George Sidebotham

Sooting behavior in temperature-controlled laminar diffusion flames☆

Abstract The sooting tendency of gaseous and liquid hydrocarbon fuels has been determined systematically in an axisymmetric laminar diffusion flame whose temperature was controlled by nitrogen dilution. Sooting tendency was measured by the minimum mass flow rate of fuel (FFM) at the smoke height. Result, plotted as log 1/FFM versus 1 T , where T is a calculated adiabatic flame temperature, show that fuel structure plays a significant role in diffusion flames. Comparison of these flame results with basic pyrolysis studies in the literature supports the concept that pyrolysis of the fuel molecule is a controlling factor in determining the overall tendency to soot, even though such tendency results from the competition of pyrolysis of the fuel and heterogeneous oxidation of the soot particles. The pyrolysis characteristics affecting the sooting process are rate, sequence and nature of products, and pyrolysis mode (pure or oxidative). The aromatics show a temperature sensitivity with respect to sooting tendency significantly lower than the other fuels. Conjugation of the initial fuel molecule and pyrolysis intermediates enhances sooting propensity.

Flame temperature, fuel structure, and fuel concentration effects on soot formation in inverse diffusion flames☆

Abstract Insights into soot formation processes are gained from chemical sampling and thermocouple probing of co-flowing inverse diffusion flames (IDFs), with the oxidizer in the center. The transition from near-to slightly sooting flames and the effects of flame temperature, fuel concentration, and fuel structure (using methane, ethene, propene and 1-butene) are investigated. The aromatic content of IDFS scales with the fuels sooting tendency, and suggests that the formation of the aromatic ring is a controlling step in soot formation. In addition to the relatively well-established reactions involving C4 and C2 species, benzene may form directly from two C3 species for fuels that readily produce C3 species during pyrolysis and/or oxidative pyrolysis. The total concentration of growth species increases almost linearly with fuel concentration, but depends more weakly on flame temperature than would be expected if pure pyrolysis governed the intermediate hydrocarbon behavior.

Laser ignition of surgical drape materials in air, 50% oxygen, and 95% oxygen

Background: Operating room fires fueled by surgical drapes and ignited by high-energy surgical tools in air and oxygen-enriched atmospheres continue to occur. Methods: The authors examined the time to ignition of huck towels and three commonly used surgical drape materials in air, 50% oxygen, and 95% oxygen using a carbon dioxide surgical laser as an ignition source. In addition, a phenol-polymer fabric was tested. Results: In air, polypropylene and phenol polymer do not ignite. For polypropylene, the laser instantly vaporized a hole, and therefore, interaction between the laser and material ceased. When tested in combination with another material, the polypropylene time to ignition assumed the behavior of the material with which it was combined. For phenol polymer, the laser did not penetrate the material. Huck towels, cotton–polyester, and non-woven cellulose–polyester ignited in air with decreasing times to ignition. All tested materials ignited in 50% and 95% oxygen. Conclusion: The results of this study reveal that with increasing oxygen concentration, the time to ignition becomes shorter, and the consequences become more severe. The possibility exists for manufacturers to develop drape materials that are safer than existing materials.

Effect of oxygen addition to a near-sooting ethene inverse diffusion flame

Abstract The pyrolysis zone of a near-sooting ethene inverse diffusion flame (IDF, with oxidizer in the central stream) has been probed for temperature and species concentrations. Oxidation processes can play an indirect but significant role on the observed intermediate hydrocarbon species profiles, and therefore on soot formation. Intermediate hydrocarbons can be formed near the main oxidation zone, and diffuse back into the colder fuel-rich region. Acetylene, C4 species (1,3 butadiene, vinylacetylene and diacetylene) and benzene are indicative of ethene pyrolysis and are observed to build up slowly with height. Methane, ethane and C4 species (allene, propyne and propene) are more indicative of ethene oxidation, and form rapidly low in the flame. The addition of a trace amount of oxygen to the fuel decreased the concentrations of the pyrolytic species and indicates that fuel pyrolysis rates were not enhanced by oxygen addition to the fuel in the present non-sooting flame. However, oxygen addition increas...

