@article{sahoo_narayanaswamy_lyons_2023, title={Quenching measurements of Kr 5p[3/2](2) <- <- 4p(61)S(0) electronic transition using absorption spectra}, volume={62}, ISSN={["2155-3165"]}, url={https://doi.org/10.1364/AO.475382}, DOI={10.1364/AO.475382}, abstractNote={Quenching rate is an important parameter to include in fluorescence measurements that are aimed at quantifying the thermochemical field of a reacting flow. Traditionally, the quenching measurements were obtained at low pressures using the direct measurements of quenching times followed by a linear scaling to the desired pressure. This approach, however, cannot account for the possible deviation from the linear pressure scaling at elevated pressures due to three and multi-body collisions. Furthermore, the best accuracy on the quenching rate is obtained with ultra-short pulse lasers that are typically not readily available. This study offsets these limitations by demonstrating a new approach for making direct quenching measurements at atmospheric conditions and using nanosecond lasers. The quenching measurements are demonstrated in a krypton-perturber system, and the 5 p [ 3 2 ] 2 ←← 4 p 6 1 S 0 two-photon electronic transition is accessed. A theoretical construct is presented that relates the absorption spectral parameters and the integrated fluorescence signal to the quenching rate, referenced to a given species and conditions. Using this formulation, the relative quenching rates for different perturber species, namely, air, C H 4 , C 2 H 4 , and C O 2 , are reported as measured at 1 atm and 300 K. As such, the present technique is limited to the measurement of the relative quenching rate, unlike the previous studies where absolute quenching rates are measured. Nonetheless, when the reference quenching rate is independently measured, the relative quenching rates can be converted to absolute values.}, number={6}, journal={APPLIED OPTICS}, publisher={Optica Publishing Group}, author={Sahoo, Abinash and Narayanaswamy, Venkateswaran and Lyons, Kevin M.}, year={2023}, month={Feb}, pages={110–117} } @article{ramachandran_narayanaswamy_lyons_2019, title={Observations on the Role of Auto-Ignition in Flame Stabilization in Turbulent Non-Premixed Jet Flames in Vitiated Coflow}, volume={141}, ISSN={["1528-8919"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85062721393&partnerID=MN8TOARS}, DOI={10.1115/1.4042807}, abstractNote={Turbulent combustion of non-premixed jets issuing into a vitiated coflow is studied at coflow temperatures that do not significantly exceed the fuel auto-ignition temperatures, with the objective of observing the global features of lifted flames in this operating temperature regime and the role played by auto-ignition in flame stabilization. Three distinct modes of flame base motions are identified, which include a fluctuating lifted flame base (mode A), avalanche downstream motion of the flame base (mode B), and the formation and propagation of auto-ignition kernels (mode C). Reducing the confinement length of the hot coflow serves to highlight the role of auto-ignition in flame stabilization when the flame is subjected to destabilization by ambient air entrainment. The influence of auto-ignition is further assessed by computing ignition delay times for homogeneous CH4/air mixtures using chemical kinetic simulations and comparing them against the flow transit time corresponding to mean flame liftoff height of the bulk flame base. It is inferred from these studies that while auto-ignition is an active flame stabilization mechanism in this regime, the effect of turbulence may be crucial in determining the importance of auto-ignition toward stabilizing the flame at the conditions studied. An experimental investigation of auto-ignition characteristics at various jet Reynolds numbers reveals that turbulence appears to have a suppressing effect on the active role of auto-ignition in flame stabilization.}, number={6}, journal={JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME}, author={Ramachandran, Aravind and Narayanaswamy, Venkateswaran and Lyons, Kevin M.}, year={2019}, month={Jun} } @article{kribs_shah_hutchins_reach_muncey_june_saveliev_lyons_2016, title={The stabilization of partially-premixed jet flames in the presence of high potential electric fields}, volume={84}, ISSN={["1873-5738"]}, DOI={10.1016/j.elstat.2016.08.002}, abstractNote={Numerous research efforts have focused on flame stabilization and emissions. Based on initial experiments, specific mechanisms resulting from DC electric fields were chosen to be investigated, namely the chemical, thermal, and ionization mechanisms. Numerical simulations were performed on premixed propane-ozone-air flames to characterize ozone effects on flame speed resulting from the formation of ozone in high potential electric fields. These results were compared against partially premixed flame experiments to observe the dominant influences within leading edge stabilization within high potential electric fields. It was found that the electromagnetic or ionization influences, serve as the dominant effect on the combustion zone.}, journal={JOURNAL OF ELECTROSTATICS}, author={Kribs, James D. and Shah, Parth V. and Hutchins, Andrew R. and Reach, William A. and Muncey, Richard D. and June, M. Sean and Saveliev, Alexei and Lyons, Kevin M.}, year={2016}, month={Dec}, pages={1–9} } @article{hutchins_kribs_lyons_2015, title={Effects of diluents on lifted turbulent methane and ethylene jet flames}, volume={137}, number={3}, journal={Journal of Energy Resources Technology}, author={Hutchins, A. R. and Kribs, J. D. and Lyons, K. M.}, year={2015} } @article{lamige_lyons_galizzi_kuehni_mathieu_escudie_2015, title={LIFTING AND SPLITTING OF NONPREMIXED METHANE/AIR FLAMES DUE TO REACTANT PREHEATING}, volume={187}, ISSN={["1563-521X"]}, DOI={10.1080/00102202.2015.1059829}, abstractNote={In order to assess the impact of initial reactant temperature on the occurrence of local extinction (LE) and the subsequent lifting process of non-premixed attached flames with increasing fuel injection velocity, hydroxyl radical planar laser-induced fluorescence (OH-PLIF) and high-speed CH*-chemiluminescence visualizations were conducted in a methane/air jet-flame, with preheating up to 1000 K. LE occurrence probability increases when approaching lifting, and the preheating level (Tox,ref) affects the probability density function (PDF) shape of LE axial origin. At low Tox,ref, partial lifting events occur near the burner lip, eventually leading the flame to lift directly from the very flame base. At higher Tox,ref, partial lifting events no longer occur, and LE is mostly witnessed in the flame breakpoint zone (axially from 1 to 3 jet diameters), resulting in a breakpoint lifting process. For very high Tox,ref (1000 K), local extinctions become widespread in the breakpoint zone so that a stable split flame is achieved prior to the lifted regime.