Effect of Strain Rate and Pressure on the Flame Structure and Emission Characteristics of Syngas Flames

2007 ◽  
Author(s):  
Sibendu Som ◽  
Anita I. Rami´rez ◽  
Jonathan Hagerdorn ◽  
Alexei Saveliev ◽  
Suresh K. Aggarwal
Keyword(s):  
Strain Rate ◽  
Reaction Zone ◽  
Laminar Flame ◽  
Flame Structure ◽  
Flame Temperature ◽  
Chemical Kinetic ◽  
No Production ◽  
Emission Characteristics ◽  
Strain Rates ◽  
Fundamental Understanding

Synthesis gas or “Syngas” is being recognized as a viable energy source worldwide, particularly for stationary power generation due to its wide flexibility in fuel sources. There are gaps in the fundamental understanding of syngas combustion and emissions characteristics, especially at elevated pressures, high strain rates and in more practical conditions. This paper presents a numerical and experimental investigation to gain fundamental understanding of combustion and emission characteristics of syngas with varying composition, pressure and strain rate. Two representative syngas fuel mixtures, 50% H2 / 50% CO and 5% H2 / 95% CO (% vol.), are chosen, three detailed chemical kinetic models are used namely, GRI 3.0, Davis et al. and Li et al. mechanisms. Davis et al. mechanism agrees best with the experimental data hence is used to simulate the partially premixed flame structures at all pressures. Results indicate that for the pressure range investigated, a typical double flame structure was observed characterized by a rich premixed reaction zone (RPZ) on the fuel side and a nonpremixed reaction zone (NPZ) at the oxidizer side nozzle with the stabilizing due to the H2 chemistry rather than the CO chemistry. Sensitivity analysis to mass burning rates for unstretched laminar flame shows that flames are more sensitive to H2 chemistry. For both representative mixtures an increase in pressure leads to a significant increase in NO due to increase in flame temperature. The emission index for these flames is also found to follow a similar behavior with pressure. Although flame temperatures were higher for flame A, total NO is lower for these flames due to increases in reburn characteristics. Thermal route dominates NO production while, prompt route is negligible. Experimental analysis on the stability of nonpremixed syngas/air flames showed that the flames were very stable for the range of strain rates investigated. At low strain rates it required 0.5% H2 to establish a stable flame.

Emission Characteristics of Syngas Flames

2006 ◽  
Author(s):  
Sibendu Som ◽  
Anita I. Ramirez ◽  
Suresh Aggarwal
Keyword(s):  
Power Generation ◽  
Flame Temperature ◽  
Chemical Kinetic ◽  
Inlet Temperature ◽  
No Production ◽  
Emission Characteristics ◽  
Atmospheric Conditions ◽  
Harmful Emission ◽  
Fundamental Understanding ◽  
Fuel Components

Synthesis gas or "Syngas" is being recognized as a viable energy source worldwide, particularly for stationary power generation due to its wide flexibility in fuel sources and superior pollutants characteristics. Although its composition may vary significantly, it generally contains CO and H2 as the dominant fuel components with varying amount of methane and diluents. There are, however, gaps in the fundamental understanding of syngas combustion and emissions, as most previous research has focused on flames burning individual fuel components such as H2 and CH4, rather than syngas mixtures. To ensure the environmental feasibility of syngas, the harmful emission, especially NOx, must comply with current and future regulations. In addition, the combustion of syngas occurs at elevated pressures and inlet temperatures. Most published research has considered the combustion of syngas constituents at atmospheric conditions. This paper presents a numerical investigation to gain fundamental understanding of combustion and emission characteristics of syngas with varying composition, pressure and inlet temperatures. Two representative syngas fuel mixtures, 50% H2/50% CO and 5% H2 / 95% CO (% vol.), are chosen based on fuel composition data from multiple power generation plants worldwide. Three detailed chemical kinetic models are used namely, GRI 3.0, Davis and Dryer mechanisms. Results indicate that for both representative mixtures an increase in reactant temperature leads to a significant increase in NOx due to increase in flame temperature caused by an increase in inlet temperature. As the pressure is increased from 1 to 6 atm, the peak NO increases rapidly, and then becomes nearly independent of pressure. This can be attributed to a similar trend in radical species responsible for NO production such as HCN and OH which both show the most significant increase at low pressures. The emission index for these flames is also found to follow a similar behavior with pressure.

