Effects Of Burner Geometry Research Articles

Effect of Burner Geometry on Heat Transfer Characteristics of an Impinging Inverse Diffusion Flame Jet with Swirl

An experimental investigation is carried out on an inverse diffusion flame (IDF) burners having central air jet and being surrounded by fuel jets for an impingement heat transfer. A thorough investigation has been performed to study the effects of the diameter of air jet, orientation of fuel jets and swirl in the central air jet on an inverse diffusion flame shapes, mainly on heat transfer characteristics. The twisted tapes of twist ratios (TR) 2.5 and 3.75 (corresponding to the swirl numbers of 0.62 and 0.41) are used for two different IDF burners to create a swirling flame jet. A comparison is made between the two IDF burners for with and without swirl conditions operating at a fixed air jet Reynolds number (Rea) of 2000 and equivalence ratio (ϕ) varying from 0.4 to 1.4 for a fixed burner surface to impingement plate distance of 20 mm. It is observed that for the same operating conditions, diameter of an air jet and orientation of fuel jets impart a substantial change in an inverse diffusion flame behavior by enhancing air–fuel mixing intensity. The experimental results show that the burner with smaller air jet diameter along with swirl produces a higher heat transfer rate to an impingement plate. An experimental work provides a contribution to improve a combustion characteristic of IDF for impingement heating on a flat surface.

Experimental Investigate the Effect of Burner Geometry on the Operation Window of the Burner

The purpose of this paper is to conduct an experimental study of a swirl burner with different lengths for a fixed diameter. Three models of rim length (5 cm, 10 cm and 15 cm) were taken. The results show that any change in the ratio of length to diameter will affect the flame position and structure of the downstream. It turns out that the flame settles near the edge as the rim length increases. The result indicates that increasing the length of the burner neck will reduce the structure of the swirl and weaken it, thus increasing the incidence of flashback phenomenon. The operating window of three burner neck models was studied above. It was found that the 5 cm rim has an equivalent ratio of (0.38-0.82) and for the 10 cm rim that is equivalent ratio (0.39-0.84), as well as for the rim 15 cm in equivalent ratio (0.4-0.83) with air velocity stabilization. For the above three models. Through the equivalent ratio of the above models. It was found that the 10 cm rim gave a larger operating window and therefore higher stability than the other two models.

Performance evaluation of novel surface flame self-aspirated porous radiant burners for cooking applications

Porous radiant burners (PRBs) are based on the principle of porous media combustion (PMC) in which both combustion and stabilization of the flame take place towards the end of combustion zone (CZ). It has lot of advantages over conventional free flame burners. The porous matrix has high thermal conductivity and high emissivity. Hence, contributions to conduction, convection and radiation in the PMC are significant. This paper presents experimental results on the thermal and emission performance of newly developed, bi-layered, self-aspirated porous radiant surface flame burners used in cooking applications. It comprises firebrick material in the CZ and steel balls in the preheating zone (PZ). Performance of this burner is compared to that of a conventional cooking burner (CB) within the operating range of 0.5–2 kW. The effect of burner geometry (one is circular and the other one is square in cross section) on the thermal performance and emission using liquefied petroleum gas (LPG) as the fuel is also studied and their thermal performances are compared to the conventional ones. The experimental results have revealed that the thermal efficiencies of circular and square PRBs are much higher than those of the conventional burner. The maximum thermal efficiency of the self-aspirated circular porous radiant burner (SCPRB) is found to be 71.78% at the flow rate (V) of 2.0 m/s with a porosity of 85%, whereas the thermal efficiency obtained from self-aspirated square porous radiant burner (SSPRB) is marginally less than that of SCPRB at the corresponding flow rate and porosity. The emission levels are much lower in these novel PRBs as compared with the conventional burner and these values are well below the World Health Organization (WHO) standard. The NOx emission values corresponding to the optimum velocity of 2.0 m/s are 87 ppm for CB, and 24 and 27 ppm, respectively, for SCPRB and SSPRB. CO emission values are 32, 33 and 155 ppm for SCPRB, SSPRB and CB, respectively, corresponding to the optimum velocity of flow.