}, number={12}, journal={COMBUSTION SCIENCE AND TECHNOLOGY}, author={Lamige, Sylvain and Lyons, Kevin M. and Galizzi, Cedric and Kuehni, Manuel and Mathieu, Eric and Escudie, Dany}, year={2015}, pages={1937–1958} } @inproceedings{hutchins_kribs_muncey_lyons_2014, title={Assessment of stabilization mechanisms of confined, turbulent, lifted jet flames: Effects of ambient coflow}, booktitle={Proceedings of the ASME Power Conference, 2013, vol 1}, author={Hutchins, A. R. and Kribs, J. D. and Muncey, R. D. and Lyons, K. M.}, year={2014} } @article{lamige_lyons_galizzi_andre_kuehni_escudie_2014, title={Burner lip temperature and stabilization of a non-premixed jet flame}, volume={56}, ISSN={["1879-2286"]}, DOI={10.1016/j.expthermflusci.2013.11.008}, abstractNote={This experimental study addresses issues on heat transfer between the nozzle and the base of a non-premixed methane/air jet-flame. The burner lip temperature as well as temperature gradients at the top of the straight tube burner are systematically thermocouple-monitored, along with axial and radial positions of the flame attachment location by means of CH*-chemiluminescence imaging. The effects on lip temperature are tested for several parameters: flame state, either attached or lifted; aerodynamic conditions, over a very wide range of fuel injection velocities, covering both laminar and turbulent pipe flow for the inlet fuel, as well as momentum and velocity ratios between fuel and coflow both lower and greater than unity; nozzle rim coating, either uncoated or black-coated; initial reactant temperature, with preheating temperatures from 295 K to 1000 K; and burner material thermal conductivity, between 2.7 and 400 W/(m K). The observed phenomena are described and discussed in relation with changes of these parameters. Some conclusions are also drawn as for the relative importance of the different modes of heat transfer in the flame attachment zone, towards a better understanding of the flame stabilization process. In particular, flame attachment height measurements reveal a critical value towards high lip temperature obtained with low burner thermal conductivity. Eventually, this work allowed identification of four regions depending on fuel injection velocity, each associated with particular evolutions in terms of flame location and lip temperature.}, journal={EXPERIMENTAL THERMAL AND FLUID SCIENCE}, author={Lamige, S. and Lyons, K. M. and Galizzi, C. and Andre, F. and Kuehni, M. and Escudie, D.}, year={2014}, month={Jul}, pages={45–52} } @article{hutchins_reach_kribs_lyons_2014, title={Effects of electric fields on stabilized lifted propane flames}, volume={136}, number={2}, journal={Journal of Energy Resources Technology}, author={Hutchins, A. R. and Reach, W. A. and Kribs, J. D. and Lyons, K. M.}, year={2014} } @inproceedings{kribs_hutchins_reach_hasan_lyons_2014, title={Effects of hydrogen enrichment on the reattachment and hysteresis of lifted methane flames}, booktitle={Proceedings of the ASME Power Conference, 2013, vol 1}, author={Kribs, J. D. and Hutchins, A. R. and Reach, W. A. and Hasan, T. S. and Lyons, K. M.}, year={2014} } @inproceedings{hutchins_kribs_muncey_reach_lyons_2014, title={Experimental observations of nitrogen diluted ethylene and methane jet flames}, booktitle={Proceedings of the ASME Summer Heat Transfer Conference - 2013, vol 2}, author={Hutchins, A. R. and Kribs, J. D. and Muncey, R. D. and Reach, W. A. and Lyons, K. M.}, year={2014} } @article{hummel_barker_lyons_2014, title={Skin Burn Translation Model for Evaluating Hand Protection in Flash Fire Exposures}, volume={50}, ISSN={["1572-8099"]}, DOI={10.1007/s10694-013-0336-7}, number={5}, journal={FIRE TECHNOLOGY}, author={Hummel, Alexander and Barker, Roger and Lyons, Kevin}, year={2014}, month={Sep}, pages={1285–1299} } @article{kribs_moore_hasan_lyons_2013, title={Nitrogen-diluted methane flames in the near-and far-field}, volume={135}, number={4}, journal={Journal of Energy Resources Technology}, author={Kribs, J. and Moore, N. and Hasan, T. and Lyons, K.}, year={2013} } @article{lamige_min_galizzi_andre_baillot_escudie_lyons_2013, title={On preheating and dilution effects in non-premixed jet flame stabilization}, volume={160}, ISSN={["1556-2921"]}, DOI={10.1016/j.combustflame.2013.01.026}, abstractNote={The impact of preheating and dilution on methane/air non-premixed flame stability are studied experimentally. Six preheating levels are considered for initial reactant temperature between 295 K and 850 K in a round jet configuration. Four diluent gases are added on the air-side, either CO2, N2, Ar or a (CO2 + Ar) mixture having the same molar heat capacity as N2. For undiluted flames, jet transition velocities between attached and lifted states are investigated depending on initial reactant temperature. The hysteresis zone defined by these stability limits is shifted towards higher jet velocities with preheating. Whereas jet and coflow temperatures were identical in similar previous experiments, the present work allows examination of the thermal effects from either fuel or oxidizer streams. Flame stability is described based on the propagative aspects of the flame leading-edge, by analogy with the temperature dependency of the laminar burning velocity of a stoichiometric mixture. Results show that the jet temperature has a major influence on the lifting of an attached flame, whereas the coflow temperature remains important for the reattachment of a lifted flame. In addition, flame stability experiments have been performed at high levels of both preheating and dilution. Stability maps of critical dilution ratios at lifting have been obtained with preheating. It appears that the ability of a diluent to break flame stability keeps the same relative order as at ambient temperature. It is even enhanced with preheating because higher temperature widens the gap between diluent molar heat capacities Cp. The Cp approach is however not sufficient to interpret the temperature dependency of the relative influence of the different dilution effects. Furthermore, the role played by the jet flow regime on attached flame stability in dilution-induced lifting experiments is highlighted when dilution is coupled with preheating.