Journal articles: 'Counter-swirl flames'

1

Gupta, A. K., M. J. Lewis, and M. Daurer. "Swirl Effects on Combustion Characteristics of Premixed Flames." Journal of Engineering for Gas Turbines and Power 123, no. 3 (November 15, 2000): 619–26. http://dx.doi.org/10.1115/1.1339987.

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The effect of radial distribution of swirl has been examined on the thermal behavior of two different premixed flames using a double concentric premixed swirl burner. The double concentric swirl burner allowed systematic variation in the radial distribution of swirl (both co- and counter-) between the inner and outer annulus of the burner. The burner had two annular jets and a central nozzle. Information on the thermal field in two flames formed by co- or counter-swirl in the outer annulus and co-swirl in the inner annulus has been examined. Specifically mean and fluctuating temperatures, integral and micro thermal time scales, and probability density distribution of temperatures have been determined at various spatial positions in the flames. The micro-thermocouple output was compensated to provide high-frequency (about 1 kHz) response of the thermocouple. Direct flame photographs were taken to provide information about the global features of flames and flame stability. The global and thermal characteristic data presented here provided a complete insight on the thermal behavior of co- and counter-swirl flames. The results show that the direction of swirl (co- or counter-) used to stabilize a flame from annular jets provides a great influence on flame symmetry. The simultaneous combination of co- and counter-swirl in the burner showed a very nonsymmetrical behavior of the flame. The global and thermal data presented here confirmed these findings. The results suggest significant effect of co- and counter-swirl distribution in flames on the NOx emission levels.

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Kotb, Ashraf, and Hany Saad. "A comparison of the thermal and emission characteristics of co and counter swirl inverse diffusion flames." International Journal of Thermal Sciences 109 (November 2016): 362–73. http://dx.doi.org/10.1016/j.ijthermalsci.2016.06.015.

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Sung, Yonmo, and Gyungmin Choi. "Non-intrusive optical diagnostics of co- and counter-swirling flames in a dual swirl pulverized coal combustion burner." Fuel 174 (June 2016): 76–88. http://dx.doi.org/10.1016/j.fuel.2016.01.011.

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Smith, Travis E., Christopher M. Douglas, Benjamin L. Emerson, and Timothy C. Lieuwen. "Axial evolution of forced helical flame and flow disturbances." Journal of Fluid Mechanics 844 (April 5, 2018): 323–56. http://dx.doi.org/10.1017/jfm.2018.151.

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This paper presents 5 kHz stereo particle image velocimetry and OH planar laser induced fluorescence measurements of transversely forced swirl flames. The presence of transverse forcing on this naturally unstable flow both influences the natural instabilities, as well as amplifies disturbances that may not necessarily manifest themselves during natural oscillations. By manipulating the structure of the acoustic forcing field, both axisymmetric and helical modes are preferentially excited away from the frequency of natural instability. The paper presents a method for spatially interpolating the phase locked $r{-}z$ and $r{-}\unicode[STIX]{x1D703}$ planar velocity and flame position data, extracting the full three-dimensional structure of the helical disturbances. These helical disturbances are also decomposed into symmetric and anti-symmetric disturbances about the jet core, showing the subsequent axial evolution (in magnitude and phase) of each of these underlying disturbances. It is shown that out-of-phase acoustic forcing excites $m=\pm 1$ modes, but the flow field preferentially amplifies the counter-winding, co-rotating helical disturbance over the co-winding, counter-rotating helical disturbance. This causes the flow and flame to transition from a transverse flapping near the jet exit to a precessing motion further downstream. In contrast, in-phase forcing promotes axisymmetric $m=0$ disturbances which dominate the flow field over the entire axial domain. In both cases, the amplitudes of the anti-symmetric disturbances about the jet core grow with downstream distance before saturating and decaying, while the symmetric disturbances appear nearly negligible. It is suggested that this saturation and decay is due to linear effects (e.g. a negative spatial growth rate), rather than nonlinear interactions.

