Computational Study of Fuel Dilution Effect on the Soot Formation in Methane-Air Laminar Confined Diffusion Flame

Author(s):  
Achin Kumar Chowdhuri ◽  
Arindam Mitra ◽  
Somnath Chakraborti ◽  
Bijan Kumar Mandal

Although diffusion flame is free from many problems associated with premixed flame, soot formation is a major problem in diffusion flame. The techniques of dilution of fuel or air with inert gases such as nitrogen and argon are used to decrease soot level in the flame. In this work, a CFD code has been developed to predict the flame height, soot volume fraction and soot number density in an axisymmetric laminar confined methane-air diffusion flame after diluting the fuel with nitrogen. The temperatures of the air and fuel at inlet are taken as 300K. Mass flow rate of the fuel stream is considered as 3.71×10−6 kg/s and mass flow rate of the air is taken as 2.2104×10−6 kg/s. The total mass flow rate through the central jet (fuel jet) is, however, kept constant. The radiation effect is also included through an optically thin radiation model. An explicit finite difference technique has been adopted for the numerical solution of reacting flow and two equations soot model with variable thermodynamic and transport properties. The prediction shows that flame height decreases with the addition of nitrogen to the fuel. Temperature of the flame is considerably reduced in the given computational domain. Both soot volume fraction and soot number density decrease with dilution by adding nitrogen in the fuel jet. The soot formation at different nitrogen dilution level of 0%, 10%, 20%, 30%, 40% and 50% are plotted and the soot get considerably reduced as the concentration of nitrogen is increased in the fuel stream.

2021 ◽  
Author(s):  
Dongsheng Zheng ◽  
Xin Hui ◽  
Xin Xue ◽  
Weitao Liu

Abstract The synergistic effect of soot formation refers to the interaction between different fuels during soot forming processes, which results in higher soot formation than any individual fuels. The present study experimentally investigates the synergistic effect of soot formation in co-flow diffusion flames of propane/ethylene fuel mixtures. The total carbon mass flow rate of the propane/ethylene mixture was kept constant at 0.5 mg/s, and the propane carbon ratio (RC) was defined as the ratio of carbon mass flow rate of propane to the total carbon mass flow rate. The laser-induced incandescence (LII) and light extinction (LE) techniques were applied to measure the soot volume fractions (SVF) at pressures of 0.1–0.5 MPa. The results showed strong synergistic effect in propane/ethylene mixtures at atmospheric conditions; however, increasing pressure weakens the synergistic effect. The LII intensity contours showed that the soot formation zone extends when synergistic effect occurs at RC = 0.1 and 0.2 for 0.1 and 0.3 Mpa. The normalized peak SVF showed that synergistic effect monotonically becomes weak with increasing pressure from 0.1 to 0.3 Mpa; meanwhile, the it still stayed strong at 0.2 Mpa when using normalized maximum soot yield, and then turned to be weaker as pressure increases. Further comparison analysis of the SVF profiles between RC = 0 and 0.1 revealed that the synergistic effect occurs at the two-wing area of the sooty flame at low axial flame height, and then gradually becomes stronger with increasing axial flame height in the soot zone for 0.1–0.3 Mpa. To illustrate the pressure effects on synergistic soot formation, numerical analysis in homogeneous closed reactor was conducted and it was found that The PAHs formation competition between C3H3 pathway and HACA mechanism results in the different soot formation phenomenon of ethylene/propane flames.


Author(s):  
Fengshan Liu ◽  
Kevin A. Thomson ◽  
Gregory J. Smallwood

Investigation of the effect of oxygen addition to fuel on the visible flame appearance and soot formation characteristics of laminar diffusion flames is important to gain comprehensive understanding of gas-phase combustion chemistry and its interaction with soot chemistry. This paper reports experimental results of oxygen addition to fuel on the visible flame height and soot volume fraction distributions in axisymmetric coflow laminar ethylene and propane diffusion flames at atmospheric flames. The carbon flow rate was maintained constant in all the experiments. Although many experimental studies have been conducted in the literature in this topic, the present investigation aimed at providing spatially resolved soot volume fraction distributions over the entire range of oxygen addition from no oxygen addition up to the point of flashback while keeping the carbon mass flow rate constant. The level of oxygen added to fuel right before flashback is about 45% (the percentage of oxygen addition is always by volume in this study) of the fuel flow rate in the ethylene flame and 300% of the fuel flow rate in the propane flame. As the added oxygen amount to ethylene increases, the visible flame height first increases. When the added oxygen flow rate is about 13% of the fuel flow rate, the flame becomes smoking, i.e., soot escapes from the flame tip. When the oxygen flow rate reaches about 42% of the fuel flow rate, the flame stops smoking. When oxygen was added to propane, the visible flame height linearly decreases with increasing the amount of oxygen. These very different effects of oxygen addition to ethylene and propane indicate that oxygen plays a drastically different role in the chemical pathways leading to soot formation in ethylene and propane flames. Distributions of soot volume fractions in these flames were measured using a 2D light attenuation technique coupled with the Abel inversion. The present study provides valuable experimental data for validating soot models.