Effect of burner geometry on swirl stabilized methane/air flames: A joint LES/OH-PLIF/PIV study

Large eddy simulation (LES) using a transported PDF model and OH-PLIF/PIV experiments were carried out to investigate the quarl effects on the structures of swirl stabilized methane/air flames. Two different quarls were investigated, one straight cylindrical quarl and one diverging conical quarl. The experiments show that the flames are significantly different with the two quarls. With the straight cylindrical quarl a compact blue flame is observed while with the diverging conical quarl the flame appears to be long and yellow indicating a sooty flame structure. The PIV results show the formation of a stronger flow recirculation inside the diverging conical quarl than that in the straight quarl. LES results reveal further details of the flow and mixing process inside the quarl. The results show that with the diverging quarl vortex breakdown occurs much earlier towards the upstream of the quarl. As a result the fuel is convected into the air flow tube and a diffusion flame is stabilized inside the air flow tube upstream the quarl. With the straight quarl, vortex breakdown occurs at a downstream location in the quarl. The scalar dissipation rate in the shear layer of the fuel jet is high, which prevents the stabilization of a diffusion flame in the proximity of the fuel nozzle; instead, a compact partially premixed flame with two distinct heat release layers is stablized in a downstream region in the quarl, which allows for the fuel and air to mix in the quarl before combustion and a lower formation rate of soot. The results showed that the Eulerian Stochastic Fields transported PDF method can well predict the details of the swirl flame dynamics.

Prediction of blowoff in a fully controllable low-swirl burner burning alternative fuels: Effects of burner geometry, swirl, and fuel composition

Although the lean-premixed low-swirl burner (LSB) has been successfully demonstrated in a variety of applications, the mechanisms of flame stabilization are not fully understood and practical approaches for predicting stability limits are lacking. Using a unique fully controllable LSB coupled with a stereoscopic particle image velocimetry system, flow field characteristics and flame stability were investigated over a wide range of inlet conditions (reactant flow rates, 400<Qtot<1200 SLPM; heat release rates, 15<HRRHHV<75kW), scales (38.1, 50.8 and 76.2mm LSB nozzles), swirl configurations (swirl angles, α of 0°, 35°, 37.5°, 40.4°, 44.4° and 47°), and fuel compositions (reference fuel of methane and 10 different alternative fuel mixtures). Two distinct stability modes were documented within the regime classically identified as low-swirl. The dominant ‘W-type’ flames were observed to be stabilized in the shear layer between the central core flow and annular flow of the LSB. The less common ‘R-type’ flames were characterized by a noticeable axial recirculation, even at low swirl numbers. Damköhler number calculations revealed that these two flame modes were separated by a transition region of roughly 0.3<Da<0.75, with blowoff in a W- and R-type mode generally occurring above and below this range. For hydrogen containing fuel mixtures, a third, attached-flame stabilization-mode was also observed at low burner exit velocities and/or high equivalence ratios. For the W-type regime, a semi-empirical correlation was developed based on the strength of the annular shear layer (Vdiff), which linearly related data for all available fuel mixtures and LSB sizes to the average exit velocity, Uave, such that (Vdiff/Uave)(SL/SL,CH4s)0.17=1.05±15% for all available data at blowoff. This result provides new insight into LSB flame stabilization and is a useful tool for LSB design applicable to a wide range of fuels, equivalence ratios, heat release rates, and scales.

Effects of Flame Lift-Off on the Differences Between the Diffusion Flames From Circular and Elliptic Burners

An experimental study conducted to determine the effects of lifting the flame base off the burner rim on the differences between the flame characteristics of diffusion flames from circular and elliptic burners is presented. The in-flame profiles of temperature, concentrations of fuel and combustion product species, and the mean and fluctuating components of axial velocity are presented. This study has shown that the effects of burner geometry in turbulent lifted flames are considerable only in the near-burner region. In the midflame and far-burner regions, the effects traceable to burner geometry are much weaker, contrary to those observed in the attached flame configuration. The observations are attributed to the turbulence and additional air entrainment into the jet prior to the flame base accompanying the lift-off process, which mitigate the effects of burner geometry.

The Effects of Burner Geometry and Fuel Composition on the Stability of a Jet Diffusion Flame

The effect of the burner configuration and fuel composition on the stability limits of jet diffusion flames issuing into a co-flowing air stream is presented. Circular and elliptic nozzles of various lip thicknesses and aspect ratios were employed with methane as the primary fuel and hydrogen, carbon dioxide, and nitrogen as additives. It was found that the effects of nozzle geometry, fuel composition, and co-flowing stream velocity on the blowout limits were highly dependent on the type of flame stabilization mechanism, i.e., whether lifted or rim-attached, just prior to blowout. The blowout behavior of lifted flames did not appear to be significantly affected by a change in the nozzle shape as long as the discharge area remained constant, but it was greatly affected by the fuel composition. In contrast, attached flame stability was influenced by both the fuel composition and the nozzle geometry which had the potential to extend the maximum co-flowing stream velocity without causing the flame to blow out. The parameters affecting the limiting stream velocity were studied.

