Norman Love

Concentration measurements of CH and OH radicals in laminar biofuel flames.

An investigation to determine the dominant route of NOx formation in biofuel flames and to confirm the relationship of the NOx increase with iodine numbers in fuels has been presented. This is done through the measurement of the concentration of OH and CH radicals, indicators of the formation of NOx through the Zeldovich and Fenimore mechanisms. A laminar partially pre-mixed flame at an initial fuel equivalence ratio (φ) = 7 was used to minimize the effects of fluid mechanics and isolate the effects of fuel chemistry. Three biofuels, with different iodine numbers, were studied: soy methyl ester (SME), canola methyl ester (CME) and methyl stearate (MS). Planar Laser-Induced Fluorescence (PLIF) images of hydroxyl radicals (OH) and CH radicals were captured with a diagnostic system consisting of a pulsed Nd:YAG laser and an Optical Parametric Oscillator (OPO) with frequency doubler option (FDO) using proper wavelengths. It was found that the population of OH radicals was low in the flames of all fuels, but significant CH radical concentrations were detected in all the flames, with the maximum population occurring in the SME fuel flame. The presence of high concentrations of CH measured in the regions of peak NOx indicate that NOx formation is primarily through the Fenimore mechanism, rather than the thermal mechanism, at this fuel-rich condition. Moreover, the fuel with highest iodine number, SME, produced significantly more NOx because of its tendency to facilitate the production of more soot, C, and CH radicals.

Effect of Iodine Number on NOx Formation in Laminar Flames of Oxygenated Biofuels

The present study employed a recently developed experimental technique to investigate the effect of iodine number on NOx formation in laminar partially premixed flames of three vaporized biofuels: canola methyl ester, soy methyl ester, and methyl stearate. The iodine numbers for the selected fuels varied over a wide range from 0.5 to 141. Key measurements included NOx concentration and temperature fields. The peak NOx concentration occurred in the near-burner region for all biofuels: 1166 ppm for soy, 1067 ppm for canola, and 414 ppm for the methyl stearate. We observed that the peak NOx concentration significantly increased with the iodine number, indicating a strong correlation between the chemical structure of the fuel and NOx emission.

A Method for the Rapid Characterization of Combustion Properties of Liquid Fuels Using a Tubular Burner

Knowledge of the combustion and pollutant emission characteristics is important in the application of both existing and newly developed fuels. A technique for the rapid characterization of flame radiation properties and emission characteristics of liquid fuels was developed for this purpose. Liquid fuel was injected into a heated air stream at known rates with a syringe pump; the feed line was heated (temperature of 425°C) to pre-vaporize the fuel before burning, to avoid the effects of evaporation parameters on measurements. Temperatures of the fuel and air were monitored using K-type thermocouples embedded within the feed lines. A laminar methane-air flame was issued from a stainless steel tubular burner (9.5mm inner diameter) and used as the ignition source. The methane supply was shut off after the onset of the burning of the vaporized liquid fuel, in order to eliminate the effects of burning methane in the measurements. Several liquid fuels were tested, including commercially available petroleum-based No. 2 diesel fuel, canola methyl ester (CME B 100) biodiesel, kerosene, methanol, toluene, and selected alkanes. A steady burning flame was achieved for all fuels. Radiative heat flux measurements were made with a high-sensitivity pyrheliometer and the radiant fraction of heat release calculated. The radiant heat fraction served as an indication of sooting tendency of the fuels. NO, CO, and CO2 emission measurements were also made. The measurements demonstrate the feasibility of the current technique for the rapid characterization of combustion properties of liquid fuels, utilizing small fuel quantities.Copyright

Effects of Equivalence Ratio on Temperature and OH Radical Concentration in Laminar Premixed Biofuel and Diesel Vapor Flames

3School of Aerospace and Mechanical Engineering, Uni versity of Oklahoma, Norman, OK, 73069 The effects of equivalence ratio on the mechanism o f formation of NO x in laminar flames of diesel and neat canola methyl ester (CME) biodie sel were investigated in this study. Equivalence ratios, ranging from 1.2 to 7, were sel ected to simulate the partially-premixed to near non-premixed flame combustion that exists in some combustors. Key parameters measured included flame length (residence time), OH concentration field, and flame temperature. These measurements were documented and correlated to the in-flame pollutant concentrations of NO x. It was found that at the lowest equivalence ratio , NO x production was a function of the flame length, temp erature, and OH concentration, therefore attributable to the thermal (Zeldovich) mechanism. At more fuel-rich equivalence ratios, a large amount of NO x was produced along or near the flame centerline in the nearburner region. At these conditions, no correlation between NO x formation and flame length, temperature, or radical concentrations was observed, thus was not attributable to the thermal mechanism. It was also observed that biofuel produced higher peak concentrations of NO x than diesel at all conditions, from 7% at φ = 1.2 to 90% at φ = 7.0.

