Showing papers on "Autoignition temperature published in 1971"

Radiative ignition of polymeric materials in oxygen/nitrogen mixtures

Abstract: The radiative ignition behavior of two polymeric fuels—polystyrene and an epoxy—in oxygen/nitrogen mixtures has been determined experimentally. A CO2 laser was adapted for use as the radiation source to simplify interpretation of the results. Ignition delay (as determined by first light emission) was measured as a function of oxygen percentage, pressure, radiant flux, and fuel absorptivity. The observed ignition delays, and the variations with pressure, oxygen fraction, and radiation intensity, conform to the predictions of a theoretical model based on the need to heat the surface to a critical ignition temperature. The most important finding is that ignition of a solid fuel by radiation is much slower than ignition by an identical heat flux applied by a hot gas source. Two main reasons for the retardation can be deduced from the experimental results: (1) the radiative transparency of the fuel, even for seemingly opaque substances, results in slower surface heating, and (2) the cool gas environment in the usual radiation ignition test suppresses the incipient ignition.

Ignition Temperatures of Metals in Oxygen Atmospheres

Abstract: The ignition temperature of ten common non-toxic metals has been determined experimentally in an oxygen environment. In this investigation a induction furnace facility that emphasized the preignition surface.oxidation effects upon the ignition temperature was used. The bulk ignition temperatures of barium, bismuth, calcium, iron, lead, magnesium, molybdenum, strontium, tin, and zinc were found and compared to the previous results of Grosse and Conway. The differences in the results are attributed to how the heating cycle is carried out and how the cycle affects the surface oxide coat.

Ignition Characteristics of a Stagnation Point Combustible Mixture

Abstract: A study was made of the ignition characteristics of a cold combustible mixture at the forward stagnation region of a flat plate. The boundary layer equations describing the reacting flow have been solved numerically for the case of Le = 1. The Van't Hoff's ignition condition has been used to calculate the ignition temperature as an eigenvalue of the problem. The effects of the First Damkohler number, inert gas concentration, temperature of the mixture, and activation energy were investigated. A critical First Damkohler number was found beyond which no ignition is possible.

Mechanisms of ignition of thermally irradiated cellulose

Abstract: The experimentally determined dependence of spontaneous ignition of radiantly heated cellulose on atmospheric variables is presented and compared with calculated responses based on an idealized model of thermal autoignition in the gas phase. The atmospheric variables are: total pressure (subatmospheric to 4 atm), oxygen concentration (pure diluent to pure oxygen), and diluent replacement (helium and carbon dioxide substituted for nitrogen). As both total pressure and oxygen concentration are increased from their ignition-limiting values (e.g., air at 0.15 atm pressure and 16% oxygen in nitrogen-oxygen mixtures at 1 atm), the times required for ignition fall monotonically from large values (relative to ignition time in air) to values that are substantially less than ignition times in air. The effect of diluent changes is similarly profound. These data render untenable previously reported speculation regarding initiation by the sudden appearance of active species among the pyrolysis products. They are shown to be consistent with the classical processes of thermal autoignition. A simplified model incorporating these processes has been developed. Details of the model and results obtained with it are reported.

Combustion of liquid hydrocarbons in a high-speed airstream

Abstract: A theoretical formulation and experimental results of the high-speed mixing, ignition, and combustion characteristics of liquid fuels injected directly into a high-velocity airstream are presented. Experiments were performed in a direct connect constant area combustor supplied by a Mach 2 air stream at a static pressure level of 1 atmosphere and at total temperatures ranging from ambient (530°R) to approximately 3300°R. The fuel was liquid hexane and was injected laterally into the supersonic flow through piloted and nonpiloted injector configurations. It was found that autoignition and stable combustion occurs for air total temperatures above about 2600°R. Furthermore, the liquid fuel was effectively ignited and burned stably below this autoignition level by employing a small reacting pilot j et. Minimum pilot size and energy requirements were then established. It was found that the pilot mass flows needed for ignition and sustained combustion were small compared to the main fuel and air flow rates. Comparison with theory indicates combustion efficiencies up to 93% were obtained.

Incineration process and unfired afterburner apparatus

Abstract: Process for achieving complete and relatively inexpensive combustion of solid, semiliquid, and liquid combustible waste materials, and combinations thereof, having low heat value, by incompletely burning a combination of such materials in a first furnace to produce a combustible gaseous exhaust stream, achieving complete combustion in a second furnace of combustible high heat value waste materials to produce a noncombustible gaseous stream, intimately admixing the two streams in an unfired afterburner, without the addition of heat from an auxiliary heat source, while maintaining a minimum admixture temperature above the temperature required for autoignition of the combustibles in the first stream, whereby the heat produced by combustion of the high heat value waste materials is utilized for the spontaneous ignition and complete combustion of the incompletely burned materials. Liquid wastes of high heat value and of low heat value are separately stored, and are variously blended for feed to the first furnace and the second furnace in accordance with the heat requirements of the system to achieve complete combustion of all wastes being burned. The apparatus particularly adapted to perform the process comprises a pair of furnaces, a refractorylined afterburner chamber having no auxiliary heat source, duct means interconnecting said afterburner chamber and each of said furnaces, and exhaust means defined by said afterburner for permitting exhaust of the burned gas stream after combustion is completed. The apparatus preferably includes appropriate draft handling, gas cooling, and particle removal means to render the gaseous atmospheric discharge relatively pollution-free.

