Showing papers on "Autoignition temperature published in 1983"

Comparative studies of methane and propane as fuels for spark ignition and compression ignition engines

Abstract: The paper reviews the combustion characteristics of the two fuels and sets out to consider their respective performance in both spark ignition and compression ignition engines Results of comparative tests involving spark ignition engines over a wide range of operating conditions are presented and discussed Some of the performance characteristics considered are those relating to power output, efficiency, tendency to knock, cyclic variations, optimum spark requirements and exhaust emissions Similarly, some of the performance characteristics in compression ignition engines considered include power output, efficiency, tendency towards knock and autoignition, exhaust emissions and low operational temperature problems Finally, the relative operational safety aspects of the two fuels are evaluated It is then suggested that in this regard, methane has some excellent physical, chemical and combustion characteristics that makes it a particularly safe fuel

Thermal and catalytic regeneration of diesel particulate traps

Abstract: Thermal and catalytic techniques for regenerating particulate traps were assessed. The thermal technique used a burner which heated engine exhaust to the ignition temperature of the particulates to achieve over 90% regeneration effectiveness. HC, CO and particulate emissions resulting from combustion of particulates and burner exhaust were 25 to 50% of the allowable vehicle emissions for one CVS cycle. The fuel consumed by the burner was 9% of the fuel consumed by a vehicle over one CVS cycle. Problems with burner nozzle clogging, ignition reliability, trap durability and control system requirements were identified. In the catalytic technique, diesel fuel containing .5 gm/gal lead and .25 gm/gal copper lowered the ignition temperature of the particulates by 425 deg F so that periodic regeneration occurred. The trap collected nearly all of the lead and copper resulting in limited trap life, and deposits on the engine fuel nozzles tended to increase HC emissions.

Catalyst for reducing the ignition temperature of diesel soot

Abstract: A process and catalyst is disclosed for the reduction of the ignition temperature of diesel soot filtered out of the exhaust fumes of diesel engines by passing the exhaust stream through a filter element. The filter element is a temperature resistant inert support onto which is deposited a catalytically effective amount of silver vanadate or a mixture of the temperature resistant carrier material and a catalytically effective amount of silver vanadate.

Analysis of Hydrocarbon Emissions From Conventional Spark-Ignition Engines

Abstract: The quench layer on the cylinder wall of a spark-ignition engine is modeled for the case where a tangential or swirl velocity exists. Both asymptotic and numerical methods of solution are used, The usual two-layer structure is employed for the turbulent boundary layer and Crocco's integral is used to relate the temperature and velocity fields. The quench layer is defined as the region in which the temperature is less than an ignition temperature. In the first analysis only quenching is considered, and it is shown that the resulting concentration of hydrocarbons is much too high compared to experimental results. Next, the model is extended to allow diffusion, and it is shown that in one stroke time the majority of the mass of unburned mixture in the original quench layer has diffused out and burned. Finally, two means of replenishing the unburned mixture in the quench layer. consisting of the desorbing of fuel from the oil film and outgassing from the first ring crevice, are included in the model....

Fuel burning stove

Abstract: A stove to burn solid fuels, said stove comprising a combustion chamber with a front (13) with a fuel charging aperture (14) therein and a door (3) with a transparent viewing panel (33) therein mounted over the aperture (14), a baffle (15) dividing the interior of the combustion chamber into a primary combustion zone (A) and a secondary combustion zone (B), a closeable port (16) in the baffle (15) connecting the primary and secondary combustion zones, a combustion gas discharge port (17) to atmosphere from the secondary combustion zone, a gas screen (24) in the gas path between the primary and secondary combustion zones, the gas screen being constructed from materials that will glow at a temperature below the ignition temperature of combustion gases, primary and secondary combustion air inlets (22 and 30) discharging into the combustion zone adjacent a top edge of the door panel (33) and the gas screen (24) respectively, manually resettable temperature actuated flow control means (34) regulating the amount of primary combustion air entering the combustion chamber.

Ignition of poly(methyl methacrylate) slabs using a small flame

Abstract: When exposed to a lean hydrogen-oxygen flat flame, slabs of poly(methyl methacrylate) ignited to flaming combustion after a delay, the length of which depended on the gas temperature and the separation between the slab and the igniting flame. The delay obeyed an Arrhenius-type expression, giving an activation energy of 96 ± 8 kJ mol−1. By the end of the delay the surface of the sample was pitted if the delay was long and almost unchanged if the delay was short. The rates of flame development measured immediately after the ignition were proportional to the ignition delay, the proportionality constant varying with the separation between slab and flame. These rates decreased as temperature increased; the slope of the linear Arrhenius plots was independent of slab-flame separation. During the delay, carbon dioxide was formed within the boundry layer and a blue preignition glow was visible at its outer edge. These data were explained by a model in which ignition delay is governed by the induction period of gas-phase reactions in or near the boundry layer. Models in which delay is governed by the time taken to heat the polymer to a critical ignition temperature did not satisfactorily explain the data.

Autoignition in a premixing-prevaporizing fuel duct using 3 different fuel injection systems at inlet air temperatures to 1250 K

Abstract: Conditions were determined in a continuous-flow, premixing-prevaporizing duct at which autoignition occurred. Test conditions were representative of an advanced, regenerative-cycle, automotive gas turbine. The test conditions inlet air temperatures from 600 to 1250 K (a vitiated preheater was used), pressures from 170 to 600 kPa, air velocities of 10 to 30 m/sec, equivalence ratios from 0.3 to 1.0, mixing lengths from 10 to 60 cm, and residence times of 2 to 100 ms. The fuel was diesel number 2. The duct was insulated and had an inside diameter of 12 cm. Three different fuel injection systems were used: One was a single simplex pressure atomizer, and the other two were multiple-source injectors. The data obtained with the simplex and one of the multiple-source injectors agreed satisfactorily with the references and correlated with an Arrenhius expression. The data obtained with the other multiple source injector, which used multiple cones to improve the fuel-air distribution, did not correlate well with residence time.

Chemical kinetics modeling of engine knock: preliminary results

Abstract: A theoretical model, including a detailed kinetic mechanism for propane oxidation, is used to examine the ignition of propane-air mixtures under conditions of pressure and temperature encountered in knocking engines. Purely kinetic calculations are used to evaluate relative time scales for the fuel-air ignition process, varying the initial pressure, temperature, and fuel-air equivalence ratio. A one dimensional model is then used to examine the combined effects of flame propagation, homogeneous ignition, and wall heat transfer on the autoignition of these mixtures. For the temperatures and pressures of concern in this study, it is found that the reaction mechanism is controlled by reactions of the hydroperoxyl radical, in contrast with similar mechanisms at higher temperatures and lower pressures. The time scales computed indicate that, in agreement with experimental evidence, propane-air ignition delay times are slightly longer than the relevant residence times in the end gases of a practical engine and that propane-air mixtures will therefore be quite resistant to knock. Extensions of the kinetic model to larger hydrocarbon fuel molecules which are more likely to knock, and to lower temperatures are discussed.

Multiphase combustion experimentation in microgravity

Abstract: This paper examines the need for and implementation of microgravity combustion studies of two phase media. Experimental and analytical aspects of several heterogeneous kinetic systems are discussed. These include: flame propagation and extinction for quiescent clouds of uniformly premixed fuel particulates in an oxidizing atmosphere; autoignition of clouds of uniformly premixed fuel particulates in a quiescent oxidizing atmosphere; and the roles of catalytically significant surfaces in gaseous autoignition processes.

Computer study of the constant pressure auto-ignition of mixtures of ethane, methane, carbon monoxide and hydrogen in air

Abstract: The autoignition of mixtures of ethane, methane, carbon monoxide and hydrogen in air at atmospheric pressure was studied theoretically using a detailed, free-radical, kinetic model. The elementary reactions for the model were chosen with the help of the sensitivity analysis of Rabitz et al., which utilizes a Green's function transformation. This technique was particularly helpful in identifying those reactions which are important during the induction period prior to ignition. The effects of equivalence ratio, initial temperature and constant rate of heating were investigated for various fuel compositions. Induction times from 10 microns to 11.5 microsec were calculated for adiabatic ignition with initial temperatures from 1300 to 2100 K. Mixtures of pure methane and air were found to have long induction times, but small additions of ethane and even lesser additions of hydrogen, produced dramatic reductions. The flamefront was broadened significantly by large initial concentrations of carbon monoxide, due to its relatively slow rate of oxidation even at high temperature. 11 references.

Apparatus for determining the carbon content of ash

Abstract: The invention relates to an apparatus for determining the unburnt carbon content of the ash in a combustion apparatus and comprises a down-tube which is electrically heated to at least the ignition temperature of the combustion, which down-tube has at the upper end a feed for a metered amount of air per unit time and for a metered amount of ash and which is connected at the lower end to a CO2 measuring apparatus.

Thermal and electrical ignitability of dust clouds. Report of investigations

Abstract: The Bureau of Mines conducted a comprehensive laboratory study of the thermal ignitability of various carbonaceous dust clouds with particular emphasis on various ranks of coal dust. The tests were conducted using a new 1.2-L furnace. Autoignition temperatures of dust clouds were obtained as a function of coal volatility and particle size. Dust particles and gas samples were collected by a rapid-sampling system in order to study the reactions involved in preignition and postignition processes. The autoignition temperatures measured in the new 1.2-L furnace were significantly lower and therefore more conservative than those measured previously in the Godbert-Greenwald furnace.

Ignition of high ash coal particles

Abstract: This article examines the combustion kinetics of high ash coals in oxidizing media. Microcine photographs of individual coal particles were taken inside a quartz microfurnace tube, with a weak oxygen flow supplied. The photographs and the physicochemical characteristics of the coals indicate that both the ash content of the fuel and the ratio of the thermal equilibrium loss temperature and the ash fusion point determine the differences in ignition. The porous mineral residue has no practical effect on the interaction between carbon and oxidizer for coals with a low ash content or fusible ash. Two limiting ignition mechanisms, thermal and thermokinetic, are identified. It is demonstrated that for coals of various brands, the ignition mechanism is determined primarily by the coal ash content and the ratio of the critical dispersed system ignition temperature to the fusion point of the fuel mineral component.

