Internal Entrainment Effects on Distributed Combustion

2015 ◽  
Author(s):  
Ahmed E. E. Khalil ◽  
Ashwani K. Gupta
Keyword(s):  
Carbon Dioxide ◽  
Oxygen Concentration ◽  
High Intensity ◽  
Flame Structure ◽  
Low Oxygen ◽  
Air Stream ◽  
Pollutants Emission ◽  
Reactive Gases ◽  
Colorless Distributed Combustion ◽  
The Impact

Colorless Distributed Combustion (CDC) has been shown to provide ultra-low emissions and enhanced combustion performance of high intensity gas turbine combustors in terms of efficiency and stability. To achieve distributed combustion, the flowfield needs to be carefully tailored for adequate mixing between reactants and hot reactive species from within the combustor to result in high temperature low oxygen concentration environment prior to ignition. Such distributed reactions result in uniform thermal field and also eliminates any hot spots for mitigating NOx emission. Though Distributed Combustion have been extensively studied using a variety of geometries, injection velocities, heat release intensities, and fuels, the role of hot reactive internally recirculated gases requires further examination. In this paper, the impact of internal entrainment of reactive gases on flame structure and behavior is investigated with focus on fostering distributed combustion and providing guidelines for designing high intensity combustors operating in distributed combustion mode. A mixture of nitrogen and carbon dioxide, used to simulate the recirculated gases, is introduced to the air stream prior to mixing with the fuel and subsequent combustion. Increase in the amounts of nitrogen and carbon dioxide (simulating increased entrainment), led to volume distributed reaction over a larger volume in the combustor with enhanced and uniform distribution of the OH* chemiluminescence intensity. At the same time, the bluish flame stabilized by the swirler is replaced with a more uniform almost invisible bluish flame. The increased recirculation also reflected on the pollutants emission, where NO emissions were significantly decreased for the same amount of fuel burned. Lowering oxygen concentration from 21% to 15% (due to increased entrainment) resulted in 80∼90% reduction in NO with no impact on CO emission with sub PPM NO emission achieved at an equivalence ratio of 0.7. The same trend was seen at higher diluents injection temperature as well, with significant pollutants emission reduction down to an oxygen concentration of 10%.

Impact of Internal Entrainment on High Intensity Distributed Combustion

2015 ◽  
Author(s):  
Ahmed E. E. Khalil ◽  
Ashwani K. Gupta
Keyword(s):  
Carbon Dioxide ◽  
Gas Turbine ◽  
Oxygen Concentration ◽  
High Intensity ◽  
Flame Structure ◽  
Flame Stabilization ◽  
Low Oxygen ◽  
Gas Turbine Combustors ◽  
Reactive Gases ◽  
The Impact

Colorless Distributed Combustion (also referred to as CDC) has been shown to provide ultra-low emissions and enhanced performance of high intensity gas turbine combustors. To achieve distributed combustion, the flowfield needs to be tailored for adequate mixing between reactants and hot reactive species from within the combustor to result in high temperature low oxygen concentration environment prior to ignition. Such reaction distribution results in uniform thermal field and also eliminates any hot spots for mitigating NOx emission. Though CDC have been extensively studied using a variety of geometries, heat release intensities, and fuels, the role of internally recirculated hot reactive gases needs to be further investigated and quantified. In this paper, the impact of internal entrainment of reactive gases on flame structure and behavior is investigated with focus on fostering distributed combustion and providing guidelines for designing future gas turbine combustors operating in distributed combustion mode. To simulate the recirculated gases from within the combustor, a mixture of nitrogen and carbon dioxide is introduced to the air stream prior to mixing with fuel and subsequent combustion. Increase in the amounts of nitrogen and carbon dioxide (simulating increased entrainment), led to volume distributed reaction over a larger volume in the combustor with enhanced and uniform distribution of the OH* chemiluminescence intensity. At the same time, the bluish flame stabilized by the swirler is replaced with a more uniform almost invisible bluish flame. The increased recirculation also reflected on the pollutants emission, where NO emissions were significantly decreased for the same amount of fuel burned. Lowering oxygen concentration from 21% to 15% (due to increased recirculation) resulted in 80∼90% reduction in NO with no impact on CO emission with sub PPM NO emission achieved at an equivalence ratio of 0.7. Flame stabilization at excess recirculation can be achieved using preheated nitrogen and carbon dioxide, achieving true distributed conditions with oxygen concentration below 13%.