Method for the ignition of in-situ combustion for the recovery of petroleum

Abstract: A method of initiating in situ combustion in a subterranean hydrocarbon-bearing formation wherein a substance capable of reacting with hydrogen peroxide is introduced into the formation via a well bore and thereafter a mixture of hydrogen peroxide containing from 10 to 20 percent by weight of water is injected to effect an exothermic reaction thereby to increase the temperature of the formation adjacent the well bore to the ignition temperature of the hydrocarbons contained therein and resulting in ignition of those hydrocarbons and the initiation of an in situ combustion.

Ignition of Aircraft Fluids by Hot Surfaces under Dynamic Conditions

Abstract: : Data are presented on the ignition characteristics of various aircraft fluids under conditions in which they impinge upon a hot surface in the presence of air flow similar to that possible in an aircraft enclosure. The fluids included two jet fuels (JP-4 and JP-8), two hydraulic fluids (MIL-H-5606 and MIL-H-83282), and an engine oil (MIL-L-7808). Generally, the ignition temperatures decreased with an increase in target diameter or surface area and increased with increasing air velocity. At all test conditions, the ignition temperatures of the fluids were noticeably highr than their minimum autoignition temperatures which are determined in uniformly heated vessels.

Effect of viscosity on the autoignition of a reacting moving mixture

Abstract: Ya. B. Zel'dovich has established [1] that in a continuous-flow reactor two ignition regimes are possible: forced ignition and autoignition.

Chemical Aspects of the Shock Initiation of Fuel Droplets.

Abstract: : A study was conducted of the shock initiation of droplets of five fuels in an oxygen atmosphere. The fuels were ethyl nitrate, propyl nitrate, nitromethane, butyl alcohol, and nitrobenzene. Only the two nitrates ignited. They also were observed to ignite in shocked argon. Their behavior is explained on the basis of their weak bonds and their ability to behave as monopropellants. Schlieren photographs showed that autoignition occurred in the wake of the droplet, and that the flame front expanded rapidly and induced a strong blast wave. The trajectories of the flame fronts and blast waves of the burning nitrate droplets were plotted, and empirical expressions were found. (Author)

Ignition temperature of gases and vapors as applied to electrical equipment for use in hazardous locations

Abstract: In order to design electrical equipment which is safe for use in flammable atmospheres, it is necessary to know the ignition temperature of the flammable atmospheres. The test methods for determining ignition temperature are presented and compared with the possible sources in an electrical system.

Gas-phase autoignition regime in the combustion of pyroxylin and n powder

Abstract: 1. The results of measurements of the temperature profile in the gas phase at different pressures and initial temperatures confirm that for burning pyroxylin and N powder the gas-phase reaction proceeds in the autoignition regime. 2. A method is proposed for determining the effective kinetic constants (activation energy and preexponential) of gas-phase reactions in the autoignition regime. The following values have been obtained: for pyroxylin (P=30–40 atm gauge) k0=106 sec−1, E=20 kcal/mole; for N powder (P=20 atm) k0=107 sec−1, E=45 kcal/mole. 3. It has been shown for pyroxylin and N powder that the gas-phase process cannot be shifted from the autoignition to the combustion regime by varying the initial temperature. At negative initial temperatures an increase in the role of the gas-phase reactions has been detected. 4. Owing to the large values of the parameters β and γ for pyroxylin and N powder there is no sharp boundary between one regime and the other for these substances.

Ignition Temperature vs Droplet Size for Hydrazine and Pentaborane in Air

Abstract: Content In the mathematical model, a spherical, liquid fuel droplet is assumed to be in velocity equilibrium with its gaseous environment, while its interior is uniformly at its boiling point for the environmental pressure (1 atm herein). A pseudosteady state prevails; the radius of the droplet (rs) is held constant in an energy balance and fuel and oxidizer mass balances, which include chemical reaction at finite, temperature-dependent rates, radial convection of energy or fuel mass resulting from evaporation at the surface, and thermal diffusion from the environment or mass diffusion due to concentration gradients. Energy transport due to diffusive mass transfer, and mass diffusion due to the temperature gradient, are neglected. The model is limited by specification of a constant density and a Lewis number of unity. Using the method of Schvab and Zeldovitch to describe boundary conditions at the surface, expressions can be written for temperature, oxidizer concentration, and the dimensionless fuel mass burning rate, a = (burning velocity) (radius) /(diffusivity). This system of equations constitutes a two-point boundary value problem for fuel mass fraction XF, with a as an eigenvalue. For prescribed boundary conditions and physical properties of the fuel-oxidizer system, conditions at the droplet surface are computed for an assumed value of a, then a dimensionless fuel mass balance is integrated numerically outward from the droplet surface to some designated, large distance where an arbitrarily small XF will be reached. Calculations for hydrocarbon fuels1-2 demonstrated that the curve for a vs environmental temperature Tm is S-shaped. Ignition due to diffusive heating is defined as the point where a discontinuity is observed in the mathematical model at the lower knee of the £-curve (i.e., two values of a both satisfy the boundary conditions). A second or reverse knee at lower Tm corresponds to the process of extinction. Diffusion-controlled combustion on the upper branch of the curve ceases, and a discrete decrease in a takes place, with a decrease in Tm, at this point.