}, number={6}, journal={COMBUSTION AND FLAME}, author={Lamige, Sylvain and Min, Jiesheng and Galizzi, Cedric and Andre, Frederic and Baillot, Francoise and Escudie, Dany and Lyons, Kevin M.}, year={2013}, month={Jun}, pages={1102–1111} } @inproceedings{hasan_kribs_lyons_2012, title={Influences of nitrogen dilution in the near flow field of transition regime lifted natural gas jet flames}, booktitle={Proceedings of the ASME International Mechanical Engineering Congress and Exposition, 2011, vol 1}, author={Hasan, T. S. and Kribs, J. D. and Lyons, K. M.}, year={2012}, pages={907–912} } @inproceedings{kribs_hasan_lyons_2012, title={Nitrogen diluted jet flames in the presence of coflowing air}, booktitle={Proceedings of the ASME International Mechanical Engineering Congress and Exposition, 2011, vol 4, pts A and B}, author={Kribs, J. D. and Hasan, T. S. and Lyons, K. M.}, year={2012}, pages={1415–1421} } @article{hummel_barker_lyons_deaton_morton-aslanis_2011, title={Development of Instrumented Manikin Hands for Characterizing the Thermal Protective Performance of Gloves in Flash Fire Exposures}, volume={47}, ISSN={["0015-2684"]}, DOI={10.1007/s10694-010-0190-9}, number={3}, journal={FIRE TECHNOLOGY}, author={Hummel, Alexander and Barker, Roger and Lyons, Kevin and Deaton, A. Shawn and Morton-Aslanis, John}, year={2011}, month={Jul}, pages={615–629} } @article{moore_terry_lyons_2011, title={Flame Hysteresis Effects in Methane Jet Flames in Air-Coflow}, volume={133}, ISSN={["0195-0738"]}, DOI={10.1115/1.4003806}, abstractNote={Presented are the results of experiments designed to investigate flame lift-off behavior in the hysteresis regime for low Reynolds number turbulent flows. The hysteresis regime refers to the situation where the jet flame has dual positions favorable to flame stabilization: attached and lifted. Typically, a jet flame is lifted off of a burner and stabilized at some downstream location at a pair of fuel and coflow velocities that is unique to a flame at that position. Since the direction from which that condition is arrived at is important, there is an inherent hysteretic behavior. To supplement previous research on hysteretic behavior in the presence of no coflow and low coflow velocities, the current research focuses on flames that are lifted and reattached at higher coflow velocities, where the flame behavior includes an unexpected downstream recession at low fuel velocities. Observations on the flame behavior related to nozzle exit velocity and coflow velocity are made using video imaging of flame sequences. The results show that a flame can stabilize at a location downstream despite a decrease in the local excess jet velocity and assist in determining the effect of coflow velocity magnitude on hysteretic behavior. These observations are of utility in designing maximum turndown burners in air coflow, especially for determining stability criteria in low fuel-flow applications.}, number={2}, journal={JOURNAL OF ENERGY RESOURCES TECHNOLOGY-TRANSACTIONS OF THE ASME}, author={Moore, N. J. and Terry, S. D. and Lyons, K. M.}, year={2011}, month={Jun} } @article{moore_kribs_lyons_2011, title={Investigation of Jet-Flame Blowout with Lean-Limit Considerations}, volume={87}, ISSN={["1386-6184"]}, DOI={10.1007/s10494-011-9334-3}, number={4}, journal={FLOW TURBULENCE AND COMBUSTION}, author={Moore, Nancy J. and Kribs, James and Lyons, Kevin M.}, year={2011}, month={Dec}, pages={525–536} } @article{june_kribs_lyons_2011, title={Measuring efficiency of positive and negative ionic wind devices for comparison to fans and blowers}, volume={69}, ISSN={["1873-5738"]}, DOI={10.1016/j.elstat.2011.04.010}, abstractNote={Many industries are pursuing alternate air moving devices to reduce the power consumption of their air cooled products. The literature suggests that ionic AMDs have low efficiency. The literature, however, does not define efficiency the same way the computer industry defines it for rotary AMDs. In this study, static efficiency of ionic AMDs was evaluated similar to rotary AMDs. Various emitter to collector distances and various ring lengths, were evaluated for positive and negative coronas. By controlling emitter to collector distance and collector length, efficiencies were obtained more reasonably compared to rotary devices.}, number={4}, journal={JOURNAL OF ELECTROSTATICS}, author={June, Michael S. and Kribs, James and Lyons, Kevin M.}, year={2011}, month={Aug}, pages={345–350} } @article{june_kribs_lyons_2010, title={Efficiency of electrostatic air moving devices}, volume={68}, ISSN={["0304-3886"]}, DOI={10.1016/j.elstat.2010.06.001}, abstractNote={An ion-driven gas flow is characterized by the breakdown of a gas into ions in the presence of a high electric potential. Ions flow due to the potential gradient. Mass transfer motivates bulk airflow. In the current study, an ionic air moving device was constructed using needles as ion sources, and a ring as collector. Airflow and efficiency were evaluated at various ring widths and with various numbers of ionization sites. Efficiency was seen to increase with ring width if airflow and distance was held constant and also increased with the number of ionization sites when airflow was held constant.}, number={5}, journal={JOURNAL OF ELECTROSTATICS}, author={June, Michael S. and Kribs, James and Lyons, Kevin M.}, year={2010}, month={Oct}, pages={419–423} } @article{moore_lyons_2010, title={Leading-edge flame fluctuations in lifted turbulent flames}, volume={182}, DOI={10.1080/00102200903355017}, abstractNote={Studies are presented that examine the fluctuations in liftoff height of lifted methane flames in the presence of air coflow. At a certain jet exit velocity, a flame will lift from the burner exit and stabilize at some downstream position. The partially-premixed flame front of the lifted flame oscillates in the axial direction, with the fluctuations becoming greater in flames stabilized further downstream. These fluctuations are also observed in flames where blowout is imminent. This work investigates the role of fuel velocity and air co-flow on flame fluctuations in both stable and unstable regimes. The results of video imaging of a lifted methane-air diffusion flame are presented and discussed. Images are used to ascertain the changes in the reaction zone that influence these fluctuations and relate the movement to blowout.}, number={7}, journal={Combustion Science and Technology}, author={Moore, N. J. and Lyons, K. M.