Effect of CO2 Dilution on Flame Structure and Soot and NO Formations in CH4-Air Nonpremixed Flames

2010 ◽  
Vol 132 (12) ◽  
Author(s):  
Arindam Samanta ◽  
Ranjan Ganguly ◽  
Amitava Datta
Keyword(s):  
Flame Structure ◽  
Flame Length ◽  
Nonpremixed Flames ◽  
Fuel Flow Rate ◽  
Heating Value ◽  
Flame Radiation ◽  
Fuel Flow ◽  
Fuel Jet ◽  
Jet Velocity ◽  
Fuel Stream

In the present work, a numerical analysis has been presented to show the variations in flame structure, flame radiation, and formations of soot and NO in methane-air laminar nonpremixed flames with different CO2 dilutions of fuel. It is observed that the flame length reduces as the dilution of the fuel stream by CO2 increases while maintaining constant fuel jet velocity at the burner tip. However, the flame length remains almost unchanged with different blends of CH4 and CO2 if the burner loading (i.e., fuel flow rate×heating value of fuel) is kept constant. Both soot and NO formations decrease monotonically when the CO2 fraction in the fuel is increased. The radiation from the flame also decreases when CO2 dilution of the fuel is increased, particularly, when the fuel jet velocity is maintained constant.

Assessment of Stabilization Mechanisms of Confined, Turbulent, Lifted Jet Flames: Effects of Ambient Coflow

2013 ◽  
Author(s):  
Andrew R. Hutchins ◽  
James D. Kribs ◽  
Richard D. Muncey ◽  
Kevin M. Lyons
Keyword(s):  
Turbulent Mixing ◽  
Leading Edge ◽  
Ambient Air ◽  
Turbulent Jet ◽  
Fuel Flow Rate ◽  
Jet Flames ◽  
Combustion Chemistry ◽  
Intermittent Behavior ◽  
Fuel Flow ◽  
Fuel Jet

The aim of this investigation is to determine the effects of confinement on the stabilization of turbulent, lifted methane (CH4) jet flames. A confinement cylinder (stainless steel) separates the coflow from the ambient air and restricts excess room air from being entrained into the combustion chamber, and thus produces varying stabilization patterns. The experiments were executed using fully confined, semi-confined, and unconfined conditions, as well as by varying fuel flow rate and coflow velocity (ambient air flowing in the same direction as the fuel jet). Methane flames experience liftoff and blowout at well-known conditions for unconfined jets, however, it was determined that with semi-confined conditions the flame does not experience blowout. Instead of the conventional unconfined stabilization patterns, an intense, intermittent behavior of the flame was observed. This sporadic behavior of the flame, while under semi-confinement, was determined to be a result from the restricted oxidizer access as well as the asymmetrical boundary layer that forms due to the viewing window. While under full confinement the flame behaved in a similar method as while under no confinement (full ambient air access). The stable nature of the flame while fully confined lacked the expected change in leading edge fluctuations that normally occur in turbulent jet flames. These behaviors address the combustion chemistry (lack of oxygen), turbulent mixing, and heat release that combine to produce the observed phenomena.

Effects of Burner Diameter and Fuel Type on Smoke Point and Radiation Characteristics of Diffusion Flames

2002 ◽  
Author(s):  
S. F. Goh ◽  
S. Kusadomi ◽  
S. R. Gollahalli
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Critical Mass ◽  
Smoke Point ◽  
Fuel Type ◽  
Fuel Flow Rate ◽  
Flame Radiation ◽  
Fuel Mass ◽  
Fuel Flow

The main purpose of this study was to comprehend the effects of burner diameter and fuel type on smoke point characteristics of a hydrocarbon diffusion flame and its radiation emission. The critical mass flow rate of pure fuel at this smoke point was measured. At nine different fractions of the critical mass flow rate, nitrogen gas was supplied along with the fuel to achieve smoke point. At each condition, flame radiation and flame height were measured. The axial radiation profile at the critical fuel mass flow rate for one burner was also measured. Three fuels of differing sooting propensities were used: ethylene (C2H4), propylene (C3H6), and propane (C3H8). Three different burners with inner diameters of 1.2 mm, 3.2 mm and 6.4 mm were used. Results showed that propylene had the highest critical fuel flow rate and the highest nitrogen dilution required to suppress smoking and total flame radiation, followed by ethylene and propane. For all fuels, the curves of nitrogen flow rate required for smoke suppression versus fuel flow rate exhibited a skewed bell shape. The variation of Reynolds number at the critical fuel mass flow rate with the burner diameter showed a linear relation. On the other hand, the variation of total flame radiation with burner diameter was nonlinear.