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Lecocq, G., S. Richard, O. Colin, and L. Vervisch. "Gradient and Counter-Gradient Modeling in Premixed Flames: Theoretical Study and Application to the LES of a Lean Premixed Turbulent Swirl-Burner." Combustion Science and Technology 182, no. 4-6 (June 10, 2010): 465–79. http://dx.doi.org/10.1080/00102200903462920.

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Ge, Bing, Shu Sheng Zang, and Pei Qing Guo. "Investigation on Non-Premixed Swirling Flame in a Multi-Hole Burner." Advanced Materials Research 347-353 (October 2011): 2428–31. http://dx.doi.org/10.4028/www.scientific.net/amr.347-353.2428.

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This paper focuses on investigating the flow structures in a multi-hole swirl burner. Using the Particle Image Velocimetry(PIV) technique, the experiment measured the velocity distributions of the swirling flame in a muti-hole burner. The experiments show that there is a central recirculation zone (CRZ) in the middle of the flow field, and two counter-rotating vortices exist along the centerline symmetrically. With fuel jet increase: the width of recirculating zone and axial mean velocity peaks changes little; length of recirculation zone and the biggest reverse flow velocity increases; the expansion angle of swirling jet increase at first, and then changes little; axial non-uniform coefficient of outlet reduces at first, and then increases. With airflow velocity increase: axial mean velocity peaks increase; the dimension of recirculating zone and the expansion angle of swirling jet are unchanged; axial non-uniform coefficient of outlet increases.The data from this experiment is helpful for optimization of the swirl burner design, and can be established as benchmarks for the development and validation of swirl combustion numerical simulations.

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Hadef, R., and B. Lenze. "Effects of co- and counter-swirl on the droplet characteristics in a spray flame." Chemical Engineering and Processing: Process Intensification 47, no. 12 (November 2008): 2209–17. http://dx.doi.org/10.1016/j.cep.2007.11.017.

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8

Chong, Cheng Tung, Su Shiung Lam, and Simone Hochgreb. "Effect of mixture flow stratification on premixed flame structure and emissions under counter-rotating swirl burner configuration." Applied Thermal Engineering 105 (July 2016): 905–12. http://dx.doi.org/10.1016/j.applthermaleng.2016.03.164.

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Singh, Parampreet, Ratna Kishore Velamati, and Subhash Chander. "Computational Fluid Dynamics Analysis of Aerodynamics and Impingement Heat Transfer From Hexagonal Arrays of Multiple Dual-Swirling Impinging Flame Jets." Journal of Heat Transfer 142, no. 8 (June 8, 2020). http://dx.doi.org/10.1115/1.4047055.

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Abstract Radiative furnaces pose significant thermal inertia and single impinging flames have been observed to cause occurrence of hotspots on the target surface. Multiple burners arranged in suitable array configuration represent one of the plausible solutions for more uniform heat transfer. In this study, computational fluid dynamics (CFD) simulations have been carried out for multiple swirling impinging flames arranged in a hexagonal array configuration. The turbulence chemistry interactions in the flame field are solved numerically using renormalization group (RNG) based k–ε/eddy dissipation model (EDM) framework. Comparison of co-and-counter-swirling configurations has been studied for interactions and spent gas release mechanism. Multiple swirling impinging flames undergo strong interactions resulting in distortions of recirculation zones (RCZ) for all the surrounding except central flame. Co-swirling flames result in development of higher turbulence in the interaction regions as compared to counter-swirl case. Results indicate that some flames in counter-swirl case are underutilized due to the fluid dynamics developed in the system and co-swirling hexagonal array configuration is a better arrangement for effective heating of target surface. Effect of interjet spacing (S/Dh = 5, 7, and 9) and separation distance (H/Dh = 3, 5, 7, and 9) studied for co-swirl case revealed that peak heat fluxes decreased with increasing interjet spacing and separation distance. Central flame represented a region of low heat flux and this region has been noticed to expand in size for increasing interjet spacings. Suppression of central flame has been observed to be maximum for minimum separation distance.