Fuel Property Effects on the Fate of Volume Distributed Combustion

2016 ◽  
Author(s):  
Ahmed E. E. Khalil ◽  
Ashwani K. Gupta
Keyword(s):  
Carbon Dioxide ◽  
Oxygen Concentration ◽  
Gas Temperature ◽  
Field Uniformity ◽  
Different Temperatures ◽  
Pollutants Emission ◽  
Reactive Gases ◽  
Colorless Distributed Combustion ◽  
The Impact ◽  
No Emissions

Colorless Distributed Combustion (CDC) has been shown to provide singular benefits on ultra-low pollutants emission, enhanced stability and thermal field uniformity. To achieve CDC conditions, fuel-air mixture must be properly prepared and mixed with hot reactive gases from within the combustor prior to the mixture ignition. Hot reactive gases reduce the oxygen concentration in the mixture while increasing its temperature. In this paper, the impact of fuel type (methane, propane, and hydrogen enriched methane) on achieving distributed combustion is investigated. A mixture of nitrogen and carbon dioxide was mixed to simulate the hot recirculated gases at different temperatures using normal air upstream of the combustor. Increasing the amounts of nitrogen and carbon dioxide reduced the oxygen concentration within the combustor. Distributed combustion was identified through OH* chemiluminescence distribution across the combustor. For methane, this oxygen concentration varied between 13.8% and 11.2% (depending on the mixture temperature) with some 85% reduction in NO emissions as compared to that without entrainment. Similar behavior was demonstrated with propane and hydrogen enriched methane, albeit at a lower oxygen concentration (13.7%–11.6% and 12.2%–10.5%), to result in 94% and 92% reduction in NO emission, respectively. The inlet gas temperature was varied between 300K and 750K. Experimental data using a variety of fuels showed NO emissions of 1 PPM or less. Analysis and extrapolation of obtained data suggest that distributed combustion can be achieved at an oxygen concentration of 9.5% for hot reactive entrained gases having a temperature of 1800K. This value may be used as a guideline to achieve distributed combustion with ultra-low emission.

Acoustic Noise Reduction Under Distributed Combustion

2017 ◽  
Author(s):  
Ahmed E. E. Khalil ◽  
Ashwani K. Gupta
Keyword(s):  
Carbon Dioxide ◽  
Heat Release ◽  
Noise Reduction ◽  
Oxygen Concentration ◽  
Acoustic Signal ◽  
Thermal Field ◽  
Field Uniformity ◽  
Pollutants Emission ◽  
Reactive Gases ◽  
Swirl Flame

Colorless Distributed Combustion (CDC) has been shown to provide unique benefits on ultra-low pollutants emission, enhanced combustion stability, and thermal field uniformity. To achieve CDC conditions, fuel-air mixture must be properly prepared and mixed with hot reactive gases from within the combustor prior to the mixture ignition. The hot reactive gases reduce the oxygen concentration in the mixture while increasing its temperature, resulting in a reaction zone that is distributed across the reactor volume, with lower reaction rate to result in the same fuel consumption. The conditions to achieve distributed combustion were previously studied using methane and other fuels with focus on pollutants emission and thermal field uniformity. In this paper, the impact of distributed combustion on noise reduction and increased stability is investigated. Such reduced noise is critical in mitigating the coupling between flame and heat release perturbations and acoustic signal to enhance the overall flame stability and reduce the propensity of flame instabilities which can cause equipment failure. Nitrogen-carbon dioxide mixture is used to simulate the reactive entrained gases from with the combustor. Increasing the amounts of nitrogen and carbon dioxide reduced the oxygen concentration within the oxidizing mixture, fostering distributed combustion. Upon achieving distributed combustion, the overall flame noise signature decreased from 80 dB to only 63 dB, as the flame transitioned from traditional swirl flame to distributed combustion. The flow noise under these conditions was 54 dB, indicating that distributed combustion has only 9 dB increase over isothermal case as compared to 26 dB for standard swirl flame. In addition, the dominant flame frequency around 490Hz disappeared under distributed combustion. For the traditional swirl flame, both the acoustic signal and heat release fluctuations (detected through CH∗ chemiluminescence) had a peak around 150Hz, indicating coupling between the heat release fluctuations and pressure variation. However, upon transitioning to distributed combustion, this common peak disappeared, outlining the enhanced stability of distributed combustion as there is no feedback between the heat release fluctuations and the recorded acoustic signal.

scholarly journals Experimental study of the effects of swirl and air dilution on biogas non-premixed flame stability

