Dawson, RW
1996
A Technique for Determining Instantaneous N2, CO2, O2, CO, and H2O Species Concentrations Using Multiplex CARS in Premixed Gaseous Flames
Dawson, R.W. and Hedman, P.O.
Proceedings at the Fall Meeting of the Western States Section/ Combustion Institute, The University of Southern California, Los Angeles, California, October 28-29, 1996. Funded by ACERC and Morgantown Energy Technology Center (ATS).
An approach for analyzing instantaneous CO, O2, CO2, and H2O species concentrations using multiplex coherent anti-Strokes Raman spectroscopy (CARS) in premixed combustion systems in introduced and demonstrated. A dual-dye, single broadband Strakes dye laser was used to produce CARS spectral signals from N2, CO, O2, and CO2. A computer code obtained Sandia National Laboratories was used to determine the temperature as well as the value Chinr/Xi where Xi is the specie mole fraction and Chinr is the signal contribution form non-resonant gases. Temperatures as well as the non-resonant signal contribution (Chinr) for each laser shot were obtained from the nitrogen spectra. Initial estimate of Chinr were made by assuming that nitrogen concentrations were known and remained constant throughout premixed combustion. Equilibrium predictions, based upon the instantaneous nitrogen temperature, were used in conjunction with the estimated value of Chinr as initial estimates needed to resolve the instantaneous CO, O2, and CO2 spectra into concentration measurements. This technique reduced the computational demand of determining the best fit between theoretical and experimental spectra.
The H2O mole fraction was determined from an oxygen elemental mass balance and the assumption that any oxygen not accounted for in the measured concentrations of CO, O2, and CO2 was in H2O. The partially reacted natural gas will bee in the form of various hydrocarbon fragments that are difficult to quantify. The hydrogen that is not reacted to water is assumed to be unaccounted for by the measurements and is lumped into a H* mole fraction, and the carbon that is not measured as CO2 or CO is unaccounted for carbon, which is lumped into a C* mole fraction. The magnitude of H* and C* gives an indication of the extent of the combustion reaction and the ratio H* to C* gives an indication of the effective composition of the partially reacted hydrocarbon gases (CXHY). The results show that this technique is effective in determining concentrations of the major combustion species in a premixed gaseous-fueled flame. The paper describes the detail of the technique and presents example results for a swirling, turbulent, premixed natural gas/air flame.
1993
Experimentally Determined Particle Number Density Statistics in an Industrial-Scal, Pulverized-Coal-Fired Boiler
Queiroz, M.; Bonin, M.P.; Shirolkar, J.S. and Dawson, R.W.
Energy & Fuels 7:(6) 842-851, 1993. Funded by ACERC.
A study on the variations of particle data rate statistics and the probability density function (PDF) of cumulative particle number density has been completed in a full-scale, tangentially fired, 85 MWe pulverized-coal-fired boiler. Variables in the tests included boiler load and coal type. It was observed that particle data rate fluctuations were greater in magnitude for small particles (<3.5 µm) and that the PDFs of particle data rate were well approximated by normal distributions. Furthermore, there were no preferential frequencies in the large (<3.5 µm) or small particle data rate fluctuations anywhere in the boiler. The PDFs of cumulative particle number density for the small particles were negatively skewed and, as compared to the large particle PDFs, were less sensitive to boiler location. The large particle PDFs were more negatively skewed near the walls and more Gaussian as distance from the wall increased. Broader distributions of cumulative particle number density with peaks at higher values were observed for the small particles for the coal with lower volatiles and higher ash content. Moreover, for the large particles, a noticeable shift of the PDFs, longer "tails" toward higher cumulative number densities, and a substantial flattening of the PDF curves were observed for the same coal. The shape of the PDF profiles did not change substantially as the boiler load changed. The effect of a lighter load on the small particle PDFs was to slightly broaden the distribution, mostly in the direction of large cumulative particle number densities. For the large particles, a shift toward higher cumulative particle number densities, a slightly broadening effect, and a reduction in the maximum PDF values were observed at lighter load.