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.

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.

Flame Stabilization and Emission Characteristics of a Prototype Gas Turbine Burner at Atmospheric Conditions

2016 ◽  
Author(s):  
Atanu Kundu ◽  
Jens Klingmann ◽  
Arman Ahamed Subash ◽  
Robert Collin
Keyword(s):  
Gas Turbine ◽  
Reaction Zone ◽  
Vector Fields ◽  
Thermal Power ◽  
Flame Structure ◽  
Flame Temperature ◽  
Flame Stabilization ◽  
Atmospheric Conditions ◽  
Pilot Fuel ◽  
Co Emission

In the present work, a downscaled prototype 4th generation Dry Low Emission gas turbine (SGT-750) burner (designed and manufactured by Siemens Industrial Turbomachinery AB, Sweden) was investigated using an atmospheric experimental facility. The primary purpose of the research is to analyze flame stability and emission capability of the burner. OH Planar Laser-Induced Fluorescence (OH-PLIF), and chemiluminescence imaging were performed to characterize the flame structure and location. From the OH-PLIF images, the reaction zone and post flame region could be identified clearly. The chemiluminescence images provide an estimation of the overall heat release from the secondary combustion zone inside the Quarl. Emission was measured using a water-cooled emission probe, placed at the exit of the combustor to sample NOx and CO concentrations. The global equivalence ratio (Φ) was varied from rich to lean limit (flame temperature change from 1950 K to 1570 K) for understanding the stable and instable reaction zones inside the Quarl. Total thermal power was varied from 70 kW to 140 kW by changing global Φ and burner throat velocity (60 to 80 m/s). Near the lean blowout (LBO) event (at global Φ ∼ 0.4), instability of reaction zone is revealed from the flame images. Incorrect modulation of Pilot and RPL fuel splits show instable flame. Flame instability mitigation was possible using higher amount of RPL and Pilot fuel (trade-off with emission performance). The main flame LBO margin was extended by applying higher Pilot fuel and using higher preheat air temperature. Numerical analysis was carried out using Fluent to understand the scalar and vector fields. A basic chemical reactor network model was developed to predict the NOx and CO emission with experimental results. NOx emission prediction showed good agreement with experiment; whereas the model is failed to capture accurate CO emission in the lean operating points.

Impact of Equivalence Ratio on the Macrostructure of Premixed Swirling CH4/Air and CH4/O2/CO2 Flames

2015 ◽  
Author(s):  
Hirotatsu Watanabe ◽  
Santosh J. Shanbhogue ◽  
Ahmed F. Ghoniem
Keyword(s):  
Strain Rate ◽  
Shear Layer ◽  
Equivalence Ratio ◽  
Burning Velocity ◽  
Flame Temperature ◽  
Flame Stabilization ◽  
Sudden Expansion ◽  
Strain Rates ◽  
Cross Point ◽  
Extinction Strain Rate

Premixed CH4/O2/CO2 flames (oxy-flames) and CH4/air flames (air-flames) were experimentally studied in a swirl-stabilized combustor. For comparing oxy and air flames, the same equivalence ratio and adiabatic flame temperature were used. CO2 dilution was adjusted to attain the same adiabatic temperature for the oxy-flame and the corresponding air-flame while keeping the equivalence ratio and Reynolds number (=20,000) the same. For high equivalence ratios, we observed flames stabilized along the inner and outer shear layers of the swirling flow and sudden expansion, respectively, in both flames. However, one notable difference between the two flames appears as the equivalence ratio reaches 0.60. At this point, the outer shear layer flame disappears in the air-flame while it persists in the oxy-flame, despite the lower burning velocity of the oxy-flame. Prior PIV measurements (Ref. 9) showed that the strains along the outer shear layer are higher than along the inner shear layer. Therefore, the extinction strain rates in both flames were calculated using a counter-flow premixed twin flame configuration. Calculations at the equivalence ratio of 0.60 show that the extinction strain rate is higher in the oxy than in the air flame, which help explain why it persists on the outer shear layer with higher strain rate. It is likely that extinction strain rates contribute to the oxy-flame stabilization when air flame extinguish in the outer shear layer. However, the trend reverses at higher equivalence ratio, and the cross point of the extinction strain rate appears at equivalence ratio of 0.64.

