scholarly journals Structures of Ethanol Spray Flames under CO2 Dilution of the Oxidizer in the Counterflow Configuration under MILD Combustion Conditions

Fluids ◽  
2020 ◽  
Vol 5 (4) ◽  
pp. 194
Author(s):  
Oscar Noreña ◽  
Eva Gutheil
Keyword(s):  
Strain Rate ◽  
Droplet Diameter ◽  
Flame Temperature ◽  
Pure Oxygen ◽  
Pure Ethanol ◽  
Mild Combustion ◽  
Spray Flames ◽  
Air Stream ◽  
Reaction Zones ◽  
Single Reaction

Structures of both gaseous and liquid ethanol flames in different oxidizing gas environments in the axisymmetric counterflow configuration at atmospheric pressure are studied. Initially, ethanol/air gas flames are considered where pure ethanol is directed against air at initial temperatures of 400 K, and N2 is successively removed to obtain structures of ethanol/O2 gas flames. Furthermore, the addition of CO2 to the oxidizer side is carried out. Then, an ethanol spray is carried by air and directed against an air stream, and the same procedure is performed as described for the gas flames. The gas strain rate at the fuel side of the configuration is increased from low values of 55/s up to extinction, and the initial droplet diameter is varied. For the combustion of gaseous ethanol in air and in pure oxygen, the nitrogen removal results in an increase in the maximum flame temperature from 2010 K to 2920 K at a gas strain rate of 55/s on the fuel side of the configuration, and the extinction strain rates are 630/s and 26,000/s, respectively. It is confirmed that ethanol spray flames in air show two reaction zones at low strain whereas the lean ethanol spray flames in pure oxygen exhibit a single reaction zone in all situations studied. For increased liquid fuel mass flow rate to a global equivalence ratio of unity, two reaction zones are retrieved. An analysis regarding the addition of CO2 in both the ethanol/oxygen gas and spray flames is also discussed and is found that CO2 dilution of the carrier gas the spray is much more efficient than diluting the opposed gas stream in the counterflow configuration for the generation of MILD combustion conditions in oxy-fuel flames.

scholarly journals Effects of strain rate and CO2 on no formation in CH4/N2/O2 counter-flow diffusion flames

2018 ◽  
Vol 22 (Suppl. 2) ◽  
pp. 769-776
Author(s):  
Fei Ren ◽  
Longkai Xiang ◽  
Huaqiang Chu ◽  
Weiwei Han
Keyword(s):  
Strain Rate ◽  
Diffusion Flames ◽  
Numerical Study ◽  
Flame Temperature ◽  
Co2 Concentration ◽  
No Production ◽  
Counter Flow ◽  
Detailed Chemistry ◽  
No Formation ◽  
Key Factor

The reduction of nitrogen oxides in the high temperature flame is the key factor affecting the oxygen-enriched combustion performance. A numerical study using an OPPDIF code with detailed chemistry mechanism GRI 3.0 was carried out to focus on the effect of strain rate (25-130 s?1) and CO2 addition (0-0.59) on the oxidizer side on NO emission in CH4 / N2 / O2 counter-flow diffusion flame. The mole fraction profiles of flame structures, NO, NO2 and some selected radicals (H, O, OH) and the sensitivity of the dominant reactions contributing to NO formation in the counter-flow diffusion flames of CH4\/ N2 /O2 and CH4 / N2 / O2 / CO2 were obtained. The results indicated that the flame temperature and the amount of NO were reduced while the sensitivity of reactions to the prompt NO formation was gradually increased with the increasing strain rate. Furthermore, it is shown that with the increasing CO2 concentration in oxidizer, CO2 was directly involved in the reaction of NO consumption. The flame temperature and NO production were decreased dramatically and the mechanism of NO production was transformed from the thermal to prompt route.

Combustion Characteristics of Isolated Free-Falling Droplets of Jet A Blended With Ethanol and Butanol

2018 ◽  
Author(s):  
Álvaro Muelas ◽  
Pilar Remacha ◽  
Javier Ballester
Keyword(s):  
Gas Turbines ◽  
Alternative Fuels ◽  
Droplet Diameter ◽  
Combustion Process ◽  
Combustion Characteristics ◽  
Shell Size ◽  
Pure Ethanol ◽  
Promising Alternative ◽  
Burning Rates ◽  
Alcohol Mixtures

Recent studies on experimental gas turbines suggest that the addition of ethanol or butanol to Jet A are viable alternatives for reducing CO and NOx emissions while maintaining similar performance to that of pure Jet A. In light of this potential, experimental data regarding the burning characteristics of Jet A/ethanol and Jet A/butanol blends are required in order to better understand their combustion process. Following a previous study on Jet A/butanol droplet combustion, the scope has been extended in order to also include ethanol and a Jet A/ethanol mixture as well as to perform a more detailed characterization. In this work the combustion characteristics of Jet A, butanol, ethanol and their mixtures (20% vol. alcohol in kerosene) are presented for different test conditions. The evaluated combustion characteristics include droplet, flame and soot shell size evolutions, burning rates and image-based soot estimations. The influence of oxygen availability is also ascertained. The evolution of droplet diameter and burning rates for Jet A and its blends with both alcohols are very similar, whereas pure ethanol and butanol display more distinct behaviors. Soot indices are found to be quite different, with a clear reduction in the sooting propensity of the Jet A/alcohol mixtures when compared to neat kerosene. These results support the feasibility of kerosene-alcohol mixtures as promising alternative fuels with similar combustion characteristics, but with much lower sooting propensity than pure kerosene.

