Vaporization of droplets in premixing chambers

Detailed measurements were made of the structures of turbulent fuel sprays vaporizing in heated airstreams. The measurements show the size dependent vaporization and dispersion of the droplets and the important influence of the large eddies in the turbulence. The measurements form a data base for the development of models of fuel spray vaporization. Two laser techniques were specially developed for the investigation. A laser tomography technique converts line-of-sight light scattering measurements into time averaged 'point' measurements of droplet size distribution and volume concentration. A laser anemometer particle sizing technique was further developed to permit accurate measurements of individual particle sizes and velocities, with backscatter collection of light. The experiments are combined with heat transfer models to analyze the performance of miniature thermocouples in liquid sprays

Air pollution from aircraft

A model which predicts nitric oxide and carbon monoxide emissions from a swirl can modular combustor is discussed. A detailed analysis of the turbulent fuel-air mixing process in the swirl can module wake region is reviewed. Hot wire anemometry was employed, and gas sampling analysis of fuel combustion emissions were performed

Air pollution from aircraft

A series of fundamental problems related to jet engine air pollution and combustion were examined. These include soot formation and oxidation, nitric oxide and carbon monoxide emissions mechanisms, pollutant dispension, flow and combustion characteristics of the NASA swirl can combustor, fuel atomization and fuel-air mixing processes, fuel spray drop velocity and size measurement, ignition and blowout. A summary of this work, and a bibliography of 41 theses and publications which describe this work, with abstracts, is included

Similarity between the primary and secondary air-assisted liquid jet breakup mechanism

we report an ultrafast synchrotron x-ray phase contrast imaging study of the primary breakup mechanism of a coaxial air-assisted water jet. We demonstrate that there exist great similarities in the phenomenology of primary breakup with that of the secondary breakup. Especially, a membrane-mediated breakup mechanism dominates the breakup process for a wide range of air speeds. This finding reveals the intrinsic connections of these two breakup regimes and has deep implications on the unified theoretical approach in treating the breakup mechanism of high speed liquid jet.Comment: 15 pages, 4 figure

Decay of far flow field in trailing vortices

A finite difference machine code is used in the wake vortex problems in the quasi-cylindrical boundary layer approximation. A turbulent energy model containing new features is developed that accounts for the major effects disclosed by more advanced models in which the parameters are not yet established. Several puzzles that arose in previous theoretical investigations of wake vortices are resolved

The investigation of time dependent flame structure by ionization probes

Ionization probes were used to measure mean ionization current and frequency spectra, auto-correlations and cross-correlations in jet flames with variation in the initial Reynolds numbers and equivalence ratios. Special attention was paid to the transitional region between the burner exit plane and the plane of onset of turbulence

Detailed investigation of a vaporising fuel spray. Part 1: Experimental investigation of time averaged spray

A laser tomographic light scattering technique provides rapid and accurate high resolution measurements of droplet sizes, concentrations, and vaporization. Measurements using a computer interfaced thermocouple are presented and it is found that the potential exists for separating gas and liquid temperature measurements and diagnosing local spray density by in situ analysis of the response characteristics of the thermocouple. The thermocouple technique provides a convenient means for measuring mean gas velocity in both hot and cold two phase flows. The experimental spray is axisymmetric and has carefully controlled initial and boundary conditions. The flow is designed to give relatively insignificant transfer of momentum and mass from spray to air flow. The effects of (1) size-dependent droplet dispersion by the turbulence, (2) the initial spatial segregation of droplet sizes during atomization, and (3) the interaction between droplets and coherent large eddies are diagnosed

DESIGN OF ATOMIZERS AND BURNERS FOR COAL-WATER SLURRY COMBUSTION

A review of the results of the current period is included. Section 1 summarizes the progress that was made during the current period. Section 2 discusses the activities planned for the next period. Section 3 summarizes the theory that was developed on the capillary flow within long filaments of liquid during the breakup of ligaments of Newtonian and Non-Newtonian Fluids. The current period was mainly dedicated to developing a theory to account for the flow into the droplet and back into the droplet attachment region in the falling droplet experiments. Six samples of coal water slurries were also tested for determination of the extensional viscosity using the falling droplet technique. A spray chamber was built to study the breakup of coal water slurry samples provided by Penn State

Imaging of Flames in Cement Kilns To Study the Influence of Different Fuel Types

The cement industry aims to use an increased amount of alternative fuels to reduce production costs and CO₂ emissions. In this study three cement plants firing different kinds and percentages of alternative fuel were studied. A specially developed camera setup was used to monitor the flames in the three cement kilns and assess the effect of alternative fuels on the flame. It was found that cofiring with solid recovered fuel (SRF) would delay the ignition point by about 2 m and lower the intensity and temperature of the kiln flame compared to a fossil fuel flame. This is related to a larger particle size and moisture content of the alternative fuels, which lowers the conversion rate compared to fossil fuels. The consequences can be a lower kiln temperature and cement quality. The longer conversion time may also lead to the possibility of localized reducing conditions in the cement kiln, which can have a negative impact on the clinker quality and process stability. The burner design may alleviate some of the issues encountered with SRF cofiring. At one of the test plants the burner was changed from a design with an annular channel for axial air to a jet design. This proved to be beneficial for an early ignition and improved dispersion of the fuel and led to an increase in cement quality and higher use of SRF

DESIGN OF ATOMIZERS AND BURNERS FOR COAL- WATER SLURRY COMBUSTION. Quarterly Report, January 1, 1996--March 31, 1996

A novel extensional rheotester was developed to measure the extensional properties of aqueous solutions of Polyacrilamide {number_sign}10 and coal water slurries (CWS). When a drop of viscoelastic liquid or CWS containing additives is allowed to form at the end of a capillary tube, it starts to fall once its weight exceeds the retaining force exerted by surface tension. In experiments with aqueous solutions of Polyacrilamide it was observed that a long filament of fluid connected the droplet to the end of the capillary tube. The filament partially supported the droplet slowing its rate of fall. In order to evaluate the transient elongational stresses an elongational viscosity that are developed in the long threads of liquid before breakup, the mass (m), the diameter (D), the velocity (V) and the acceleration (a) of the suspended droplet along with the diameter of the filament (d) are measured. The length of the trailing filament is also measured as a function of time in order to determine the filament stretch rate {dot {epsilon}}. The time dependent behavior of the filament diameter was also measured using a laser attenuation technique. The strain rate of the filament was determined from the experimental values of {dot L}/L and {minus}2{dot d}/d, where the dot refers to differentiation with respect to time. Seven different aqueous solutions of Polyacrilamide E10 were prepared spanning a wide range of polymer concentration (0.5{percent}, 0.25{percent}, 0. 125{percent}, 0.0625{percent}, 0.03125{percent}, 0.015625{percent}, 0. 0078125{percent}). The data gave a single relaxation time for each solution. This relaxation time for uniaxial extension is found to increase with E10 concentration. 4 refs., 10 figs., 2 tabs