}, year={2010}, pages={777–793} } @article{wu_mosher_lyons_zeng_2010, title={Reducing Ability and Mechanism for Polyvinylpyrrolidone (PVP) in Silver Nanoparticles Synthesis}, volume={10}, ISSN={["1533-4899"]}, DOI={10.1166/jnn.2010.1915}, abstractNote={Recently, it has been found that polyvinylpyrrolidone (PVP), a popular stabilizer in nanoparticles syntheses, possesses reducing ability for Ag+. Previous explanations of the reduction are, however, thought to be plausible. Based on detailed characterizations including UV-Vis, FTIR-ATR and XPS, we uncover the existence of Ag+ -O interaction, and demonstrate that the Ag+ -PVP complex is first formed via the coordination between Ag+ and O in the carbonyl group, which facilitates electron exchange between Ag+ and adjacent N atom on the pyrrolidone ring. The N atoms with lone pair electrons serve as an electron donator, leading reduction of Ag- to form PVP-capped Ag nanoparticles ultimately.}, number={4}, journal={JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY}, author={Wu, Chunwei and Mosher, Brian P. and Lyons, Kevin and Zeng, Taofang}, year={2010}, month={Apr}, pages={2342–2347} } @article{wilson_lyons_2009, title={On Diluted-Fuel Combustion Issues in Burning Biogas Surrogates}, volume={131}, ISSN={["0195-0738"]}, DOI={10.1115/1.4000152}, abstractNote={This paper describes an analysis of the burning velocity of pure and diluted fuels, with implications for the development and operation of biogas-fueled combustors. Background work in the area of flame stabilization and propagation are introduced from the combustion literature. Fuels examined in this paper were methane and ethylene; the diluents were primarily nitrogen, as well as argon, carbon dioxide, and helium. Trends in terms of burning velocities as functions of equivalence ratio are reported for a variety of fuels. Additionally, flame temperatures and associated burning velocities as a function of diluent composition are reported. Implications for several flame stabilization theories are discussed, as well as point to potential issues in converting combustors to accept biogas as a fuel permitting stable operation.}, number={4}, journal={JOURNAL OF ENERGY RESOURCES TECHNOLOGY-TRANSACTIONS OF THE ASME}, author={Wilson, David A. and Lyons, Kevin M.}, year={2009}, month={Dec} } @article{wilson_lyons_2008, title={Effects of dilution and co-flow on the stability of lifted non-premixed biogas-like flames}, volume={87}, ISSN={["1873-7153"]}, DOI={10.1016/j.fuel.2007.05.012}, abstractNote={This paper describes experiments and analysis of turbulent, lifted, non-premixed flames in co-flow, and with dilution, with implications for the development and operation of biogas-fueled combustors. Fuels utilized in this study were methane and ethylene; the diluent used was nitrogen. General trends were observed in the liftoff and reattachment behavior as affected by dilution of the fuel stream. Initial liftoff velocity was observed to decrease linearly with dilution, whereas the initial lift height behavior was bimodal. Reattachment conditions were similar in overall behavior to liftoff conditions. Dilution was found to decrease the radial stabilization distance, and co-flow tended to increase the radial stabilization distance. For a given liftoff height, the stabilization velocity was found to decrease with dilution faster than laminar burning velocity with dilution and was also found to increase rapidly with dilution beyond a certain diluent concentration. Flames were also found to taper inward and become more cylindrical in shape as dilution increases. Implications for several flame stabilization theories are discussed as well as considerations for input to biogas combustor design.}, number={3}, journal={FUEL}, author={Wilson, David A. and Lyons, Kevin M.}, year={2008}, month={Mar}, pages={405–413} } @article{lyons_moore_mccraw_watson_carter_donbar_2008, title={On flame-edge propagation}, volume={80}, ISSN={["1573-1987"]}, DOI={10.1007/s10494-008-9137-3}, number={3}, journal={FLOW TURBULENCE AND COMBUSTION}, author={Lyons, K. M. and Moore, N. J. and McCraw, J. L. and Watson, K. A. and Carter, C. D. and Donbar, J. M.}, year={2008}, month={Apr}, pages={405–410} } @article{mccraw_moore_lyons_2007, title={Observations on Upstream Flame Propagation in the Ignition of Hydrocarbon Jets}, volume={79}, ISSN={1386-6184 1573-1987}, url={http://dx.doi.org/10.1007/s10494-007-9071-9}, DOI={10.1007/s10494-007-9071-9}, number={1}, journal={Flow, Turbulence and Combustion}, publisher={Springer Science and Business Media LLC}, author={McCraw, J. L. and Moore, N. J. and Lyons, K. M.}, year={2007}, month={Mar}, pages={83–97} } @article{mccraw_moore_lyons_2007, title={Observations on upstream flame propagation in the ignition of hydrocarbon jets}, volume={79}, DOI={10.1007/s10494-006-9071-9}, number={1}, journal={Flow, Turbulence and Combustion}, author={McCraw, J. L. and Moore, N. J. and Lyons, K. M.}, year={2007}, pages={83–97} } @misc{lyons_2007, title={Toward an understanding of the stabilization mechanisms of lifted turbulent jet flames: Experiments}, volume={33}, ISSN={["1873-216X"]}, DOI={10.1016/j.pecs.2006.11.001}, abstractNote={This review discusses recent progress in understanding turbulent, lifted hydrocarbon jet flames and the conditions under which they stabilize. The viewpoint is from that of the empiricist, focusing on experimental results and the physically based theories that have emerged from their interpretations, as well as from the theoretically founded notions that have been supported. Pertinent concepts from laminar lifted flame stabilization studies are introduced at the onset. Classification in broad categories of the types of turbulent lifted flame theories is then presented. Experiments are discussed which support the importance of a variety of effects, including partial premixing, edge-flames, local extinction, streamline divergence and large-scale structures. This discussion details which of the categories of theories are supported by particular experiments, comments on the experimental results themselves and their salient contributions. Overall conclusions on the state of the field are drawn and future directions for research are also discussed.}, number={2}, journal={PROGRESS IN ENERGY AND COMBUSTION SCIENCE}, author={Lyons, Kevin M.