A. S. Gordon

Nanotubes from methane flames

Abstract Entangled multi-walled carbon nanotubes with a diameter range of 20–60 nm were found to grow on a Ni–Cr wire in laminar co-flow methane-air diffusion flames. Nickel oxide particles were inside some of the nanotubes, suggesting that their particles, formed on the wire at the early stage of the synthesis, acted as catalyst. The carbon nanotubes can grow by a root-growth mechanism in a limited region inside the flame where oxygen plays an important role in the formation of nanotubes.

A Study of the Early History of Soot Formation in Various Hydrocarbon Diffusion Flames

Abstract Diffusion flames of methane, ethane, ethene, acetylene, propane, allene 1-butene, 1,3-butadiene and benzene in coflowing normal atmospheric air were investigated by analyzing samples of malerials collected on fine probes inserted into the flames. To focus attention on early slages of soot formation, small flames (heights 2cm to 4cm) on a burner 1.6cm in diameter were studied, and the more heavily sooting fuels were diluted with nitrogen (up to a nitrogen mole fraction of 90% for acetylene). Radiation-corrected thermocouples were employed to measure temperatures in the regions of earliest soot deposits, and the distances from the point of earliest deposit to that of the first visible soot emissions of radiation were also recorded. Scanning electron micrography (SEM) and X-ray photoelectric spectroscopy (ESCA) were applied lo the samples to investigate changes in soot morphology with increasing axial distance. The results showed the earliest deposils to be highly fuel-specific but later deposits to...

Near-limit downward propagation of hydrogen and methane flames in oxygennitrogen mixtures

Abstract Measurements are reported on nitrogen concentrations required to prevent downward propagation of hydrogen oxygen and methane oxygen flames in open tubes of 2.5 and 5.1 cm diameter. Limits plotted as functions of the fuel oxygen ratio show that quenching is most difficult the fuel-lean side for hydrogen flames and near stoichiometric for methane flames. Cellular patterns were observed near flammability limits, and near-limit flame speeds were measured. Results are interpreted mainly in terms of conductive losses from cellular flames since alternative mechanisms appear to produce qualitatively inconsistent predictions.

Some aspects of structures of turbulent pool fires

The results of an experimental study of the burning of JP-5 and methanol pools emphasize structural differences between JP-5 and methanol fires as well as the importance of radiant feedback of energy to the pool surface in controlling rates of burning.

A Simplified Method for the Computation of Burke-Schumann Flames in Infinite Atmospheres

Highly overventilated laminar coflow diffusion flames in axisymmetric geometry are addressed for Lewis numbers of unity in the reaction-sheet approximation with effects of buoyancy taken into account. A simple method of numerical integration with the boundary-layer approximation in stream-function coordinates is given, and results for flame structures and for Lagrangian histories are presented for hydrocarbon-air flames. Computed flame heights are shown to be in good agreement with experiment. The computational approach can efficiently employ standard routines on low-power work stations and personal computers.

A Study of the Two-Color Soot Zone for Small Hydrocarbon Diffusion Flames

Abstract A small orange emission region, separated by a sharp boundary from a yellow one, is reported for hydrocarbon-air diffusion flames. The phenomenon, which has not been previously reported, occurs only in very small flames, only over a small range of fuel flow rates, and it has been demonstrated on a cylindrical as well as a slot burner. It has been shown to occur for the ten different aliphatic fuels tested and appears to be a general phenomenon. Thermocouple measurements showed that the gas temperature of the flame interior increases monotonically along the axis; the yellow color is in a lower temperature gas than the orange. Since color temperatures can be deceptive, temperatures in each zone were surveyed by a Kurlbaum method, as well as by a spectral measurement in the two regions. Both methods gave a higher soot particle temperature in the yellow zone than in the orange. Furthermore, measured composition profiles showed that the olefinic concentration approaches zero at the interface between t...

Laser-Desorption Time-of-Flight Mass-Spectrometry Analysis of Soot from Various Hydrocarbon Fuels

Laser-desorption time-of-flight mass spectrometry (LDMS) was used to analyze soot collected from seven different hydrocarbon fuels (methane, n-hexane, n-heptane, n-octane, n-decane, benzene and toluene) burning with air under normal atmospheric pressure. To evaluate the technique, samples of two different types of furnace blacks, two types of graphite, a synthetic diamond and a C 70 fullerene also were analyzed. With proper experimental design, the C 70 produced a single peak of mass 840 Da, thereby showing the ability of LDMS to remove and singly ionize large intact molecular species from the sample for the purpose of chemical analysis. The LDMS soot analysis showed that each mature soot has a unique chemical fingerprint. A family of fuels (e.g., normal alkanes) produces soot that is similar in appearance when mature and that therefore might be expected to yield similar mass spectra, but it is found instead that each spectrum has unique features that are different for each parent fuel. These initially surprising results point to the need for further study of fuel pyrolysis in flames.

AFFF spreading properties at elevated temperatures

The authors calculated spreading coefficients for aqueous film forming foams and hydrocarbon fuels from surface and interfacial tensions measurements made over a temperature range from 20° C to 90° C.

Visible Flame Heights of Laminar Coflow Diffusion Flames

Results of experiments are reported for overventilated buoyancy-controlled flames of various fuel mixtures in normal atmospheric air. The fuels studied were C2H6, C2H4, C2H2 and CH4, as well as fixed hydrogen-hydrocarbon mixtures of the first three, to give C2H6+H2, C2H4+H2, C2H2+H2 and C2H2+2H2. The focus of the work was to test the concept of flame height correspondence between pure fuels and “synthetic” fuels, synthetic methane being C6vH+H2, synthetic ethylene C2H2+H2 and synthetic ethane C2H4+H2 and C2H2+2H2. Adiabatic flame temperatures Taf were controlled by addition of N2 to the fuels, and comparisons were made at fixed Taf,. In accordance with theory, excellent flame-height agreements were obtained for ethane and the two synthetic ethanes. Agreements were somewhat poorer for synthetic ethylene and especially poor for synthetic methane. The former discrepancy is associated with differing sooling tendencies of the different fuels, while the latter is readily attributable to influences of molecular ...

Anomalous Quenching of Hydrogen Diffusion Flames in Coflow Configurations

Abstract It has been reported that coflow hydrogen diffusion flames stabilized at the exit of a tube in laminar flow require increasing quencher concentrations for extinguishment with increasing linear velocity of fuel flow through the burner port. This is contrary to the behavior of most other flames and to the predictions of liftoff theories. The present work was designed to try to understand this apparent anomaly. The qualitative relations previously reported were confirmed experimentally. Additional experiments were performed using D2 in place of H2 and showed the same anomaly. Various physical quenchers were employed as well as four different tube surfaces, both uncooled and cooled, and a Pyrex burner pretreated with nitric acid; wall temperatures were measured in addition to liftoff conditions. The results suggest that the increasing stabilization of hydrogen and deuterium diffusion flames with increasing linear flow results from the increasing temperature of the port lip with increasing flow veloci...