Pamela K. Barr

NOx and CO emissions from a pulse combustor operating in a lean premixed mode

Abstract Control over the combustion fluid dynamics was used to minimize the emission of NO x and CO. The combustion kinetics were controlled by operating the combustor premixed and were varied by modifying the equivalence ratio over the lean stability envelope. A wide dynamic range in fluid dynamic mixing characteristics was also investigated by modifying the degree of macroscopic mixing and microscopic mixing. The residence time at high temperature was controlled by modifying the frequency of the periodic reacting flow in a pulse combustor. It was found that controlling the flame temperature, chemical kinetics, and residence time at high temperature was best accomplished by controlling the equivalence ratio and the degree of macroscopic mixing rather than controlling the microscopic mixing over the dynamic range obtainable by the techniques used in this study. Emission levels below 5.0 ppm NO x , with corresponding levels of 5.0 ppm CO (corrected to 3% O 2 ), were achieved in a pulse combustor operating in a lean premixed mode, without the use of any postcombustion cleanup technologies. Both NO x and CO emissions were invariant to changes in the power input.

Pulse combustor modeling demonstration of the importance of characteristic times

A numerical model has been developed to study the sensitivity of a pulse combustors performance to changes in the relative timing between several of the dominant physical processes. The model is used to demonstrate the importance of the characteristic times associated with acoustics, fluid mixing, and chemical kinetics, which have been identified from both theoretical and experimental evidence. The combination of submodels for acoustics, injection, and combustion produces a pulse combustor model that is dynamic in that it fully couples the injection and mixing processes to the acoustic waves. Comparisons of simulations with experimental results show good agreement, verifying the model over a wide range of operating conditions. Because the model provides more control of the dominant processes than can be obtained in experiments, the parametric study establishes the cause-effect relation between the characteristic times and the resulting combustor performance.

Premixed combustion in a periodic flow field. Part II: The importance of flame extinction by fluid dynamic strain

Abstract A numerical model has been developed to study the importance of flame extinction by fluid dynamic strain that occurs during premixed combustion in an oscillating flow field. This is the second of a pair of papers that reports on the fundamental mechanisms that ensure the correct phase relation between the energy release and the resonant pressure waves, which is required by Rayleighs criterion for stable oscillations. The axisymmetric model is based on the vortex dynamics method combined with a flame sheet algorithm. The model is used to demonstrate that flame extinction by fluid dynamic stretch plays a dominant role in delaying reaction until later in the cycle. Without the extinction mechanism significant energy release occurs during the peak of injection, at a time when experimental observation shows it proceeds through a minimum. Additionally, the predicted rate of energy release decreases as the reactant injection rate decreases, but the experimental observation shows an increase in the energy release rate at this cycle time. By including extinction due to stretch in the flame model the onset of ignition of the fresh reactants is significantly delayed, giving much better agreement with the experimental data. Results are presented that show that the effect due to flame extinction by stretch dominates the effects due to either the expansion of the reactants as they burn or the shape of the injection profile. These results also show that although reactants injected during one cycle may still be burning during the next cycle, they are not the source of ignition for the subsequent cycles. This implies that the ignition mechanism is either thermal or radical, or both. Although the flow field studied here is from a pulse combustor, the conclusions are applicable to combustor configurations where a large vortical structure is formed during injection of reactants.

Pulse Combustion: Tailpipe Exit Jet Characteristics*

Abstract A preliminary study of the convective transfer rates of scalar quantities in a strongly oscillating free jet (+70 m/s to -50 m/s at 100 Hz generated by a pulse combustor) has been performed. This work is described in two parts: This paper discusses the free jet character, whereas the companion paper discusses the impinging jet characteristics associated with the convective heat transfer rate to a plate normal to the jet axis. In this paper the essential differences between the steady and oscillating jets are described. Rayleigh temperature measurements and flow visualizations (schlieren photography and laser Mie scattering) were used to quantify the jet characteristics. The method of vortex dynamics was used to model the vorticity and velocity fields of the pulsating jet. The modeling results support the conclusions drawn from experimental data. The steady jet exhibited typical axial and radial temperature profiles for an axisymmetric jet and, hence, it had typical decay rates. The character of t...

Lithographic characterization of improved projection optics in the EUVL engineering test stand

Static and scanned images of 100nm dense features for a developmental set of l/14 optics (projection optics box # 1, POB 1) in the Engineering Test Stand (ETS) were successfully obtained with various LPP source powers last year. The ETS with POB1 has been used to understand initial system performance and lithographic learning. Since then, numerous system upgrades have been made to improve ETS lithographic performance to meet or exceed the original design objectives. The most important upgrade is the replacement of POB 1 with an improved projection optics system, POB2, having lower figure error (l/20 rms wavefront error) and lower flare. Both projection optics boxes are a four-mirror design with a 0.1 numerical aperture. Scanned 70-nm dense features have been successfully printed using POB2. Aerial image contrast measurements have been made using the resist clearing method. The results are in good agreement to previous POB2 aerial image contrast measurements at the subfield exposure station (SES) at Lawrence Berkeley National Laboratory. For small features the results deviate from the modeling predictions due to the inherent resolution limit of the resist. The intrinsic flare of POB2 was also characterized. The experimental results were in excellent agreement with modeling predictions. As predicted, the flare in POB2 is less than 20% for 2μm features, which is two times lower than the flare in POB1. EUV flare is much easier to compensate for than its DUV counterpart due to its greater degree of uniformity and predictability. The lithographic learning obtained from the ETS will be used in the development of EUV High Volume Manufacturing tools. This paper describes the ETS tool ETS tool setup, both static and scanned, that was required after the installation of POB2. The paper will also describe the lithographic characterization of POB2 in the ETS and cmpare those results to the lithographic results obtained last year with POB1.

System and process learning in a full-field, high-power EUVL alpha tool

Full-field imaging with a developmental projection optic box (POB 1) was successfully demonstrated in the alpha tool Engineering Test Stand (ETS) last year. Since then, numerous improvements, including laser power for the laser-produced plasma (LPP) source, stages, sensors, and control system have been made. The LPP has been upgraded from the 40 W LPP cluster jet source used for initial demonstration of full-field imaging to a high-power (1500 W) LPP source with a liquid Xe spray jet. Scanned lithography at various laser drive powers of >500 W has been demonstrated with virtually identical lithographic performance.

Recent advances in the Sandia EUV 10x microstepper

The Sandia EUV 10x microstepper system is the result of an evolutionary development process, starting with a simple 20x system, progressing through an earlier 10x system, to the current system that has full microstepper capabilities. The 10x microstepper prints 400-micrometers -diameter fields at sub- 0.10-micrometers resolution. Upgrades include the replacement of the copper wire target with a pulsed xenon jet target, construction of an improved projection optics system, the addition of a dose monitor a d an aerial image monitor, and the addition of a graphical user interface to the system operation software. This paper provides an up-to-date report on the status of the microstepper.