}, year={2007}, month={Apr}, pages={211–231} } @article{lyons_watson_carter_donbar_2007, title={Upstream islands of flame in lifted-jet partially premixed combustion}, volume={179}, ISSN={["1563-521X"]}, DOI={10.1080/00102200600910858}, abstractNote={Abstract Contemporary interest exists in understanding the roles of leading edge flow deflection, secondary jet instabilities and islands of ignited gases in permitting lifted flames to stabilize. To assess these issues, elements of the leading-edge of a lifted turbulent jet flame have been investigated using laser-imaging techniques. Images of flame position, morphology and dynamics are presented primarily from CH planar laser-induced fluorescence (CH-PLIF) measurements. In particular, evidence of flame islands, or flame fragments, upstream of the bulk-flame leading edge are reported and discussed. This evidence is presented in the form of sequential CH-PLIF images and well as CH-PLIF/Rayleigh scattering images. Images showing thermal characteristics of the regions surrounding the edge flame are also described.}, number={5}, journal={COMBUSTION SCIENCE AND TECHNOLOGY}, author={Lyons, K. M. and Watson, K. A. and Carter, C. D. and Donbar, J. M.}, year={2007}, pages={1029–1037} } @article{terry_lyons_2006, title={Turbulent lifted flames in the hysteresis regime and the effects of coflow}, volume={128}, ISSN={["0195-0738"]}, DOI={10.1115/1.2358147}, abstractNote={A study of the characteristics of turbulent lifted-jet flames in the hysteresis regime was performed using methane and ethylene fuels in laminar and turbulent air coflows. Reattachment velocities and lifted flame heights just prior to reattachment vary linearly as for laminar flames in coflow. The flow regime of the coflow (i.e., laminar or turbulent) did not appear to affect the behavior of these flames. These observations are of utility in designing maximum turndown burners in air coflow, especially for determining stability criteria in low fuel-flow applications.}, number={4}, journal={JOURNAL OF ENERGY RESOURCES TECHNOLOGY-TRANSACTIONS OF THE ASME}, author={Terry, S. D. and Lyons, K. M.}, year={2006}, month={Dec}, pages={319–324} } @article{terry_lyons_2005, title={Low Reynolds number turbulent lifted flames in high co-flow}, volume={177}, ISSN={["1563-521X"]}, DOI={10.1080/00102200500240489}, abstractNote={ABSTRACT This study presents the results of experiments designed to investigate flame lift-off behavior to nozzle velocity, co-flow velocity, fuel-type, and nozzle size for low Reynolds Number turbulent flows (in and near the hysteresis regime). Local excess jet velocities are computed using jet relations from Tieszen et al. The results show that the local excess jet velocity remains linear with respect to nozzle velocity through most of the hysteresis regime, even though flame lift-off height is not linear. This suggests a non-linear relation not captured by Kalghatgi (1984) for lift-off in the near field and hysteresis regime. Local excess jet velocities at the reattachment point were also computed for flames that are lifted more than three nozzle diameters above the burner. The results show that there is a minimum excess jet velocity for which a flame can stabilize. This minimum velocity is inversely proportional to the laminar burning velocity of the fuel squared. A new relation for lift-off height at the reattachment point for flames in the hysteresis region is derived and compared to experimental data.}, number={11}, journal={COMBUSTION SCIENCE AND TECHNOLOGY}, author={Terry, SD and Lyons, KM}, year={2005}, month={Nov}, pages={2091–2112} } @article{lyons_watson_carter_donbar_2005, title={On flame holes and local extinction in lifted-jet diffusion flames}, volume={142}, ISSN={["0010-2180"]}, DOI={10.1016/j.combustflame.2005.04.006}, abstractNote={This work examines the dynamics of confined bluff body flames in the process of lean blowoff (LBO) using simultaneous stereo-PIV (particle image velocimetry), OH PLIF (planar laser induced fluorescence) and formaldehyde (CH2O) PLIF. Flames at high density ratios blow off in at least two distinct stages: stage 1, where intermittent extinction occurs along the flame front, but the flame and flow remain qualitatively similar to stable conditions, and stage 2, where there is permanent downstream flame extinction and large-scale changes in dynamic flow characteristics. This paper particularly focuses on stage 2 processes, with the goal of understanding what ultimately leads to irrecoverable flame blowoff. A test facility was developed with the flexibility to achieve two goals: (1) approach LBO by keeping the parameters that influence its hydrodynamic stability approximately constant, particularly flow velocity (ubulk) and gas expansion ratio (σ), and (2) compare near-LBO dynamics under conditions where, well away from blowoff, the flame is globally stable (high σ case) and globally unstable (low σ case, where the Bénard-Von Karman, BVK, instability of the flow is present). The latter case was of particular interest as most prior detailed diagnostic studies of LBO have been performed at high σ, BVK-suppressed conditions. We find that the transient blowoff process remains largely unchanged in the high and low σ cases, apparently due to the fact that the BVK instability reappears in either case under conditions very close to LBO. In all cases, blowoff is preceded by permanent downstream extinction that moves progressively closer to the bluff body as LBO is approached. We also find that near-LBO dynamics are intrinsically three dimensional, due to both secondary instabilities of the shear layer and large out-of-plane motions believed to be due to confinement effects associated with bluff body-wall interactions. These three-dimensional structures often manifest themselves as burning reactant fingers which are caught in the backflow of the recirculation zone; under very near LBO conditions they impinge on the back of the bluff body and extinguish as well. At the very edge of blowoff, the recirculation zone is no longer composed of hot products and is unable to autoignite the oncoming reactant flow, leading to global extinction. The characteristic time associated with this feedback between downstream extinction and wake structure alteration that leads to blowoff is about two orders of magnitude larger than the characteristic flow time, D/ubulk. We also discuss several implications of these results on computations of LBO - in particular, LBO's intrinsically three-dimensionality and the need for many flow through times to capture it.