@article{chaos_chen_welle_roberts_2005, title={Fuel Lewis number effects in unsteady Burke-Schumann hydrogen flames}, volume={177}, ISSN={["1563-521X"]}, DOI={10.1080/00102200590883660}, abstractNote={ABSTRACT Flame response (as determined by temperature and flame thickness) to unsteady hydrodynamics has been measured in acoustically pulsed Burke–Schumann hydrogen flames at two different oscillation frequencies and amplitudes. The effect of fuel Lewis number (Le F) on flame dynamics is isolated by investigating steady and unsteady 40% H2/60% He (Le F > 1) and 40% H2/60% Ar (Le F < 1) flames. For a given flame with Le F < 1, local temperature was found to increase with stretch imparted on the reaction zone by the unsteady flow, whereas the opposite trend was observed for the Le F > 1 flame. Unsteadiness might qualitatively alter the effect of the fuel Lewis number. Notably, for Le F < 1 flames under oscillations of sufficiently high frequency and amplitude, the temperature at the flame tip is higher than that in the shoulder regions, and is different from the temperature field of both steady and low-frequency oscillation flames. This suggests that the effect of unsteady flame stretch may overwhelm that of the flame curvature for sufficiently high unsteadiness.}, number={1}, journal={COMBUSTION SCIENCE AND TECHNOLOGY}, author={Chaos, M and Chen, RH and Welle, EJ and Roberts, WL}, year={2005}, month={Jan}, pages={75-+} }
 @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{welle_roberts_carter_donbar_2003, title={The response of a propane-air counter-flow diffusion flame subjected to a transient flow field}, volume={135}, ISSN={["0010-2180"]}, DOI={10.1016/S0010-2180(03)00167-6}, abstractNote={OH planar laser-induced fluorescence (PLIF) and particle image velocimetry have been used to study the frequency response of laminar C3H8-air counterflow diffusion flames to assess the adequacy of the steady-flamelet models. Particle image velocimetry was used to determine the flame strain rate, while OH PLIF was used both to measure temperature at the flame front, using the two-line PLIF technique, and the reaction-zone width. Both measurements demonstrate that the frequency response of flames subjected to a time-varying flow field is diffusion-limited. At the 30-Hz and 50-Hz forcing frequencies, the maximum reaction-zone temperature and width were found to respond quasi-steadily. However, at higher forcing frequencies-i.e., 100 and 200 Hz-transient behavior is evident from the phase relationship between the imposed sinusoidal strain rate and the resulting peak temperature and reaction-zone width. The measured values of the OH-field widths were well fit by an offset sine function. In all cases when the oscillation amplitude is normalized by the cycle mean strain rate and plotted against the non-dimensional flow field frequency, the results collapse onto a single line having a steep negative slope.}, number={3}, journal={COMBUSTION AND FLAME}, author={Welle, EJ and Roberts, WL and Carter, CD and Donbar, JM}, year={2003}, month={Nov}, pages={285–297} }
 @article{welle_roberts_decroix_carter_donbar_2000, title={Simultaneous particle-imaging velocimetry and OH planar laser-induced fluorescence measurements in an unsteady counterflow propane/air diffusion flame}, volume={28}, ISSN={["1873-2704"]}, DOI={10.1016/s0082-0784(00)80609-8}, abstractNote={To study the transient response of a diffusion flame to an unsteady flowfied, quatitative measurements of velocity, using particle-imaging velocimetry, and OH measurements, using planar laser-induced fluorescence, were made simultaneously in an oscillating conterflow diffusion flame. These non-intrusive measurements were performed to spatially and tempoerally resolved flowrield and flame characteristics as a function of initial strain rate and forcing frequency. For the forcing frequencies considered in this study, the strain rate fluctuations were found to lag the velocity fluctuations, but the phase difference decresed with increasing forcing frequency. At lower forcing frequencies, the width of the OH field responded quasi-steadily, but as the forcing frequency increased, the OH field showed transient effects. The dilatation velocity, defined as the difference between the minimum velocity in the preheat zone and the maximum velocity in the reaction zone, was used as a flame temperature indicator. The dilatation velocity revealed that the phase difference between the velocity and the temperature increased with increasing forcing frequency, confirming the existence of a diffusion limited response. The resuls presented here help to illuminate the interconnecting relationships between the chemistry, fluid dynamics, and reactant transport times.}, journal={PROCEEDINGS OF THE COMBUSTION INSTITUTE}, author={Welle, EJ and Roberts, WL and Decroix, ME and Carter, CD and Donbar, JM}, year={2000}, pages={2021–2027} }