Jongmook Lim

A study of the effects of air preheat on the structure of methane/air counterflow diffusion flames

Abstract The effects of air preheat on flame structure are studied in counterflow methane–air diffusion flames, considering air temperatures in the range 300 to 560 K. Species concentrations for H 2 , O 2 , N 2 , CH 4 , CO, CO 2 , C 2 H 2 , and C 2 H 4 were measured using sampling and gas chromatography. Concentrations of NO were measured using sampling and chemiluminescence analysis. Results of numerical calculations using GRI-Mech 2.11 were compared with the measurements. The results of the numerical calculations and the measurements show excellent agreement for O 2 , N 2 , CH 4 , and good agreement for CO 2 , H 2 , and CO. However, they show poor agreement for C 2 H 2 and C 2 H 4 . Independent of the air temperature in the range 300 to 560 K, measured and predicted concentrations of CH 4 , CO 2 , O 2 , and N 2 collapse reasonably well when plotted against the local equivalence ratio. The peak CO and H 2 concentrations increase with increasing air preheat. The peak CO concentrations increase because of enhanced dissociation of CO 2 . The peak H 2 concentrations increase because of an increase in H atom concentrations causing enhanced rates of the reaction CH 4 + H → CH 3 + H 2 . Both the measured and the predicted NO profiles showed approximately a 70% increase in the peak mole fractions with the increase in air temperature. The predictions of NO mole fractions in the fuel-lean region and near the peak are within 10% of the measurements. However, in the fuel-rich region, the predicted NO mole fractions are lower by up to 70% than the measured NO mole fractions. The increase in peak NO mole fractions with air preheat occurs primarily through the enhanced reaction rate of the prompt initiation reaction N 2 + CH → HCN + N. The NO production by the thermal mechanism increases significantly with air preheat, but still remains a very small portion of the total. The effects of air preheat on many species and reaction rates manifest through the increased H atom concentrations.

Fast infrared array spectrometer with a thermoelectrically cooled 160-element PbSe detector

A fast infrared array spectrometer (FIAS) with a thermoelectrically cooled 160-element PbSe detector was demonstrated using measurements of instantaneous infrared radiation intensities simultaneously over the 1.8–4.9 μm wavelength range at a sampling rate of 390 Hz. A three-point second-degree Lagrange interpolation polynomial was constructed to calibrate the FIAS because of the nonlinear response of the infrared array detector to the incident radiation beam. This calibration method gave excellent measurements of blackbody radiation spectra except for a narrow band at wavelength of 4.3 μm due to absorption by room carbon dioxide, which is one of the two major gas radiation peaks (2.7 and 4.3 μm) from the lean premixed hydrocarbon/air combustion products in the midinfrared spectrum. Therefore, the absorption coefficient of room carbon dioxide was conveniently measured on site with the blackbody reference source, and was used in the calibration of the FIAS and also in the calculations of the radiation spect...

Transient cooling of a cylindrical glass gob

Transient cooling of a hot glass gob by internal combined conduction and radiation is analyzed. The spectral dependence of the absorption coefficient on wavelength and temperature is appropriately accounted for by solving the radiative transfer equation for the axisymmetric cylindrical geometry. Specularly reflecting boundaries are considered and Fresnels equations are used to predict the spectral directional reflection and transmission characteristics of the interfaces. The finite volume method is used to solve numerically the thermal energy equation, and discrete ordinates method (DOM, S–N method) is employed to solve the radiative transfer equation. Dynamic cooling calculations have been performed and transient temperature distributions, temperature gradients, convective and combined convective plus radiation results are presented and discussed. The results show that for the initial and thermal conditions of interest, the interior of the glass cools primarily by radiation and only in the surface layers (0.8

A Comparison of Phase Doppler Analyzer (Dual-PDA) and Optical Patternator Data for Twin-Fluid and Pressure-Swirl Atomizer Sprays

