An Experimental and Theoretical Study of Radiative Extinction of Diffusion Flames

The objective of this research was to experimentally and theoretically investigate the radiation-induced extinction of gaseous diffusion flames in microgravity. The microgravity conditions were required because radiation-induced extinction is generally not possible in 1-g but is highly likely in microgravity. In 1-g, the flame-generated particulates (e.g. soot) and gaseous combustion products that are responsible for flame radiation, are swept away from the high temperature reaction zone by the buoyancy-induced flow and a steady state is developed. In microgravity, however, the absence of buoyancy-induced flow which transports the fuel and the oxidizer to the combustion zone and removes the hot combustion products from it enhances the flame radiation due to: (1) transient build-up of the combustion products in the flame zone which increases the gas radiation, and (2) longer residence time makes conditions appropriate for substantial amounts of soot to form which is usually responsible for most of the radiative heat loss. Numerical calculations conducted during the course of this work show that even non-radiative flames continue to become "weaker" (diminished burning rate per unit flame area) due to reduced rates of convective and diffusive transport. Thus, it was anticipated that radiative heat loss may eventually extinguish the already "weak" microgravity diffusion flame. While this hypothesis appears convincing and our numerical calculations support it, experiments for a long enough microgravity time could not be conducted during the course of this research to provide an experimental proof. Space shuttle experiments on candle flames show that in an infinite ambient atmosphere, the hemispherical candle flame in microgravity will burn indefinitely. It was hoped that radiative extinction can be experimentally shown by the aerodynamically stabilized gaseous diffusion flames where the fuel supply rate was externally controlled. While substantial progress toward this goal was made during this project, identifying the experimental conditions for which radiative extinction occurs for various fuels requires further study. Details concerning this research which are discussed in published articles are included in the appendices

An Experimental and Theoretical Investigation into Burning Characteristics of PPS-Glass Fiber Composites

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77086/1/AIAA-2002-2887-844.pd

An Experimental and Theoretical Study of Radiative Extinction of Diffusion Flames

In a recent paper on 'Observations of candle flames under various atmospheres in microgravity' by Ross et al., it was found that for the same atmosphere, the burning rate per unit wick surface area and the flame temperature were considerably reduced in microgravity as compared with normal gravity. Also, the flame (spherical in microgravity) was much thicker and further removed from the wick. It thus appears that the flame becomes 'weaker' in microgravity due to the absence of buoyancy generated flow which serves to transport the oxidizer to the combustion zone and remove the hot combustion products from it. The buoyant flow, which may be characterized by the strain rate, assists the diffusion process to execute these essential functions for the survival of the flame. Thus, the diffusion flame is 'weak' at very low strain rates and as the strain rate increases the flame is initially 'strengthened' and eventually it may be 'blown out'. The computed flammability boundaries of T'ien show that such a reversal in material flammability occurs at strain rates around 5 sec. At very low or zero strain rates, flame radiation is expected to considerably affect this 'weak' diffusion flame because: (1) the concentration of combustion products which participate in gas radiation is high in the flame zone; and (2) low strain rates provide sufficient residence time for substantial amounts of soot to form which is usually responsible for a major portion of the radiative heat loss. We anticipate that flame radiation will eventually extinguish this flame. Thus, the objective of this project is to perform an experimental and theoretical investigation of radiation-induced extinction of diffusion flames under microgravity conditions. This is important for spacecraft fire safety

Transient Measurements of Temperature and Radiation Intensity in Spherical Microgravity Diffusion Flames

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76396/1/AIAA-2006-746-159.pd

Effect of fuel dilution by CO2 on spherical diffusion flames in microgravity

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76100/1/AIAA-2001-622-741.pd