}, number={3}, journal={COMBUSTION AND FLAME}, author={Lyons, KM and Watson, KA and Carter, CD and Donbar, JM}, year={2005}, month={Aug}, pages={308–313} } @article{marley_welle_lyons_2004, title={Combustion structures in lifted ethanol spray flames}, volume={126}, ISSN={["1528-8919"]}, DOI={10.1115/1.1688768}, abstractNote={The development of a double flame structure in lifted ethanol spray flames is visualized using OH planar laser-induced fluorescence (PLIF). While the OH images indicate a single reaction zone exists without co-flow, the addition of low-speed co-flow facilitates the formation of a double flame structure that consists of two diverging flame fronts originating at the leading edge of the reaction zone. The outer reaction zone burns steadily in a diffusion mode, and the strained inner flame structure is characterized by both diffusion and partially premixed combustion exhibiting local extinction and re-ignition events.}, number={2}, journal={JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME}, author={Marley, SK and Welle, EJ and Lyons, KM}, year={2004}, month={Apr}, pages={254–257} } @article{marley_welle_lyons_roberts_2004, title={Effects of leading edge entrainment on the double flame structure in lifted ethanol spray flames}, volume={29}, DOI={10.1016/j.ecpthermflusci.2004.01.009}, number={1}, journal={Experimental Thermal and Fluid Science}, author={Marley, S. K. and Welle, E. J. and Lyons, K. M. and Roberts, W. L.}, year={2004}, pages={23–31} } @article{marley_lyons_watson_2004, title={Leading-edge reaction zones in lifted-jet gas and spray flames}, volume={72}, ISSN={["1573-1987"]}, DOI={10.1023/B:APPL.0000014906.91990.4e}, number={1}, journal={FLOW TURBULENCE AND COMBUSTION}, author={Marley, SK and Lyons, KM and Watson, KA}, year={2004}, pages={29–47} } @article{watson_lyons_donbar_carter_2003, title={On scalar dissipation and partially premixed flame propagation}, volume={175}, DOI={10.1080/00102200390196386}, number={4}, journal={Combustion Science and Technology}, author={Watson, K. A. and Lyons, K. M. and Donbar, J. M. and Carter, C. D.}, year={2003}, pages={649–664} } @article{watson_lyons_donbar_carter_2003, title={On scalar dissipation and partially premixed flame propagation}, volume={175}, ISSN={0010-2202 1563-521X}, url={http://dx.doi.org/10.1080/00102200302393}, DOI={10.1080/00102200302393}, abstractNote={Measurements of the scalar dissipation rate in the region immediately upstream of a lifted jet flame are presented. The scalar dissipation is determined in this isothermal region from a planar measurement of a two-dimensional conserved scalar (jet fluid) using laser Rayleigh scattering. Fields of the scalar dissipation rate are presented in addition to tabulated values for three different liftoff heights ( Re d =4800, 6400, and 8300). Scalar dissipation rates do not reach levels thought to cause extinction of the leading edge based on comparison with extinction data for counterflow diffusion flames. Additionally, results are presented on the axial flame propagation velocities relative to the jet flow. The data indicate that over the three flow conditions, the flame velocity relative to the flow is approximately constant during the case of a quasi-stationary lifted flame. In light of these findings, it is suggested that concepts involving partially premixed flame propagation, rather than those of critical scalar dissipation rate, are central to modern lifted flame stabilization models.}, number={4}, journal={Combustion Science and Technology}, publisher={Informa UK Limited}, author={Watson, K.A. and Lyons, K.M. and Donbar, J.M. and Carter, C.D.}, year={2003}, month={Apr}, pages={649–664} } @article{kodal_watson_roberts_lyons_2003, title={Turbulence filter and POD analysis for velocity fields in lifted CH4-air diffusion flames}, volume={70}, ISSN={["1386-6184"]}, DOI={10.1023/B:APPL.0000004914.21646.c4}, number={1-4}, journal={FLOW TURBULENCE AND COMBUSTION}, author={Kodal, A and Watson, KA and Roberts, WL and Lyons, KM}, year={2003}, pages={21–41} } @article{watson_lyons_carter_donbar_2002, title={Simultaneous two-shot CH planar laser-induced fluorescence and particle image velocimetry measurements in lifted CH4/air diffusion flames}, volume={29}, ISSN={["1873-2704"]}, DOI={10.1016/S1540-7489(02)80231-0}, abstractNote={Joint two-shot CH planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV) measurements near the stabilization region of lifted methane/air diffusion flames stabilized under different flow conditions are presented. The simultaneous technique allows for a determination of the propagation rate of the CH zone relative to the fuel flow. Simultaneous single-shot CH-PLIF and PIV techniques have been used in the past to examine lifted jet flames: however, the double-shot technique of the current study is desirable because it yields information on flame dynamics—as indicated by sequential CH-PLIF—relative to the unburned mixture. Three flow conditions were examined corresponding to three different liftoff heights. While the average velocity at the stabilization point varies between 0.83 m/s for the lowest flow condition (Red=4800) and 1.28 m/s for the highest (Red=8300), the velocity at the stabilization point during instances of zero CH movement (during the time interval of the CH pulses) is constant for all three flow conditions (1.14±0.4 m/s). Furthermore, the flame is able to stabilize itself against the incoming unburned mixture only when the gas velocity is below a certain limit, above which the flame is convected downstream with the flow.}, journal={PROCEEDINGS OF THE COMBUSTION INSTITUTE}, author={Watson, KA and Lyons, KM and Carter, CD and Donbar, JM}, year={2002}, pages={1905–1912} } @article{lyons_watson_2001, title={Visualizing diffusion flame formation in the wake of partially premixed combustion}, volume={123}, ISSN={["1528-8994"]}, DOI={10.1115/1.1385518}, abstractNote={Results are presented on the formation of a diffusion flame in a methane nonpremixed jet following the propagation of partially premixed combustion. An initially nonreacting turbulent methane jet (Re=2700) in quiescent air is ignited at a downstream location x/d=70. High-speed video images (125 and 250 Hz) were obtained that chart the evolution of the combustion process. Partially premixed flame propagation is witnessed as the combustion front moves upstream (downward) toward the nozzle exit. As the front propagates, the blue (premixed) character of the flame is diminished, the combustion region narrows, and the transition to diffusion-limited combustion along the stratified methane/air layer takes place. Before reaching the nozzle exit, axial wisps of blue flame emission are witnessed along the jet-edge near the fuel/air interface (i.e., at larger radii than the eventual diffusion flame boundary). Luminosity from soot is first apparent just upstream of an axisymmetric flame bulge as the diffusion flame forms, and within 100 ms, soot attains levels present in the steady-state turbulent diffusion flame. Images are presented portraying the phenomenon, and three regimes are proposed to characterize the propagation of combustion.