Prediction of Premixed Laminar Flame Structure and Burning Velocity of Aviation Fuel-Air Mixtures

2001 ◽  
Author(s):  
A. G. Kyne ◽  
P. M. Patterson ◽  
M. Pourkashanian ◽  
C. W. Wilson ◽  
A. Williams
Keyword(s):  
Reaction Mechanism ◽  
Laminar Flame ◽  
Burning Velocity ◽  
Flame Structure ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Aviation Fuel ◽  
Measured Temperature ◽  
Premixed Laminar ◽  
Increasing Temperature

The structure of a rich burner stabilised kerosene/O2/N2 flame is predicted using a detailed chemical kinetic mechanism where the kerosene is represented by a mixture of n-decane and toluene. The chemical reaction mechanism, consisting of 440 reactions between 84 species, is capable of predicting the experimentally determined flame structure of Douté et al. (1995) with good success using the measured temperature profile as input. Sensitivity and reaction rate analyses are carried out to identify the most significant reactions and based on this the reaction mechanism was reduced to one with only 165 reactions without any loss of accuracy. Burning velocities of kerosene-air mixtures were also determined over an extensive range of equivalence ratios at atmospheric pressure. The initial temperature of the mixture was also varied and burning velocities were found to increase with increasing temperature. Burning velocities calculated using both the detailed and reduced mechanisms were essentially identical.

scholarly journals Experimental and Kinetic Evaluation of Pressurized Lean Premixed Hydrogen-Air Flame Stability With Carbon Dioxide and Steam Dilution

2020 ◽  
Author(s):  
Jon Runyon ◽  
Daniel Pugh ◽  
Anthony Giles ◽  
Burak Goktepe ◽  
Philip Bowen ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Strain Rate ◽  
Equivalence Ratio ◽  
Laminar Flame ◽  
Flame Temperature ◽  
Flame Speed ◽  
Flame Stability ◽  
Laminar Flame Speed ◽  
Adiabatic Flame Temperature ◽  
Extinction Strain Rate

Abstract A study has been undertaken to experimentally and numerically evaluate the use of carbon dioxide or steam as premixed fuel additive in hydrogen-air flames to aid in the development of lean premixed (LPM) swirl burner technology for low NOx operation. Chemical kinetics modelling indicates that the use of CO2 or steam in the premixed reactants reduces H2-air laminar flame speed and adiabatic flame temperature within the well-characterized range of preheated LPM methane-air flames, albeit in markedly different proportions; for example, nearly 65 %vol CO2 as a proportion of the fuel is required for a reduction in laminar flame speed to equivalent CH4-air values, while approximately 30 %vol CO2 in the fuel is required for an equivalent reduction in adiabatic flame temperature, significantly impacted by the increased heat capacity of CO2. The 2nd generation high-pressure generic swirl burner, designed for use with LPM CH4-air, was therefore utilized to experimentally investigate the influence of CO2 and steam dilution on pressurized (up to 250 kW/MPa), preheated (up to 573 K), LPM H2-air flame stability using high-speed OH* chemiluminescence. In addition, exhaust gas emissions, such as NOx and CO, have been measured in comparison with equivalent thermal power conditions for CH4-air flames, showing that low NOx operation can be achieved. Furthermore, pure LPM H2-air flames are characterized for the first time in this burner, stabilized at low equivalence ratio (approximately 0.24) and increased Reynolds number at atmospheric pressure compared to the stable CH4-air flame (equivalence ratio of 0.55). The influence of extinction strain rate is suggested to characterize, both experimentally and numerically, the observed lean flame behavior, in particular as extinction strain rate has been shown to be non-monotonic with pressure for highly-reactive and diffuse fuels such as hydrogen.

scholarly journals Fire Safety Evaluation of High-Pressure Ammonia Storage Systems

Energies ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 520
Author(s):  
Yong Ho Chung ◽  
Won-Ju Lee ◽  
Jun Kang ◽  
Sung Hwan Yoon
Keyword(s):  
High Pressure ◽  
Strain Rate ◽  
Oxygen Concentration ◽  
Flame Structure ◽  
Flame Temperature ◽  
Safety Evaluation ◽  
Fire Spread ◽  
Flammability Limit ◽  
Radiation Heat Loss ◽  
Auto Ignition