Author(s):  
Milad Kelidari ◽  
Ali Jabari Moghadam

Different-radius of curvature pipes are experimentally investigated using distilled water and Fe3O4–water nanofluid with two different values of the nanoparticle volume fraction as the working fluids. The mass flow rate is approximately varied from 0.2 to 0.7 kg/min (in the range of laminar flow); the wall heat flux is nearly kept constant. The experimental results reveal that utilizing the nanofluid increases the convection heat transfer coefficient and Nusselt number in comparison to water; these outcomes are also observed when the radius of curvature is decreased and/or the mass flow rate is increased (equivalently, a rise in Dean number). The resultant pressure gradient is, however, intensified by an increase in the volume concentration of nanoparticles and/or by a rise in Dean number. For any particular working fluid, there is an optimum mass flow rate, which maximizes the system efficiency. The overall efficiency can be introduced to include hydrodynamic as well as thermal characteristics of nanofluids in various geometrical conditions. For each radius of curvature, the same overall efficiency may be achieved for two magnitudes of nanofluid volume concentration.


Author(s):  
S. F. Goh ◽  
S. R. Gollahalli

An experimental study to compare the smoking characteristics of diffusion flames of propylene diluted nitrogen, argon, carbon dioxide and helium was performed. The mass flow rate of propylene at smoke point condition, which was defined as the critical fuel mass flow rate (CFMFR), was first determined. Then, CFMFR was divided into ten different fractions for the study of the mechanism of inert gas dilution on smoke point. The mass flow rate of each different inert gas to achieve the smoke point condition was then determined in the same manner. Flame radiation and the visible flame height for all the diluted fuel flames were measured. The axial soot concentration profiles of nitrogen-diluted smoke point flames were also measured using the laser induced incandescence (LII) method for selective conditions. The inert gas dilution study showed two distinct regions (chemical and momentum controlled regions). The study shows the amount diluent needed to achieve smoke point was in the decreasing order of Ar, CO2, N2 and He on mass basis. The analysis of the results showed that the main reason for this phenomenon was the heat sink capability of the gas. Hence, the specific heat of the gas was an important parameter. In general, nitrogen-diluted flames had higher flame length than other inert gas diluted flames. At higher CFMFR, in helium-diluted flames radiation was higher than in other flames.


2011 ◽  
Vol 110-116 ◽  
pp. 3657-3662
Author(s):  
S. Alikhani ◽  
A. Behzadmehr ◽  
S. Mirmasoumi

Fully developed laminar mixed convection of a nanofluid (water/Al2O3) in a horizontal curved tube is numerically investigated. Three-dimensional elliptic governing equations have been solved to show how nanoparticle concentration affects on thermal and hydrodynamic parameters while these parameters are impressed by centrifugal and buoyancy forces under constant mass flow rate and heat flux. Comparisons with previously published experimental works on horizontal curved tubes show good agreements between the results. Results which are obtained using the two – phase mixture model indicate that adding the nanoparticles causes changes in the properties of nanofluid and finally increases the temperature of the flow. Furthermore, increasing nanoparticles volume fraction at first augments the heat transfer coefficient of nanofluid and then, for higher concentration of particles, decreases this thermal parameter of nanofluid.


Author(s):  
Bijan Kumar Mandal ◽  
Amitava Sarkar ◽  
Amitava Datta

A numerical investigation of the transient development of flame and soot distributions in a laminar axisymmetric coflowing diffusion flame of methane in air has been carried out considering the air preheating effect. The gas phase conservation equations of mass, momentum, energy, and species concentrations along with the conservation equations of soot mass concentration and number density are solved simultaneously, with appropriate boundary conditions, by an explicit finite difference method. Average soot diameters are then calculated from these results. It is observed that the soot is formed in the flame when the temperature exceeds 1300 K. The contribution of surface growth toward soot formation is more significant compared with that of nucleation. Once the soot particles reach the high temperature oxygen-enriched zone beyond the flame, the soot oxidation becomes important. During the initial period, when soot oxidation is not contributing significantly, some of the soot particles escape into the atmosphere. However, under steady condition the exhaust product gas is nonsooty. Preheating of air increases the soot volume fraction significantly. This is both due to more number of soot particles and the increase in the average diameter. However, preheating of air does not cause a qualitative difference in the development of the soot-laden zone during the flame transient period.


