Air Swirl Research Articles

Use of response surface methodology to optimize NOx emissions and efficiency of W-type regenerative radiant tube burner under plasma-assisted combustion

Abstract To address the challenges involved in industrial energy efficiency improvement and tightening of emission requirements, we have made efforts in areas of both design and technology toward the development of a W-type regenerative radiant tube burner that can be adapted to heat treatment furnaces. This design comprises several features of air staging, air swirling, and plasma-assisted combustion technology to improve performance and minimize NOx emissions. Using response surface methodology (RSM), an optimal experimental design was adopted and resulting data was subjected to analysis of variance (ANOVA) to examine the significance of the operating parameters, including excess air ratio and switching time. Interactions between variables were statistically validated. The results illustrate that the radiant tube can significantly reduce the temperature deviation and induce uniform temperature distribution on the furnace wall. ANOVA analysis showed that the process, properly represented by a second-order polynomial model, was significant (p

Emission characteristics of turbulent non-premixed ammonia/air and methane/air swirl flames through a rich-lean combustor under various wall thermal boundary conditions at high pressure

This study is dedicated to understanding the combustion and emission characteristics of turbulent non-premixed ammonia (NH3)/air and methane (CH4)/air swirl flames in a rich-lean gas turbine−like combustor at high pressure under various wall thermal boundary conditions. In this study, the emission characteristics of both flames were obtained through numerical simulations using large−eddy simulations with the finite-rate chemistry technique. In addition, for NH3/air flames, simultaneous NO and OH planar laser−induced fluorescence (PLIF) images were acquired in order to qualitatively verify the numerical results. The results show that the minimum NO emission could be obtained when the primary zone global equivalence ratio (ϕglobal/pri) was 1.1, irrespective of the wall thermal condition, using a rich-lean combustor in NH3/air flames, whereas in CH4/air flames, the maximum NO emission was obtained with a ϕglobal/pri value of 1.0. Moreover, in NH3/air flames, the local NO concentration is largely dependent on the local OH concentration, whereas in CH4/air flames, the local NO concentration is largely dependent on the local temperature. The NO−OH correlation in NH3/air flames was experimentally verified using simultaneous NO and OH PLIF images. Additionally, it was found that, in NH3/air flames, the wall heat losses due to the combustor wall cooling greatly affected the NH3 oxidation and led to significant emissions of unburnt NH3, although lower NO emission resulted from the combustor wall cooling. This was primarily because of the lower OH concentration level in the flame region owing to the wall heat losses.

On the influence of geometrical parameters on the spray characteristics of high shear injectors

We discuss the influence of geometrical parameters over the performance of high shear injector. High shear injector usually consists of a series of air swirlers (primary and secondary) with diverging flare at the exit and centrally mounted fuel nozzle. In this study, we have considered only parameters pertaining to air swirler i.e. geometrical swirl number (SNgeo), flow split ratio (γ), area ratio (Δ), flare angle (θ) and flow orientation of primary and secondary swirlers (co/counter rotation). The above parameters were categorized into two paradigms, first, SNgeo, γ, Δ are designated as internal geometrical parameters, which induces variations in the bulk Reynolds number at the exit. On the other hand, parameters like flare angle (θ), flow orientation doesn’t yield any variations in bulk Reynolds number. Time resolved PIV (Particle Image Velocimetry; ~ 3500 frames/s) is employed to extract the topological structures of the flow field. The length scale (W/Df), which embodies the radial extent of the recirculation zone is governed by near field swirl number (SN10) and Reynolds number for cases with variations in SNgeo, γ, Δ. Contrarily, with variations in θ and flow orientation, (W/Df) is found to be a function of near field swirl number f (SN10) only. The spatial distribution of the spray shows linear relationship with the W/Df. Finally, the droplet size spectrum obtained from 3D PDI (Phase Doppler interferometer) also shows insensitivity with respect to the different test cases. This clearly indicates that in high shear atomizer configuration, spread of the spray can be altered without deterioration in uniformity and droplet size distribution.

Mole fraction measurement through a transparent quarl burner using filtered Rayleigh scattering.