The goal of this study was to determine when patternation information derived from Phase Doppler Analyzer (Dantec Dynamics, Skovlunde, Denmark, dual-PDA) measurements of volume flux, drop velocity, and mean size agreed with corresponding values measured using an optical patternator (Enurga, Inc., West Lafayette, IN, SetScan OP-600). To achieve this, data from each instrument were transformed into spatially resolved absorptances (equivalent to drop surface area per unit spray volume) and compared. Key conclusion is absorptance agreement to within 20% in many cases. However, discrepancies between phase Doppler analyzer (PDA)-calculated and optical patternator-measured absorptances become larger as the drop arrival rate increases, as the mean drop size decreases, and when a significant drop size-velocity correlation is present. These discrepancies are attributed to an underestimation of the volume flux (which becomes more important with increasing droplet arrival rate), an over-reporting of the mean drop diameter (which is the result of the restrictive data acquisition scheme applied when ensuring mass closure for the PDA measurements), the limited PDA dynamic range (which can preclude simultaneously accounting for both the largest and smallest drops in the spray), and by the optical patternators number-density based measurement scheme (which will not yield the same results as the flux-based PDA when a drop size-velocity correlation is present).

Statistical absorption tomography for turbulent flows

Abstract A Monte-Carlo method for the tomographic reconstruction of the mean and the RMS of local transmittance of radiation through a correlated turbulent Gaussian field is derived. Previous statistical reconstruction of turbulent flow fields have neglected spatial correlation resulting in very low spatial resolution. The present method provides for very high spatial resolution since the spatial correlation of local transmittance is considered. The validity of the method is examined using synthetically generated path-integrated transmittance data. If spatial correlations are neglected, the tomographic reconstruction method yielded local transmittances that are substantially different from the synthetic data. If spatial correlation is considered, the tomographic reconstruction method provided the mean and RMS of local transmittances within 5% and the local spatial integral length scale within 20% of the synthetic data.

Structure of Plumes from Burning Aluminized Propellant Estimated Using Fan Beam Emission Tomography

Fan beam emission tomography in the 1–5-� m band is used to estimate the structure of a solid rocket propellant plume. Fan beam emission tomography consists of two components. The first is a pair of orthogonal high-speed imaging spectrometers and scanners that measures the spectral radiation intensities from 1.3 to 4:8 � m at 256 view angles. The second is a robust deconvolution algorithm that estimates the structure of the plume from the spectral radiation intensity measurements. The deconvolution algorithm is based on the maximum likelihood estimation method in conjunction with a linearized radiative transfer equation. The radiation intensity measurements were completed in a series of burns using 2.5-cm-diam by 1.25-cm-long strands of aluminized solid rocket composite propellant.Ingeneral,thealuminumdiffusion-flameparticulatetemperaturesintheplumearemuchhigherthanthe gastemperatures.Thegaseouscombustionproductconcentrationsaremuchlowerinthemiddleoftheplumethanat the outer edges. This indicates a diffusion-flame-type structure for the plume, caused by the fact that the composite solid rocket propellant isfuel-rich. Theresults indicate thatreliable plume-structure measurements can be obtained using fan beam emission tomography. Nomenclature d = diameter of the burning surface, cm

Time-dependent line-of-sight extinction tomography for multi-hole GDI injectors:

Finely atomized sprays from multi-hole gasoline direct injection (GDI) fuel injectors make them an ideal choice for automobile applications. A knowledge of the factors affecting the performance of these injectors is hence important. In the study presented here, we employ statistical extinction tomography to examine the transient characteristics of two GDI fuel injectors with five and six holes. Two axial locations, 25 mm and 35 mm from the injector exit, are chosen for experimental measurements, and the dependence of injection pressure and ambient temperature on plume locations and angles is examined from these measurements. A pressure chamber with opposing windows is used which permits the nozzle to be rotated 12 times (30° each rotation) to obtain information on the complete spray structure. Additionally, the plume centroid locations are measured and compared with those obtained with a mechanical patternator. The centroid locations from the two instruments compare favorably.