scholarly journals Numerical study of turbulent normal diffusion flame CH4-air stabilized by coaxial burner

2013 ◽  
Vol 17 (4) ◽  
pp. 1207-1219 ◽  
Author(s):  
Zouhair Riahi ◽  
Ali Mergheni ◽  
Jean-Charles Sautet ◽  
Ben Nasrallah
Keyword(s):  
Equivalence Ratio ◽  
Numerical Study ◽  
Mixture Fraction ◽  
Turbulent Flame ◽  
Flame Structure ◽  
Premixed Combustion ◽  
Air Jet ◽  
Fuel Jet ◽  
Jet Velocity ◽  
Lift Off

The practical combustion systems such as combustion furnaces, gas turbine, engines, etc. employ non-premixed combustion due to its better flame stability, safety, and wide operating range as compared to premixed combustion. The present numerical study characterizes the turbulent flame of methane-air in a coaxial burner in order to determine the effect of airflow on the distribution of temperature, on gas consumption and on the emission of NOx. The results in this study are obtained by simulation on FLUENT code. The results demonstrate the influence of different parameters on the flame structure, temperature distribution and gas emissions, such as turbulence, fuel jet velocity, air jet velocity, equivalence ratio and mixture fraction. The lift-off height for a fixed fuel jet velocity is observed to increase monotonically with air jet velocity. Temperature and NOx emission decrease of important values with the equivalence ratio, it is maximum about the unity.

Orifice Diameter Effects on Diesel Fuel Jet Flame Structure

2005 ◽  
Vol 127 (1) ◽  
pp. 187-196 ◽  
Author(s):  
Lyle M. Pickett ◽  
Dennis L. Siebers
Keyword(s):  
Diesel Fuel ◽  
Direct Injection ◽  
Flame Structure ◽  
Air Entrainment ◽  
Flame Length ◽  
Turbulent Flames ◽  
Orifice Diameter ◽  
Jet Flame ◽  
Fuel Jet ◽  
Lift Off

The effects of orifice diameter on several aspects of diesel fuel jet flame structure were investigated in a constant-volume combustion vessel under heavy-duty direct-injection (DI) diesel engine conditions using Phillips research grade #2 diesel fuel and orifice diameters ranging from 45 μm to 180 μm. The overall flame structure was visualized with time-averaged OH chemiluminescence and soot luminosity images acquired during the quasi-steady portion of the diesel combustion event that occurs after the transient premixed burn is completed and the flame length is established. The lift-off length, defined as the farthest upstream location of high-temperature combustion, and the flame length were determined from the OH chemiluminescence images. In addition, relative changes in the amount of soot formed for various conditions were determined from the soot incandescence images. Combined with previous investigations of liquid-phase fuel penetration and spray development, the results show that air entrainment upstream of the lift-off length (relative to the amount of fuel injected) is very sensitive to orifice diameter. As orifice diameter decreases, the relative air entrainment upstream of the lift-off length increases significantly. The increased relative air entrainment results in a reduced overall average equivalence ratio in the fuel jet at the lift-off length and reduced soot luminosity downstream of the lift-off length. The reduced soot luminosity indicates that the amount of soot formed relative to the amount of fuel injected decreases with orifice diameter. The flame lengths determined from the images agree well with gas jet theory for momentum-driven nonpremixed turbulent flames.

scholarly journals EXPERIMENTAL STUDY OF TURBULENT LPG TURBULENT INVERSE DIFFUSION FLAME IN COAXIAL BURNER

2013 ◽  
pp. 184-190
Author(s):  
S.SREENATHA REDDY ◽  
K.L.N MURTHY ◽  
V. PANDURANGADU
Keyword(s):  
Experimental Study ◽  
Diffusion Flame ◽  
Flame Structure ◽  
Flame Length ◽  
Global Strain ◽  
Fuel Jet ◽  
Inverse Diffusion ◽  
Inverse Diffusion Flame ◽  
Global Strain Rate ◽  
Centerline Temperature

The present experimental study investigates the turbulent LPG Inverse Diffusion Flame (IDF) stabilized in a coaxial burner in terms of flame appearance, visible flame length, centerline temperature distribution and oxygen concentration and NOX emission characteristics. The effect of air-fuel jet velocities on visible flame length is interpreted using global strain rate and a new devised parameter called Modified Momentum Ratio. The centerline temperature exhibits a steeper increase in the lower premixed zone of the IDF due to the enhanced premixing. Subsequently it declines gradually in the upper luminous portion owing to soot radiation and heat losses to the ambient. Further, the centerline oxygen depletes rapidly in the lower blue zone but found to increase gradually in the upper luminous portion of IDF. The centerline temperature and oxygen distribution along the flame length revealed the dual flame structure of IDF. The EINOX values exhibited a bell shaped profile and reached a maximum value around stoichiometric overall equivalence ratio.

