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Rapid detection of coal and fly ash is significant to improve the efficiency of thermal power plants and reduce environmental pollution. Given its fast response, high sensitivity, real-time, and non-contact [...]

Holographic interferometry (HI) has proved to be a useful tool for nonintrusive temperature measurements in flames (and thereafter for inference of the local composition based on the state relationship approach) with high spatial and temporal resolution. Digital holographic interferometry (DHI) is a relatively new imaging and measurement technique that electronically records a hologram (e.g., on a CCD) and reconstructs it by a numerical method. Cumbersome chemical processing of the hologram is avoided in Dill, which thereby provides greater flexibility, speed, and the potential for real-time processing. In conventional holography, fringes that are neither bright nor dark on a hologram cannot be accurately resolved. The DHI technique has not yet to our knowledge been used for combustion applications. Herein we evaluate its efficacy for making temperature measurements in flames and assess its applicability through a simulation. Each part of a double exposure associated with the holographic technique is considered to be recorded by a hypothetical CCD sensor at a separate time from the other part. We applied the principles of Fourier optics to develop two numerical methods for hologram reconstruction, and we show that both methods provide an accurate reconstruction of the phase image associated with a flame. Because of the periodic nature of the wave function, the reconstructed phase values are limited to the interval [-[pi]/2, [pi]/2]. Thus an unwrapping algorithm is provided that produces a continuous phase distribution based on the condition that the reconstructed phase is jumped by a value of -[pi] or [pi]. We have also developed an iterative calculation method to adjust the value of the digital reference wave parameters that determines the phase imaging reconstruction in DHI. OCIS codes: 090.2880, 120.1740, 280.2470, 100.5070.

A modified Price-Boggs-Derr model is applied to compute the linear and nonlinear combustion response properties of monopropellant ammonium perchlorate (AP). The kinetics constants were changed to achieve good agreement with response function data as well as with steady-state data. The numerical method was first validated with the classical theory. Computations using the Levine and Culick boundary condition in the limit of small perturbations were compared with the exact mathematical solution for linear response, and the effect of perturbation amplitude was explored. Then, using the AP model for the boundary condition, various linear and nonlinear computations were performed. Supplemental mathematical analyses relate the AP model to the basic two parameters of the classical theory and show the key factors determining the nature of the combustion response.

An investigation of products of incomplete combustion profiles in flue gas at a one megawatt pilot combustion plant under disturbed and normal steady state conditions was performed. The sampling point was located in the high-temperature area of the plant at the post-combustion chamber outlet between temperatures of 650 and 880 degrees Celsius, before any emission reduction devices. The study determines that flue gas combustion byproducts can be changed dramatically for a long time.

The optimized structures, energy minima at 0 K and enthalpies of atoms and molecules involved in the ignition and/or combustion of boron were calculated using the density functional B3PW91/6-311+G(2df,2pd) and ab initio CBS-Q. The BO + F = FBO and BO + O = BO2 were found to be the most exothermic. Results also showed that the B3PW91 method is more reliable for obtaining geometries, while the CBS-Q is more accurate in obtaining heats of formation and reaction.

Partial premixing can be induced by design in combustors, occurs inadvertently during turbulent nonpremixed combustion, or arises through inadequate fuel-air mixing. Therefore, it is of interest to investigate the effect of partial premixing in a burner that mimics conditions that might occur under practice. In this investigation, we report on similitude of partially premixed flames encountered in practical complex and multi-dimensional burners with simpler, less complex flames, such as counterflow flamelets. A burner is designed to simulate the more complex multi-dimensional flows that might be encountered in practice, and includes the effects of staging, swirl, and possible quenching by introduction of secondary air. The measurements indicate that the structure of partially premixed flames in complex, practical devices can be analyzed in a manner similar to that of flamelets, even if substantial heat transfer occurs. In particular, the flame structure can be characterized in terms of a modified mixture fraction that differentiates the lean and rich zones, and identifies the spatial location of the flame.

A direct shock tube kinetics technique was used to examine the chemical reactions CF3 + H2 -> CF3H + H and CF3H + H -> CF3 + H2. The experiment, which coupled the shock tube technique with H-atom atomic resonance absorption spectrometry, was conducted under temperature ranging from 1168 to 1673 K for the first reaction and 1111 to 1550 K for the second. Equilibrium constants and thermal rate behavior were predicted.

