTIR and non-isothermal differential scanning calorimetry (DSC), which showed that the composites had completely cured with multiple polymerization mechanisms according to the oxazine ring-opening and epoxy resin (EP) polymerization. The thermal properties of the organic–inorganic polybenzoxazine (PBZ) nanocomposites were analyzed by DSC and thermogravimetric analysis (TGA). Furthermore, the X-ray diffraction analysis and the scanning electron microscopy (SEM) micrographs of the SPOSS-PBZ-E nanocomposites indicated that SPOSS was chemically incorporated into the hybrid nanocomposites in the size range of 80–200 nm. The flame retardancy of the benzoxazine epoxy resin composites was investigated by limiting oxygen index (LOI), UL 94 vertical burn test, and cone calorimeter tests. When the amount of SPOSS reached 10% or more, the vertical burning rating of the curing system arrived at V-1, and when the SPOSS-BOZ content reached 20 wt %, the thermal stability and flame retardancy of the material were both improved. Moreover, in the cone calorimeter testing, the addition of SPOSS-BOZ hindered the decomposition of the composites and led to a reduction in the peak heat release rate (pHRR), the average heat release rate (aHRR), and the total heat release (THR) values by about 20%, 25%, and 25%, respectively. The morphologies of the chars were also studied by SEM and energy dispersive X-ray spectroscopy (EDX), and the flame-retardant mechanism of POSS was mainly a condensed-phase flame retardant. The ceramic layer was formed by the enrichment of silicon on the char surface. When there are enough POSS nanoparticles, it can effectively protect the combustion of internal polymers.

scholarly journals Numerical study of the laminar flame propagation in ethane-air mixtures

2014 ◽  
Vol 12 (3) ◽  
pp. 391-402 ◽  
Author(s):  
Venera Giurcan ◽  
Domnina Razus ◽  
Maria Mitu ◽  
Dumitru Oancea
Keyword(s):  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Laminar Flame ◽  
Numerical Study ◽  
Flame Temperature ◽  
Chemical Species ◽  
Main Reaction ◽  
Flame Thickness ◽  
Wide Range

AbstractThe structure of premixed free one-dimensional laminar ethane-air flames was investigated by means of numerical simulations performed with a detailed mechanism (GRI-Mech version 3.0) by means of COSILAB package. The work provides data on ethane-air mixtures with a wide range of concentrations ([C2H6] = 3.0–9.5 vol.%) at initial temperatures between 300 and 550 K and initial pressures between 1 and 10 bar. The simulations deliver the laminar burning velocities and the profiles of temperature, chemical species concentrations and heat release rate across the flame front. The predicted burning velocities match well the burning velocities measured in various conditions, reported in literature. The influence of initial concentration, pressure and temperature of ethane-air mixtures on maximum flame temperature, heat release rate, flame thickness and peak concentrations of main reaction intermediates is examined and discussed.

scholarly journals Comparisons of the Uncoupled Effects of CO2 on the CH4/O2 Counterflow Diffusion Flame under High Pressure

2021 ◽  
Vol 11 (4) ◽  
pp. 1768
Author(s):  
Ying Chen ◽  
Jingfu Wang ◽  
Xiaolei Zhang ◽  
Conghao Li
Keyword(s):  
High Pressure ◽  
Thermal Effect ◽  
Diffusion Flame ◽  
Dominant Role ◽  
Flame Temperature ◽  
Chemical Effect ◽  
Temperature Reduction ◽  
Transport Effect ◽  
Counterflow Diffusion Flame ◽  
Opposite Manner

A comprehensive numerical investigation of the uncoupled chemical, thermal, and transport effects of CO2 on the temperature of CH4/O2 counterflow diffusion flame under high pressure up to 5 atm was conducted. Three pairs of artificial species were introduced to distinguish the chemical effect, thermal effect, and the transport effect of CO2 on the flame temperature. The numerical results showed that both the chemical effect and the thermal effect of the CO2 dilution in the oxidizer side can decrease the flame temperature significantly, while the transport effect of CO2 can only slightly increase the flame temperature and can even be ignored. The reduction value of the temperature caused by the chemical effect of CO2 grows linearly, while that caused by the thermal effect increases exponentially. The RPchem and RPthermal are defined to explain the temperature reduction percentage due to the chemical effect and the thermal effect of CO2 in the total temperature reduction caused by CO2 dilution, respectively. The RPchem decreases with the increase of the pressure, the strain rate, and the CO2 dilution ratio, while the RPthermal behaves in the opposite manner. In the above conditions, the chemical effect plays a dominant role on the flame temperature reduction.

Analysis of Heat Release Rate in the Partially Premixed Flame Structures During Autoignition of Unstrained, Laminar Mixing Layers

2012 ◽  
Author(s):  
Inkant Awasthi ◽  
George Gogos
Keyword(s):  
Heat Release ◽  
Release Rate ◽  
Diffusion Flame ◽  
Mixing Layer ◽  
Premixed Flame ◽  
Release Rates ◽  
Laminar Mixing ◽  
Flame Structures ◽  
Partially Premixed Flame ◽  
Fuel Stream

Autoignition in an unstrained, laminar mixing layer of methanol/air is investigated using detailed reaction mechanism and full multicomponent mass diffusion formulation. The temperature of the fuel stream is varied from 400 K to 1200 K, whereas the oxidizer stream is held at a fixed temperature of 1200 K. The calculations are performed for pressure p = 1 bar. Transient evolution of the autoignition kernel from initial partially premixed flame structures to final diffusion flame is demonstrated. The flame structures have been analysed for individual heat release rates. For equal fuel and oxidizer stream temperatures (1200 K), heat release in extremely fuel rich locations (with mixture fraction values up to 0.8) is found. A transient triple flame structure (two deflagrations and, one diffusion flame) is shown to exist even in cases when the temperature difference between the two streams is large. The heat release rates in the deflagrations depend on the temperatures of the two streams. When compared with the surviving diffusion flame, the heat release rate in the short-lived deflagrations is one to two orders of magnitude higher. It is shown that increasing the fuel stream temperature also decrease the ignition delay time in the mixing layer.

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