}, number={3}, journal={JOURNAL OF ENERGY RESOURCES TECHNOLOGY-TRANSACTIONS OF THE ASME}, author={Lyons, KM and Watson, KA}, year={2001}, month={Sep}, pages={221–227} } @article{lyons_watson_2000, title={Partially premixed combustion in lifted turbulent jets}, volume={156}, ISSN={["0010-2202"]}, DOI={10.1080/00102200008947298}, abstractNote={This article reports observations of structures consistent with triple flame reaction zones in the stabilization region of turbulent nonpremixed jet flames. Previous studies of laminar mixing layers and nonpremixed jets show Hi brachial structures, however reports of triple flame structures in turbulent flowfields are sparse, The asymmetric coflow, which facilitates visualizing the luminous flame structure, is described and the observed double and triple flame structures are discussed. Flame luminosity data is presented and the relevance to CH planar laser-induced fluorescence (PLIF) studies of leading edge flame structures is discussed. Furthermore, connection is drawn to select theoretical studies of triple flames and partially premixed combustion.}, journal={COMBUSTION SCIENCE AND TECHNOLOGY}, author={Lyons, KM and Watson, KA}, year={2000}, pages={97–105} } @article{watson_lyons_donbar_carter_2000, title={Simultaneous Rayleigh imaging and CH-PLIF measurements in a lifted jet diffusion flame}, volume={123}, ISSN={["0010-2180"]}, DOI={10.1016/S0010-2180(00)00133-4}, abstractNote={Simultaneous Rayleigh scattering and CH planar laser-induced fluorescence (PLIF) measurements near the stabilization region of a lifted methane–air diffusion flame are presented. The goals of this investigation are to establish flow patterns responsible for complete breaks in the CH profile that indicate local flame extinction and evaluate the stabilization mechanisms over a range of flow conditions. Considerable attention has been given to vortex–flame interactions as a primary extinction mechanism of turbulent diffusion flames. The existence of holes in the flame zone is thought to result from the radial penetration of the flame by vortices from the internal fuel jet. In this investigation, Rayleigh scattering is used as a qualitative indication of gas temperature, thereby providing valuable information about the fluid near regions of local extinction, as indicated by well-defined breaks in the CH layer. The extent of premixedness in the region upstream from the CH structure is also assessed from the Rayleigh signal level. Furthermore, the roles of premixedness in flame stabilization, the nature of the leading edge, and lift-off height oscillation are discussed.}, number={1-2}, journal={COMBUSTION AND FLAME}, author={Watson, KA and Lyons, KM and Donbar, JM and Carter, CD}, year={2000}, month={Oct}, pages={252–265} } @article{watson_lyons_donbar_carter_1999, title={Observations on the leading edge in lifted flame stabilization}, volume={119}, ISSN={["1556-2921"]}, DOI={10.1016/S0010-2180(99)00056-5}, abstractNote={The objective of this paper is to report some of the first experimental evidence for the “leading edge” flame as the stabilization mechanism in lifted jet diffusion flames 1, 2, 3, 4, 5. CH fluorescence has been used to indicate the flame front location (i.e., region of chemical reaction) and thereby characterize features of the stabilization region 5, 6. The “leading edge” flame phenomenon reported within refers to the outward-extending branch of CH fluorescence at the base of the streamwise CH zones. Whether the “leading edge” flame is a special case of the more general triple flame is a question which remains unanswered. It is evident from previous computational studies 7, 8 that the triple flame, when interacting with a vortex or pair of vortices, can take on characteristics of the “leading edge” flames introduced in the present study. Veynante et al. [8] illustrate the contortion of the premixed branches of the triple flame by the flowfield where the premixed branches are swept into the trailing diffusion flame. These simulated triple flame/vortex interactions are consistent with the results of this study which show a trailing diffusion flame and the leading edge reaction zone structure.The test conditions and measurement locations for this investigation are shown in Fig. 1. Download : Download high-res image (204KB)Download : Download full-size imageFig. 1. Test conditions and measurement locations for (a) the lowest flow rate and (b) the highest flow rate. The intermediate flow rate (not shown) corresponds to a methane velocity of 21.2 m/s while the bottom of the image region is 37.4 mm from the jet exit and includes both sides of the lifted flame. The axisymmetric burner consists of a 5-mm inner diameter fuel jet surrounded by a 150-mm i.d. coflow tube. Methane is delivered through the fuel jet, while low-speed air (∼0.15 m/s) passes through the coflow annulus. The stabilization regions of three lifted flames are investigated by varying the methane and air flow rates and adjusting the burner position accordingly so that the image region includes the leading edge of the reaction zone. The methane exit velocities are 15.8, 21.2, and 27.5 m/s, corresponding to jet Reynolds numbers of 4800, 6400, and 8300, respectively. Both sides of the lifted flame are imaged during the two lower flow rates (Fig. 1a) while the turbulent fluctuations and wider stabilization region resulting from the highest flow rate limit this case to one side of the flame (Fig. 1b). Fig. 1. Test conditions and measurement locations for (a) the lowest flow rate and (b) the highest flow rate. The intermediate flow rate (not shown) corresponds to a methane velocity of 21.2 m/s while the bottom of the image region is 37.4 mm from the jet exit and includes both sides of the lifted flame. The CH planar laser-induced fluorescence (CH-PLIF) technique has been described elsewhere 5, 6. The setup includes a Nd:YAG-pumped dye laser which excites the Q1(7.5) transition of the B2Σ−–X2π(0,0) band of CH at λ = 390 nm. Fluorescence from the A–X(1,1), (0,0) and B-X(0,1) bands between λ = 420 and 440 nm is recorded. This approach has resulted in acceptable CH signal levels and excellent image quality (i.e., spatial resolution and contrast), which the authors find superior to the 431.5 nm laser excitation employed in earlier studies 9, 10. The authors believe the excellent resolution resulting from the signal levels and laser sheet characteristics in this study are extremely important in uncovering the leading edge premixed branch, which is generally weaker in signal level than the trailing diffusion flame. It is likely that these stabilizing leading edge flame observations are not reported in studies with less spatial resolution or are possibly not at all detectable due to limitations in the specific CH excitation/detection scheme. Several diagnostic studies involving lifted flames present the lifted flame structure as a continuous flame surface, similar to a distorted cylindrical object, emanating from a ring-shaped structure where the flame is stabilized 4, 5, 11. Most previous work, however, does not give experimental evidence of the mechanism of lifted flame stabilization. Figure 2Download : Download high-res image (3MB)Download : Download full-size imageFig. 