The concentration and pressure dependence of dual-pump coherent anti-Stokes Raman spectroscopy (CARS) signals from nitrogen and methane was investigated. CARS spectra were acquired from a gas cell at pressures of 0.007 to 2.24 MPa and methane concentrations of 0.5 to 50%. The square root of the methane signal intensity divided by the nitrogen signal intensity was found to have a near-linear dependence on methane concentration at all pressures investigated. The pressure dependence of this integrated intensity ratio decreased with increasing pressure and became negligible at the highest pressures tested. The shot-to-shot variation at concentrations determined from single-laser-shot measurements was less than 7%. Single-laser-shot CARS spectra of nitrogen and methane were obtained from the cylinder of a firing direct-injection natural gas engine.

It has been possible to link a time-derivative preconditioning technique with implicit multigrid acceleration to produce a promising method for rapid calculations of fully coupled, reactive flows at all speeds. The success of the multigrid method seems to be connected with whether the positions of the reaction fronts are correctly represented on the coarser grids. Mixing-limited combustion models generally perform quite well when used with multigrid methods, because of the direct dependence of the reaction rates on the turbulent mixing field.

In a recent publication [3], the authors tentatively explored the prediction of propane flame speeds using the calculated burned gas temperature ([T.sub.b]) and the predicted flame extinction temperature ([T.sub.i]). A formula was developed that utilized these temperatures together with correction factors for inlet temperature and the oxygen/inert ratio. The present paper has extended this technique so that data from 20 different fuels have been examined over a range of conditions, which include significant variations of both inlet temperature and pressure. Limitations of the technique are discussed, as are possible related applications to other premixed systems such as laminar flames and well-stirred reactors.

The two-dimensional, unsteady, laminar conservation equations for mass, momentum, energy, and species transport in the gas phase are solved numerically in spherical coordinates in order to study heat and mass transfer, and combustion around a single spherical droplet. The droplet mass, momentum, and energy equations are also solved simultaneously with the gas phase equations in order to investigate the effects of droplet entrainment and heating in the oscillating flow with and without a steady velocity. The numerical solution for the case of single droplet combustion gives the droplet diameter and temperature variation as well as the gas phase velocity, temperature, and species concentrations as a function of time. The effects of frequency, amplitude of oscillating flow, and velocity ratio of oscillating flow amplitude to the steady velocity on droplet combustion are also investigated. The droplet burning history is not governed by the [d.sup.2]-law in the presence of oscillating flow, unlike the case of quiescent ambient conditions.

A multizone thermodynamic method has been developed to determine combustion rate and NO formation from measured cylinder pressures and performance of two-stroke diesel engines. Integral to the analytical method is a nonlinear fit to the combustion chamber heat loss; the fit is consistent with the overall energy balance and with measured fuel consumption rate and exhaust temperature. The method assumes equilibrium combustion properties except for NO, whose relatively slow formation is estimated using the extended Zeldovich mechanism in the post-flame gas during a period of one mixing time. Application of the method to a 2-stroke diesel engine indicates a post-flame mixing time of 0.55 ms or 4 deg crank angle at 1250 rpm, yielding exhaust concentrations of NO considerably less than what would have been expected from equilibrium-then-sudden-freezing considerations.

Dual-pump coherent anti-Stokes Raman scattering (CARS) has been demonstrated for the simultaneous measurement of gas-phase temperature and concentrations of molecular nitrogen and oxygen. A polarization technique was used to vary the relative intensities of the two CARS signals and expand the dynamic range of the relative concentration measurements. Detailed temperature and oxygen mole fraction measurements were performed in the stabilization region of a hydrogen-nitrogen jet diffusion flame. These results indicate that there is a region below the nozzle exit where significant amounts of oxygen are found on the fuel side of the peak flame temperature profile. Key words: CARS, dual-pump CARS, three-laser CARS, diffusion flames.

KrF excimer lasers are often employed as high-power excitation sources in planar laser-induced fluorescence (PLIF) imaging experiments to measure the distributions of [O.sub.2], OH, and [H.sub.2]O - all important species in combustion phenomena. However, due to the predissociative nature of these molecules, the high laser pumping rates typically required in such PLIF experiments may significantly deplete the ground-state population. The proper interpretation of the ground-state number density and/or the temperature from the fluorescence signals then requires the inclusion of photobleaching effects. We compare the results of a five-level rate-equation model incorporating photobleaching effects to the time-resolved PLIF signals from [O.sub.2] as obtained in the products of a fuel-lean C[H.sub.4] air flame. The results indicate that the fluorescence signals in a typical predissociated PLIF imaging experiment are subject to significant amounts of photo-bleaching. In an effort to provide a convenient way to account for photobleaching, a simple three-level model is developed. This model provides an analytic solution that describes satisfactorily the time-integrated fluorescence signal when compared with both the five-level model and the measurements. The results also indicate that at the low laser irradiances required to minimize the effects of photobleaching, the correspondingly low fluorescence signal levels make the acquisition of single-shot PLIF images a challenge to currently available camera systems.