A filtered Rayleigh scattering system is developed and applied to measure the mole fraction of methane in a methane-air swirl flow through a transparent conical quartz quarl. Light scattering from the location where the laser beam is incident on the surface of the quarl is orders of magnitudes larger than Rayleigh scattering from the gas mixture of interest. This diffusive scattering is suppressed using molecular absorption by an iodine cell and using spatial filtering by an optical aperture. Residual stray light accounted for up to 5% of the total signal and had to be removed for accurate measurements. The flow consisted of a nonpremixed mixture of methane and air in the central jet surrounded by a strong swirling air flow. Measurements were conducted at a height of 4 mm from the fuel tube's exit for six different conditions of the swirl flow to demonstrate the ability of the instrument to study the effects of swirl strength and fuel flow rate on the mixing process. By using a four-leg pulse stretcher to allow higher laser energies in the probe volume, large collection optics and a reference iodine cell to monitor laser wavelength variations, standard deviations of ∼0.006 in air and ∼0.012 in a laminar methane flow were achieved for mole fraction measurements.

Copper Cathode’s Ablated Structure Operated in a 50 Megawatt Arc Heater

An oxygen-free high-conductivity copper cathode was tested in a 50 MW arc heater with working currents up to 2600 A and power up to 13.6 MW by using air as the test gas. After testing, the structure of the ablated cathode was measured and analyzed. The erosion rate of the cathode was . An arc foot area and an oxide layer area appeared and were located at the end of the cathode. The arc foot area was covered with molten signs, ablated pits, and deformations. The oxide layer was composed of parallel traces that were generated by melted liquid. The grain size at the cathode’s thinnest wall thickness was refined from the original to due to recrystallization. The grain size increased and the phenomenon of abnormal grain growth appeared, with an increase of the distance from the arc foot. The Vickers hardness agreed well with the grain size. The erosion mass loss includes not only vaporization removal but also melting removal via shear force generated by swirl air, considering the erosion rate and ablated phenomena. A modified particle ejection model is proposed to describe the erosion mechanism that agrees with the ablated phenomena of the test.

Experimental detergent drying analysis in a counter-current spray dryer with swirling air flow

The paper presents an experimental analysis of the spray drying conditions on the product properties in a pilot plant counter-current spray dryer with swirling air flow. The influence of slurry – atomizing air ratio, drying air flow rate and swirl number on the product properties and the efficiency of the drying process was examined. The increase of the slurry – atomizing air ratio promotes agglomeration, ultimately leading to the development of wet, coarse granules. Through experimentation, the slurry-to-atomizing-air ratio can be optimized to maximize capacity ratio (i.e. acceptable product vs. total spray dried powder) and energy efficiency whilst achieving the desired product quality.

The impact of swirling flow strength on lean-dome LDI pilot mixers’ operability and emissions

In an effort to reduce the environmental impact of aviation, lean-dome combustion concepts such as lean direct injection (LDI) are being pursued for their potential to achieve very low emissions. However, low-emissions potentials may be accompanied by operability challenges. In the present effort – part of a series of fundamental investigations into LDI operability challenges – systematic experiments of lean-dome-relevant pilot combustor devices are conducted in a single-element methane-fueled combustor test rig with two different LDI configurations by using a suite of optical diagnostics. While maintaining all other design features constant, the clockwise vane angle of the outer air swirler is altered between 60° (LDI-60-CW configuration) and 45° (LDI-45-CW configuration), representing strong and weak swirling flows, respectively. Measurements of the non-reacting/reacting flow fields and flame characteristics are performed as a function of overall equivalence ratio via time-resolved particle image velocimetry, OH*/CH*/NO2* chemiluminescence, OH planar laser-induced fluorescence, and broadband flame imaging. It is found that a large center recirculation zone exists only with the LDI-60-CW configuration, while the LDI-45-CW flow is dominated by a swirling jet flow. In addition, it is shown that the center recirculation zone in the LDI-60-CW configuration results in noticeably lower lean blowout limits than the LDI-45-CW configuration, but at the cost of much higher NOx production for vigorously-burning equivalence ratios. At lower equivalence ratios near lean blowout conditions, both configurations result in similar NOx production. These results are discussed in terms of identifying possible research directions for optimizing LDI designs for reduced NOx emissions while maintaining or improving operability relative to current rich-dome combustion technology.

Assessment of Exit Temperature Pattern Factors in an Annular Gas Turbine Combustor: An Overview

Abstract The present paper overviews the works carried out on achieving desired temperature pattern factors at combustor exit in gas turbine engines. These pattern factors are very important from the point of engine performance and life of turbine blades and vanes. They are controlled by a number of geometrical parameters such as liner front-end air passages, primary air holes, atomizer characteristics and air swirl number and dilution zone geometrical configuration. Combustor inlet pressure, Mach number, velocity profile and fuel-air ratio are the major operating parameters that influence the pattern factors. Due to the design uniqueness and importance of pattern factors, it is always a challenge to assess the pattern factors over a wide range of mission points for a gas turbine combustor designed for combat aircraft.