Experimental Researches on Micro-Droplet Freezing on a Solid Surface Under Atmospheric Conditions: Part I

2008 ◽  
Author(s):  
Heyun Liu ◽  
Xiaohui Ma
Keyword(s):  
Transmission Lines ◽  
Power Transmission ◽  
Electrostatic Force ◽  
Droplet Diameter ◽  
Ccd Camera ◽  
Freezing Process ◽  
Ice Accretion ◽  
Power Transmission Lines ◽  
Atmospheric Conditions ◽  
Air Stream

Atmospheric ice accretion on structures is a problem of fundamental importance to a number of industries. Examples of engineering problems caused by ice accretion involving aircraft, power transmission lines, telecommunication towers, electrical railway contact-wires, and other structures. Under atmospheric icing conditions two basic types of ice may form; rime or glaze. The supercooled micro-droplets in clouds are an important factor in icing. The objective of this study was to develop a new experimental method to investigate a single supercooled micro-droplet freezing process, in order to better understand the mechanism of rime or glaze ice accretion. The experimental device and principles are described in this paper. The experimental set has two small cold rooms, which is separated by a board with a central hole. A droplet with diameter of 15∼40 μm, temperature of 0∼−5°C was levitated in the cold air stream by electrostatic force. A CCD camera tracked its trace. The air temperature is from 0∼−10°C, the micro-droplet diameter is from 15∼40μm, and its temperature is from 0∼−5°C in the experimental study. This article focused on the experimental set and the experimental principles, and the next article will focus on the experimental data analysis.

The Combustion of a Liquid Fuel Droplet during Forced Convection

1994 ◽  
Vol 12 (1) ◽  
pp. 44-61
Author(s):  
Andrzej Teodorczyk ◽  
Stanislaw Wójcicki
Keyword(s):  
Reynolds Number ◽  
Forced Convection ◽  
Droplet Diameter ◽  
Fuel Droplet ◽  
Combus Tion ◽  
Air Stream ◽  
Freely Suspended ◽  
High Reynolds ◽  
Additional Support ◽  
Physical And Mathematical Models

A new experimental technique was used to investigate single fuel droplet combustion during forced convection: the burning droplet was freely suspended in the controlled air stream, without any additional support. Based on the photo-records of the burning process, the characteristics of the change of square of droplet diameter with time were made and the actual values of burning constants were determined for four hydrocarbon fuels: ben zene, n-heptane, iso-octane and toluene. The experiments were also carried out under micro-gravity and free convection conditions for the same set of fuels. The investigations have allowed the comparison of the burning mechanism of a single droplet for the three different external conditions and have compared quantitatively the burning constants. On the basis of the color pictures of the droplet burning under forced convection conditions and the temperature and gas concentration measurements within the flame, the mechanism of combus tion of fuel droplet was explained. The physical and mathematical models of the process have been proposed which included the aerodynamics of the droplet located in the high Reynolds number air stream, the energy balance of the evaporating droplet and the chemical reaction in the flow. The models have made it possible to determine the quantitative dependence of the burning con stant of different kinds of fuels on Reynolds number, the flow field parameters and the physical and chemical parameters of the liquid and its close surround ings. The calculated values of the parameters describing the burning pro cess have been compared to the experimental data and to the results reported by other investigators. The model has revealed the importance of the feed back mechanism between physical processes involved during droplet combus tion.

The Structure of Two-Stage Counterflow n-Heptane-Air Flames

2000 ◽  
Author(s):  
S. K. Aggarwal ◽  
H. S. Xue
Keyword(s):  
Strain Rate ◽  
Reaction Zone ◽  
Equivalence Ratio ◽  
Flame Structure ◽  
Premixed Combustion ◽  
Premixed Flame ◽  
Partially Premixed Combustion ◽  
Reaction Zones ◽  
Partially Premixed ◽  
Partially Premixed Flame

