Dale R. Tree

LDA Measurements in a Pulverized Coal Flame at Three Swirl Ratios

A two-color Laser Doppler Anemometer (LDA) was used to obtain axial and tangential velocity information in a 0.2 MW pulverized coal flame. In addition to the reacting flow data, a study on the accuracy of using coal as a seed panicle to measure gas phase velocity using LDA was performed. Non reacting flow velocity measurements were also obtained near the fuel inlet and in the quarl region of a geometrically identical burner to identify the velocity profile at several burner settings and to assist in establishing modeling inlet conditions. Both the reacting and non reacting velocity data were obtained at three or more swirl settings and various axial positions allowing a study of the affect of swirl on inlet turbulence and flame structure. The velocity results were compared with effluent NOx measurements. At the flow rates and accelerations experienced in this study, the coal particles were shown to be useful as seed particles for LDA gas phase velocity measurements. The coal-flame velocity indicated a cen...

Local temperature measurements in a full-scale utility boiler with overfire air

Gas temperature and effluent NOx measurements were obtained in a full-scale (160 MWe) pulverized coal cornerfired utility boiler with separate overfire air. The measurements are the first of this kind in a full-scale boiler operated with overfire air and low-NOx burners. At test matrix of seven operating conditions was used to compare temperature and NOx with changes in overfire air, coal type, load and burner tilt. Peak temperatures were 1500–1600°C and occurred just above the top burner. The measurements detailed the profile of temperature through a traverse of a coal burner, close-coupled overfire air port and separate overfire port. The data in the near-burner and overfire air regions showed evidence of reduced swirl as overfire air was increased. Little difference was seen in the temperatures for two coals with volatile fractions of 28 and 36 wt%. Temperature changes were quantified in the overfire air region for changes in burner tilt and load. Temperature was approximately the same in the overfire air region as load was decreased, but increased in this region as the burners were tilted from +50° to −5°.

Optical Measurements of Soot Particle Size, Number Density, and Temperature in a Direct Injection Diesel Engine as a Function of Speed and Load

Abstract : In-cylinder measurements of soot particle size, number density and temperature have been made using optical measurements in a direct injection diesel engine. The measurements were made at one location approximately 5 mm long and 1.5 mm wide above the bowl near the head. Two optical techniques were used simultaneously involving light scattering extinction and radiation. An optical probe was designed and mounted in a modified exhaust valve which introduced a beam of light into the cylinder and collected the scattered and radiating light from the soot. The resulting measurements were semi-quantitative, giving an absolute uncertainty on the order of + or - 50% which was attributed mainly to the uncertainty of the optical properties of the soot and the heterogeneous nature of the soot cloud. Measurements at three speeds and three overall equivalence ratios were made. For all of the operating conditions the soot in the measurement volume increased in size to a maximum followed by a rapid decrease. The peak soot diameters were in a range of 30 - 50 nm. Peak soot diameter, soot volume fraction, and soot temperature appeared to increase with equivalence ratio at the measurement location. The results also suggested the soot cloud to be very dense with peak soot volume fraction near 4-6 x 10-6 and thick with a soot cloud thickness approximately 0.4 - 0.6 times the length from the piston to the head.

Fuel Composition and Molecular Structure Effects on Soot Formation in Direct-Injection Flames Under Diesel Engine Conditions

Numerous investigations have been conducted to determine the effect of fuel composition and molecular structure on particulate emissions using exhaust gas analysis, but relatively few measurements have been obtained in-cylinder or under conditions where fuel effects can be isolated from other variables. Recent work has shown that the amount of air entrained upstream of the lift-off length is critical to soot formation and therefore must be controlled when making relative comparisons of soot formed from various fuels. In this work, dimethoxymethane was used as the base fuel to produce a non-sooting flame with relatively constant lift-off length in a constant volume combustion vessel at 1000 K, and a density of 16.6 kg/m 3 . A second fuel was then mixed into the dimethoxymethane (DMM) to determine a point at which soot formation begins. Line-of-sight extinction measurements of soot produced in binary fuel mixture flames was used as the primary diagnostic tool to determine if a correlation existed between soot and fuel properties such as the number of C-C bonds, C/H ratio or C/O ratio. Tests to date show that fuels with different molecular structures have the same incipient soot limit at a C/H ratio near 0.4, while further increases in C/H ratio produce a linear increase in soot concentration, but with a different slope for each fuel. Soot was first formed with the addition of 10 vol% toluene to DMM, while it took 40 vol% undecane and 50 vol% n-heptane. The incipient soot oxygen-to-carbon ratio at the assumed 12 mm lift-off length was 0.6 for toluene, 0.37 for undecane, and 0.3 for n-heptane. These data indicate that the aromatic toluene has a greater tendency to produce soot than the alkanes.

In-Situ Species, Temperature and Velocity Measurements in a Pulverized Coal Flame

A study of detailed species, velocity and temperature data of a pulverized coal flame is important to understanding the mechanisms which sustain the flame and lead to the formation of various pollutants such as NOx. The data can be particularly useful when compared to comprehensive combustion models which encapsulate the sub-models and processes of combustion. This data set contains in-situ axial and radial temperature, velocity and species concentrations for three swirl ratios of a pulverized coal flame located in a cylindrical, down-fired, 0.2 MWt reactor. Species measurements include CO, CO2, NO and O2. Velocity measurements were obtained using Laser Doppler Anemometry (LDA) and are summarized here after the method and results were reported in detail in a companion paper. The data show the change in structure of the coal flame as swirl is increased. At zero swirl the flame was located along a centerline jet, but as swirl increased, a recirculation zone was created which carried the combustion products ...