Linear stability analysis of a non-Newtonian liquid jet in a coaxial swirling air

The instability behavior of a power law liquid jet moving in a swirling air is investigated theoretically. The power law model is selected to describe the viscosity of the non-Newtonian jet. The corresponding dispersion relation is obtained by a linear stability analysis. Besides, the effects of air swirl strength, non-axisymmetric mode, liquid Weber number, generalized Reynolds number, power law index and consistency coefficient on the instability of the power law liquid jet surrounded by a swirling gas are studied in the Rayleigh and Taylor modes. The results show that the shear-thickening liquid jet is more unstable than the Newtonian and shear-thinning liquids when the air swirl is introduced. The air swirl is a stabilizing factor on the instability of the power law liquid jet in Rayleigh and Taylor modes. It is also found, when the air swirl is introduced, the maximum growth rate of the power liquid jet decreases as the liquid Weber number increases in Rayleigh mode, while it increases in Taylor mode. Moreover, the viscous forces of the liquid always prevent the jet from breaking up.

Oxygenated sunflower biodiesel: Spectroscopic and emissions quantification under reacting swirl spray conditions

The spray combustion characteristics of sunflower (Helianthus annuus) biodiesel/methyl esters (SFME) and 50% SFME/diesel blend and diesel were investigated via a liquid swirl flame burner. The swirl flame was established at atmospheric condition by using a combined twin-fluid atomiser-swirler configuration at varied atomising air-to-liquid ratios (ALR) of 2.0–2.5. Diesel flame showed a sooty flame brush downstream of the main reaction zone, as opposed to the biodiesel flame which showed a non-sooty, bluish flame core. Biodiesel flame exhibited a more intense flame spectra with higher OH* radicals as compared to diesel. Higher preheating main swirl air temperature led to higher NO emission, while CO correspondingly decreased. Sunflower-derived biodiesel generally exhibited slightly higher NO and CO levels than diesel when compared at the same power output, mostly due to higher flame temperature and fuel chemistry effect. By increasing ALR, a significant reduction of NO and CO for both fuel types were concurrently achieved, presenting a strategy to control emissions and atomise biodiesel with higher viscosity under swirl combustion mode.

Effects of air swirler geometry on air and spray droplet interactions in a spray chamber

In this work, interactions between cold spray and swirl airflow are characterized experimentally and numerically for various air swirler geometries. The number of vanes, vane angle, vane curvature, and air velocity are varied for the swirling airflow. Spray visualization and phase Doppler interferometry techniques have been employed to obtain important parameters such as spray cone angle and mean drop size. In the numerical work, the Realizable [Formula: see text] turbulence model has been employed along with the Linearized Instability Sheet Atomization and Taylor Analogy Breakup to simulate spray field. The predicted results for the airflow field compare well with available experimental results in published literature. Good match is also found between the present predictions and measured spray data. The radial distribution of Sauter mean diameter exhibits peak values at the periphery of the spray near the injector, due to liquid swirl. The peak Sauter mean diameter shifts to the spray axis, beyond the recirculation zone, due to entrainment of droplets by the swirling air stream. The volume fraction of droplets exhibits multi-modal distribution, due to the interactions between spray droplets and recirculating airflow. A curved swirler gives rise to finer spray compared to a flat swirler, due to lower losses and better utilization of momentum.

An Efficient Method to Reproduce the Effects of Acoustic Forcing on Gas Turbine Fuel Injectors in Incompressible Simulations

Previous studies have highlighted the importance of both air mass flow rate and swirl fluctuations on the unsteady heat release of a swirl stabilised gas turbine combustor. The ability of a simulation to correctly resolve the heat release fluctuations or the flame transfer function (FTF), important for thermoacoustic analysis, is therefore dependent on the ability of the method to correctly include both the swirl number and mass flow rate fluctuations which emerge from the multiple air passages of a typical lean-burn fuel injector. The fuel injector used in this study is industry representative and has a much more complicated geometry than typical premixed, lab-scale burners and the interaction between each flow passage must be captured correctly. This paper compares compressible, acoustically forced, CFD (computational fluid dynamics) simulations with incompressible, mass flow rate forced simulations. Incompressible mass flow rate forcing of the injector, which is an attractive method due to larger timesteps, reduced computational cost and flexibility of choice of combustion model, is shown to be incapable of reproducing the swirl and mass flow fluctuations of the air passages given by the compressible simulation as well as the downstream flow development. This would have significant consequences for any FTF calculated by this method. However, accurate incompressible simulations are shown to be possible through use of a truncated domain with appropriate boundary conditions using data extracted from a donor compressible simulation. A new model is introduced based on the Proper Orthogonal Decomposition and Fourier Series (PODFS) that alleviates several weaknesses of the strong recycling method. The simulation using this method is seen to be significantly computationally cheaper than the compressible simulations. This suggests a methodology where a non-reacting compressible simulation is used to generate PODFS based boundary conditions which can be used in cheaper incompressible reacting FTF calculations. In an industrial context, this improved computational efficiency allows for greater exploration of the design space and improved combustor design.