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10

Ma, Jinglong, Xin Hui, Meng Han, Xiao Han, Xinyao Wang, Jianchen Wang, and Zixin Chi. "Influence of the co- and counter-swirl on combustion instability of the centrally staged combustor." Physics of Fluids 35, no. 8 (August 1, 2023). http://dx.doi.org/10.1063/5.0157777.

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The centrally staged combustor is an effective way to reduce NOx emissions from combustors. However, combustion instability caused by the mutual coupling between flames and acoustics during the combustion process is almost unavoidable. To better understand this problem, the effect of the swirl rotational direction is investigated in this paper using two different schemes with co-swirl and counter-swirl configurations. Pressure fluctuations and flame dynamics are investigated under self-excited combustion oscillation conditions. The CH* chemiluminescence distribution captured by a high-speed camera is utilized to characterize the flame macrostructure and heat release fluctuations. Furthermore, non-oscillating reaction velocity fields are acquired using particle image velocimetry (PIV) technology. The results indicate that the amplitude and frequency of the counter-swirl scheme are higher than those of the co-swirl scheme at varying main stage equivalence ratios. Combining the results from dynamic mode decomposition and the local Rayleigh index, it is found that the heat release regions of the counter-swirl scheme are mainly concentrated in the shear layer. Higher velocity gradients, vorticities, and strain rates in the inner shear layer (ISL) and outer shear layer (OSL) for the counter-swirl scheme are verified using PIV technology. The driving sources of thermoacoustic oscillations are located in the regions of the ISL, OSL, and the area where the flame impinges on the sidewall of the liner. Additionally, the counter-swirl scheme exhibits larger vorticities and strain rates in the ISL and OSL, facilitating the development of thermoacoustic oscillations.

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11

Ahn, Byeonguk, and Kyutae Kim. "Effect of Counter- and Co-swirl On Low-frequency Combustion Instabilities of Jet A-1 Spray Flames." Journal of Engineering for Gas Turbines and Power, August 25, 2022. http://dx.doi.org/10.1115/1.4055354.

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Abstract The present article experimentally investigates the influence of pilot swirling directions on low-frequency combustion instabilities of pilot diffusion flames in a laboratory-scale combustor with Jet A-1 fuel and air at atmospheric pressure. Airblast atomization nozzles with either counter-rotating (CTR) or co-rotating (COR) pilot swirl flows were examined using nonlinear time-series analyses and high-speed flame imaging measurements under idle and sub-idle operating conditions. We show that while the amplitude and frequency of limit cycle oscillations are observed to be similar for both cases, detailed examinations of measured experimental data reveal marked differences in stabilization mechanisms and pressure-heat release coupling processes. The spray flame dynamics subjected to counter-rotating swirl flows are governed by large-amplitude pressure oscillations, even under the influence of destructive pressure-heat release rate interference. The mechanism of destructive interference is closely related to the interactions between a spiral diffusion flame and a periodically-detached reaction zone. Non-premixed liquid-fueled flames involving co-rotating swirl, on the other hand, feature a more compact and intense reaction zone.

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12

Singh, Parampreet, Ratna Kishore Velamati, and Subhash Chander. "A Numerical Investigation on Fluid Dynamics and Heating Characteristics of Co-and-Counterrotating Multiple Swirling Impinging Flames Arranged in 3 × 3 Inline Array." Journal of Thermal Science and Engineering Applications 12, no. 3 (February 28, 2020). http://dx.doi.org/10.1115/1.4046023.

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Abstract Swirling impinging flame jets possess the potential of uniformly heating the target surface. Numerical simulations have been carried out for multiple reacting swirling flows arranged in square 3 × 3 array. The turbulence chemistry interactions in the flow field are modeled using RNG based k-ε/ eddy dissipation model (EDM) framework. Co-and-counterrotating configurations have been compared for interactions and spent gas release mechanism at fixed inter-jet spacing and separation distance. Multiple swirling impinging flames undergo strong interactions resulting in distortions of recirculation zones (RCZs) for all the surrounding but central flame. Co-swirling flames result in development of higher turbulence in the interaction regions as compared with counter-swirl case. Tilted heat flux contours have been noticed for co-swirling impinging flames, whereas heat flux impressions are straight for counter-swirl case. Effect of inter-jet spacing (C/Dh = 5, 7, and 9) and separation distance (H/Dh = 3, 5, 7, and 9) studied for co-swirl case revealed that peak heat fluxes decreased with increasing inter-jet spacing and separation distance. With increase in inter-jet spacing, the width of central flame increased due to increased suppression effect induced by the recirculating gases. Increase in separation distance resulted in decrease of width of central flame and thermal dilution taking place led to decrease in heat flux magnitudes.