Comparison of Particle Dynamics Analyzer (PDA) and SetScan Optical Patternator Results

The primary goal of this study was to determine when patternation information derived from Particle Dynamics Analyzer (Dantec Dynamics dual-PDA) measurements of volume flux, velocity and mean drop size agreed with corresponding values measured using an optical patternator (En’Urga, Inc SetScan OP-600). To achieve this, data from each instrument was transformed into spatially resolved absorptances (equivalent to drop surface area per unit volume) and compared. The secondary goal of this study was to explain the cause of any discrepancies in comparison of the two absorptance sets when they occurred. Key conclusions drawn from this study are: absorptance agreement to within 20% can be achieved in many cases; however, the difference between the PDA-calculated and optical patternator-measured absorptances becomes larger as the drop arrival rate increases, as the drop size decreases, and when a significant drop size-velocity correlation is present. These discrepancies are attributed to an underestimation of the volume flux (which becomes more important with increasing droplet arrival rate), an over-reporting of the mean drop diameter (which is the result of the restrictive data acquisition scheme applied when ensuring mass closure), the limited PDA dynamic range (which can preclude simultaneously accounting for both the largest and smallest drops in the spray), and by the optical patternator’s number-density based measurement scheme (which will not yield the same results as the flux-based PDA when a drop size-velocity correlation is present).Copyright

Estimating velocity in Gasoline Direct Injection sprays using statistical pattern imaging velocimetry

Statistical pattern imaging velocimetry (SPIV) is a new technique for the estimation of the planar velocity field from the high-speed videos. SPIV utilizes an ensemble of either backlit or side lit videos to obtain full planar velocities in sprays and flames. Unlike conventional particle imaging velocimetry, statistical pattern imaging velocimetry does not require well-resolved images of particles within turbulent flows. Instead, the technique relies of patterns formed by coherent structures in the flow. Therefore, SPIV is well suited for the estimating planar velocities in sprays and turbulent flames, both of which have well-defined patterns embedded in the flow videos. The implementation of the SPIV technique is relatively quite straightforward since high-speed videos can be readily obtained either in a laboratory or production floor setting. The biggest challenge for the SPIV techniques is that the procedure is computationally expensive even with an ordinary mega-pixel camera. To improve the computation speed, a successive partitioning scheme was employed. In addition, to improve spatial resolution to subpixel dimensions, a weighted central averaging scheme was used. With these two enhancements, the SPIV method was used to obtain planar radial and axial velocities in a spray emanating from a GDI injector. Sprays from GDI injectors are very dense (with obscuration levels close to the injector being greater than 99%), and velocity measurements are difficult. However, further away from the nozzle, a Phase Doppler Anemometer can be used to obtain velocity measurements. The velocities obtained using these two methods showed reasonable agreement.

Flame Radiation, Structure, and Scalar Properties in Microgravity Laminar Fires

Results from microgravity combustion experiments conducted in the Zero Gravity Research Facility (ZGF) 5.18 second drop facility are reported. The results quantify flame radiation, structure, and scalar properties during the early phase of a microgravity fire. Emission mid-infrared spectroscopy measurements have been completed to quantitatively determine the flame temperature, water and carbon dioxide vapor concentrations, radiative emissive power, and soot concentrations in microgravity laminar methane/air, ethylene/nitrogen/air and ethylene/air jet flames. The measured peak mole fractions for water vapor and carbon dioxide are found to be in agreement with state relationship predictions for hydrocarbon/air combustion. The ethylene/air laminar flame conditions are similar to previously reported results including those from the flight project, Laminar Soot Processes (LSP). Soot concentrations and gas temperatures are in reasonable agreement with similar results available in the literature. However, soot concentrations and flame structure dramatically change in long-duration microgravity laminar diffusion flames as demonstrated in this report.