Critical Temperatures of Soot Formation

A review of critical temperatures for soot formation considering new experimental results from Princeton University and other sources is given. From this the conclusion is drawn that incipient particle formation controls the total mass of soot formed in any process. Approaches to preventing soot formation and growth should be to prevent any soot particles from forming.

Pyrolysis Zone Structure of Allene, 1,3 Butadiene and Benzene Smoke Point Diffusion Flames*

Abstract In an effort to further understand smoke point flames, species and temperature profiles were measured in the pyrolysis zones of diffusion flames using the heavily sooting fuels, allene, 1,3 butadiene and benzene. All three flames were at the smoke point and approximately the same visible flame height to provide a common basis for data comparison. The fuel was observed to be governed by a convective/diffuse-ive balance in the pre-soot flame zone; fuel depletion along the axis is due to radial diffusion, not to local pyrolysis. Possible correlations of mixture fraction (a conserved scaler) with concentration and temperature are discussed. Flame results are interpreted based on flow reactor and shock tube pyrolysis and oxidation data. The benzene flame produced much lower concentrations of aliphatic intermediates than the allene and butadiene flames. The formation rate of benzene is approximately the same in the allene and butadiene flames, but the mechanism of formation is different. The experiment...

Intraluminal flame spread in tracheal tubes.

Intraluminal combustion in polyvinyl chloride tracheal tubes was investigated. Two flame types were observed: intraluminal and downstream. The flame‐spread velocity, burning rate, and equivalence ratio of the intraluminal flame were determined. The products of the intraluminal flame were analyzed, revealing compounds capable of further combustion.

A Test Method for Measuring the Minimum Oxygen Concentration to Support an Intraluminal Flame

A test method for measuring the minimum concentration .to support an intraluminal flame is described. An oxidizer is flowed through a plastic tube, and an ignition source is applied to the free end of the tube. If the oxygen concentration is sufficient, a flame propagates along the inner surface of the tube, termed an intraluminal flame. The minimum concentration of oxygen, or limiting oxygen index (LOI), that will support such a flame is determined. Results are reported for polyvinyl chloride tubing and compared to those using the standard ASTM D 2863, the candle-type flammability test. In the intraluminal test, the LOI with helium as the diluent gas is lower than that with nitrogen as the diluent, in contrast to results using ASTM D 2863. The effects of buoyancy are reduced in the intraluminal test, and the results may therefore be more applicable to low gravity environments.

Endotracheal tube fires: A flame spread phenomenon

Three flame types can result when an ignition source is applied to a tube of a combustible material through which an oxidizer flows. If the oxygen concentration inside the tube is greater than the tube materials limitingoxygen index (LOI), an opposed flow flame can spread along the inner surface of the tube (primary intraluminal flame). This flame, which requires a forced flow, consumes the supplied oxygen (fully or in part) and produces combustible, toxic gases which emerge from the free end (and ignition hole where applicable). These gases can then react with the oxygen in the ambient environment and thereby support the second flame type (secondary jet diffusion flame). If the LOI is exceeded outside the tube, an extraluminal flame (the third flame type) can occur, and be supported by natural convection.

Few-Node Transient Models

Try this experiment. Fill a ceramic mug with boiling water and immediately grab its side. Close your eyes and concentrate on what it feels like. You’ve just experienced the mug heating phase, the topic of this chapter. In order to observe the separate behavior of the coffee and the mug, the capacitance of the coffee and the mug must be treated separately, creating a 2-node model. The goal of this chapter is to develop a general scheme for doing so. The term “Few-Node Model” is loosely defined as one in which space is discretized into clearly identifiable regions that can be given clear names (as opposed to numbers). In the next chapter, called “multi-node,” space will be discretized into finer elements in a way that there is no clear sense of how many nodes there should be beforehand.