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13

Nemitallah, Medhat A., Mohamed Elzayed, Abdulrahim Alshadidi, Mohanad Abualkhair, Ahmed Abdelhafez, Fahad M. Alzahrani, and Abdul Gani Abdul Jameel. "Stratified flames in dual annular counter-rotating swirl burner for wider operability gas turbines." Journal of Energy Resources Technology, July 26, 2022, 1–36. http://dx.doi.org/10.1115/1.4055095.

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Abstract This study investigates numerically the effects of equivalence ratio (Φ) on flow/flame interactions and emissions of stratified oxy-methane (CH4/O2/CO2) flames in a dual annular counter-rotating swirl (DACRS) burner for wider operability and environmental-friendly gas turbines. The flow mixture entering the combustor is split into two coaxial streams of different equivalence ratios. The central stream is characterized by higher F to continuously ignite the flame for enhanced flame stability, whereas the annular stream is highly lean mixture to sustain the environmental performance of the combustor. The partially premixed combustion model is adopted in the Ansys-Fluent 2021-R1 software to model the reaction kinetics of the generated stratified flames in the two-dimensional axisymmetric domain. Nine cases of the same inlet velocity ratio (Primary stream to secondary stream) of 3.0 are examined at fixed oxygen fraction (OF: volumetric percentage of oxygen in the O2/CO2 mixture) of both streams of 30%. Flame stratification is achieved by varying the equivalence ratios of the primary (Φp = 0.9, 0.8, and 0.7) and secondary (Φs = 0.7, 0.55, and 0.4) streams. The results indicate effective flame/flow interactions, complete combustion, and reduced emissions for the DACRS stratified flames.

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Nemitallah, Medhat A., Abdulhammed K. Hamzat, and Kehinde G. Ismaila. "Role of oxidizer mixture composition on stabilizing stratified oxy-flames in dual lean premixed combustors for gas turbines." Journal of Energy Resources Technology, August 16, 2022, 1–17. http://dx.doi.org/10.1115/1.4055226.

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Abstract The study investigates the effects of oxidizer composition on stability and combustion and emission characetristics of stratified premixed CH4-O2-CO2 flames in a dual annular counter-rotating swirl (DACRS) burner for wider near blowout operability of gas turbines. Flame stratification was achieved by dividing the incoming reactants into primary and secondary streams of different oxygen fractions (OF). The effects of primary and secondary OFs (primary OFs: 60%, 50%, and 30%; and secondary OFs: 60%, 50%, 40%, and 30%) were investigated at fixed inlet throat velocities and equivalence ratios (φ) of the primary and the secondary streams of 6m/s and 2m/s and of 0.9 and 0.55, respectively. Two distinct flame shapes, the v-shaped and the conical-shaped, were identified as function of the oxidizer composition. V-shaped flames with enhanced flow mixing, strong inner and outer recirculation zones (IRZ and ORZ), and intensive interactions between both streams at lower Damkohler number (Da) were recorded for OFs within 30% to 50%. This indicates the ability of the DACRS burner to extend the lean blow-out limit by holding stratified stable flames of lower OFs. The flame shape turned into a conical shape at OFs of 60%-60% for both streams, the IRZ disappeared, intensive reaction rates of higher Da attained, and the flashback mechanism approached. Weake flame/flow interactions were observed at OFs higher than 50% with excessive combustion temperature near the burner tip. CH4 disspeared very close to the burner tip indicating fast reactions.

