Flame Structure and Combustion Capability of Non-Premixed Rifled Nozzles

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Kuo C. San ◽  
Hung J. Hsu ◽  
Shun C. Yen
Keyword(s):  
Flame Structure ◽  
Mixing Efficiency ◽  
Gas Analyzer ◽  
Jet Flame ◽  
Gas Concentration ◽  
Air Jet ◽  
Fuel Jet ◽  
Schlieren Photography ◽  
Flame Behavior ◽  
Jet Velocities

The target of this study is to promote combustion capability using a novel rifled nozzle which was set at the outlet of a conventional (unrifled) combustor. The rifled nozzle was utilized to adjust the flow swirling intensity behind the traditional combustor by changing the number of rifles. The rifle mechanism enhances the turbulence intensity and increases the mixing efficiency between the central-fuel jet and the annular swirled air-jet by modifying the momentum transmission. Specifically, direct photography, Schlieren photography, thermocouples, and a gas analyzer were utilized to document the flame behavior, peak temperature, temperature distribution, combustion capability, and gas-concentration distribution. The experimental results confirm that increasing the number of rifles and the annular swirling air-jet velocity (ua) improves the combustion capability. Five characteristic flame modes—jet-flame, flickering-flame, recirculated-flame, ring-flame and lifted-flame—were obtained using various annular air-jet and central fuel-jet velocities. The total combustion capability (Qtot) increases with the number of rifles and with increasing ua. The Qtot of a 12-rifled nozzle (swirling number (S) = 0.5119) is about 33% higher than that of an unrifled nozzle. In addition, the high swirling intensity induces the low nitric oxide (NO) concentration, and the maximum concentration of NO behind the 12-rifled nozzle (S = 0.5119) is 49% lower than that behind the unrifled nozzle.

Combustion Characteristics of a Peripheral Vortex Reverse Flow Combustor With Coaxial Fuel Injection

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Raghav Sood ◽  
Preetam Sharma ◽  
Vaibhav Kumar Arghode
Keyword(s):  
Liquid Fuel ◽  
Fuel Injection ◽  
Reverse Flow ◽  
Flame Structure ◽  
Operating Conditions ◽  
Single Digit ◽  
Air Jet ◽  
Fuel Jet ◽  
Primary Breakup ◽  
Reaction Zones

Abstract This paper deals with an experimental investigation of a novel and simple reverse flow combustor, operated stably with a liquid fuel (ethanol) for heat release intensities ranging from 16 to 25 MW/(m3·atm) with very low NOx and CO emissions. The liquid fuel is injected coaxially with the air jet along the centerline of the combustor. The high velocity air annulus helps in primary breakup of the liquid fuel jet. Air injection along the combustor centerline results in a strong peripheral vortex inside the combustor leading to enhanced product gas recirculation, internal preheating of the reactants, and stabilization of reaction zones. Single-digit NOx emissions were obtained for both coaxial fuel injection (non-premixed) and a premixed–prevaporized (PP) cases for all operating conditions. CO emissions for both the modes were less than 100 ppm (ϕ < 0.75). CH* chemiluminescence images revealed two distinct flame structures for coaxial fuel injection case. A single flame structure for PP case was observed extending from the injector exit to the bottom of the combustor. The instantaneous (spatially averaged) CH* intensity fluctuations were significantly lower for the PP case as compared to the coaxial fuel injection case.

Aspect Ratio Effects of Elliptic Co-Flow on Turbulent Jet Flame Structures

2002 ◽  
Author(s):  
Ahsan R. Choudhuri ◽  
Sayela P. Luna ◽  
S. R. Gollahalli
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Flame Structure ◽  
Major Axis ◽  
Combustion Characteristics ◽  
Flame Height ◽  
Pollutant Emission ◽  
Jet Flame ◽  
Fuel Jet ◽  
Emission Flame