Partially premixed flames are formed by mixing air (in less than stoichiometric amounts) into the fuel stream prior to the reaction zone, where additional air is available for complete combustion. Such flames can occur in both laboratory and practical combustion systems. In advanced gas turbine combustor designs, such as a lean direct injection (LDI) combustor, partially premixed combustion represents an impotent mode of burning. Spray combustion often involves partially premixed combustion due to the locally fuel vapor-rich regions. In the present study, the detailed structure of n-heptane/air partially premixed flame in a counterflow configuration is investigated. The flame is computed by employing the Oppdif code and a detailed reaction mechanism consisting of 275 elementary reactions and 41 species. The partially premixed flame structure is characterized by two-stage burning or two distinct but synergistically coupled reaction zones, a rich premixed zone on the fuel side and a ‘nonpremixed zone on the air side. The fuel is completely consumed in the premixed zone with ethylene and acetylene being the major intermediate species. The reactions involving the consumption of these species are found to be the key rate-limiting reactions that characterize interactions between the two reaction zones, and determine the overall fuel consumption rate. The flame response to the variations in equivalence ratio and strain rate is examined. Increasing equivalence ratio and/or strain rate to a critical value leads to merging of the two reaction zones. The equivalence ratio variation affects the rich premixed reaction zone, while the variation in strain rate predominantly affects the nonpremixed reaction zone. The flame structure is also characterized in terms of a modified mixture fraction (conserved scalar), and laminar flamelet profiles are provided.

scholarly journals Turbulent Combustion Modelling and Experiments: Recent Trends and Developments

2019 ◽  
Vol 103 (4) ◽  
pp. 847-869 ◽  
Author(s):  
A. Giusti ◽  
E. Mastorakos
Keyword(s):  
Turbulent Combustion ◽  
Mixture Fraction ◽  
Moment Closure ◽  
Combustion Model ◽  
Complex Geometries ◽  
Conditional Moment ◽  
Practical Applications ◽  
Spray Flames ◽  
Reaction Zones ◽  
Soot Emissions

AbstractThe development of better laser-based experimental methods and the fast rise in computer power has created an unprecedented shift in turbulent combustion research. The range of species and quantities measured and the advent of kHz-level planar diagnostics are now providing great insights in important phenomena and applications such as local and global extinction, pollutants, and spray combustion that were hitherto unavailable. In simulations, the shift to LES allows better representation of the turbulent flow in complex geometries, but despite the fact that the grid size is smaller than in RANS, the push towards realistic conditions and the need to include more detailed chemistry that includes very fast species and thin reaction zones emphasize the necessity of a sub-grid turbulent combustion model. The paper discusses examples from current research with experiments and modelling that focus on flame transients (self-excited oscillations, local extinction), sprays, soot emissions, and on practical applications. These demonstrate how current models are being validated by experimental data and the concerted efforts the community is taking to promote the modelling tools to industry. In addition, the various coordinated International Workshops on non-premixed, premixed, and spray flames, and on soot are discussed and some of their target flames are explored. These comprise flames that are relatively simple to describe from a fluid mechanics perspective but contain difficult-to-model combustion problems such as extinction, pollutants and multi-mode reaction zones. Recently, swirl spray flames, which are more representative of industrial devices, have been added to the target flames. Typically, good agreement is found with LES and some combustion models such as the progress variable - mixture fraction flamelet model, the Conditional Moment Closure, and the Transported PDF method, but predicting soot emissions and the condition of complete extinction in complex geometries is still elusive.

scholarly journals Reaction Zones and Their Structure in MILD Combustion

2014 ◽  
Vol 186 (8) ◽  
pp. 1075-1096 ◽  
Author(s):  
Y. Minamoto ◽  
N. Swaminathan ◽  
R. S. Cant ◽  
T. Leung
Keyword(s):  
Mild Combustion ◽  
Reaction Zones

scholarly journals A Numerical Study on the Effect of CO Addition on Flame Temperature and NO Formation in Counterflow CH4/Air Diffusion Flames

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
Hongsheng Guo ◽  
W. Stuart Neill
Keyword(s):  
Carbon Monoxide ◽  
Strain Rate ◽  
Diffusion Flames ◽  
Numerical Study ◽  
Formation Rate ◽  
Flame Temperature ◽  
No Emission ◽  
No Formation ◽  
Air Diffusion ◽  
Emission Index

A numerical study was carried out to understand the effect of CO enrichment on flame temperature and NO formation in counterflow CH4/air diffusion flames. The results indicate that when CO is added to the fuel, both flame temperature and NO formation rate are changed due to the variations in adiabatic flame temperature, fuel Lewis number, and chemical reaction. At a low strain rate, the addition of carbon monoxide causes a monotonic decrease in flame temperature and peak NO concentration. However, NO emission index first slightly increases, and then decreases. At a moderate strain rate, the addition of CO has negligible effect on flame temperature and leads to a slight increase in both peak NO concentration and NO emission index, until the fraction of carbon monoxide reaches about 0.7. Then, with a further increase in the fraction of added carbon monoxide, all three quantities quickly decrease. At a high strain rate, the addition of carbon monoxide causes increase in flame temperature and NO formation rate, until a critical carbon monoxide fraction is reached. After the critical fraction, the further addition of carbon monoxide leads to decrease in both flame temperature and NO formation rate.

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