A Numerical Simulation of Gas Jet Diffusion Flames Enveloped by a Cascade of Venturis

1999 ◽  
Author(s):  
Ala R. Qubbaj ◽  
S. R. Gollahalli
Keyword(s):  
Diffusion Flames ◽  
Co2 Concentration ◽  
Reaction Model ◽  
Numerical Results ◽  
Pollutant Emissions ◽  
Gas Jet ◽  
University Of Oklahoma ◽  
Burner Exit ◽  
Baseline Case ◽  
O2 Concentration

Abstract “Venturi-cascading” technique has been developed in the Combustion Laboratory at the University of Oklahoma. The goal was to control the pollutant emissions of diffusion flames by modifying the air infusion rate into the flame. The modification was achieved by installing a cascade of venturis around the burning gas jet. The basic idea behind this technique is controlling the stoichiometry of the flame through changing the flow dynamics and rates of mixing in the combustion zone with a set of venturis surrounding the flame. A propane jet diffusion flame at burner-exit Reynolds number of 5100 was examined with a set of venturis of specific sizes and spacing arrangement. The thermal and composition fields of the baseline and venturi-cascaded flames were numerically simulated using CFD-ACE+, an advanced computational environment software package. The instantaneous chemistry model was used as the reaction model. The concentration of NO was determined through CFD-POST, a post processing utility program for CFD-ACE+. The numerical results showed that, in the near-burner, mid-flame and far-burner regions, the venturi-cascaded flame had lower temperature by an average of 13%, 19% and 17%, respectively, and lower CO2 concentration by 35%, 37%. and 32%, respectively, than the baseline flame. An opposite trend was noticed for O2 concentration; the cascaded flame has higher O2 concentration by 7%, 26% and 44%, in average values, in the near-burner, mid-flame and far-burner regions, respectively, than in the baseline case. The results also showed that, in the near-burner, mid-flame, and far-burner regions, the venturi-cascaded flame has lower NO concentrations by 89%, 70% and 70%, in average values, respectively, compared to the baseline case. The simulated results were compared with the experimental data. Good agreement was found in the near-burner region. However, the agreement was poor in the downstream regions. The numerical results substantiate the conclusion, which was drawn in the experimental part of this study, that venturi-cascading is a feasible method for controlling the pollutant emissions of a burning gas jet. In addition, the numerical results were useful to interpret the experimental measurements and understand the thermo-chemical processes involved. The results showed that the prompt-NO mechanism plays an important role besides the conventional thermal-NO mechanism.

Laser-Induced Fluorescence Measurements in Venturi-Cascaded Propane Gas Jet Flames

1999 ◽  
Author(s):  
Ala R. Qubbaj ◽  
S. R. Gollahalli
Keyword(s):  
Diffusion Flames ◽  
Concentration Field ◽  
Laser Induced Fluorescence ◽  
Pollutant Emissions ◽  
Average Decrease ◽  
Burner Exit ◽  
Fluorescence Measurements ◽  
Air Mixing ◽  
Flame Region ◽  
Lif Spectroscopy

Abstract “Venturi-cascading” technique is a means to control pollutant emissions of diffusion flames by modifying air infusion and fuel-air mixing rates through changing the flow dynamics in the combustion zone with a set of venturis surrounding the flame. A propane jet diffusion flame at a burner-exit Reynolds number of 5100 was examined with a set of venturis of specific sizes and spacing arrangement. The venturi-cascading technique resulted in a decrease of 33% in NO emission index along with a 24% decrease in soot emission from the flame, compared to the baseline condition (same flame without venturis). In order to understand the mechanism behind these results, Laser Induced Fluorescence (LIF) spectroscopy was employed to study the concentration field of the radicals (OH, CH and CN) in the baseline and venturi-cascaded flames. The LIF measurements, in the near-burner region of the venturi-cascaded flame, indicated an average decrease of 18%, 24% and 12% in the concentrations of OH, CH and CN radical, respectively, from their baseline values. However, in the mid-flame region, a 40% average increase in OH, from its baseline value, was observed. In this region, CH or CN radicals were not detected. The OH radical, in the downstream locations, was mostly affected by soot rather than by temperature. In addition, prompt-NO mechanism appeared to play a significant role besides the conventional thermal-NO mechanism.