1992
The Effect of Fuel Droplets on Temperature Dissipation Statistics in a Gaseous Jet Flame
Dawson, R.W. and Queiroz, M.
IV Encontro Nacional de Ciencias Termicas (ENCIT 92), Rio de Janeiro, Brazil, December 1992. Funded by ACERC.
Presented in this paper is an experimental investigation of the effects of fuel droplets on temperature dissipation. For this purpose, temperature dissipation measurements have been completed in a lifted premixed propane flame issuing from a converging nozzle. Hexane droplets with initial diameter of 50µm were then introduced into the core of the flame while dissipation measurements were repeated. Profiles of dissipation show that the evaporating droplets cause a reduction in the temperature gradient at the core of the flame and at the outer shear layer. Deviations from the lognormal distributions in the outer shear layer are shown to be less significant and occur closer to the centerline when droplets are present.
1991
A Dual Thermocouple Probe for Measuring Temperature Dissipation Statistics in Reacting Flows
Dawson, R.W.; Boyer, L. and Queiroz, M.
Heat Transfer in Combustion Systems, 166:59-67, (R.J. Santoro and J.D. Felske, eds.), The American Society of Mechanical Engineers, 1991. Funded by ACERC.
This paper discusses the design of a dual thermocouple probe to measure temperature dissipation statistics in turbulent reacting flows. The probe is described in detail and an analysis is made of its advantages and accuracy, including a parametric study on the effect of wire spacing, sampling frequency, time constant, and cutoff frequency on the calculations of temperature dissipation statistics. Also, measurements performed with the probe in a partially premixed, lifted propane flame are briefly discussed to demonstrate the probe's capability. The measurements reported include mean and rms profiles and normalized probability density function of the lognormal radial component of temperature dissipation, as well as joint statistics between the temperature and its dissipation, represented by joint probability density functions.
Dawson, RW
1996
A Technique for Determining Instantaneous N2, CO2, O2, CO, and H2O Species Concentrations Using Multiplex CARS in Premixed Gaseous Flames
Dawson, R.W. and Hedman, P.O.
Proceedings at the Fall Meeting of the Western States Section/ Combustion Institute, The University of Southern California, Los Angeles, California, October 28-29, 1996. Funded by ACERC and Morgantown Energy Technology Center (ATS).
An approach for analyzing instantaneous CO, O2, CO2, and H2O species concentrations using multiplex coherent anti-Strokes Raman spectroscopy (CARS) in premixed combustion systems in introduced and demonstrated. A dual-dye, single broadband Strakes dye laser was used to produce CARS spectral signals from N2, CO, O2, and CO2. A computer code obtained Sandia National Laboratories was used to determine the temperature as well as the value Chinr/Xi where Xi is the specie mole fraction and Chinr is the signal contribution form non-resonant gases. Temperatures as well as the non-resonant signal contribution (Chinr) for each laser shot were obtained from the nitrogen spectra. Initial estimate of Chinr were made by assuming that nitrogen concentrations were known and remained constant throughout premixed combustion. Equilibrium predictions, based upon the instantaneous nitrogen temperature, were used in conjunction with the estimated value of Chinr as initial estimates needed to resolve the instantaneous CO, O2, and CO2 spectra into concentration measurements. This technique reduced the computational demand of determining the best fit between theoretical and experimental spectra.
The H2O mole fraction was determined from an oxygen elemental mass balance and the assumption that any oxygen not accounted for in the measured concentrations of CO, O2, and CO2 was in H2O. The partially reacted natural gas will bee in the form of various hydrocarbon fragments that are difficult to quantify. The hydrogen that is not reacted to water is assumed to be unaccounted for by the measurements and is lumped into a H* mole fraction, and the carbon that is not measured as CO2 or CO is unaccounted for carbon, which is lumped into a C* mole fraction. The magnitude of H* and C* gives an indication of the extent of the combustion reaction and the ratio H* to C* gives an indication of the effective composition of the partially reacted hydrocarbon gases (CXHY). The results show that this technique is effective in determining concentrations of the major combustion species in a premixed gaseous-fueled flame. The paper describes the detail of the technique and presents example results for a swirling, turbulent, premixed natural gas/air flame.
