Publications

Abstract not provided.

We have designed an opposed-flow flame system to investigate the chemical composition of non-premixed flames using in situ flame-sampling molecular-beam mass spectrometry with synchrotron-generated tunable vacuum-ultraviolet light as an ionization source. This paper provides details of the experimental apparatus, sampling method, and data-reduction procedures. To test the system, we have investigated the chemical composition of three low-pressure (30-50 Torr), non-premixed, opposed-flow acetylene( Ar)/O2(Ar) flames. We measured quantitative mole-fraction profiles as a function of the distance from the fuel outlet for the major species and several intermediates, including the methyl and propargyl radicals. We determined the temperature profiles of these flames by normalizing a sampling-instrument function to thermocouple measurements near the fuel outlet. A comparison of the experimental temperature and major species profiles with modeling results indicates that flame perturbations caused by the sampling probe are minimal. The observed agreement between experimental and modeled results, apparent for most combustion species, is similar to corresponding studies of premixed flames. © 2012 The Combustion Institute.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

As the U.S. and the International Community come to grips with anthropogenic climate change, it will be necessary to develop accurate techniques with global span for remote measurement of emissions and uptake of greenhouse gases (GHGs), with special emphasis on carbon dioxide. Presently, techniques exist for in situ and local remote measurements. The first steps towards expansion of these techniques to span the world are only now being taken with the launch of satellites with the capability to accurately measure column abundances of selected GHGs, including carbon dioxide. These satellite sensors do not directly measure emissions and uptake. The satellite data, appropriately filtered and processed, provide only one necessary, but not sufficient, input for the determination of emission and uptake rates. Optimal filtering and processing is a challenge in itself. But these data must be further combined with output from data-assimilation models of atmospheric structure and flows in order to infer emission and uptake rates for relevant points and regions. In addition, it is likely that substantially more accurate determinations would be possible given the addition of data from a sparse network of in situ and/or upward-looking remote GHG sensors. We will present the most promising approaches we've found for combining satellite, in situ, fixed remote sensing, and other potentially available data with atmospheric data-assimilation and backwarddispersion models for the purpose of determination of point and regional GHG emission and uptake rates. We anticipate that the first application of these techniques will be to GHG management for the U.S. Subsequent application may be to confirmation of compliance of other nations with future international GHG agreements. ©2010 IEEE.

Abstract not provided.

Abstract not provided.

Abstract not provided.

The ionospheric disturbance dynamo signature in geomagnetic variations is investigated using the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model. The model results are tested against reference magnetically quiet time observations on 21 June 1993, and disturbance effects were observed on 11 June 1993. The model qualitatively reproduces the observed diurnal and latitude variations of the geomagnetic horizontal intensity and declination for the reference quiet day in midlatitude and low-latitude regions but underestimates their amplitudes. The patterns of the disturbance dynamo signature and its source 'anti-Sq' current system are well reproduced in the Northern Hemisphere. However, the model significantly underestimates the amplitude of disturbance dynamo effects when compared with observations. Furthermore, the largest simulated disturbances occur at different local times than the observations. The discrepancies suggest that the assumed high-latitude storm time energy inputs in the model were not quantitatively accurate for this storm.

Abstract not provided.

This paper presents a derivation of an expression to estimate the accommodation coefficient for gas collisions with a graphite surface, which is meant for use in models of laser-induced incandescence (LII) of soot. Energy transfer between gas molecules and solid surfaces has been studied extensively, and a considerable amount is known about the physical mechanisms important in thermal accommodation. Values of accommodation coefficients currently used in LII models are temperature independent and are based on a small subset of information available in the literature. The expression derived in this study is based on published data from state-to-state gas-surface scattering experiments. The present study compiles data on the temperature dependence of translational, rotational, and vibrational energy transfer for diatomic molecules (predominantly NO) colliding with graphite surfaces. The data were used to infer partial accommodation coefficients for translational, rotational, and vibrational degrees of freedom, which were consolidated to derive an overall accommodation coefficient that accounts for accommodation of all degrees of freedom of the scattered gas distributions. This accommodation coefficient can be used to calculate conductive cooling rates following laser heating of soot particles.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Double-pulse laser-induced desorption with elastic laser scattering (LIDELS) is a diagnostic technique capable of making time-resolved, in situ measurements of the volatile fraction of diesel particulate matter (PM). The technique uses two laser pulses of comparable energy, separated in time by an interval sufficiently short to freeze the flow field, to measure the change in PM volume caused by laser-induced desorption of the volatile fraction. The first laser pulse of a pulse-pair produces elastic laser scattering (ELS) that gives the total PM volume, and also deposits the energy to desorb the volatiles. ELS from the second pulse gives the volume of the remaining solid portion of the PM, and the ratio of these two measurements is the quantitative solid volume fraction. In an earlier study, we used a single laser to make real-time LIDELS measurements during steady-state operation of a diesel engine. In this paper, we discuss the advantages and disadvantages of the two LIDELS techniques and present measurements made in real diesel exhaust and simulated diesel exhaust created by coating diffusion-flame soot with single-component hydrocarbons. Comparison with analysis of PM collected on quartz filters reveals that LIDELS considerably under-predicts the volatile fraction. We discuss reasons for this discrepancy and recommend future directions for LIDELS research. Copyright © 2005 SAE International.