The aspect ratio effects of elliptic co-flow on the structure of a turbulent propane diffusion flame from a circular tube have been presented. Pollutant emission, flame radiation, flame structure, and soot concentration have been measured. The fuel jet exit Reynolds number is 2700, and the exit Reynolds number for the co-flow is 4010 and 8025 based on the minor and major axis respectively. The results are compared with the measurements from the experiments in a circular co-flow, which is the baseline condition for the present study. The pollution characteristics and the structure of the flame in the elliptic co-flow are significantly different from those in the circular co-flow. The NO emission is higher and the CO emission is lower in the elliptic co-flow. Elliptic co-flow flame produces less soot than circular co-flow flame. The study shows that the elliptic co-flow aspect ratio has a controlling influence on various combustion characteristics. In general, it is seen that as the aspect ratio of the elliptic co-flow is increased from 2:1 to 4:1, the entrainment of air increases and thus the combustion characteristics are enhanced. Compared to 2:1 AR co-flow flames, the flames with 4:1 AR co-flow are more stable, have a lower flame height, produce more NO and less CO, the flame peak temperature is higher, are less sooty, and radiate less. Flame spectral measurements show that the 4:1 aspect ratio flames produce more OH, CH, C2 and H2O radicals in the near-burner region than the 2:1 co-flow flames as a result of higher fuel oxidation.

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.

Controlling Plane-Jet Flame by a Fluidic Oscillation Technique

2013 ◽  
Vol 136 (4) ◽  
Author(s):  
Hsiu F. Yang ◽  
Ching M. Hsu ◽  
Rong F. Huang
Keyword(s):  
Combustion Product ◽  
Thermal Structure ◽  
Jet Impingement ◽  
Co2 Concentration ◽  
Maximum Temperature ◽  
Jet Flame ◽  
Fluidic Oscillator ◽  
Fuel Jet ◽  
Flame Behavior ◽  
Plane Jet

A plane-jet flame was manipulated by passing the fuel jet through a jet-impingement fluidic oscillator. The plane fuel jet bifurcated into two streams of self-sustained pulsating jets in the cavity of the fluidic oscillator and issued out of two slits on the exit plane of the fluidic oscillator. The oscillation of the bifurcated plane fuel jets caused the flame behavior and combustion characteristics to change significantly compared with the corresponding behavior and characteristics of a nonoscillating plane-jet flame. The oscillation frequency, flame behavior, thermal structure, and combustion-product distributions of the fluidic-oscillator flame were experimentally examined and compared with the nonoscillating plane-jet flame. The flame behavior was studied with instantaneous and long-exposure photography. The temperature distributions were measured with a fine-wire thermocouple. The combustion-product concentrations were detected with a gas analyzer. The results showed that the length and width of the fluidic-oscillator flame were reduced by approximately 45% and enlarged by approximately 40%, respectively, compared with the length and width of the nonoscillating plane-jet flame. The transverse temperature profiles of the fluidic-oscillator flame presented a wider spread than did the plane-jet flame. The fluidic-oscillator flame’s maximum temperature was approximately 100 °C higher than that of the plane-jet flame. The fluidic-oscillator flame presented a larger CO2 concentration and a smaller unburned C3H8 concentration than did the plane-jet flame. The experimental results indicated that the combustion in the fluidic-oscillator flame was more complete than that in the plane-jet flame.

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.

Temperature Profile of Thermal Impinging Flow Induced by Horizontally Oriented Rectangular Jet Flame Upon an Opposite Plate

2019 ◽  
Vol 11 (5) ◽  
Author(s):  
Bingyan Dong ◽  
Youbo Huang ◽  
Jinxiang Wu
Keyword(s):  
Aspect Ratio ◽  
Temperature Profile ◽  
Vertical Temperature ◽  
Jet Flame ◽  
Opposite Wall ◽  
Aspect Ratios ◽  
Fuel Jet ◽  
Jet Velocity ◽  
Jet Velocities ◽  
Impinging Flow

