Spatially resolved absolute concentration and fluorescence-lifetime determination of H2CO in atmospheric-pressure CH4/air flames

Using laser-induced fluorescence (LIF), spatially resolved concentration profiles of formaldehyde (H₂CO) were obtained in the preheating zone of atmospheric-pressure premixed CH₄/air flames stabilized on the central slot of a multiple-slot burner similar in construction to domestic boilers. The isolated pQ₁(6) rotational line (339.23 nm) in the 2¹ ₀4¹ ₀ vibronic combination transition in the ?¹A₂- ¹A₁ electronic band system around 339 nm was excited in the linear LIF intensity regime. For a quantification of quenching effects on the measured LIF signal intensities, relative fluorescence quantum yields were determined from direct fluorescence lifetime as a function of height above the slot exit. Absolute H₂CO number densities in the flames were evaluated from a calibration of measured LIF signal intensities versus those obtained in a low-pressure sample with a known H₂CO vapor pressure. Peak concentrations in the slightly lean and rich flames reached (994±298) and (174±52) ppm, respectively. Received: 25 September 2000 / Published online: 30 November 2000     

Effect of scalar nonlinearity on zonal flow generation by Rossby waves

Effects of scalar nonlinearity on the generation of zonal flow by Rossby waves in shallow rotating fluid are considered. Zonal flows are generated via the action of Reynolds stress due to vector nonlinearity together with the effects of scalar nonlinearity. It is shown that the scalar nonlinearity reduces the amplitude threshold of the zonal flow instability. In addition, it increases the range of wave vectors of unstable modes subjected to the instability. The growth rate of the instability as a function of the spectrum of primary waves is calculated. The spectrum is assumed to be arbitrary with emphasizing the case of two monochromatic waves.     

Impact of fast vertical and radial plasma movement on type-I ELMs in ASDEX upgrade

For the ITER project it is clear that steps have to be taken in order to avoid or mitigate type-I ELMs when operating in the standard H-mode scenario. Otherwise, divertor power loads induced by intrinsic ELMs will result in an intolerably short divertor life time. Amongst others, “magnetic triggering” based on a fast vertical movement of the plasma column has proven its ability to achieve ELM frequency control and hence mitigation by locking the ELM frequency to the imposed motion. Here, we report on an attempt to widen this approach by applying a cyclic radial plasma shift. Although motional cycle amplitudes sufficient for ELM frequency locking were achieved even easier than in the vertical case, no ELM control was established for the radial case. Analysis of this different behaviour can allow for better insight into underlying ELM release mechanisms and might potentially be a useful tool for mapping out ELM stability boundaries. Presented at the Workshop “Electric Fields, Structures and Relaxation in Edge Plasmas”, Roma, Italy, June 26–27, 2006.     

Characterization of poly(styrene‐co‐methacrylonitrile)s obtained by low‐temperature radiation polymerization and thermal degradation behavior measured by Py‐GC and CRTG

Poly(styrene‐co‐methacrylonitrile)s were polymerized in solutions with different polarities (n‐hexane and THF) by low‐temperature γ‐ray irradiation polymerization in a temperature range of −83.6–30 °C. It was found by IR measurement that the composition of the copolymers changed remarkably due to the effects of the polarity of solvents and the polymerization temperature. The thermal degradation behavior in the flash pyrolysis and in the continuous heating pyrolysis of these copolymers was measured by Py‐GC and controlled rate thermogravimetry (CRTG). The effects of the copolymer composition and sequence distribution on the thermal degradation behavior were investigated. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3569–3577, 2000     

C2 creation,emission, and laser-induced fluorescence in flames and cold gases

We describe photochemical production of C₂ in the upper (d ³_g) and the lower (a ³_u) levels of the Swan-band transitions by 266 and 292-nm laser irradiation of flames and room-temperature flows of acetylene and ethylene. Topics treated include the spectroscopy of the Swan bands, lifetimes and quenching of the Swan-band emission, intensity dependences of the Swan-band emission in several environments, profiles of C₂ in low-pressure hydrocarbon flames, and the affect of Swan-band emission on three-photon-excited fluorescence detection of atomic hydrogen in hydrocarbon flames.This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences