Showing papers on "Autoignition temperature published in 1975"

A Mathematical Model for Hydrocarbon Autoignition at High Pressures

Abstract: We have developed a generalized mathematical model for the autoignition of hydrocarbons under the conditions of high pressure and temperature achieved in a rapid-compression machine. The model is able to simulate the essential phenomena of the two-stage autoignition of alkanes under these conditions; these are a well-defined cool flame that is often quenched rapidly and completely before the onset of a sharp ignition. It also pre­dicts correctly the transition to single-stage autoignition at even higher temperatures and the variation with temperature of the characteristic induction periods. The model is based on a degenerate-branched-chain mechanism. We show that it must contain as necessary features two termination processes, one linear and the other quadratic in radial concen­tration, and two routes for the formation of branching agent, one of which involves intermediate products of oxidation. The model also predicts, without any adjustment of the kinetic parameters, the essential pheno­mena of cool-flame and ignition behaviour that are observed at low pressures.

Thermal Theory of Metal Particle Ignition

Abstract: A set of equations of metal particles, oxidation kinetics, and thermal balance is considered. Critical conditions for ignition are investigated. It is shown that, in the general case, ignition is not necessarily connected with melting of oxide film and can occur as a result of self-accelera ting temperature increase by the thermal explosion mechanism. It is found when the Friedman-Macek theory is valid. Ignition of the titanium-nitrogen, aluminumoxygen, and tantalum-oxygen systems has been studied by heating a metallic wire with electrical current of constant power in a gas flow. The experiments permit checking the conclusions of the theory. I. Introduction A :CORDING to the ideas developed by Friedman and Macek, as well as by Mellor and Glassman,1'2 ignition of metal particles of aluminum type in gaseous oxidant occurs when an initial oxide film loses its protective properties, which usually takes place on melting. Heating of the particle up to the melting temperature of the oxide film T% is realized mainly at the cost of heat supplied from the outer source (hot gas) and partly as a result of self-heating from an oxidation reaction. Friedman and Macek have developed the theory of self-heating using the assumption that the rate of heat release depends on the temperature only. It has been shown that critical ignition temperature 7^crjt is close to T*, and the dependence of the T* — T0 crjt difference on the parameters was calculated. In the studies of the present author carried out together with B. I. Khaikin, V. N. Bloshenko, Yu. M. Grigorjev, Yu. A. Gal'chenko, A. P. Aldushin, and S. L. Khafatyan,3"8 a different and more general viewpoint was developed regarding the mechanism of metal ignition. The mathematical theory of the process was created and the theoretical conclusions were verified experimentally. This paper presents some results of these studies.

Summary of Ignition Properties of Jet Fuels and Other Aircraft Combustible Fluids

Abstract: : This report was prepared at the request of the Air Force to summarize the various ignition properties of jet fuels and other aircraft combustible fluids. The initial part is devoted to theory and definitions that are pertinent to ignition phenomena and the application of any experimental data. Other parts of this report summarize the various data that are available on ignition energies, ignition quenching distances and ignition temperatures of aircraft fuels, engine oils, hydraulic fluids and lubricants. Data are presented on the following types of ignition sources: Electrical sparks or arcs, frictional sparks, heated vessels or tubes, heated wires or rods, heated metal targets, jets of hot gases, shock wave and adiabatic compression, incendiary ammunition and self-heating. (Author)

Autoignition of Flowing Hydrogen-Air Mixtures

Abstract: A shock tube was used to determine the cause of autoignitions occurring at low temperatures in flowing hydrogen-air mixtures. For flow speeds above 750 m/sec, ignitions were observed at temperatures 400K below that established in static mixtures by the thermal explosion limit method. Gasdynamic processes which can produce high local static temperatures were absent. Therefore, the classical concept of "ignition temperature" does not seem to apply to these spontaneous ignitions. The onset of ignition has been experimentally correlated to the flow speed, the density in the boundary layer, the wall temperature, and the stagnation temperature of the flow. It has been concluded that the low temperature ignition originates in the boundary layer and is caused by friction induced ionization of the hydrogen molecule at the surface of the tube. When the boundary layer is turbulent, the low temperture ignitions do not occur.

Criteria of incipient combustion in coal mines

Abstract: The formation of carbon monoxide (CO) and other gases by various American coals was investigated to determine their relevance to spontaneous heating and to the problem of incipient fire detection. Desorption experiments under constant volume showed that ground samples of the coals yield CO/O 2 ratios that are essentially constant for extended exposure periods in air at 25°C and are highest for coals from mines suspected of having a self-heating hazard; the latter coals also yield high CO/CO 2 ratios. These ratios vary with particle size and surface moisture content and correlate best with the oxygen content of the coal, although the correlation was not always consistent with the absolute level of CO production. Similar experiments in an atmosphere containing the 18 O 2 isotope revealed that the O 2 reduction at ambient temperature is most likely due to chemisorption and the CO and CO 2 formation is attributable to decarbonylation, decarboxylation, or desorbed products from previous reaction of the coal in its virgin state. Results of flow experiments at various temperatures indicated that the CO/O 2 and CO/CO 2 ratios are highly sensitive to temperature. The temperature dependence of the rate of CO or CO 2 production between 50° and 150°C was approximately comparable to that derived from the adiabatic self-heating rate for each coal; apparent activation energies were between 10 and 20 kcal/mole. Below 50°C, the rate data were meager but supported the assumption that oxidation was not a significant factor at ambient temperature. The sensitivity and reliability of combustion product sensors as mine fire detectors were investigated with heated coal samples in flowing air. Submicron particulates appeared earlier than measurable CO emissions, suggesting that pyrolysis is a precursor to rapid oxidation. Data are presented to compare the autoignition temperature of the coal and the detection threshold temperature as functions of particle size of the coal.

Spontaneously Combustible Solids -- A Literature Search

Abstract: : Existing information on spontaneously combustible solids including pyrophoric-air hazardous materials and water reactive materials has been reviewed Pertinent data on (a) the causes and prevention of spontaneous combustion in organic and inorganic materials due to air and water reactivity, (b) the application of various mathematical treatments to spontaneously combustible materials, and (c) available test methods for assessing the flammable properties of spontaneously combustible materials, eg, autoignition temperature and spontaneous heating are also included (Author)

Determination of calorific value of fuel gas - involves feeding at least part of gas together with air to mixing device

Abstract: Fuel gas and air mixture leaving the mixing device is passed through a perforated brick impregnated with a catalyst and is heated above the ignition temperature, so that complete combustion of the mixture takes place. The calorific value is determined eithe rfrom the temperature of the combustion gases, or from the temperature change of the perforated brick or from the change of the heat output from the brick or from the change of its resistance. When the combustion gas temperature is measured, the perforated brick temperature and the air to fuel gas ratio are kept constant; when the perforated brick temperature change is measured, heat delivery from the brick and gas mixture are kept constant; when change of heat delivery by the brick is measured, its temperature and gas mixture are kept constant.

A study of liquid propellant autoignition

Abstract: Data and theory pertinent to the autoignition of liquid oxygen/liquid hydrogen and liquid oxygen propellants were reviewed. Physical models of the processes supporting or contributing to autoignition were developed. Emphasis was placed on the description of the physical environment and its relationship to the autoignition phenomenon.