Ammonia combustion is a promising energy source as a carbon free fuel without greenhouse gas emissions. However, since the auto-ignition temperature is 651 degrees Celsius and the range of flammability limit is not wide compared to other fuels, fundamental studies on ammonia fires have rarely been conducted so far. Therefore, this study aims to numerically estimate fire spread characteristics when ammonia fuel in a high-pressure state leaks to the outside, especially focusing on the flammability limit according to oxygen concentration. Three kinds of reaction mechanism for numerical analysis were adopted to compare the flame structure, flammability limit, and combustion characteristics. Plank-mean absorption coefficients of nitrogen species were taken for the radiation model, in addition to the optically thin model. The effect of radiation heat loss could be identified from the maximum flame temperature trend at a low strain rate. It was confirmed that the pyrolysis of ammonia in the preheated zone results in hydrogen production, and the generated hydrogen contributes to heat release rate in the flame zone. It is found that the contribution of hydrogen would be an important role in the flammability limit of ammonia combustion. Finally, Karlovitz and Peclet numbers showed well the extinction behaviors of ammonia combustion as a result of LOC (Limit Oxygen Concentration) analysis as a function of global strain rate.

scholarly journals Numerical Study of the Structure and NO Emission Characteristics of N2- and CO2-Diluted Tubular Diffusion Flames

Energies ◽  
2019 ◽  
Vol 12 (8) ◽  
pp. 1490
Author(s):  
Harshini Devathi ◽  
Carl A. Hall ◽  
Robert W. Pitz
Keyword(s):  
Diffusion Flames ◽  
Numerical Study ◽  
Reaction Pathway ◽  
Flame Structure ◽  
Reaction Rates ◽  
No Production ◽  
Emission Characteristics ◽  
No Emission ◽  
Nitrogen Radicals ◽  
Lower Temperature

The structure of methane/air tubular diffusion flames with 65 % fuel dilution by either CO2 or N2 is numerically investigated as a function of pressure. As pressure is increased, the reaction zone thickness reduces due to decrease in diffusivities with pressure. The flame with CO2-diluted fuel exhibits much lower nitrogen radicals (N, NH, HCN, NCO) and lower temperature than its N2-diluted counterpart. In addition to flame structure, NO emission characteristics are studied using analysis of reaction rates and quantitative reaction pathway diagrams (QRPDs). Four different routes, namely the thermal route, Fenimore prompt route, N2O route, and NNH route, are examined and it is observed that the Fenimore prompt route is the most dominant for both CO2- and N2-diuted cases at all values of pressure followed by NNH route, thermal route, and N2O route. This is due to low temperatures (below 1900 K) found in these highly diluted, stretched, and curved flames. Further, due to lower availability of N2 and nitrogen bearing radicals for the CO2-diluted cases, the reaction rates are orders of magnitude lower than their N2-diluted counterparts. This results in lower NO production for the CO2-diluted flame cases.

The effects of strain and strain rate on residual microstructures in copper

1986 ◽  
Vol 44 ◽  
pp. 420-421
Author(s):  
M. F. Stevens ◽  
P. S. Follansbee
Keyword(s):  
Strain Rate ◽  
Applied Stress ◽  
Threshold Stress ◽  
Rate Sensitivity ◽  
Viscous Drag ◽  
Strain Rates ◽  
Strain And Strain Rate ◽  
Threshold Strength ◽  
Mechanism Transition ◽  
Intrinsic Strength

The strain rate sensitivity of a variety of materials is known to increase rapidly at strain rates exceeding ∼103 sec-1. This transition has most often in the past been attributed to a transition from thermally activated guide to viscous drag control. An important condition for imposition of dislocation drag effects is that the applied stress, σ, must be on the order of or greater than the threshold stress, which is the flow stress at OK. From Fig. 1, it can be seen for OFE Cu that the ratio of the applied stress to threshold stress remains constant even at strain rates as high as 104 sec-1 suggesting that there is not a mechanism transition but that the intrinsic strength is increasing, since the threshold strength is a mechanical measure of intrinsic strength. These measurements were made at constant strain levels of 0.2, wnich is not a guarantee of constant microstructure. The increase in threshold stress at higher strain rates is a strong indication that the microstructural evolution is a function of strain rate and that the dependence becomes stronger at high strain rates.

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