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15

Biagioli, Fernando, Alessandro Innocenti, Steffen Terhaar, and Teresa Marchione. "Experimental and Numerical Analysis of Gas Premix Turbulent Flames Stabilized in a Swirl Burner with Central Bluff Body." Journal of Engineering for Gas Turbines and Power, October 29, 2020. http://dx.doi.org/10.1115/1.4048977.

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Abstract Lean premixed gas turbulent flames stabilized in the flow generated by an industrial swirl burner with a central bluff body are experimentally found to behave bi-stable. This bi-stable behaviour, which can be triggered via a small change in some of the controlling parameters, for example the bulk equivalence ratio, consists in a rather sudden transition of the flame from completely lifted to well attached to the bluff body. While several experimental investigations exist on this topic, numerical analysis is limited. The present work is therefore also of numerical nature, with a two-fold scope: a) simulation and validation with experiments of the bi-stable flame behaviour via Computational Fluid Dynamics (CFD) in the form of Large Eddy Simulation (LES) and b) analysis of CFD results to shed light on the flame stabilization properties. LES results, in case of the lifted flame, show that the vortex core is sharply precessing at a given frequency. Phase averaging these results at the frequency of precession clearly indicates a counter-intuitive and unexpected presence of reverse flow going all the way through the flame apex and the bluff body tip. A simple one-dimensional flame stabilization model is applied to explain the bi-stable flame behaviour.

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16

Nemitallah, Medhat A., Hussain Aldawood, Ahmed Abdelhafez, Awad Alquaity, Abdul Gani Abdul Jameel, and Mansur Aliyu. "Flow/flame and emissions fields of premixed oxy-methane stratified flames in a dual annular counter-rotating swirl burner." International Journal of Thermofluids, July 2022, 100185. http://dx.doi.org/10.1016/j.ijft.2022.100185.

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17

Ariatabar, B., R. Koch, H. J. Bauer, and D. A. Negulescu. "Short Helical Combustor: Concept Study of an Innovative Gas Turbine Combustor With Angular Air Supply." Journal of Engineering for Gas Turbines and Power 138, no. 3 (September 22, 2015). http://dx.doi.org/10.1115/1.4031362.

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An innovative design of a gas turbine annular combustor is investigated analytically and numerically. Its principal feature is the helical arrangement of the burners around the turbine shaft. Hence, a shorter combustor with lower aerodynamic losses and cooling air demand might be realized. A generic model of the combustor is developed and analyzed by means of a parametric study. Scaling laws for the geometry of the flame tube and the burners are derived. Thereby, the relevant similarity parameters for fluid flow, combustion, and heat transfer are maintained constant. Subsequently, nonreacting and reacting flow regimes of selected design variants are numerically investigated. It is shown that a double annular (DA) configuration with a tilting angle of β = 45 deg, where circumferentially adjacent swirls are corotating and radially are counter-rotating, is the superior design in terms of (1) maintaining the relevant similarity rules, (2) size and location of the recirculation zones and swirl flames, and (3) flow pattern at the combustor exit. The deflection angle of the nozzle guide vanes (NGV) as well as the axial length of such a short helical combustor (SHC) could be reduced by approximately 30%.

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Nemitallah, Medhat A., Md Azazul Haque, Muzafar Hussain, Ahmed Abdelhafez, and Mohamed A. Habib. "Stratified and hydrogen combustion techniques for higher turndown and lower emissions in gas turbines." Journal of Energy Resources Technology, September 23, 2021, 1–42. http://dx.doi.org/10.1115/1.4052541.