2. CH-PLIF images illustrating the leading edge phenomenon where the CH zone extends outward at the stabilization point. (a)–(c) are from the lowest Re = 4800 flow condition (Fig. 1a); (d)–(h) are from the intermediate Re = 6400 flow condition; (i)–(l) are from the highest Re = 8300 flow condition and only include the right side of the flame (Fig. 1b). consists of several instantaneous 35.1 mm × 23.4 mm CH-PLIF images which provide such evidence. The images clearly show a continuous vertical distribution of CH which represents the primary diffusion flame reported in many previous studies. In addition to the vertical trailing diffusion flame, a structure is witnessed near the flame base which curls toward the outside, or fuel-lean, portion of the reaction zone. In comparison to ideal, laminar tribrachial structures, evidence of both rich and lean branches of premixed flame is not present, only the one branch extending outward near the jet edge. However, the rich branch on the fuel side of the diffusion flame may be overlapped into the diffusion flame by the flowfield as illustrated by Veynante et al. [8]. It is believed that the branch in the CH zone is a leading edge flame, stabilized by opposing the flow in the relatively low-speed region (∼1.0 m/s) near the outside edge of the jet. Fig. 2. CH-PLIF images illustrating the leading edge phenomenon where the CH zone extends outward at the stabilization point. (a)–(c) are from the lowest Re = 4800 flow condition (Fig. 1a); (d)–(h) are from the intermediate Re = 6400 flow condition; (i)–(l) are from the highest Re = 8300 flow condition and only include the right side of the flame (Fig. 1b). This branch of CH is not obviously present in all of the data; it only appears in approximately 30% of the images. The authors reason that the leading edge phenomenon may not be present around all 360 degrees of the stabilizing “ring,” but only in a portion of the flame sufficient to generate enough thermal energy to stabilize the flame globally. The reader must keep in mind that while the laser imaging techniques allow one to investigate the flame in detail locally, global behavior, most notably out-of-sheet activity, may be dominant at any given instant. With the flow inherently three-dimensional and time-dependent 11, 12, sheet imaging techniques often provide data to support a theory, but rarely provide definitive evidence. Since the measurements only investigate the flowfield in one plane, it is feasible that the leading edge structure could be present outside the measurement slice during the instances when no premixed CH branch is witnessed. In addition, recent cross-sectional images of lifted flames near the stabilization zone clearly render three-dimensional lobed structures that are consistent with this theory 11, 12. The extent of mixing and the entrainment of ambient air into the fuel is of central importance to this problem. Based on comparisons with mixture fraction images presented by Stårner et al. [13], which illustrate that the portion at the base of a lifted methane flame has a flammable composition, the authors are confident that the leading edge flame lies in a flammable mixture fraction region. Furthermore, fluctuations in the axial location of the leading edge, along with its orientation relative to the trailing diffusion flame, imply axial propagation into the unburned gas region. These observations imply that the physics of flame stabilization is likely a combination of multiple mechanisms based on premixedness, strain rate considerations 6, 14, and flame propagation into nonhomogeneous flowfields with flow separation, scalar gradients, and a range of mixture fractions [13].}, number={1-2}, journal={COMBUSTION AND FLAME}, author={Watson, KA and Lyons, KM and Donbar, JM and Carter, CD}, year={1999}, month={Oct}, pages={199–202} } @article{watson_lyons_donbar_carter_1999, title={Scalar and velocity field measurements in a lifted CH4-air diffusion flame}, volume={117}, ISSN={["0010-2180"]}, DOI={10.1016/S0010-2180(98)00086-8}, abstractNote={Experiments have been performed to investigate the leading edge of a lifted jet diffusion flame. The first portion of this study is a simultaneous particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) investigation of a lifted methane flame. The simultaneous technique is an approach for establishing the 2-D velocity field in conjunction with the flame front location indicated by laser-induced fluorescence from CH radicals within the reaction zone. The results show that the lifted flame stabilizes in a region of relatively low incoming gas velocity. Furthermore, the radial movement of large-scale vortices appears to play a crucial role in local flame extinction. The second set of experiments involves a simultaneous CH and OH PLIF investigation of the same lifted flame. The relative positions of the two radical fields have remarkable agreement. The CH profile is indicative of the fuel-rich region of the reaction zone and closely follows the inner edge of the OH profile. Furthermore, the OH zone is more than three times as thick as the CH zone, and the structures in both images support the radial motion of vortices established by the joint PIV/CH-PLIF measurements.}, number={1-2}, journal={COMBUSTION AND FLAME}, author={Watson, KA and Lyons, KM and Donbar, JM and Carter, CD}, year={1999}, month={Apr}, pages={257–271} } @article{brown_watson_lyons_1999, title={Studies on lifted jet flames in coflow: The stabilization mechanism in the near- and far-fields}, volume={62}, ISSN={["1386-6184"]}, DOI={10.1023/A:1009925500084}, number={3}, journal={FLOW TURBULENCE AND COMBUSTION}, author={Brown, CD and Watson, KA and Lyons, KM}, year={1999}, pages={249–273} }