Terry Parker

Vibrational band strengths and temperatures of nitric oxide by time-resolved infrared emission spectroscopy in a shock tube

Abstract Infrared emission spectra from the fundamental vibration—rotation band of NO are observed as functions of time in a shock tube using a specially constructed infrared array spectrometer. Emission is observed from shock-heated, dilute NO/Ar mixtures behind reflected shocks at temperatures between 800 and 2500 K and pressures of ≈1 atm. The spectrally resolved measurements cover the range 4.5–6.6 μm at a spectral resolution of 0.2 μm/pixel. The spectral intensity distributions on the long wavelength side of the band sample higher vibrational levels and thus provide a sensitive measure of vibrational temperature. Absolute spectral intensities in optically thin portions of the band determine the NO number density once the temperature is known. The integrated band intensities determine the temperature-dependent photon yields for vibrationally excited NO(v), which are in turn reduced by a rigorous anharmonic oscillator analysis to determine the thermally averaged Einstein coefficient for the optical transition from v = 1 to v = 0. The resulting value is A(v = 1) = 13.2(± 10%) sec-1, which is in excellent agreement with several determinations at temperatures near and below 300 K. This result establishes temperature independence for the NO Einstein coefficients up to 2500 K.

Fiber-coupled multiple-line infrared emission measurements to determine temperature, CO2, and H2O

Abstract This paper presents the design of a custom fiber-based system designed to simultaneously monitor carbon dioxide and water column densities and line-of-sight averaged temperature. The system utilizes zirconium fluoride optical fibers to transmit infrared radiation (2– 5 μm ) from high-temperature combustion effluent. Bandpass filters are used to separate emission from different species and optically thick emission from carbon dioxide is used to determine temperature. The temperature and molecule specific spectral profiles of the radiating gases, as well as atmospheric absorption, dictates high-resolution modeling of system radiation. Using this information, band models have been created that relate the net emissivity for a particular bandpass filter to the temperature and column densities of the flow field. Initial testing has been done on a methane burner; the ability to follow fluctuations for each constituent has been demonstrated. The band models have been used to reduce the flame radiance data for each filter; column density and temperature results from several flame conditions are reported.

Multiple-scattering effects on infrared scattering measurements used to characterize droplet size and volume fraction distributions in diesel sprays

We quantify the maximum error due to multiple-scattering effects for an infrared scattering droplet izing technique. Errors in Sauter mean diameters (SMDs) and liquid volume fractions were estimated lased on experimentally determined polarization properties of the scattered light. Light that is multiply scattered from spherical particles becomes randomly polarized, whereas singly scattered light from a spherical particle contains no cross-polarization scattering component. Therefore measurement of the cross-polarization component (in this case parallel) of the scattering signal is a measure of the multiply scattered light. A ratio of parallel to perpendicular polarized scattered light was experimentally determined and used to calculate an error due to multiple scattering. The infrared scattering measurements and polarization measurements used to quantify the multiple-scattering errors were applied to a typical diesel spray that was injected into three different background conditions: a room ambient condition; a room-temperature, high-pressure condition; and a combusting condition. Droplet SMD, liquid volume fraction, and multiple-scattering errors were determined for a number of locations within the spray; results indicate that the combusting case is negligibly affected by multiple scattering. However, the room ambient case exhibited notable errors due to multiple scattering near the centerline of the spray, and the high-pressure case demonstrated susceptibility to multiple scattering throughout all regions investigated. It is important to note, however, that multiple-scattering errors in many cases translate into relatively small effects on the reported droplet sizes.

A constant volume diesel spray combustion facility and the corresponding experimental diagnostics

A facility was built to examine the diesel spray/combustion process. The facility centers around a constant volume vessel, which consists of a visible and infrared optically accessible cold-wall, heated-interior pressure vessel coupled to an injection system. The combustion vessel is capable of operation at 50 atm and 1000 K (before injection), was used to simulate preinjection diesel in-cylinder conditions, and was coupled to a repeatable (for each fuel type), single shot, high pressure, metering fuel injection system. A number of experimental diagnostics have been applied to the facility and will be briefly discussed and examples of typical results offered. These diagnostics include: extractive post-combustion gas concentration experiments, droplet sizing measurements, and emission/absorption temperature measurements. Results from this facility capture the critical aspects of diesel spray combustion but do not include the change in pressure associated with heat release in a small volume and volume expansion due to piston motion.

Design methodology for a Fabry-Perot interferometer used as a concentration sensor

We present the design methodology for a sensor that can nonintrusively monitor target gas concentration levels in a power plant exhaust flow. The measurement is based on radiative emission by rovibrational transitions that are well isolated from emission features of other constituents and requires both moderate spectral resolution (typically 1 nm or below) and relatively high optical throughput. A Fabry-Perot interferometer provides this capability, and its conceptual design is discussed at length. High-temperature radiative emission of nitric oxide in a background of water was used as a sample system for the design of a prototype Fabry-Perot interferometer. Predictions for the instrument are a minimum resolvable NO column density of 100 parts per million times meter based on a simple background subtraction scheme with a gas temperature of 800 K. Improved order sorting can dramatically lower this minimum. The prototype instrument was calibrated and tested with a laboratory simulator; results are presented and compared with predictions.