2020 ◽  
Vol 103 (3) ◽  
pp. 003685042095105
Author(s):  
Jianming Yuan ◽  
Mingzhi Li ◽  
Fangping Ye ◽  
Zhenhui Zhou

Vertical screw conveyors are used widely in industry for elevating bulk materials over relatively short distances, but the problem of insufficient feeding and low conveying efficiency always exist in the vertical conveying process. In this paper, a vertical screw conveyor with variable screw section is presented, and the characteristics of vertical screw conveyor are investigated under the variable screw sections using discrete element method (DEM). The results show that the particle volume fraction in the inlet and the mass flow rate increase in the condition of variable screw section, and the screw rotational speed has a significant influence on mass flow rate. It is evident that the design of variable screw section provides an effective way in improving the particle feeding rate and the conveying efficiency.


Author(s):  
Hyun I. Joo ◽  
O¨mer L. Gu¨lder

The effects of pressure on soot formation and the structure of the temperature field were studied in co-flow methane-air laminar diffusion flames over a wide pressure range, from atmospheric to 6 MPa (60 atm) in a high-pressure combustion chamber. The selected fuel mass flow rates provided diffusion flames in which the soot was completely oxidized within the visible flame envelope and the flame was stable at all pressures considered. The spatially resolved soot volume fraction and soot temperature were measured by spectral soot emission as a function of pressure. The visible (luminous) flame height remained almost unchanged, about 9 mm, from 1 to 10 MPa, whereas it increased considerably from atmospheric to 1 MPa. Between 1 MPa and 6 MPa, the cross-sectional area of the flame (measured from the radius defined by either the maximum soot or maximum temperature annuli) showed an inverse dependence on pressure. Peak soot concentrations showed a strong dependence on pressure from 1 MPa to 4 MPa; however this dependence got relatively weaker between 4 MPa and 6 MPa.


2014 ◽  
Vol 664 ◽  
pp. 221-225
Author(s):  
Mega Nur Sasongko

This study aims to determine the effect of the percentage of CO2 in the biogas to the characteristics of biogas diffusion flame. Counterflow configuration was used in this study to investigate detail structure of diffusion flame and the flame stability of biogas. The concentration of CO2 in the biogas was varied from 0% to 50% while the mass flow rate of the reactants was varied from 4 to 14 L / min. The results showed that the CO2 in the biogas fuel affect the diffusion flame characteristics, especially the area of luminous yellow flame formed in the fuel flow. In the low oxygen concentration, percentage of CO2 did not affect the diffusion flame stability. However, the flame stability was more influenced by the rate of diffusion between fuel and oxygen. Therefore, the combustion of biogas is more recommended to be done in the low oxygen concentration.


2019 ◽  
Vol 142 (1) ◽  
Author(s):  
M. M. Ibrahim ◽  
A. Attia ◽  
A. Emara ◽  
H. A. Moneib

The present work is an experimental investigation that aims at studying the effects of different fuel additives on the soot volume fraction and temperature in a well-defined vertical laminar diffusion flame configuration, and these additives include a diluent (argon) that suppresses the formation of soot and a soot promoter (acetylene) that accelerates and intensifies the soot formation. Three different measuring techniques are employed throughout the whole experimental program, namely, a high-resolution digital camera (up to 3.7 fps) for flame visualization, a bare wire Pt/Pt-13% rhodium fine thermocouple of 15 µm wire diameter for measuring the mean gas temperature inside the flame region and a laser system for measuring the in-flame soot volume fraction. The results indicated that the soot inception zone (deep dark parabolic shape) occurs at the immediate vicinity of the burner. The soot oxidation zone is characterized by high luminosity, and it begins after the fuel is largely consumed. The increased percentages of acetylene in the fuel mixture would lead to extending the length of this zone to ultimately occupy the whole visible flame length, where the luminosity becomes independent of the amount of soot. The temperature within the soot surface growth zone (orange color) continues increasing but at a lower rate that reflects the domination of diffusion combustion mode. Limited partial oxidation may be anticipated within this zone due to the relatively high temperature, which is not high enough to cause luminosity of the soot particles.


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