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.

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.

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

2007 ◽  
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 carbon monoxide enrichment on flame temperature and NO formation in counterflow methane/air diffusion flames. Detailed chemistry and complex thermal and transport properties were employed. The results indicate that when carbon monoxide 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. The combination effects of three factors result in the different characteristics of flame temperature and NO formation at various strain rates, when carbon monoxide is added. 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. When the value of strain rate is moderate, the addition of carbon monoxide 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. When strain rate is increased to a value close to the strain extinction limit of pure methane/air diffusion flame, 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. The paper also analyzed the variation in the mechanism of NO formation, when carbon monoxide is added.

A Numerical Study on the Effect of Water Addition on NO Formation in Counterflow CH4/Air Premixed Flames

2005 ◽  
Author(s):  
Hongsheng Guo ◽  
Stuart W. Neill ◽  
Gregory J. Smallwood
Keyword(s):  
Numerical Study ◽  
Temperature Drop ◽  
Flame Temperature ◽  
Premixed Flames ◽  
Chemical Effect ◽  
Water Addition ◽  
Detailed Chemistry ◽  
Effect Of Water ◽  
No Formation ◽  
The Rich

The effect of water addition on NO formation in counterflow CH4/air premixed flames was investigated by numerical simulation. Detailed chemistry and complex thermal and transport properties were employed. The results show that the addition of water to a flame suppresses the formation of NO primarily due to the flame temperature drop. Among a lean, a stoichiometric and a rich premixed flame, the effectiveness of water addition is most significant for the stoichiometric flame and least for the rich flame, since the dominant NO formation mechanism varies. The addition of water also reduces the formation of NO in a flame because of chemical effect that increases the concentration of OH, while reduces the concentrations of O and H. Compared to the stoichiometric flame, the chemical effect is intensified in the lean and rich flames.

scholarly journals A Numerical Study on the Effect of Water Addition on NO Formation in Counterflow CH4/Air Premixed Flames

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
Hongsheng Guo ◽  
W. Stuart Neill ◽  
Gregory J. Smallwood
Keyword(s):  
Numerical Study ◽  
Temperature Drop ◽  
Flame Temperature ◽  
Premixed Flames ◽  
Chemical Effect ◽  
Water Addition ◽  
Detailed Chemistry ◽  
Effect Of Water ◽  
No Formation ◽  
The Rich

The effect of water addition on NO formation in counterflow CH4/air premixed flames was investigated by numerical simulation. Detailed chemistry and complex thermal and transport properties were employed. The results show that the addition of water to a flame suppresses the formation of NO primarily due to flame temperature drop. Among a lean, a stoichiometric, and a rich premixed flame, the effectiveness of water addition is most significant for the stoichiometric flame and least for the rich flame. The addition of water also reduces the formation of NO in a flame because of the chemical effect. Compared to the stoichiometric flame, the chemical effect is intensified in the lean and rich flames.

COMPUTATIONAL STUDY ON COMBUSTION AND EMISSION CHARACTERISTIC OF PILOTED FLAMES BY VARYING COMPOSITION CO2 OF SIMULATED BIOGAS

2017 ◽  
Vol 79 (7-3) ◽  
Author(s):  
Khor Chin Keat ◽  
M. F. Mohd Yasin ◽  
M. A. Wahid ◽  
A. Saat ◽  
A. S. Md Yudin
Keyword(s):  
Computational Study ◽  
Flame Temperature ◽  
Dilution Effect ◽  
Co2 Concentration ◽  
Nox Emission ◽  
Combustion Model ◽  
Emission Characteristic ◽  
Measured Temperature ◽  
Flamelet Model ◽  
Detailed Chemistry