The horizontally oriented jet flame induced by rectangular source impinging upon the opposite wall is actually common in the chemical industry, but the related studies are limited. In this paper, the computational fluid dynamics codes are carried out to investigate the temperature profile in thermal impinging flow of the horizontally oriented methane jet flame with rectangular source, which the rectangular orifice is 400 mm2 with three different aspect ratios (L/W = 1, 2, 4); besides, the jet velocities vary from 27.5 m/s to 125 m/s. As the horizontally oriented methane jet flame impinges on the vertical plate in front of the fuel orifice directly, the vertical temperature along the opposite plate is focused on. Results show that the temperature near the impingement point is the same for different jet velocities, but the temperature along the vertical direction is larger with increasing fuel jet velocity. Moreover, the orifice aspect ratio has a significant effect on the temperature, which increases with the aspect ratio at a given position for the momentum-controlled flame. The effective heat release rate on the basis of unburned fuel and ellipse flame shape hypothesis is put forward to correlate the temperature profile. Finally, a new correlation to illustrate the vertical temperature rising along the opposite plate is proposed in light of the orifice aspect ratio and fuel jet velocity, and the predictions obtained by the proposed model agree well with the numerical results, which is applicable for the horizontally oriented flame with rectangular source impinging upon the opposite wall.

scholarly journals Experimental Investigation of Flame Structure and Combustion Limit During Premixed Methane/Air Jet Flame and Sidewall Interaction

2021 ◽  
Vol 118 (1) ◽  
pp. 37-52
Author(s):  
Ying Chen ◽  
Jianfeng Pan ◽  
Qingbo Lu ◽  
Yu Wang ◽  
Chenxin Zhang
Keyword(s):  
Experimental Investigation ◽  
Flame Structure ◽  
Jet Flame ◽  
Air Jet ◽  
Combustion Limit

Improving Combustion Intensity and Modulating Flame Behaviors Using Helical-Grooved Cones

2012 ◽  
Vol 29 (2) ◽  
pp. 273-280 ◽  
Author(s):  
S. C. Yen ◽  
C. L. Shih
Keyword(s):  
Angular Momentum ◽  
Bluff Body ◽  
Flame Length ◽  
Tangential Component ◽  
The Other ◽  
Body Effect ◽  
Jet Flame ◽  
Air Jet ◽  
Fuel Jet ◽  
Air Mixing

AbstractFour helical-grooved cones were installed behind an unconfined combustion nozzle to increase the bluff-body effect and turbulence intensity (T.I.). The cone configurations included a smooth cone and the other three cones cut with 1, 2 and 3 helical v-grooves. Experimental results showed that the helical v-grooves transformed the axial momentum (or the axial velocity) to the angular momentum (or the angular velocity). TheT.I.was enhanced by increasing the tangential component of fuel-jet momentum. The direct photography and thermocouple were utilized to observe the flame structures and to delineate the characteristic flame modes, flame length, temperature distribution, and combustion intensity. The flame modes were classified as jet flame, flickering flame, bubble flame, recirculation flame, lifted flame and ring flame. The flame length decreases as the groove number increases. The increasedT.I.and groove number (or bluff-body effect) improve the fuel-air mixing. The total combustion intensity increases with annular-air jet and with the groove number.

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.

Characteristics of Flow and Flame Behavior Behind Rifled/Unrifled Nozzles

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
Kuo C. San ◽  
Hung J. Hsu
Keyword(s):  
Turbulent Flame ◽  
Flow Characteristics ◽  
Combustion Efficiency ◽  
Flame Height ◽  
Mixing Efficiency ◽  
Jet Flame ◽  
Annular Jet ◽  
Image Velocimetry ◽  
Flame Behavior ◽  
The Relationship

A novel rifled nozzle was installed behind a conventional combustion exhauster to improve combustion efficiency. The rifled nozzles improve the momentum transmission, turbulent strength, and mixing efficiency between the central jet and annular jet. The flow characteristics behind the nozzles (rifled and unrifled) were visualized and detected using the smoke-wire flow visualization, particle image velocimetry, and hot-wire anemometry. The cold flow structures were categorized into four modes—jet flow, single bubble, dual bubble, and turbulent flow. The topological scheme was adopted to analyze and verify these flow modes. The flame structures behind the nozzles (rifled and unrifled) are classified into three modes—jet flame, flickering flame, and turbulent flame—using the direct-photo visualization. The flame height of a 12-rifled nozzle is decreased by about 50% under that of an unrifled nozzle. The flame shedding frequency declines rapidly in the flickering flame mode and the relationship between the Strouhal number (Sr) and annular velocity (ua) is Sr=0.0238+0.13/ua.

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