2015 ◽  
Vol 19 (6) ◽  
pp. 2161-2169 ◽  
Author(s):  
Amir Rowhani ◽  
Sadegh Tabejamaat
Keyword(s):  
Carbon Dioxide ◽  
Flame Structure ◽  
Premixed Flame ◽  
Flame Stability ◽  
Negative Effects ◽  
Air Stream ◽  
The Stability ◽  
Carbon Dioxide Co2 ◽  
Flame Behavior ◽  
Stability Limits

An experimental investigation of the stability limits of biogas in a swirling non-premixed burner has been carried out. A mixture of 60% methane (CH4) and 40% carbon dioxide (CO2) was used to reach the typical biogas composition. Vane swirlers with 30?, 45? and 60? angles were used to make the swirling air. The biogas stability limits and flame behavior under swirling conditions were tested. Besides, effects of air dilution with nitrogen (N2) and CO2 on biogas stability limits were investigated. The results show that using swirl can enhance the flame stability limits approximately four or five times comparing to non-swirling air stream. Adding N2/CO2 to the air had negative effects on the flame stability but no changes were observed in the flame structure. The maximum air dilution was also obtained when 27% and 15% N2 was added to the swirling air under strong and weak swirl, respectively.

Effects of oxygen concentration on the metabolism of

1989 ◽  
Vol 1 (2) ◽  
pp. 99 ◽  
Author(s):  
NK Khurana ◽  
RG Wales
Keyword(s):  
Carbon Dioxide ◽  
Oxygen Concentration ◽  
Glycogen Content ◽  
Carbon Dioxide Production ◽  
Morphological Development ◽  
Low Oxygen ◽  
Beneficial Effects ◽  
Low Oxygen Concentration ◽  
Oxygen Concentrations

The utilization of the acid-soluble glycogen pool in pulse-labelled embryos was significantly enhanced during 24- and 48-h chase culture under low oxygen concentrations of 5, 2.5 and 1%. The lower the oxygen tension the greater was the turnover in the pool. The morphological development of embryos was equally as good at very low oxygen concentrations as when embryos were cultured in 5-20% oxygen. Reduction in oxygen concentration enhanced the oxidative utilization of substrate, as measured by rate of carbon dioxide production. The present study could provide an explanation for the discrepancy in glycogen content between mouse blastocysts developing in utero and in vitro and for the reported beneficial effects of low oxygen concentration during development of embryos in culture.

Environmental factors constraining adventitious root formation during flooding of Solanum dulcamara

2017 ◽  
Vol 44 (9) ◽  
pp. 858 ◽  
Author(s):  
Qian Zhang ◽  
Heidrun Huber ◽  
Jannah W. T. Boerakker ◽  
Daniek Bosch ◽  
Hans de Kroon ◽  
...  
Keyword(s):  
Environmental Factors ◽  
Oxygen Concentration ◽  
Adventitious Root ◽  
Root Formation ◽  
Adventitious Root Formation ◽  
Plant Performance ◽  
Low Oxygen ◽  
Submerged Plants ◽  
Solanum Dulcamara ◽  
The Impact

Flooding is a compound stress, imposing strong limitations on plant development. The expression of adaptive traits that alleviate flooding stress may be constrained if floodwater levels are too deep. For instance, adventitious root outgrowth is typically less profound in completely submerged plants than in partially submerged plants, suggesting additional constraints in full submergence. As both oxygen and carbohydrates are typically limited resources under submergence, we tested the effects of oxygen concentration in the floodwater and carbohydrate status of the plants on flooding-induced adventitious root formation in Solanum dulcamara L. Partially submerged plants continued to form adventitious roots in low-oxygen floodwater, whereas completely submerged plants developed hardly any roots, even in floodwater with twice the ambient oxygen concentration. This suggests that contact with the atmosphere, enabling internal aeration, is much more important to optimal adventitious root formation than floodwater oxygen concentrations. If plants were depleted of carbohydrates before flooding, adventitious root formation in partial submergence was poor, unless high light was provided. Thus, either stored or newly produced carbohydrates can fuel adventitious root formation. These results imply that the impact of an environmental stress factor like flooding on plant performance may strongly depend on the interplay with other environmental factors.

scholarly journals Physiological Effects of Physical Postharvest Treatments on Insects