Orifice Diameter Effects on Diesel Fuel Jet Flame Structure

2001 ◽  
Author(s):  
Lyle M. Pickett ◽  
Dennis L. Siebers
Keyword(s):  
Diesel Fuel ◽  
Direct Injection ◽  
Flame Structure ◽  
Air Entrainment ◽  
Flame Length ◽  
Turbulent Flames ◽  
Orifice Diameter ◽  
Jet Flame ◽  
Fuel Jet ◽  
Lift Off

Abstract The effects of orifice diameter on several aspects of diesel fuel jet flame structure were investigated in a constant-volume combustion vessel under heavy-duty, direct-injection (DI) diesel engine conditions using Phillips research grade #2 diesel fuel and orifice diameters ranging from 45 μm to 180 μm. The overall flame structure was visualized with time-averaged OH chemiluminescence and soot luminosity images acquired during the quasi-steady portion of the diesel combustion event that occurs after the transient premixed burn is completed and the flame length is established. The lift-off length, defined as the farthest upstream location of high-temperature combustion, and the flame length were determined from the OH chemiluminescence images. In addition, relative changes in the amount of soot formed for various conditions were determined from the soot incandescence images. Combined with previous investigations of liquid-phase fuel penetration and spray development, the results show that air entrainment upstream of the lift-off length (relative to the amount of fuel injected) is very sensitive to orifice diameter. As orifice diameter decreases, the relative air entrainment upstream of the lift-off length increases significantly. The increased relative air entrainment results in a reduced overall average equivalence ratio in the fuel jet at the lift-off length and reduced soot luminosity downstream of the lift-off length. The reduced soot luminosity indicates that the amount of soot formed relative to the amount of fuel injected decreases with orifice diameter. The flame lengths determined from the images agree well with gas jet theory for momentum-driven, non-premixed turbulent flames.

Numerical Modeling of Flame Lift-Off Phenomenon in a Combustion Chamber With Three Cylinder Methane Fuel Injector

1992 ◽  
Author(s):  
T. O. Mohieldin ◽  
S. K. Chaturvedi
Keyword(s):  
Flame Structure ◽  
Primary Objective ◽  
Two Dimensions ◽  
Fuel Injector ◽  
Lifted Flame ◽  
Fuel Jet ◽  
Fast Chemistry ◽  
Jet Velocity ◽  
Lift Off ◽  
Langley Research Center

Abstract This work summarizes results for a three cylinder fuel injector that has been adopted as a model for investigating combustion phenomenon in the 8-Foot High Temperature Tunnel (HTT) at NASA Langley Research Center. The primary objective here is to understand the flame lift-off phenomenon in the three cylinder fuel injector geometry in two-dimensions. Three chemistry models, namely fast chemistry, one-step kinetics and two-step kinetics are employed in conjunction with a computational fluid dynamics code to analyze the flame structure and flame lift-off characteristics downstream of the fuel injector. Effects of fuel jet velocity and chemistry model on the flame lift-off phenomenon from the injector surface are analyzed by considering simultaneously the combined convection (outside the cylinders) and conduction (inside the cylinders). Results indicate that as the fuel jet velocity is increased, the flame is transformed from a wrap around configuration to a clearly lifted flame configuration. Of the three chemistry models considered in the present study, only the two-step chemistry model predicts a clearly lifted flame. The ability of the CFD code to predict lifted flame is important since a slightly lifted but stable flame is of paramount importance to the operation of the combustor.

