Characteristics Of Large Diffusion Flames Burning In A Vitiated Atmosphere

Experiments concerning properties of large diffusion flames burning steadily in a vitiated atmosphere under conditions similar to those which may arise in a room fire are described. The effects of vitiation on the products of combustion and flame lengths, and the extinction limits are described for natural gas and ethylene diffusion flames stabilized on 8.9-, 19- and 50-cm pool-type burners. As vitiation was increased and the flame extinction limit was approached, the flame length increased slightly. Close to the limit, radiation from soot in the flame became imperceptible, leaving only a weakly luminous blue flame. Even with significant reductions in both the flame height and luminosity near the limit conditions, the hydrocarbon fuels were completely oxidized in the flame to water and carbon dioxide and no measurable concentrations of products of incomplete combustion were produced. A. comparison of limiting oxygen concentrations and limiting flame temperatures for these experiments with the results of other investigations shows reasonably good agreement despite widely varying experimental techniques. These results are contrasted with those obtained in the unsteady situation which arises when a large buoyant diffusion flame burns in an enclosed space such that the upper part of the flame is in a strongly vitiated layer composed of a mixture of air and products of combustion, and the lower part in fresh air

THE INFLUENCE OF URBAN AREAS ON FARMLAND VALUES

Farmland Values, Urban-Influence, Land Economics/Use, Q15, R30,

DECOUPLED PAYMENTS IN A CHANGING POLICY SETTING

The studies in this report analyze the effects of decoupled payments in the Federal Agriculture Improvement and Reform (FAIR) Act on recipient households, and assess land, labor, risk management, and capital market conditions that can lead to links between decoupled payments and production choices. Each study contributes a different perspective to understanding the response of U.S. farm households and production to decoupled income transfers. Some use new microdata on farm households collected through USDA's Agricultural Resource Management Survey (ARMS), initiated in 1996, and its predecessor survey. These data are used to compare household and producer behavior and outcomes before and after the FAIR Act. Other studies use applied or conceptual models to characterize the impact of introducing decoupled payments. Collectively, the chapters represent an early stage in the empirical analysis of decoupled payments. The studies address many aspects of the payments' household impacts but remaining issues call for additional analysis. As the analytical paradigm changes with the evolution of farm programs, the development of appropriate data and models will improve our understanding of farm program impacts on the behavior and well-being of U.S. farm households, and the agricultural sector.Agricultural and Food Policy,

Chemical Species Produced in Fires Near the Limit of Flammability

Sustaining a diffusion flame requires sufficient concentrations of fuel and oxidizer to maintain the combustion reaction. When the quantity of oxygen in the environment falls below a minimum value, combustion processes will be extinguished. An experimental technique is described which was used to determine the oxygen concentration in a vitiated environment of combustion products mixed with air which only just supports a large-scale diffusion flame. Measurements were taken of limiting oxygen concentrations and chemical species produced in fires near this flammability limit for methane (natural gas) and ethylene fuels. As limiting conditions were approached, radiation from soot in the reaction zone became imperceptible, leaving only a weakly luminous blue flame. Even with significant reductions in both the flame height and luminosity at these conditions, the fire completely consumed the fuel and generated no measurable amounts of products of incomplete combustion. A comparison of limiting oxygen concentrations and limiting flame temperatures for these experiments with the results of other investigations shows reasonably good agreement despite widely varying experimental techniques

Species Production and Heat Release Rates in Two-Layered Natural Gas Fires

A fire burning in an enclosure with restricted ventilation will result in the accumulation of a layer of warm products of combustion mixed with entrained air adjacent to the ceiling. For many conditions, the depth of this layer will extend to occupy a significant fraction of the volume of the room. Eventually, the interface between this vitiated ceiling layer and the uncontaminated environment below will position itself so that a large portion of the combustion processes occur in this vitiated layer. A description is given here of experimental work concerning the rates of formation of product species and heat release in a turbulent, buoyant natural gas diffusion flame burning in this two-layered configuration. The enclosure was modeled by placing a hood above a burner so that it accumulated the plume gases, and the unsteady development of the ceiling layer was modeled by the direct addition of air into the upper portion of the hood. Measurements of the composition of these gases allowed the computation of stoichiometries and heat release rates. These investigations showed that the species produced in the flame depend primarily on the stoichiometry of the gases present in the ceiling layer and weakly on the temperature of the layer, but are independent of the fuel-air ratio of the mass transported into the layer by the plume. Heat release rates in the fires were compared to a theoretical limit based on a stoichiometric reaction of fuel and air with excess components left unchanged by the combustion