Effect of Local Flow Field Fluctuations on the Characteristics of Turbulent Flames

This paper focuses on the experimental measurements of turbulence and its effect on the local consumption speed of premixed syngas-air mixtures. The flow field visualization using Particle Imaging Velocimetry (PIV) technique is also implemented to make a better understanding of the turbulence characteristics of syngas (H2-CO)-air combustion. The velocity fluctuations, turbulence intensities and local propagation velocities along the burner exit had been determined at different blockage ratios. With the increase of blockage ratios the velocity fluctuations increased in axial direction for both isothermal and reacting flows at a fixed Reynolds number (Re=2000) and equivalence ratio(Ф=.9).For reacting flows the fluctuations decreased up to the reaction zone then increased substantially at both blockage ratios. Turbulent flame propagation velocities were also determined at constant laminar burning velocity for different syngas mixtures. The effect of diluents (N2 and CO2) on turbulent burning velocities of syngas is determined at a constant adiabatic flame temperature of 1900K and at different blockage ratios. Turbulent flame propagation velocities increase with the increase in the blockage ratios. Turbulent flame propagation velocities increase with increase in hydrogen content in the syngas mixtures at constant laminar burning velocity.

Effect of degree of unsaturation on nox formation in partially premixed flames of biofuels

The effect of iodine number on NOx formation in laminar flames of three oxygenated biofuels was studied at an equivalence ratio of 2. Neat soy methyl ester, neat canola methyl ester, and methyl stearate, which had similar energy content and carbon chain length, were tested. The iodine numbers for these fuels varied from 0.5 to 142. Inflame NOx concentration and temperature were measured. The peak NOx concentration occurred in the near-burner region for all biofuels: 404 ppm for soy, 388 ppm for canola, and 123 ppm for the methyl stearate fuel, and did not correlate with the location of the peak temperature. Therefore, the peak concentration in this region was traced to the Fenimore mechanism. Also, the peak NOx concentration was significantly increased with iodine numbers (degree of unsaturation of the fuel molecule). Thus, a strong correlation exists between the chemical structure of the fuel and the NOx emission of the premixed flame.© 2009 ASME

Analysis of a directly heated oxyfuel supercritical power generation system

Directly heated supercritical oxy-fuel gas turbines have potential to provide a higher thermal efficiency with carbon capture compared to current gas turbine systems. Furthermore, due to the higher density of the working fluids the turbomachinery footprint can be reduced significantly. Motivated by the advantages of the directly heated supercritical power system, this paper presents the analysis of such a system. The analysis was conducted using ASPEN HYSYS assuming two different phases of combustion feed system including the gaseous and liquid phases. P-v diagrams for both cycles were generated and compared to each other to determine which is more efficient. The analysis revealed that the liquid phase feeding system produced a higher net power than the gaseous phase feeding system. The investigation showed that the system yielded a higher net efficiency of 55.1% when gaseous carbon dioxide is employed as a diluent.

Laminar Burning Velocity of Synthetic Gas Premixed Flames Near Extinction Conditions

Synthetic gas premixed flames have received considerable attention in the past. Recent interest in lean premixed combustion requires the fundamental combustion properties at fuel-lean conditions. This paper presents an experimental study on the laminar burning velocity of synthetic gas premixed flames at close to extinction conditions. CH4-H2 and CO-H2 fuel blends at different mixture compositions simulating coal-derived synthetic gases were investigated. A water-cooled nitrogen-stabilized flat flame burner with a diameter of 6 cm was employed for this purpose. The planar laser induced fluorescence technique was employed to precisely measure the flame width. Hydroxyl radical (OH) concentration was used as the marker of reaction field. A pulsed Nd:YAG laser was used in conjunction with an optical parametric oscillator to generate a vertical laser sheet at a wavelength of 283.5 nm. An intensified CCD camera was used to capture the fluorescence signals from OH radicals. For each fuel blend mixture composition, the lean blowout condition was first determined. All measurements were then taken at this condition. For CH4-H2 fuel blends, the burning velocity near extinction varied between 6.88 cm/s and 10.13 cm/s. Burning velocities of CO-H2 fuel blends near extinction varied between 4.36 cm/s and 6.27 cm/s.

Large eddy simulation of reacting centerbody stabilized swirled flow in a gas turbine combustor

This study is focused on understanding the changes in the flowfield when the operating conditions of a gas turbine combustor shift closer to the flashback regime. Flow visualization techniques and Computational Fluid Dynamics (CFD) technologies are used to analyze the complex flow-flame interactions that develop in the combustor. It is concluded in this study that when the combustor is operating in a stable condition, there is a bubble type recirculation zone anchored at the centerbody of the swirler. However, when the operating conditions shift closer to the flashback point, the bubble type vortex breakdown transforms into a spiral type vortex, which is characterized by a rapid deceleration of the flow, followed by a corkscrew-shaped twisting of the flow.

Investigation of Gas-Solid Fluidized Bed Dynamics with Spherical and Non-Spherical Particles

The hydrodynamic behavior of a gas-solid fluidized bed operating with both spherical and non-spherical particles is presented in this paper. For this purpose a plexiglass tube with an outside diameter of 3.8cm and a wall thickness of 0.318cm was used as the fluidized bed. With air as the carrier gas spherical borosilicate glass beads with a diameter of 1mm were used as the spherical particles and borosilicate glass with mean particle size of 717 �� m were used as non-spherical particles. Methodology of the particle size distribution and sphericity analysis is presented in this paper. Pressure measurements and high-speed imaging were utilized to characterize flows in a 5cm static packed bed. Mapping of bed pressure drop and superficial gas velocity across the bed was done and showed much lower pressure drop occurring for the non-spherical particle. The minimum fluidization and terminal velocity conditions for the specified fluidized bed and particles is also presented in this paper. MatPIV analysis of high-speed images, captured with a high-speed camera shows the flowfield velocity vectors and vorticity for both spherical and non-spherical particles.