Shapes of Elliptic Methane Laminar Jet Diffusion Flames

2004 ◽  
Vol 128 (1) ◽  
pp. 1-7 ◽  
Author(s):  
Jorge R. Camacho ◽  
Ahsan R. Choudhuri
Keyword(s):  
Flow Rate ◽  
Diffusion Flames ◽  
Theoretical Method ◽  
Flame Length ◽  
Fuel Flow Rate ◽  
Laminar Jet ◽  
Jet Diffusion Flames ◽  
Fuel Flow ◽  
Microgravity Research ◽  
Research Aircraft

Buoyant and nonbuoyant shapes of methane flames issued from a 2:1 aspect ratio elliptic tube burner were measured. Nonbuoyant conditions were obtained in the KC-135 microgravity research aircraft operated by NASA’s Johnson Space Center. A mathematical model based on the extended Burke-Schumann flame theory is developed to predict the flame length of an elliptic burner. The model utilizes Roper’s theoretical method for circular burners and extends the analysis for elliptic burners. The predicted flame length using the theoretical model agrees well with experimental measurements. In general for the elliptic burner the nonbuoyant flames are longer than the buoyant flames. However, measured lengths of both buoyant and nonbuoyant flame lengths change proportionally with the volumetric fuel flow rate and support the L vs Q correlation. The maximum flame width measured at buoyant and nonbuoyant conditions also show a proportional relation with the volumetric fuel flow rate. Normalized buoyant and nonbuoyant flame lengths of the elliptic burner correlate (L∕d∝Re) with the jet exit Reynolds number and exhibit a higher slope compared to a circular burner. Normalized flame width data show a power correlation (w∕d=cFrn) with the jet exit Froude number.

Dynamic Simulation of a HRSG System for a Given Start-Up/Shut Down Curve

2011 ◽  
Author(s):  
Hun Cha ◽  
Yoo Seok Song ◽  
Kyu Jong Kim ◽  
Jung Rae Kim ◽  
Sung Min KIM
Keyword(s):  
Dynamic Analysis ◽  
Gas Turbine ◽  
Flow Rate ◽  
Exhaust Gas ◽  
Fuel Flow Rate ◽  
Fuel Flow ◽  
Start Up ◽  
Gas Turbine Exhaust ◽  
Main Steam ◽  
Duct Burner

An inappropriate design of HRSG (Heat Recovery Steam Generator) may lead to mechanical problems including the fatigue failure caused by rapid load change such as operating trip, start-up or shut down. The performance of HRSG with dynamic analysis should be investigated in case of start-up or shutdown. In this study, dynamic analysis for the HRSG system was carried out by commercial software. The HRSG system was modeled with HP, IP, LP evaporator, duct burner, superheater, reheater and economizer. The main variables for the analysis were the temperature and mass flow rate from gas turbine and fuel flow rate of duct burner for given start-up (cold/warm/hot) and shutdown curve. The results showed that the exhaust gas condition of gas turbine and fuel flow rate of duct burner were main factors controlling the performance of HRSG such as flow rate and temperature of main steam from final superheater and pressure of HP drum. The time delay at the change of steam temperature between gas turbine exhaust gas and HP steam was within 2 minutes at any analysis cases.

Model Analysis of Syngas Combustion and Emissions for a Micro Gas Turbine

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Chi-Rong Liu ◽  
Hsin-Yi Shih
Keyword(s):  
Gas Turbine ◽  
Flow Rate ◽  
Heat Input ◽  
Emission Characteristics ◽  
Nox Emissions ◽  
Fuel Flow Rate ◽  
Micro Gas Turbine ◽  
Fuel Flow ◽  
Temperature Distributions ◽  
Flame Structures

The purpose of this study is to investigate the combustion and emission characteristics of syngas fuels applied in a micro gas turbine, which is originally designed for a natural gas fired engine. The computation results were conducted by a numerical model, which consists of the three-dimension compressible k–ε model for turbulent flow and PPDF (presumed probability density function) model for combustion process. As the syngas is substituted for methane, the fuel flow rate and the total heat input to the combustor from the methane/syngas blended fuels are varied with syngas compositions and syngas substitution percentages. The computed results presented the syngas substitution effects on the combustion and emission characteristics at different syngas percentages (up to 90%) for three typical syngas compositions and the conditions where syngas applied at fixed fuel flow rate and at fixed heat input were examined. Results showed the flame structures varied with different syngas substitution percentages. The high temperature regions were dense and concentrated on the core of the primary zone for H2-rich syngas, and then shifted to the sides of the combustor when syngas percentages were high. The NOx emissions decreased with increasing syngas percentages, but NOx emissions are higher at higher hydrogen content at the same syngas percentage. The CO2 emissions decreased for 10% syngas substitution, but then increased as syngas percentage increased. Only using H2-rich syngas could produce less carbon dioxide. The detailed flame structures, temperature distributions, and gas emissions of the combustor were presented and compared. The exit temperature distributions and pattern factor (PF) were also discussed. Before syngas fuels are utilized as an alternative fuel for the micro gas turbine, further experimental testing is needed as the modeling results provide a guidance for the improved designs of the combustor.

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