Numerical investigation into the effect of burner swirl direction on furnace and superheater heat absorption for a 620 MWe opposing wall-fired pulverized coal boiler

The paper investigates the effects of pulverized coal swirl burners’ secondary air swirl directions on furnace water-wall, platen superheater and high temperature superheater heat absorption by using numerical simulations. The resultant effect on the carbon-monoxide and unburnt carbon levels was also investigated to establish the furnace performance. The conventional RANS approach was used along with a two-equation turbulence closure model to simulate the multispecies gas phase flow. Fuel particles were modeled as a discrete phase. The gas phase combustion was simulated using the eddy dissipation finite rate kinetics model and the surface reactions using a diffusion-kinetics limited model. To establish the validity of the modelling approach an actual 620 MWe boiler furnace and its superheaters were modelled, and the results compared to processed plant data. Once the model showed that it can predict the plant performance with reasonable accuracy it was used to investigate the performance changes for various burner swirl arrangements. Six swirl arrangement cases were simulated to determine the effect on the furnace performance indicators. It was found that by swirling all the burners per wall in the same direction that the furnace heat absorption could be increased by up to 6.67% and the unburned carbon fraction reduced from 0.029% to 0.022% when compared to the current boiler swirl configuration results, which has a staggered swirl direction arrangement. Furthermore, it was shown that the enhanced mixing in the volume adjacent to the burners also reduced the carbon-monoxide levels. The simulations demonstrated, for the given modelling methodology, that there is indeed interaction between adjacent burners which influences the combustion rate and in turn heat absorption in the water-cooled furnace walls and platen superheater for the modelled boiler.

Effect of tangential swirl air inlet angle on the combustion efficiency of a hybrid powder-solid ramjet

A new ramjet configuration using powder and solid fuel as propellant is investigated, namely, hybrid powder-solid ramjet (HPSR). Boron particles were used as the powder in this study. In order to improve combustion efficiency of boron and simplify the engine structure, a tangential swirl air inlet is adopted on the HPSR. Ignition model based on the multi-layer oxide structure and Global reaction combustion model of boron particles, the Lagrangian particle trajectory model and the realizable k-ε turbulence model were implemented to calculate three-dimensional two-phase flow and combustion in the HPSR with the different tangential air inlet angles (0°,5°, 10°, 15°, 20°, 25°). The effects of tangential air inlet angles on the ignition and combustion of boron were analyzed. The results show that when the tangential swirl air inlet angle is 10°, the combustion efficiency of boron particles and the total combustion efficiency of engine are the highest; the temperature distribution in the second combustion chamber is uniform, and the ignition distance of particles is small, for the HPSR configuration tested.

Flames of Swirling Double-Concentric Jets Subject to Acoustic Excitation at Resonance

The effects of acoustic excitation at resonance on the flame appearances, flame lengths, flame temperatures, and combustion product concentrations of combusting swirling dual-disk double-concentric jets were studied. The Reynolds number of the annular swirling air jet was varied, while it was fixed at 2500 for the central propane jet. The central fuel jet was acoustically forced by a loudspeaker, which was installed using downstream longitudinal irradiation. The central jet pulsation intensities were measured by a calibrated, one-component hot-wire anemometer. The instantaneous full-length and close-up flame images were captured to identify the characteristic flame modes. Long-exposure flame images were taken to measure the flame lengths. The axial and radial temperature distributions of flames were measured using a homemade, fine-wire R-type thermocouple. The concentrations of combustion products were measured by a gas analyzer. Four characteristic flame modes, blue-base wrinkled flame, yellow-base anchored flame, blue-base anchored flame, and lifted flame, were observed in the domain of central jet pulsation intensity and annular swirling jet Reynolds number. The lifted flame, which was formed at large central jet pulsation intensities, presented characteristics of a premixed flame due to significant mixing induced by violent, turbulent flow motions. It was short and stable, with high combustion efficiency and low toxic emissions, when compared with the unexcited flame and other excited characteristic flame modes, which presented characteristics of diffusion flame.