The mean temperature field, majority species and turbulence intensity distribution of an H2-air jet engine burner were measured using new ultraviolet laser-based multidimensional measurement methods. The methods include two-dimensional Rayleigh scattering and one-dimensional Raman scattering. The techniques were accurate in calculating the burner's flow structures and overall combustion performance.

Laser-induced incandescence from soot was analyzed with a time-dependent, numerical model of particle heating and cooling processes that includes spatial and temporal intensity profiles associated with laser sheet illumination. For volume fraction measurements, substantial errors result primarily from changes in gas temperature and primary soot particle size. The errors can be reduced with the proper choice of detection wavelength, prompt gating, and high laser intensities. Two techniques for primary particle size measurements, based on ratios of laser-induced incandescence signals from a single laser pulse, were also examined. Compared with the ratio of two integration times, the newly proposed ratio of two detection wavelengths is better suited for simultaneous volume fraction and size measurements, because it is less temperature sensitive and produces stronger signals with, however, a lower sensitivity to size changes. Key words: Laser-induced incandescence, soot volume fraction, soot sizing, combustion diagnostics, planar imaging.

Methods used for analysis of soil microbial biomass N and C are limited in precision and are time consuming. A method involving direct combustion of evaporated soil extracts was developed for use with an automated nitrogen and carbon analyzer (ANCA). The objectives of this study were to: (i) evaluate the usefulness of ANCA determination of microbial C and N, and (ii) ascertain whether the microbial C isotope ratios determined by the ANCA method would reflect C contributions from actively growing crops of wheat (Triticum aestivum L.) and maize (Zea mays L.) differing in C isotope ratio. Cropped and fallow soils were sampled at planting, anthesis, and maturity. Field-moist soils were fumigated with chloroform and extracted with 0.05 M [K.sub.2]S[O.sub.4] for the ANCA method and with 0.5 M [K.sub.2]S[O.sub.4] for Kjeldahl analysis. Small volumes of the 0.05 M [K.sub.2]S[O.sub.4] extracts were evaporated on cone-shaped tin disks that were analyzed using combustion at 1700 [degrees] C and mass spectrometry. Reproducible values for C, N, and [Delta]13C were obtained with less effort than that typically expended for Kjeldahl N analysis of similar extracts. Temporal changes in microbial [Delta]13C occurred in both cropped and fallow soils during a single growing season. At maturity of the maize crop, an estimated 23% of the soil microbial C was derived from the plant material of the current maize crop. Carbon contribution from the wheat crop to the soil microbial biomass was not detected. Further refinements in the ANCA method may make the procedure routinely usable for enhancing the understanding of chloroform labile C and N as indicators of microbial dynamics in the soil.

The potential energy surface of the reaction of C2H3 with O2 was determined using a combined high-level ab initio molecular orbital and statistical rate constant calculation. The estimated rate constants were consistent with the theoretical results. The highest rate constant was obtained for the CHO + CH2O channel in the temperature range 500-900 Kelvin. The major products of the reaction were C2H3O and oxygen.

Spatial averaging is a potential problem in the application of coherent anti-Stokes Raman spectroscopy (CARS) to combustion diagnostics when varying temperatures and composition are present at spatial scales smaller than the typical 1-2-mm spatial resolution of CARS. The observed CARS spectrum is then a mixture of the hot and cold components. We show that simulated, spatially averaged spectra, generated by the incoherent addition of intensities, can be significantly different from those obtained by the coherent addition of the electric field amplitudes of the component spectra. The analyses of these simulated, spatially averaged CARS spectra demonstrate that the use of theoretical CARS spectra, generated by the addition of intensities of the hot and cold components of a binary gas mixture, can lead to errors in the estimated flame temperatures. Key words: Spatial averaging, temperature, coherent anti-Stokes Raman spectroscopy.