Laser-Induced Fluorescence Measurements in Venturi-Cascaded Propane Gas Jet Flames

2000 ◽  
Vol 123 (2) ◽  
pp. 158-166
Author(s):  
Ala R. Qubbaj ◽  
S. R. Gollahalli
Keyword(s):  
Diffusion Flames ◽  
Concentration Field ◽  
Laser Induced Fluorescence ◽  
Pollutant Emissions ◽  
Average Decrease ◽  
Burner Exit ◽  
Fluorescence Measurements ◽  
Air Mixing ◽  
Lif Spectroscopy ◽  
Cn Radicals

Venturi-cascading is a technique to control pollutant emissions from diffusion flames by modifying air infusion and fuel-air mixing rates through changing the flow dynamics in the combustion zone with a set of venturis surrounding the flame. A propane jet diffusion flame at a burner-exit Reynolds number of 5100 was examined with a set of venturis of specific sizes and spacing arrangement. The venturi-cascading technique resulted in a decrease of 33 percent in NO emission index along with a 24-percent decrease in soot emission from the flame, compared to the baseline condition (same flame without venturis). In order to understand the mechanism behind these results, laser-induced fluorescence (LIF) spectroscopy was employed to study the concentration field of the radicals (OH, CH, and CN) in the baseline and venturi-cascaded flames. The LIF measurements, in the near-burner region of the venturi-cascaded flame, indicated an average decrease of 18, 24 and 12 percent in the concentrations of OH, CH, and CN radicals, respectively, from their baseline values. However, in the midflame region, a 40-percent average increase in OH from its baseline value was observed. In this region, CH or CN radicals were not detected. The OH radical concentration in the downstream locations was mostly affected by soot rather than by temperature.

Reaction Model Development of Selected Aromatics as Relevant Molecules of a Kerosene Surrogate – The Importance of M-Xylene Within the Combustion of 1,3,5-Trimethylbenzene

2021 ◽  
Author(s):  
Astrid Ramirez Hernandez ◽  
Trupti Kathrotia ◽  
Torsten Methling ◽  
Marina Braun-Unkhoff ◽  
Uwe Riedel
Keyword(s):  
Atmospheric Pressure ◽  
Burning Velocity ◽  
Model Development ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Reaction Model ◽  
Pollutant Emissions ◽  
Similar Species ◽  
Ignition Delay Times ◽  
Wide Range

Abstract The development of advanced reaction models to predict pollutant emissions in aero-engine combustors usually relies on surrogate formulations of a specific jet fuel for mimicking its chemical composition. 1,3,5-trimethylbenzene is one of the suitable components to represent aromatics species in those surrogates. However, a comprehensive reaction model for 1,3,5-trimethylbenzene combustion requires a mechanism to describe the m-xylene oxidation. In this work, the development of a chemical kinetic mechanism for describing the m-xylene combustion in a wide parameter range (i.e. temperature, pressure, and fuel equivalence ratios) is presented. The m-xylene reaction submodel was developed based on existing reaction mechanisms of similar species such as toluene and reaction pathways adapted from literature. The sub-model was integrated into an existing detailed mechanism that contains the kinetics of a wide range of n-paraffins, iso-paraffins, cyclo-paraffins, and aromatics. Simulation results for m-xylene were validated against experimental data available in literature. Results show that the presented m-xylene mechanism correctly predicts ignition delay times at different pressures and temperatures as well as laminar burning velocities at atmospheric pressure and various fuel equivalence ratios. At high pressure, some deviations of the calculated laminar burning velocity and the measured values are obtained at stoichiometric to rich equivalence ratios. Additionally, the model predicts reasonably well concentration profiles of major and intermediate species at different temperatures and atmospheric pressure.

Hypoxia-induced changes in shivering and body temperature

1987 ◽  
Vol 62 (6) ◽  
pp. 2477-2484 ◽  
Author(s):  
H. Gautier ◽  
M. Bonora ◽  
S. A. Schultz ◽  
J. E. Remmers
Keyword(s):  
Central Nervous System ◽  
Body Temperature ◽  
Room Temperature ◽  
Co2 Concentration ◽  
Hypoxic Conditions ◽  
O2 Concentration ◽  
The Central Nervous System ◽  
Induced Changes ◽  
Maintain Body Temperature ◽  
Ambient Hypoxia

Experiments were carried out on conscious cats to evaluate the general characteristics and modes of action of hypoxia on thermoregulation during cold stress. Intact and carotid-denervated (CD) conscious cats were exposed to ambient hypoxia (low inspired O2 fraction) or CO hypoxia in prevailing laboratory (23–25 degrees C) or cold (5–8 degrees C) environments. In the cold, both groups promptly decreased shivering and body temperature when exposed to either type of hypoxia. Small increases in CO2 concentration reinstituted shivering in both groups. At the same inspired concentration of O2, CD animals decreased shivering and body temperature more than intact cats. While this difference resulted, in part, from a lower alveolar PO2 in CD cats, a difference between intact and CD cats was apparent when the two groups were compared at the same alveolar PO2. During more prolonged hypoxia (45 min), shivering returned but did not reach normoxic levels, and body temperature tended to stabilize at a hypothermic value. Exposure to various levels of hypoxia produced graded suppression of shivering, with the result that the change in body temperature varied directly with inspired O2 concentration. Hypoxia appears to act on the central nervous system to suppress shivering and sinus nerve afferents appear to counteract this direct effect of hypoxia. In intact cats, this counteraction appears to be sufficient to maintain body temperature under hypoxic conditions at room temperature but not in the cold.

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.