1993
Experimentally Determined Particle Number Density Statistics in an Industrial-Scal, Pulverized-Coal-Fired Boiler
Queiroz, M.; Bonin, M.P.; Shirolkar, J.S. and Dawson, R.W.
Energy & Fuels 7:(6) 842-851, 1993. Funded by ACERC.
A study on the variations of particle data rate statistics and the probability density function (PDF) of cumulative particle number density has been completed in a full-scale, tangentially fired, 85 MWe pulverized-coal-fired boiler. Variables in the tests included boiler load and coal type. It was observed that particle data rate fluctuations were greater in magnitude for small particles (<3.5 µm) and that the PDFs of particle data rate were well approximated by normal distributions. Furthermore, there were no preferential frequencies in the large (<3.5 µm) or small particle data rate fluctuations anywhere in the boiler. The PDFs of cumulative particle number density for the small particles were negatively skewed and, as compared to the large particle PDFs, were less sensitive to boiler location. The large particle PDFs were more negatively skewed near the walls and more Gaussian as distance from the wall increased. Broader distributions of cumulative particle number density with peaks at higher values were observed for the small particles for the coal with lower volatiles and higher ash content. Moreover, for the large particles, a noticeable shift of the PDFs, longer "tails" toward higher cumulative number densities, and a substantial flattening of the PDF curves were observed for the same coal. The shape of the PDF profiles did not change substantially as the boiler load changed. The effect of a lighter load on the small particle PDFs was to slightly broaden the distribution, mostly in the direction of large cumulative particle number densities. For the large particles, a shift toward higher cumulative particle number densities, a slightly broadening effect, and a reduction in the maximum PDF values were observed at lighter load.
1992
The Effect of Fuel Droplets on Temperature Dissipation Statistics in a Gaseous Jet Flame
Dawson, R.W. and Queiroz, M.
IV Encontro Nacional de Ciencias Termicas (ENCIT 92), Rio de Janeiro, Brazil, December 1992. Funded by ACERC.
Presented in this paper is an experimental investigation of the effects of fuel droplets on temperature dissipation. For this purpose, temperature dissipation measurements have been completed in a lifted premixed propane flame issuing from a converging nozzle. Hexane droplets with initial diameter of 50µm were then introduced into the core of the flame while dissipation measurements were repeated. Profiles of dissipation show that the evaporating droplets cause a reduction in the temperature gradient at the core of the flame and at the outer shear layer. Deviations from the lognormal distributions in the outer shear layer are shown to be less significant and occur closer to the centerline when droplets are present.
1991
A Dual Thermocouple Probe for Measuring Temperature Dissipation Statistics in Reacting Flows
Dawson, R.W.; Boyer, L. and Queiroz, M.
Heat Transfer in Combustion Systems, 166:59-67, (R.J. Santoro and J.D. Felske, eds.), The American Society of Mechanical Engineers, 1991. Funded by ACERC.
This paper discusses the design of a dual thermocouple probe to measure temperature dissipation statistics in turbulent reacting flows. The probe is described in detail and an analysis is made of its advantages and accuracy, including a parametric study on the effect of wire spacing, sampling frequency, time constant, and cutoff frequency on the calculations of temperature dissipation statistics. Also, measurements performed with the probe in a partially premixed, lifted propane flame are briefly discussed to demonstrate the probe's capability. The measurements reported include mean and rms profiles and normalized probability density function of the lognormal radial component of temperature dissipation, as well as joint statistics between the temperature and its dissipation, represented by joint probability density functions.