Numerical and experimental analysis of the velocity field of air flowing through swirl diffusers

The air swirl diffusers are popular for the ceiling level air supply system and have been widely used for Indoor Air Quality. They are nowadays one of the most popular diffusers commonly used in airconditioning systems [1, 2]. The swirl diffusers are intended to use in low- and medium-pressure ventilation systems. They allow for obtaining the swirl airflow and are especially recommended to use in spaces with the height from 3m up to 12m, where heating and cooling is performed by the ventilation system and where the exact setting of supply air velocity is important [3-6]. In the case of swirl diffusers,fluid flow is usually significantly influenced by the characteristics of different diffuser designs. In the ventilation system design phase, a typically focus on ventilation effectiveness and takes into account a large number of parameter. However, the discrepancy between design and practice are often experienced mainly because operating conditions don’t correspond to the designing conditions [7-9]. Inthis work, the airflow of swirl diffuser has been studied using Particle Image Velocimetry (PIV) method to analyse the mean airflow and geometry influence on the results. The paper presents a comparison of the results of velocity field measurements using the PIV method and the results obtained by means ofnumerical analysis CFD. Based on the analysis the velocity flow field was evaluated and the range of effective operation of the diffuser have been determined [10].

Generation of plasma torch by 2.45 GHz microwaves from a solid-state power amplifier

High efficiency electrodeless plasma at atmospheric pressure was generated using 2.45 GHz microwaves with a solid state power amplifier (SSPA) to achieve greater plasma efficiency in a type WR340 rectangular resonator, in comparison with magnetron. Plasma flames were sustained in a discharge tube with an inner diameter of 26 mm by swirl flow. With an applied power of 3.3 kW and the injection of 50 lpm swirl air, the plasma flame length of the SSPA was 630 mm, demonstrating an almost 30% increase compared with the magnetron flame length. Subsequently, the Q factors, indicating energy efficiencies of the magnetron and SSPA, were calculated using frequency analysis data. The obtained Q factors demonstrated an increase in plasma efficiency by almost one order of magnitude with the SSPA on the WR340 resonator as compared to the magnetron.

On Low-Emission Annular Combustor Based on Designing of Liner Air Admission Holes

Numerical experiments was carried out to predict the total temperature characteristics and formation of nitrogen oxide emissions and pattern factor in an annular combustor liner based on geometrical parameters and location and rows of different air admission holes, for 6 various cases, using computational fluid dynamics (CFD) .The simulation has been performed using ANSYS CFX including finite rate chemistry and eddy dissipation model, for simulation of liquid kerosene (Jet A) – air combustion after fuel droplet evaporation. The spray modeling was performed, including Rosin-Rammler droplet distribution. Thermal and prompt nitrogen oxide (NO x ) formation was performed to predicting NO x emission characteristics with a k -e model of turbulent. In this investigation the 3D CAD model of the realistic annular combustion chamber is presented for the simulation with double radial air swirler for the better mixing fuel with air. Beside this the characteristic and the flame structure is presented including the contour plots of total temperature and NO concentration at the outlet of the combustor liner and in cross section plane along the X axis from the injector center of the combustor including the chart of the velocity and NO, CO, CO 2 , O 2 and the total temperature along the liner from the injector center. For the combustion of kerosene with air 2 step kinetic schemes are presented in this study. The results show that the best result with the low concentration of NO is the case 5 but with a high percentage of pressure drop and the case 3 have the maximum concentration of NO with the low percentage of pressure drop.

Modeling of air flow in industrial rooms

Abstract The article is devoted to the air distribution in a room by swirl and laying air jets. Dynamic parameters of air flow that is created due to swirl and laying air jets at their leakage in a room has been determined. The mathematical model of air supply with swirl and laying air jets in the industrial rooms is improved. Simulation of air flow is performed due to CFD FLUENT (Ansys FLUENT). Solution of the equation by using k-ε model of turbulence is presented. Dynamic parameters of air flow that is created due to swirl and laying air jets at their leakage at variable regime and creation of dynamic microclimate in a room has been determined. Results of experimental investigations of air supply into the room by air distribution device which creates swirl air jets for creation more intensive turbulence air flow in the room are presented. The results of theoretical researches of influence of dynamic microclimate to the human organism are presented.

Heat exchange of a mixture of gases with different Prandtl numbers under a swirl flow in a circular heated channel

The results of experimental studies of hydrodynamics and heat transfer in a swirl air flow (Pr = 0.7) and a helium-xenon mixture (Pr = 0.2) in heated circular channels with original screw inserts in a wide range of Reynolds numbers are presented. The efficiency analysis of heated channels with a swirl of the flow is compared with the efficiency analysis of the channels without swirling the flow using the energy necessary for pumping the gas through the heated channel.