Measurements and error analysis of droplet size in optically thick diesel sprays

Two measurement techniques capable of monitoring droplet sizes and number density in optically thick sprays are presented: both techniques use infrared probe beams in order to minimize the attenuation from the high number density of droplets in the spray. The first technique relies on multiple wavelength extinction from coaxial beams (wavelengths 1.06 and 9.27 μm). This method provides a line-of-sight measurement of the Sauter mean diameter for the spray. The second technique uses forward scattering from a 9.27-μm beam and 90° scattering from a 1.06-μm beam to produce size, again Sauter mean diameter, at specific locations within the spray. Simultaneous application of the two techniques to the same region of the spray has been used to cross-validate the measurements: agreement on droplet size is excellent and well within the predicted error levels. In addition to providing details of the diagnostic technique, this paper discusses potential sources of error for the measurement, namely, detector noise and calibration, size distribution effects, multiple-scattering and beam-steering considerations, droplet sphericity, optical thickness effects and a correction for optical thickness, and the effect of size distribution widths. Results for the example spray used in this work, a pressure-atomized single-hole diesel injector, indicate droplet diameters of 3 μm at 25 mm from the injector tip along the spray axis on the spray centerline, compared with 4 and 7 μm at radii 2 and 3 mm from the centerline, respectively. The diagnostic shows great promise for providing detailed information on the structure and temporal character of diesel-type sprays in a region that is relatively unexplored: the optically thick zone near the injector orifice.

A pulsed particle injection system for shock tube studies of powders

Shock tubes offer a unique method for studying high temperature properties and/or combustion of particulate. The particles are simply introduced into the shock tube prior to firing and are subsequently heated by gases behind the shock waves. For dilute particle systems, the temperature of the particulate rapidly equilibrates with that of the processed gas; the experimenter can then monitor the high temperature behavior of the particles until the event is quenched by the wave processes within the shock tube. However, effective delivery of particles into the shock tube is not a trivial task and a method that has been proven to be effective is the subject of this article. The injection system uses mass loadings much less than 1 g, produces a uniform cloud at the end of a shock tube, and can be tailored to operate with a variety of different particle types. This system has been used to study the high temperature optical properties of Al2O3 (Parker et al., 18th JANNAF Conference, Monterey, CA, 1989; Rawlins et...

Power plant exhaust gas simulator for the development of optical diagnostics

A power plant simulator was designed and built for development and calibration of optical diagnostics in power plant flows. This article describes the important features of this simulator as well as it performance. The simulator was constructed using a 120-mm-i.d., approximately 3-m-long quartz tube enclosed in a custom manufactured multizone furnace. Simulation of power plant flows requires combustion effluent; this is provided by a propane burner. Additional gases may be seeded into the flow using ports positioned before the entry into the 3 m quartz tube. Thus, flow with specified concentrations of pollutants of interest (i.e., NO, NH3, SO2, etc.) can be produced. Temperature control for the gas flow entering the quartz tube is provided by a 4-m-long heat exchanger positioned between the burner and the 3-m-long quartz tube. Optical access is provided at the tube ends using NaCl windows, which were chosen for their transmissive characteristics in the visible and infrared. These windows are protected the...

Least-mean-squares algorithm to determine submicrometer particle diameter, volume fraction, and size distribution width by elastic light scattering

A computationally fast method to determine values and their uncertainty for particulate system volume median diameter, volume fraction, and size distribution width is presented. These properties cannot be obtained for submicrometer particulate by diffraction-based methods. The technique relies on a least-mean-squares method applied over a prespecified size range and distribution width. Prespecifying the range significantly reduces the number of calculations required to determine the particulate parameters from experimental data, allowing the practical evaluation of large data sets. The solution method that was developed has significant advantages over ratio-style calculations that are more commonly performed, the primary of which is a simple method to determine errors in the measurement parameters. We evaluated the predicted performance for a specific experimental system for various levels of noise, with monodisperse and log-normal distributions, by analyzing synthetic data with the algorithm. Results were a quantitative statement of system accuracy. In addition, synthetic log-normal data evaluated with monodisperse models revealed significant and systematic errors in the predicted volume median diameter. These errors indicate that, in general, systems with a significant size distribution width must be analyzed with a model that includes this size distribution. Finally, calibrated polystyrene spheres were measured with an experimental system that used four simultaneous scattering measurements, and all diameters were within the reported uncertainty.

Infrared measurements of droplets in the dense region of diesel fuel sprays

The dense spray region (the high droplet number density area near the injector outlet) is exceptionally important to practical combustion devices since this is where the fuel transitions from an intact liquid stream at the nozzle exit into droplets, vapor, and a combustible mixture. Unfortunately, properties and processes within the dense spray are exceptionally difficult to monitor due to the high obscuration levels produced by the large droplet number densities. This paper reports results from extinction measurements at 1.06 um and 10.6 urn for single orifice, diesel sprays. Results indicate droplet sizes in the 3 um to greater than 9 um size range with significant spatial and temporal variations. Diameters and apparent droplet size fluctuation frequencies appear to increase with distance from the spray centerline (starting at 2.5 mm from the centerline) and spray tip (starting 25 mm from the tip). In addition, infrared scattering measurements which extend the useful sizing range for the measurements are presented.