This study investigates the performance of flamelet model technique in predicting the behavior of piloted flame.A non-premixed methane flame of a piloted burner is simulated in OpenFOAM. A detailed chemistry of methane oxidation is integrated with the flamelet combustion model using probability density function (pdf) approach. The turbulence modelling adopts Reynolds Average Navier Stokes (RANS) framework with standard k-ε model. A comparison with experimental data demonstrates good agreement between the predicted and the measured temperature profiles in axial and radial directions. Recently, one of major concern with combustion system is the emission of pollution specially NOx emission. Reduction of the pollutions can be achieved by varying the composition of CO2 in biogas. In addition, the effect of the composition of biogas on NOx emission of piloted burner is still not understood. Therefore, understanding the behavior composition of CO2 in biogas is important that could affect the emission of pollution. In the present study, the use of biogas with composition of 10 to 30 percent of CO2 is simulated to study the effects of biogas composition on NOx emission. The comparison between biogas and pure methane are done based on the distribution of NOx, CO2, CH4, and temperature at different height above the burner. At varying composition of CO2 in biogas, the NOx emission for biogas with 30 percent CO2 is greatly reduced compared to that of 10 percent CO2. This is due to the reduction of the post flame temperature that is produced by the dilution effect at high CO2 concentration.  

scholarly journals Frequency Response of Counter Flow Diffusion Flames to Strain Rate Harmonic Oscillations

2008 ◽  
Vol 180 (5) ◽  
pp. 767-784 ◽  
Author(s):  
A. Cuoci ◽  
A. Frassoldati ◽  
T. Faravelli ◽  
E. Ranzi
Keyword(s):  
Strain Rate ◽  
Frequency Response ◽  
Diffusion Flames ◽  
Counter Flow ◽  
Harmonic Oscillations

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.

Numerical study of the effects of radiative heat losses on diffusion flames

2006 ◽  
Vol 220 (8) ◽  
pp. 1189-1199
Author(s):  
M D Gaustad ◽  
T Shamim
Keyword(s):  
Radiation Effects ◽  
Diffusion Flames ◽  
Numerical Study ◽  
Flame Structure ◽  
Combustion Products ◽  
Chemical Mechanism ◽  
Strain Rates ◽  
Detailed Chemistry ◽  
Extinction Limit ◽  
Radiative Losses

The effects of thermal radiation are numerically investigated for a methane-air counterflow diffusion flame, using ‘detailed’ chemistry. The radiative losses from combustion products (CO2 and H2O) were considered by using a thin gas approximation. The results show a significant effect of radiative losses causing extinction at low strain rates. On the basis of the radiative losses from gaseous combustion products, an extinction limit was found to be 0.7 s−1. The presence of soot will move this limit to higher strain rates. The radiation effects are relatively less at moderate and high strain rates, where they may cause a reduction in the peak temperatures by ∼ 10 per cent. In addition to decreasing peak temperatures and combustion products, the radiative losses also reduce the flame width. The results show the importance of including detailed chemical mechanism in correctly predicting the extinction limit and the influence of radiative losses on flame structure.

Two-Dimensional Numerical Study of Temperature, Species Distributions in Coflow Laminar Diffusion Flames

2012 ◽  
Vol 516-517 ◽  
pp. 80-83
Author(s):  
You Ning Xu ◽  
Jun Rui Shi ◽  
Zhi Jia Xue ◽  
Shu Qun Wang ◽  
Mao Zhao Xie
Keyword(s):  
Gas Phase ◽  
Mass Fraction ◽  
Diffusion Flames ◽  
Numerical Study ◽  
Flame Temperature ◽  
Species Distributions ◽  
Phase Reaction ◽  
Laminar Diffusion Flames ◽  
Gas Phase Reaction ◽  
Air Diffusion

Abstract. temperature and species distributions of an atmosphere coflow laminar CH4/air diffusion flame was studied by numerical simulation. We solve the steady equations for the species mass fraction, energy, momentum with detailed gas-phase reaction mechanism and complex thermal and transport properties to predict the velocity, temperature, species distributions for different dilute level. Results indicated that the predicted temperature and species are in excellent with available experiment date at different dilute level. In addition, it is indicated that adding N2in the fuel has a significant influence on the flame temperature and species distribution.

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