2003 ◽  
Vol 13 (2) ◽  
pp. 272-275 ◽  
Author(s):  
Lisa G. Neven
Keyword(s):  
Carbon Dioxide ◽  
Temperature Extremes ◽  
Physiological Effects ◽  
X Rays ◽  
Low Oxygen ◽  
Agricultural Chemicals ◽  
Modified Atmospheres ◽  
Insect Mortality ◽  
Physical Treatments ◽  
The Impact

As concerns about the safety of our food supply increase along with concerns about the impact of agricultural chemicals on our environment, the development of nonchemical quarantine treatments to meet export requirements become increasingly necessary. The types of physical treatments used have been largely determined by commodity tolerances and processing practices. The most common physical treatments use temperature extremes such as heat [>40 °C (104.0 °F)] and cold [<10 °C (50.0 °F)]. Other physical treatments commonly include the use of controlled or modified atmospheres (low oxygen, elevated carbon dioxide). Current technology has led to investigations in the application of energy to control infesting insects. These treatments include ionizing radiation, microwaves, ultraviolet radiation, infrared radiation, radio frequency, electron beam, X-rays, and electricity. Although the effects of these physical treatments can impact commodity quality, the goal of the treatments is to kill infesting (real or in certain instances, potential) insects to meet quarantine requirements. The effects of physical treatments on insect mortality and fecundity are discussed.

The effects of carbon dioxide and oxygen concentrations on superficial scald of Granny Smith apples

1963 ◽  
Vol 14 (6) ◽  
pp. 765 ◽  
Author(s):  
EA Roberts ◽  
EG Hall ◽  
KJ Scott
Keyword(s):  
Carbon Dioxide ◽  
Oxygen Concentration ◽  
Carbon Dioxide Concentration ◽  
Good Control ◽  
Controlled Atmosphere ◽  
Low Oxygen ◽  
Controlled Atmosphere Storage ◽  
Zero Carbon ◽  
Regression Techniques ◽  
Atmosphere Storage

In the past, experiments on controlled atmosphere storage have tested specific combinations of carbon dioxide and oxygen, usually in a manner which precludes determination of the effect of change in concentration of these gases. The data from the series of trials discussed in this paper permitted an investigation of the effect of concentrations of carbon dioxide and oxygen on the incidence of scald with simple and multiple linear regression techniques. The method was applied to data from three types of controlled atmosphere storage: (1) Carbon dioxide 2.5–10% at 2.5% oxygen, (2) Oxygen 1.25–20%, at near zero carbon dioxide, (3) Carbon dioxide 3.3–10.9% oxygen 2.2–16%. The relation between scald (Y), carbon dioxide concentration (x), and the reciprocal of oxygen concentration (z), was described by the regression equation: Y = y + b(x – x) + c(z – z), which implies that scald is directly proportional to carbon dioxide concentration and indirectly proportional to oxygen concentration. The effects of changes in concentration of the gases, as estimated by the regression coefficients, were consistent for size of fruit, season, and orchard, but the effect for oxygen was dependent on the method of maintaining the atmosphere. Good control of scald was obtained with low oxygen atmospheres, even after storage for 6–7 months.

Climate-forced changes of bio-productivity of Belorussian terrestrial ecosystems

2019 ◽  
pp. 77-88
Author(s):  
S. A. Lysenko
Keyword(s):  
Climate Change ◽  
Carbon Dioxide ◽  
Vegetation Index ◽  
Precipitation Amount ◽  
Terrestrial Ecosystems ◽  
Vegetation Period ◽  
Climatic Trend ◽  
Vegetation Growth ◽  
Current Century ◽  
The Impact

The spatial and temporal particularities of Normalized Differential Vegetation Index (NDVI) changes over territory of Belarus in the current century and their relationship with climate change were investigated. The rise of NDVI is observed at approximately 84% of the Belarus area. The statistically significant growth of NDVI has exhibited at nearly 35% of the studied area (t-test at 95% confidence interval), which are mainly forests and undeveloped areas. Croplands vegetation index is largely descending. The main factor of croplands bio-productivity interannual variability is precipitation amount in vegetation period. This factor determines more than 60% of the croplands NDVI dispersion. The long-term changes of NDVI could be explained by combination of two factors: photosynthesis intensifying action of carbon dioxide and vegetation growth suppressing action of air warming with almost unchanged precipitation amount. If the observed climatic trend continues the croplands bio-productivity in many Belarus regions could be decreased at more than 20% in comparison with 2000 year. The impact of climate change on the bio-productivity of undeveloped lands is only slightly noticed on the background of its growth in conditions of rising level of carbon dioxide in the atmosphere.

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