Flue-Gas Versus Fuel-Injection Recirculation: Effects on Structure and Pollutant Emissions

2005 ◽  
Author(s):  
Ala R. Qubbaj
Keyword(s):  
Flue Gas ◽  
Fuel Injection ◽  
No Reduction ◽  
The Other ◽  
Pollutant Emissions ◽  
Air Stream ◽  
Baseline Case ◽  
Co Reduction ◽  
Air Diffusion ◽  
Fuel Stream

In this study, a co-flow methane/air diffusion flame at Reynolds number of 6000 was numerically simulated. The co-flow air and fuel streams were diluted with Nitrogen in the range of 0% to 20%. The thermal and composition fields in the far-burner reaction zone (close to the exhaust) were computed, and the effects of diluent’s addition to the air stream (simulating FGR) and to the fuel stream (simulating FIR) were investigated. The results show that air-side dilution is very effective up to 5% diluent’s addition. For which, 95% and 65% drops in NO and CO emissions, respectively, along with a 16% increase in temperature, are predicted compared to the baseline case (0% dilution). However, beyond 5% dilution, no effect (reaction) has been predicted. On the other hand, the fuel-side dilution has shown an effect for all simulated diluent’s addition (i.e. 0%–20%). However, that effect is not systematic neither on temperature, CO or NO concentrations. For a similar 5% dilution to the fuel-side, a 14% increase in NO and a 97% decrease in CO are predicted, along with a 5.6% increase in temperature. The simulated results revealed that air-side dilution (simulating FGR) has a dramatic greater effectiveness in NO reduction, whereas, fuel-side dilution (simulating FIR) has a greater effectiveness in CO reduction. Besides, the results suggest an important role for Prompt-NO Fenimore mechanism.

Measurement of blood O2 and CO2 concentrations using PO2 and PCO2 electrodes

1978 ◽  
Vol 44 (5) ◽  
pp. 818-820 ◽  
Author(s):  
A. L. Harabin ◽  
L. E. Farhi
Keyword(s):  
Carbon Monoxide ◽  
Blood Volume ◽  
Whole Blood ◽  
Co2 Concentration ◽  
Saturated Solution ◽  
Additional Step ◽  
Co2 Concentrations ◽  
O2 Concentration ◽  
Co2 Electrode ◽  
Small Blood Volume

Accurate dilution of a small blood volume with a carbon monoxide-saturated solution allows measurement of the whole blood O2 concentration as an increase in O2 tension in the solution. We have improved the method by simplifying both equipment and procedure. We also suggest an additional step in which the mixture is acidified, thereby allowing the measurement of CO2 concentration in the same solution with a CO2 electrode. The accuracy of both the O2 and CO2 determinations compares favorably with that obtained with other micromethods.

Fuel Flexibility Test Campaign on a GE10 Gas Turbine: Experimental and Numerical Results

2006 ◽  
Author(s):  
Antonio Andreini ◽  
Bruno Facchini ◽  
Luca Mangani ◽  
Stefano Cocchi ◽  
Roberto Modi
Keyword(s):  
Natural Gas ◽  
Gas Turbine ◽  
Load Condition ◽  
Co2 Concentration ◽  
Flame Stabilization ◽  
Pollutant Emissions ◽  
Nox Emissions ◽  
Predictive Tool ◽  
Fuel Flexibility ◽  
Base Load

Medium- and low-LHV fuels are receiving a continuously growing interest in stationary power applications. Besides that, since in many applications the fuels available at a site can be time by time of significantly different composition, fuel flexibility has become one of the most important requirements to be taken into account in developing power systems. A test campaign, aimed to provide a preliminary assessment of a small power gas turbine’s fuel flexibility, was carried over a full-scale GE10 prototypical unit, located at the Nuovo-Pignone manufacturing site, in Florence. The engine is a single shaft, simple cycle gas turbine designed for power generation applications, rated at 11 MW electrical power and equipped with a silos-type combustor. A variable composition gas fuel was obtained by mixing natural gas with CO2 to about 40% by vol. at engine base-load condition. Tests involved two different diffusive combustion systems: the standard version, designed for operation with natural gas, and a specific system designed for low-LHV fuels. Tests performed aimed to investigate both ignition limits and combustors’ performances, focusing on hot parts’ temperatures and pollutant emissions. Regarding NOx emissions, data collected during standard combustor’s tests were matched a simple scaling law (as a function of cycle parameters and CO2 concentration in the fuel mixture), which can be used in similar applications as a NOx predictive tool. In a following step, a CFD study was performed in order to verify in detail the effects of LHV reduction on flame structure and to compare measured and calculated NOx. STAR-CD™ code was employed as main CFD solver while turbulent combustion and NOx models were specifically developed and implemented using STAR’s user-subroutine features. Both models are based on classical laminar-flamelet approach. Three different operating points were considered at base-load conditions, varying CO2 concentration (0%, 20% and 30% vol. simulated). Numerical simulations point out the flexibility of the GE10 standard combustor to assure flame stabilization even against large variation of fuel characteristics. Calculated NOx emissions are in fairly good agreement with measured data confirming the validity of the adopted models.

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