The combustion and emissions of waste tires and coal in pulverized form was investigated by burning the two fuels at 1150 degrees Centigrade. Tire particles burned two to three times faster than pulverized coal. Coal particles revealed distinct volatile and char combustion phases, and both fuels produced comparable levels of sulfur dioxide emissions. Pulverized coal produced nitric oxide emissions that were three to four times greater than those of pulverized rubber. Both produced low levels of polynuclear aromatic hydrocarbon emissions at fuel-rich conditions.

We have applied a line UV Raman, Rayleigh, and laser-induced predissociation fluorescence technique for measurement of turbulent hydrocarbon flames. The species concentration of C[O.sub.2], [O.sub.2], CO, [N.sub.2], C[H.sub.4], [H.sub.2]O, OH, and [H.sub.2] and the temperature are measured instantaneously and simultaneously along a line of 11.4 mm, from which the gradients with respect to mixture fraction and spatial direction are obtained. The technique has been successfully tested in a laminar premixed stoichiometric methane flame and a laminar hydrogen diffusion flame. In addition the technique has been tested in a highly turbulent rich premixed methane flame. The data show that the technique can be used to provide instantaneous measurements of local profiles that describe the local flame structure in highly turbulent flames.

A multiplexed diode-laser sensor system is used for effective single-path measurements of temperature, pressure and mole fraction. The sensor system contains two diode lasers and fiber-optic components. The sensor uses both scanned- and fixed-wavelength laser absorption spectroscopy techniques. The peak line-intensity ratios are used to estimate the gas temperature. The values of temperature and species concentration in the postflame gases of an H2-O2 flame, obtained by the sensor, agree with those obtained by thermocouples.

A radiotracer technique was used to detect residuals of polycyclic aromatic hydrocarbons (PAH) in emissions from the combustion of five 14C-radiolabeled PAH. A linear relationship was observed between the survival of individual PAH and the energy levels for each molecule. This suggests that the survival of PAHs are determined by their chemical kinetics instead of thermodynamic stabilities.

Planar laser-induced fluorescence images of OH have been obtained in liquid-fueled spray flames burning heptane, ethanol, and methanol over a range of pressures from 0.1 to 1.0 MPa. In addition to the OH fluorescence, a nonresonant fluorescence interference that increased rapidly with pressure was detected. Examination of the spectrum of this interference indicates that it arises from hydrocarbon fuel-fragment species in the fuel-rich zones of the flame. The pressure dependence of the fluorescence signal is examined in both steady-state and time-dependent analyses, and a model for evaluation of pressure effects and quenching variations in quantitative imaging measurements in nonpremixed flame environments is presented. The results indicate that increased combustor pressure results in a rapid rise of the volume fraction of hydrocarbon fragments and a decrease in the OH volume fraction. Key words: Fluorescence, combustion diagnostics, high-pressure combustion, OH, polycyclic aromatic hydrocarbon, spray flame.

We report the development of a pump-probe instrument that uses a high-repetition-rate (82-MHz) picosecond laser. To maximize laser power and to minimize jitter between the pump- and the probe-pulse trains, we choose the asynchronous optical sampling (ASOPS) configuration. Verification of the method is obtained through concentration measurements of atomic sodium in an atmospheric methane-air flame. For the first time to our knowledge, ASOPS measurements are made on a quantitative basis. This is accomplished by calibration of the sodium concentration with atomic absorption spectroscopy. ASOPS measurements are taken at a rate of 155.7 kHz with only 128 averages, resulting in a corresponding detection limit of 5 X [10.sup.9] [cm.sup.-3]. The quenching-rate coefficient is obtained in a single measurement with a variation of ASOPS, which we call dual-beam ASOPS. The value of this coefficient is in excellent agreement with literature values for the present flame conditions. Based on our quantitative results for detection of atomic sodium, a detection limit of 2 X [10.sup.17] [cm.sup.-3] is predicted for the [Q.sub.1] (9) line of A 2[[Sigma].sup.+] (v = 0)-[X.sup.2][Phi](v = 0) hydroxyl at 2000 K. Although this value is too large for practical flame studies, a number of improvements that should lower the ASOPS detection limit are suggested. Key words: Combustion, turbulence, sodium, picosecond phenomena, mode-locked lasers, absorption, spectroscopy.