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Abstract This review overviews combustion technologies for reduced emissions and better fuel economy in industrial gas turbine. Lean premixed combustion (LPM) technology is introduced as a low-temperature combustion technique to control NOx emissions. The Dry Low NOx (DLN) is one of the most promising LPM-based combustors for controlling NOx emissions. However, DLN combustors suffer from limited flame stability, especially under low load (near blowout) operating conditions, in addition to the difficulty of separating CO2 from the exhaust stream for reducing the gas-turbine carbon footprint. Trying to overcome such difficulties, the gas turbine manufacturers developed enhanced-design burners for higher turndown and lower NOx emissions, including the Dual Annular Counter Rotating Swirl (DACRS) and environmental-Vortex (EV) burners. The volume of the DACRS combustors is almost twice the conventional burners, which provide ample residence time for complete combustion. The mixing effectiveness is improved in EV-burners resulting in higher flame stability at low load or startup conditions. To widen the operability, control the emissions, and improve the turndown ratio of gas turbine combustors, the concept of flame stratification, i.e., heterogenization of the overall equivalence ratio, was introduced. This technique can widen the stability range of existing LPM flames for industrial applications. Integrating stratified combustion technique with oxy-fuel combustion technology is a way forward that may result in complete control of gas turbine emissions with higher operability turndown ratio. The recent developments and challenges towards the application of hydrogen gas turbine are introduced.

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19

Degeneve, A., R. Vicquelin, C. Mirat, J. Caudal, and T. Schuller. "Impact of co- and counter-swirl on flow recirculation and liftoff of non-premixed oxy-flames above coaxial injectors." Proceedings of the Combustion Institute, September 2020. http://dx.doi.org/10.1016/j.proci.2020.06.279.

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20

Yang, Jinxin, Lingzhe Rao, Charitha de Silva, and Sanghoon Kook. "The influence of inter-jet spacing and jet-swirl interaction on flame image velocimetry (FIV) derived flow fields in a small-bore diesel engine." International Journal of Engine Research, August 4, 2021, 146808742110384. http://dx.doi.org/10.1177/14680874211038432.

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This study applies Flame Image Velocimetry (FIV) to show the in-flame flow field development with an emphasis on the jet-jet interaction and jet-swirl interaction phenomena in a single-cylinder small-bore optically accessible diesel engine. Two-hole nozzle injectors with three different inter-jet spacing angles of 45°, 90° and 180° are prepared to cause different levels of jet-jet interaction. The engine has a swirl ratio of 1.7, which is used to evaluate jet-swirl interaction of the selected 180° inter-jet spacing nozzle. High-speed soot luminosity imaging was performed at a high frame rate of 45 kHz for the FIV processing. For each inter-jet spacing angle, a total of 100 individual combustion cycles were recorded to address the cyclic variations. The ensemble averaged flow fields are shown to illustrate detailed flow structures while the Reynolds decomposition using spatial filtering is applied to analyse turbulence intensity. The results showed reduced bulk flow magnitude and turbulence intensity at smaller inter-jet spacing, suggesting the two opposed wall-jet heads colliding immediately after the jet impingement on the wall can cause flow suppression effects. This raised a concern on the mixing as lower inter-jet spacing creates more fuel-rich mixtures in the jet-jet interaction region. Despite lower flow magnitude, the cyclic variation was also estimated higher for narrower inter-jet spacing, which is another drawback of the significant jet-jet interaction. Regarding the jet-swirl interaction, the wall-jet head penetrating on the up-swirl side showed lower bulk flow magnitude as the counter-flow arrangement suppressed the flow, similar with the narrower interact-jet spacing results. However, the turbulence intensity was measured higher on the up-swirl side, suggesting the relatively weaker swirl flow vectors opposed to the penetrating wall-jet head could in fact enhance the mixing.

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21

Mardani, Amir, Benyamin Asadi, and Amir Agha Beige. "Investigation of Flame Structure and Precessing Vortex Core Instability of a Gas Turbine Model Combustor with Different Swirler Configurations." Physics of Fluids, July 26, 2022. http://dx.doi.org/10.1063/5.0097430.