Effect of Burner Geometry on the Blowout Limits of Jet Diffusion Flames in a Co-Flowing Oxidizing Stream

The effects of changes in the jet nozzle geometry, i.e., nozzle shape and lip thickness, on the blowout limits of jet diffusion flames in a co-flowing air stream were experimentally investigated for a range of co-flow air stream velocities. Circular and elongated nozzles of different axes rations were employed. Preliminary results showed that nozzles with low major-to-minor axes ratios improved, while high ratios reduced, the blowout limit of attached flames compared with that for an equivalent circular nozzle. The nozzle shape had no apparent influence on the blowout limits lifted flames and the limiting stream velocity. The experimental blowout limits of lifted flames were found to be a function of the co-flowing stream velocity and jet discharge area. On the other hand, the stability of attached flames was a function of the co-flowing stream velocity, jet discharge area as well as the nozzle shape. The effect of premixing a fuel with the surrounding air was also studied. Generally, the introduction of auxiliary fuel into the surrounding stream either increased or decreased the blowout limit depending on the type of flame stabilization mechanism prior to blowout. The stability mechanism of the flame was found to be a function of the co-flow stream velocity and the auxiliary fuel employed.

Controlling NOx emission from high-temperature air-preheat burners with air-staging

High air-preheat temperatures have been used widely to increase thermal efficiencies in industrial processes. The higher flame temperatures generally result in greater NO x emissions. In this study the distribution of temperature and the concentrations of major chemical species were determined for nominal 586 kW thermal input turbulent-diffusion flame burners firing natural gas and air, and the burners operated in an unstaged or air-staged mode. Experimental results indicated that raising air-preheat temperatures from 800 to 1250 K increased NO x emissions by a factor of 11 for the unstaged burner and 5 for the staged burner. By means of air-staging, a reduction in NO x emissions levels of approximately 50-60% was achieved for air temperatures within the range 1160-1300 K. These reductions were less at lower preheat temperatures. Changing the firing rate over a moderate range of 25% did not significantly affect NO x emitted. Numerical computations of temperature and species concentration (including NO x ) in a regenerative burner and combustion chamber are compared with experimental results. A good qualitative agreement was obtained between experimental results and theoretical prediction. With the numerical model used in this study, it is possible to make reasonable predictions of NO x emissions for burners of different geometries. The difference between the measured and predicted NO x emissions is 22%. However, the simulation provides good trend studies to investigate the effects of burner geometry and input variations. This indicates that the combination of experiments and modelling can be considered a generally useful method of solving complex engineering problems.

Burner geometry effects on combustion and NO(x) emission characteristics using a variable geometry swirl combustor

The effects of burner geometry on combustion efficiency and NO(x) emissions are investigated using an experimental stationary-type gas-turbine combustor. The previous configuration of the University of Maryland variable-geometry multiannular swirl burner (Gupta et al., 1977 and 1988), in which fuel and air are introduced at the center and outer annuli, respectively, is compared with a novel configuration in which a fuel-air mixture is introduced at the center. The results are presented in extensive graphs and discussed in detail. It is found that the new configuration can be adjusted to produce significantly lower NO(x) emissions while maintaining high combustion efficiency over wide range of burner loadings. 14 references.

Rates of fuel conversion and heat release in turbulent combustion of methane-air mixtures in tunnel burners

The experimental results presented in this paper deal with fuel conversion and heat-releaserates in experimental and commercial tunnel burners. Methane was used as fuel, and was premixed with air before entering the combustion chamber. Measurements of radial and axial distributions of temperature, concentration of stable components, and fluid velocity were used to calculate local conversion rates of combustibles and local heat-release rates. The effect of burner geometry, fuel throughput, air-fuel ratio, and turbulence intensity of the inlet mixture stream were also studied. The results show that the maximum local fuel-conversion rates and local heat-release rates occur in regions of large velocity gradients. The maximum heat-release rates obtained are much lower than in a homogeneous reactor. When the fuel throughput exceeds certain limits, unburned gases escape from the burner, resulting in lower mean combustion efficiencies. Combustion efficiencies close to 1 can only be achieved for an excess of air of more than 20 per cent stoichiometric. Conclusions for the optimum design of tunnel burners are drawn.