Measurement of radical concentrations is important in understanding the chemical kinetics involved in combustion. Application of optical techniques allows for the nonintrusive determination of specific radical concentrations. One of the most challenging problems for investigators is to obtain flame data that are independent of the collisional environment. We seek to obviate this difficulty by the use of picosecond pump-probe absorption spectroscopy. A picosecond pump-probe absorption model is developed by rate-equation analysis. Implications are discussed for a laser-pulse width that is much smaller than the excited-state lifetime of the absorbing atom or molecule. The possibility of quantitative, quenching-independent concentration measurements is discussed, and detection limits for atomic sodium and the hydroxyl radical are estimated. For a three-level absorber-emitter, the model leads to a novel pump-probe strategy, called dual-beam asynchronous optical sampling, that can be used to obtain both the electronic quenching-rate coefficient and the doublet mixing-rate coefficient during a single measurement. We discuss the successful demonstration of the technique in a companion paper. Key words: Combustion, sodium, picosecond phenomena, absorption, spectroscopy.

Laser-induced incandescence (LII) is ideally suited for obtaining high temporally and spatially resolved measurements of soot volume fraction in transient combustion phenomena. We demonstrate qualitative two-dimensional nonintrusive optical measurements of the soot evolution versus time from single fiber-supported burning fuel droplets of heptane and decane. Quantitative measurement of the soot volume fraction is also demonstrated through calibration of the LII signal against a small coflow ethylene diffusion flame.

A temporally resolved approach for measurement of two-dimensional temperature fields in reacting flows is experimentally investigated. The method, based on planar laser-induced fluorescence of the hydroxyl (OH) radical, is applicable in many combustion environments, including variable density flow fields. As a means of examining the accuracy of the technique, temperature images, from 1300 to 3000 K and 0.4 to 3 atm, have been acquired in shock-heated [H.sub.2]-[O.sub.2]-Ar flows with a two-laser, two-image ratio scheme. A complete measurement system for producing accurate, effectively instantaneous temperature images is described; the system includes single-shot monitors for laser-sheet energy distributions and spectral profiles. Temperature images obtained with the OH A 2[[Sigma].sup.+] [arrow to the left] X 2[Pi] (1, 0) [P.sub.1](7)-[Q.sub.2](11) transition pair exhibit a systematic error of only 7% over the entire range of conditions, with the error most likely dominated by shot-to-shot fluctuations in the lasers' spectral profiles. The largest error source in the instantaneous temperature images is photon shot noise. A group of OH transition pairs that provide good temperature sensitivity and strong signals for reduced shot-noise error over a range of flow-field conditions is also presented.

A quasiglobal model for evaluating ethylene's finite rate combustion yields results that agree well with data from a kinetic model. The quasiglobal model uses a reduced number of species and reactions to describe the reaction mechanisms. The model is valid for computational fluid dynamics codes.

One of the most important tools for the development of Diesel engines is the numerical simulation of the combustion processes. One of the key variables for such simulations is the liquid-phase temperature. The potential study of a fluorescence thermometer for Diesel spray investigations is discussed. Nonintrusive measurements of the liquid-phase temperature in a Diesel spray have been carried out for the first time to the author's knowledge. The results are presented as two-dimensional temperature maps.

An inert medium with a high concentration of pores reveals premixed combustion. The porous solid and flowing gas show chemical kinetics and exchange of energy. The combustion is studied by multi-step kinetics and the thermo-physical characteristics of solids. A rise in the convective transfer of heat and effective thermal conductivity of the solid cause a rise in the preheating effect. More cells in the porous solid increase the convective transfer of heat, but bigger cells with less density cause a fall in the absorption coefficient. A methane-air flame shows an extension of the lean limit by its baseline characteristics, and the peak-flame temperature is higher than the adiabatic flame temperature.

We report on spatially resolved simultaneous measurements of temperature and majority species concentrations along a line segment in a premixed laminar H2-air flame. The results are obtained from Raman and Rayleigh scattering by using a narrow-band KrF excimer laser and a spectrally and spatially resolving detector system that consists of a high-throughput spectrometer and a gated, intensified, two-dimensional CCD camera. The data presented here are integrated over 100 laser shots. Absolute density profiles of N2, O2, H2O, and H2, as well as temperature profiles at various heights through the flame, are presented. A discussion of the required calibration procedures and a summary of the necessary spectroscopic background are also included in this paper.

An experiment involving flame temperature measurement is conducted by monitoring an alkali emission doublet. Innovations on this conventional line reversal technique is introduced by the use of a filtered reference source and the monitoring of two closely spaced transition lines. Thus eliminating the need of balancing the backgroundradiation source as it facilitates real-time measurements. The use of optical filtering reduces the apparent temperature of the source as it enables the new technique to probe flames as hot as 2800 Kelvin.