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Numerical simulation of a dual swirl Gas Turbine Model Combustor (GTMC) is performed under cold and reacting flow conditions using a three-dimensional Unsteady Reynolds-Averaged Navier-Stokes (URANS) approach. A multi-species chemical mechanism is used in this study for the analysis of the numerous radicals participating in the ignition process and the flame structure. The other objective of this study is to investigate the flow field under different injector configurations, including both co-rotating and counter-rotating swirler arrangements, different swirl intensities, and vane areas. A comparison of the results with experimental data shows that the predicted velocity and temperature profiles follow the experimental data reasonably. In these studies, a precessing vortex core (PVC) is found in the shear layer of the inner recirculation zone (IRZ) for all injector arrangements considered, and a co-rotating vortex exists in the outer shear layer (OSL) for some of these arrangements. OH mass fraction field shows that the reactions take place mostly near the vortex core. Furthermore, it is shown that the build-up process of H2O2 and CH2O inside the cold jet has an important effect on combustion initiation. In addition, the formation and consumption of the H atoms in the recirculation zones and the balance between OH and H2O2 are shown to have important roles in the flame formation process. Finally, the precession frequency of the PVC is found to scale almost linearly with the spatial gradient of swirl velocity in the inner swirler and is almost independent of the inclusion of the combustion reactions.

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Banerjee, Siddhartha, Clayton Naber, Michael Willcox, Charles E. A. Finney, and Dean K. Edwards. "High-Performance Computing and Analysis-Led Development of High Efficiency Dilute Opposed Piston Gasoline Engine." Journal of Engineering for Gas Turbines and Power 140, no. 10 (June 19, 2018). http://dx.doi.org/10.1115/1.4039845.

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Pinnacle is developing a multicylinder 1.2 L gasoline engine for automotive applications using high-performance computing (HPC) and analysis methods. Pinnacle and Oak Ridge National Laboratory executed large-scale multidimensional combustion analyses at the Oak Ridge Leadership Computing Facility to thoroughly explore the design space. These HPC-led investigations show high fuel efficiency (∼46% gross indicated efficiency) may be achieved by operating with extremely high charge dilution levels of exhaust gas recirculation (EGR) at a light load key drive cycle condition (2000 RPM, 3 bar brake mean effective pressure (BMEP)), while simultaneously attaining high levels of fuel conversion efficiency and low NOx emissions. In this extremely dilute environment, the flame propagation event is supported by turbulence and bulk in-cylinder charge motion brought about by modulation of inlet port flow. This arrangement produces a load and speed adjustable amalgamation of swirl and counter-rotating tumble which provides the turbulence required to support stable low-temperature combustion. At higher load conditions, the engine may operate at more traditional combustion modes to generate competitive power. In this paper, the numerical results from these HPC simulations are presented. Further HPC simulations and test validations are underway and will be reported in future publications.

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Liu, Cunxi, Fuqiang Liu, Yanhui Mao, Yong Mu, and Gang Xu. "Experimental Investigation of Performance of an Air Blast Atomizer by Planar Laser Sheet Imaging Technique." Journal of Engineering for Gas Turbines and Power 136, no. 2 (November 1, 2013). http://dx.doi.org/10.1115/1.4025235.

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It is widely recognized that the fuel-air mixing process is a critical factor in improving combustion efficiency and in minimizing pollutants such as NOx. Enhancement of fuel-air mixing can lead to lower pollutant emissions and greater efficiency. However, swirling flows in lean combustors play the role of fuel-air mixing and flame stability. The complex fluid dynamic phenomena encountered in swirling two-phase flow contribute to the difficulty in complete understanding of the different processes occurring in combustors. Fortunately, optical and laser-based visualization techniques available in our lab are important nonintrusive tools for visualizing flow process, especially for fuel injection and fuel-air mixing. To provide for a better understanding of effects of counter-rotating flow on droplets in atomization process, this study is a detailed characterization of the spray generated by an airblast atomizer by planar laser sheet imaging method. Optical facility for spray diagnostics with fuel planar laser induced fluorescence (fuel-PLIF) method for fuel distribution and particle image velocimetry (PIV) method for the velocity of droplets is used to evaluate the performance of an airblast atomizer. The results show that the performance of secondary atomization is influenced by swirling flow and primary atomization simultaneously; the swirling flow exhibits significant influence on the droplet size and space distribution relative to that of primary atomization. The primary swirling air reopens the spray cone generated by pressure-swirl atomizer, and the secondary swirling air affects the fuel distribution by forming the recirculation zone. The results provide critical information for the design and development of combustion chambers.

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Journal articles on the topic 'Counter-swirl flames'

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