Radiant extinction of gaseous diffusion flames

The absence of buoyancy-induced flows in microgravity significantly alters the fundamentals of many combustion processes. Substantial differences between normal-gravity and microgravity flames have been reported during droplet combustion, flame spread over solids, candle flames, and others. These differences are more basic than just in the visible flame shape. Longer residence time and higher concentration of combustion products create a thermochemical environment which changes the flame chemistry. Processes such as flame radiation, that are often ignored under normal gravity, become very important and sometimes even controlling. This is particularly true for conditions at extinction of a microgravity diffusion flame. Under normal-gravity, the buoyant flow, which may be characterized by the strain rate, assists the diffusion process to transport the fuel and oxidizer to the combustion zone and remove the hot combustion products from it. These are essential functions for the survival of the flame which needs fuel and oxidizer. Thus, as the strain rate is increased, the diffusion flame which is 'weak' (reduced burning rate per unit flame area) at low strain rates is initially 'strengthened' and eventually it may be 'blown-out'. Most of the previous research on diffusion flame extinction has been conducted at the high strain rate 'blow-off' limit. The literature substantially lacks information on low strain rate, radiation-induced, extinction of diffusion flames. At the low strain rates encountered in microgravity, flame radiation is enhanced due to: (1) build-up of combustion products in the flame zone which increases the gas radiation, and (2) low strain rates provide sufficient residence time for substantial amounts of soot to form which further increases the flame radiation. It is expected that this radiative heat loss will extinguish the already 'weak' diffusion flame under certain conditions. Identifying these conditions (ambient atmosphere, fuel flow rate, fuel type, etc.) is important for spacecraft fire safety. Thus, the objective is to experimentally and theoretically investigate the radiation-induced extinction of diffusion flames in microgravity and determine the effect of flame radiation on the 'weak' microgravity diffusion flame

Tunneling spectroscopy measurement of the superconductor gap parameter of MgB_2

Cryogenic scanning tunneling microscopy and magnetization measurements were used to study the superconducting properties of MgB_2. The magnetization measurements show a sharp superconductor transition onset at T_c = 38.5 K, in agreement with previous works. The tunneling spectra exhibit BCS gap structures, with gap parameters in the range of 5 to 7 meV, yielding a ratio of 2delat/KT_c ~ 3-4. This suggests that MgB_2 is a conventional BCS (s-wave) superconductor, either in the weak-coupling or in the `intermediate-coupling` regimeComment: accepted to PRB, revised versio

Final report on the project entitled: Highly Preheated Combustion Air System with/without Oxygen Enrichment for Metal Processing Furnaces

This work develops and demonstrates a laboratory-scale high temperature natural gas furnace that can operate with/without oxygen enrichment to significantly improve energy efficiency and reduce emissions. The laboratory-scale is 5ft in diameter & 8ft tall. This furnace was constructed and tested. This report demonstrates the efficiency and pollutant prevention capabilities of this test furnace. The project also developed optical detection technology to control the furnace output

A novel method of waste heat recovery from high temperature furnaces to create radiative flameless combustion

One of the largest heat losses in high temperature furnaces is the loss of flue gas enthalpy. Currently, up to 60% of the heating value of natural gas (or any other fuel) used in high temperature furnaces is lost via the flue gases. This work discusses the benefits and technology of re-circulating the hot flue gases back into the furnace to avoid the large heat loss and supplementing the flue gases with oxygen to maintain the desired oxygen concentration. The energy-savings benefits are derived from two factors: (i) recirculating the hot flue gases back into the furnace, and (ii) a reduction in the mass of flue gases due to the use of oxygen. In addition to these energy benefits, environmental benefits are derived from a reduction in NOx production. In fact, flue gas recirculation (FGR) is a common method used to control NOx in engines and furnaces. The simple heat recovery device described in this paper can: (i) economically capture greater than 50% of the energy lost via the exhaust gases, (ii) provide a long trouble-free operational life of the heat recovery device at a significantly reduced installation cost, (iii) provide a method to control NOx produced by the furnace by FGR recirculation, (iv) increase furnace gas radiation and hence productivity, (v) can be profitably employed even with the high temperature recuperator, (vi) can be profitably used with 100% oxygen furnaces, and (vii) will work with both batch and continuous furnaces

Final Technical Report for University of Michigan Industrial Assessment Center

The UM Industrial Assessment Center assisted 119 primary metals, automotive parts, metal casting, chemicals, forest products, agricultural, and glass manufacturers in Michigan, Ohio and Indiana to become more productive and profitable by identifying and recommending specific measures to improve energy efficiency, reduce waste and increase productivity. This directly benefits the environment by saving a total of 309,194 MMBtu of energy resulting in reduction of 0.004 metric tons of carbon emissions. The $4,618,740 implemented cost savings generated also saves jobs that are evaporating from the manufacturing industries in the US. Most importantly, the UM Industrial Assessment Center provided extremely valuable energy education to forty one UM graduate and undergraduate students. The practical experience complements their classroom education. This also has a large multiplier effect because the students take the knowledge and training with them