Burner for pulverulent, gaseous and/or liquid fuels

Abstract: The burner for pulverulent, gaseous and/or liquid fuels has an ignition chamber (20) with a wall (8) which opens out and having the rotation symmetry, as well as an exhaust pipe (17, 17') connected thereto. At the center of the chamber wall, there is arranged the inlet of a pipe (1) for the admission of a fuel jet (A) as well as an air supply (50) surrounding said inlet, for the admission of a vortex of combustion air which produces inside the ignition chamber a hot recirculation stream (B) mixing the fuel jet and heating the latter at the ignition temperature. The air quantity of the vortex supplied to the ignition chamber is only a portion of the total combustion air required. In the area between the chamber wall and the exhaust pipe there is provided a second air admission pipe (60) through which another portion of the combustion air (C) may be introduced in the ignition chamber, said portion being totally or partially mixed with the fuel jet. The sum of the combustion air portions participating within the ignition chamber to the mixture with the fuel jet (and hence to the ignition and initiation of the combustion) is adjusted so as not to exceed 50 % of the total combustion air required. By conjugating all those measures, there is provided a burner particularly appropriate for the production of heat for industrial process and further having at intermediary and variable power rates a stable ignition producing a flame with an elongate and thin form in the combustion chamber and thus with a low radial deflection of particles.

High-pressure flame visualization of autoignition and flashback phenomena with liquid-fuel spray

Abstract: A study was undertaken to determine the effect of boundary layers on autoignition and flashback for premixed Jet-A fuel in a unique high-pressure windowed test facility. A plate was placed in the center of the fuel-air stream to establish a boundary layer. Four experimental configurations were tested: a 24.5-cm-long plate with either a pointed leading edge, a rounded edge or an edge with a 0.317-cm step, or the duct without the plate. Experiments at an equivalence ratio ranging from 0.4 to 0.9 were performed at pressures to 2500 kPa (25 atm.) at temperatures of 600, 645, and 700 K and velocities to 115 meters per second. Flame shapes were observed during flashback and autoignition using high speed cinematography. Flashback and autoignition limits were determined.

Coupling of Transport and Chemical Processes in Catalytic Combustion

Abstract: Catalytic combustors have demonstrated the ability to operate efficiently over a much wider range of fuel air ratios than are imposed by the flammability limits of conventional combustors. Extensive commercial use however needs the following: (1) the design of a catalyst with low ignition temperature and high temperature stability, (2) reducing fatigue due to thermal stresses during transient operation, and (3) the development of mathematical models that can be used as design optimization tools to isolate promising operating ranges for the numerous operating parameters. The current program of research involves the development of a two dimensional transient catalytic combustion model and the development of a new catalyst with low temperature light-off and high temperature stablity characteristics.

Catalytic combustion system with fiber matrix burner

Abstract: A combustion system which includes a catalytic burner of a fiber matrix composition for combusting an air-fuel mixture with high efficiency and low NOX emissions. The burner matrix is comprised of high temperature resistant fibers randomly oriented and packed together to form interstitial spaces for the mixture flow path. The thickness of the matrix and density of the fibers are within an optimum range for maintaining combustion in a shallow heterogeneous reaction zone at a temperature below the use temperature of the fiber by radiating heat transfer from the zone. The matrix forms a heat insulation barrier to maintain the matrix temperature at the inlet side below the ignition temperature of the mixture for preventing flashback. Strands of a catalytic material can be interspersed through the matrix. The matrix can be in the form of a hollow cylindrical shell for use within the combustion chamber of a firetube boiler system.

Estimation of the minimum energy of ignition of a layer of metal particles ignited by an instantaneous source

Abstract: The authors of this paper propose an approximate method of calculating one of the commonest measures of fire and explosion risk encountered in safety engineering practice: the minimum ignition energy of a layer of gaseous suspension of metal particles. This determination is also associated with the estimation of the critical mass particle concentration, above which, for a given value of the igniting pulse, the particle system ignites. It should be noted that it is correct to speak of the existence of three types of ignition concentration limits, associated with the autoignition of the system, the propagation of a flame, and focal ignition. Whereas in the first two cases the concentration limits are associated with the relation between the heat supplied by the exothermic oxidation reaction and the reaction's external heat losses, in the latter case the concentration limit also depends on the intensity of the igniting pulse.

Spontaneous combustion and ignition of metals in an oxidizing atmosphere

Abstract: This paper considers the problem of spontaneous combustion of a body located in contact with an oxygen medium at temperature T /SUB o/. The possibility of a stationary solution to a given equation is studied. A special case of this problem under study is that of ignition of an instantaneously heated specimen or instantaneous insertion of a heated specimen into an oxidizer. The ignition of a solid object by a thermal pulse is considered, and the problem which it presents solved by the finite difference method as shown. A table presents the results of calculating ignition temperature by the method of the present study, and also by use of ignition criteria for various values of dimensionless thermal flux as given in equation. It is found that the rate of change of temperature and ignition energy decreases with increase in source intensity.