Optical Soot Particle Size And Number Density Measurements In A Direct Injection Diesel Engine

Abstract Abstract–Optical measurements of soot particle size and number density have been made in-situ in a direct injection diesel engine using a light scattering and extinction measurement technique. Simultaneously, the radiation from the soot particles was measured and used to estimate the thickness of the soot cloud and temperature of the soot particles. The measurement was taken at a fixed location near the center of the spray plume. Soot particle size was found to increase slightly during the combustion event reaching a peak diameter of approximately 40 nm. As the injection process and combustion ended, the soot particle size dropped rapidly to below 20 nm before the signal became too small to measure. Soot volume fraction reached a maximum near 7 x 10-5. The soot cloud was not only dense but thick, indicating that the soot was not confined to a thin reaction layer but rather filled more than half of the path length from the piston to the cylinder head. Rates of soot formation and oxidation appeared...

Predictions of NOX in a Laboratory Pulverized Coal Combustor Operating under Air and Oxy-Fuel Conditions

A new approach to modeling NOX under oxy-fuel combustion conditions in a simple staged-oxidizer flow field is presented. The approach is centered on the combination of devolatilization and char oxidation models with a detailed kinetic mechanism for light hydrocarbon combustion. NOX chemistry is included by the users selection of the detailed mechanism, while the devolatilization model consists of the chemical percolation devolatilization (CPD) model modified to be independent of oxidizer composition. Literature-based correlations provide elemental composition of the volatiles. Model predictions were compared to experimental measurements with good agreement in several respects. The model provides insights for the interpretation of experimental oxy-fuel combustion NOX results, and recommendations are given for computational fluid dynamics (CFD) modeling of NOX in oxy-fuel combustion.

Two-color transmittance measurements in a pulverized coal reactor

A two-color extinction diagnostic technique has been investigated for the measurement of soot and other fine particulate in pulverized-coal flames. The measurements were made using two helium-neon lasers at 633 nm (red) and 543.5 nm (green) in a 0.2 MW, pulverized-coal, down-fired reactor. Parameters inves-tigated included axial position, swirl, and equivalence ratio. Under lean conditions, coal, char, and ash partiele transmittance was found to be insensitive to the wavelength, and transmittance increased with downstream axial distance showing char burnout. When soot was visually apparent in the reactor, the shorter wavelength (543.5 nm) was attenuated more than the longer wavelength (633 nm). Thus, the presence of soot and relative amounts of soot could be determined from the transmittance measurements. Soot was seen to form in the first 800 mm of the reactor, after which it reached a steady value. Soot was found to decrease with increasing swirl from 0.5 to 1.5, but the lowest amount of soot was found to be at zero swirl where previous measurements have shown the flame to be lifted. Near the exit, no soot was measured until the equivalence ratio in the flame reached a value of =1.1, after which increasing the equivalence ratio increased the soot volume fraction dramatically. An appropriate model for the soot and the coal, char, and ash was used to determine the soot volume fraction from the transmittance data and Mie theory. The highest measured value of soot was at =1.5; resulting in a soot volume fraction of 0.88 ×10 −6 . At higher equivalence ratios, the soot transmittance was below the detector noise level. Caleulations showed that at the sootiest conditions, approximately one-fifth of the volatiles were being converted to soot.

Experimental Results on the Effect of Piston Surface Roughness and Porosity on Diesel Engine Combustion

Measurements have been made to determine the effect of piston crown surface properties on combustion. Back-to-back engine tests were conducted to compare surface modified pistons to a production piston. Each modified piston was found to prolong combustion duration. Porous coatings and a non porous, roughened piston were observed to increase fuel consumption. Increase in fuel consumption was determined to be the result of increased heat release duration. The data show surface roughness alone affects the duration of heat release. The shift in magnitude of the centroid of heat release was similar to the shift observed in insulated engine experiments.

Temperature Measurement Using Infrared Spectral Band Emissions From H2O

Temperature Measurement Using Infrared Spectral Band Emissions From H2O Daniel Jared Ellis Department of Mechanical Engineering, BYU Master of Science Currently there is no known method for accurately measuring the temperature of the gas phase of combustion products within a solid fuel flame. The industry standard is a suction pyrometer and thermocouple which is intrusive, both spatially and temporally averaging, and difficult to use. In this work a new method utilizing the spectral emission from water vapor is investigated through modeling and experimental measurements. This method was demonstrated along a 0.75m line of sight, averaged over 1 minute in the products of a natural gas flame but has the potential to produce a spatial resolution on the order of 5 cm and a temporal resolution of less than 1 millisecond. The method employs the collection of infrared emission from water vapor over discrete wavelength bands and then uses the ratio of those emissions to infer temperature. A 12.5 mm lens has been positioned within a water cooled probe to focus flame product gas emission into an optical fiber where the light is transmitted to a Fourier Transform Infrared Spectrometer (FTIR). The same optical setup was also used to collect light from a black body cavity at a known temperature in order to calibrate the spectral sensitivity of the optical system and FTIR detector. Experiments were conducted in the product gas of a 150 kWth methane flame comparing the optical emission results to a suction pyrometer with type K thermocouple. The optical measurement produced gas temperatures approximately 1 4% higher than the suction pyrometer. Broadband background emission was also seen by the optical measurement and was removed assuming grey body radiation. This background emission can be used to determine particle emission temperature and intensity. Additional work will be needed to demonstrate the method under conditions with significant particle emission. Additional work is also needed to demonstrate the work over a smaller path length and shorter time scale.