External Ignition Research Articles

A simple model of ignition modes of dense droplet clouds

Multiphase combustion is of practical importance in many applications and has received growing interest in the last few decades. However, all the details of the mechanisms involved in this field of research are far from being fully understood. The aim of this work is to bring a new insight to the coupling between vaporization and ignition of a dense cloud of droplets. Therefore, a system of one-dimensional equations including source terms for the vaporization is solved numerically for a spherical cloud of fuel droplets in a hot, oxidizing atmosphere. The different cases investigated show two main ignition modes: internal homogeneous or external diffusion ignition. The analysis of the results proceeds in two steps: first, analytical expressions are derived for the temporal evolution of the cloud before ignition: second, the characteristic time of homogenous and diffusion ignition is estimated continuously during the vaporization process. This decomposition provides useful information about the dynamics of the phenomenon. The coupling between cooling and chenical reaction is explained on the basis of this decomposition. A classification of the ignition modes follows from this analysis, and an ignition diagram is proposed.

Effects of Sample and Test Variables on Electrical Wire Insulation Flammability

Abstract A new test method has been adopted to evaluate the flammability of electrical wire insulation materials. In this test, wire insulation is exposed to an external ignition source while the electrical conductor is internally heated by an electric current. The repeatability of the test and the effects of wire gage and insulation thickness, internal wire temperature, and sample orientation on the wire insulation flammability were evaluated. Experimental results showed that the new test is a practical and repeatable method for evaluating flammability of wire insulation materials.

Combustion Characteristics Of Several Flammable Gases With Chlorine Trifluoride

There are several flammable gases used in semiconductor industries, and some oxidizing gas such as chlorine trifluoride (ClF3) is also used in the same production apparatus. As knowledge of the combustion characteristics of flammable gases with oxidizing gases other than oxygen are lacking, an experimental study to evaluate combustion characteristics was performed. Chlorine trifluoride, the oxidizing gas used in this study was commercialized recently for etching and cleaning purposes because of its powerful oxidizing ability. As flammable gases, tetraethyl orthosilicate (TEOS: Si (OC2H5)4), hydrogen (H2) and ammonia (NH3) were investigated. These gases are toxic, except for hydrogen, and have high reactivity, so these gases were fist diluted with nitrogen separately. The diluted TEOS and ammonia gases were found to ignite spontaneously while being mixed with the diluted ClF3 gas. On the other hand, the diluted hydrogen gas could be mixed with the diluted ClF3 gas without spontaneous ignition. And a H2/ClF3/N2 mixture could be ignited by an electric spark. Therefore, for TEOS and ammonia, "flammable limit" means the limit of spontaneous combustion, and for hydrogen the flammable limit means the usual limit of ignitability by an external ignition source. The flammability diagrams of TEOS/ClF3/N2, NH [3/CW3/N2 and H2/ClF3/N2 mixtures were determined. And reaction kinetics between them were discussed from observed combustion characteristics.

Analysis of dropwise ignition versus external ignition for dilute multicomponent fuel sprays

An attempt has been made to identify conditions for dropwise ignition and spray ignition. Both pure as well as multicomponent fuels are considered. For dropwise ignition, an existing ignition criterion has been modified to account for the nonlinear dependence of reaction rate on fuel and oxygen concentrations and to account for the multicomponent nature of the fuel. The external or spray ignition is considered through the zero heat flux condition at the ignition source. The effect of chemical kinetics is examined by employing reaction schemes with unity as well as nonunity exponents of fuel and oxygen concentrations. Results indicate that for most of the conditions considered, the individual droplet ignition is favored over the external ignition. Only when the drop diameter is smaller than 30 μm does the spray ignite earlier than droplets. The addition of a small amount of a volatile component significantly enhances the ignitability of both modes. However, the effect is stronger for the dropwise ignition mode.

Fabrication of Titanium Carbide‐Alumina Composites by Combustion Synthesis and Subsequent Dynamic Consolidation

Dispersed‐phase composites of TiC‐Al2O3 were fabricated from low‐cost reactants by external ignition of powder compacts followed by dynamic consolidation of the hot products using explosives. Near full densification was achieved using shock pressures as low as 1 GPa. Care must be taken to allow for the escape of evoled gases during exothermic reaction, and rapid cooling of the consolidated composite must be avoided to prevent cracking.

4678726 Multicell electric storage battery with combined means for wastegas drying and flame-protection

In a multicell electric storage battery designed for central gas release, before being released into the open air the battery gases pass through a container positioned on the block casing in which the acid particles and moisture are separated from the gases as a consequence of the gases being repeatedly deflected by a series of walls placed in the path of the gases, which may be perforated if desired, and the dehumidified gases are then passed through a porous flame-protection frit. Flashback of a flame caused by external ignition of the gases is prevented by rapid burn-off of the gases in a flame extinguishing chamber preceding the frit.

A Relationship between the Flash Point, Boiling Point and the Lean Limit of Flammability of Liquid Fuels

The premise: of this paper is that a flame would flash over the surface of a liquid fuel, upon subjecting to Ian external ignition source, only if the (fuel vapor+air) mixture in gas phase contains...

Investigation of the laws of ignition of titanium powders

The study of the ignition characteristics of powders of the refractory transition metals is of scientific and practical importance. It is of interest to investigate the effect on the ignition process of such parameters as the composition of the gaseous oxidizer, the heat transfer conditions, the specimen dimensions, and the grade of metal powder. The article is devoted to the question of the ignition of transition metal powders, with titanium serving as an example. On the basis of the experimental data, several conclusions may be drawn. First, it was found that nitrogen has a chemical effect on the ignition of titanium powder in air only in the presence of an oxygen deficit. Second, a gas flow has a significant effect on the critical ignition temperature, reducing it at low and increasing it at high gas flow rates. It was further found that the titanium powder ignition process can develop in the autoignition and external ignition regimes. Generally good agreement was found between the theoretical and experimental values of the critical ignition temperature for titanium powder.

The group combustion of a spherical cloud of monodisperse fuel droplets

The vaporization and combustion of a spherical, uniform monodisperse cloud of fuel drops in equilibrium with a quiescent atmosphere is considered. For typical fuel sprays in which the drops are separated by five to ten drop diameters only the droplets within a thin inwardly propagating vaporization wave at the edge of the cloud will vaporize. In analogy with single drop theory the cloud radius is found to decrease acording to a “ d 2 law,” although with a modified vaporization constant for both purely vaporizing and burning clouds. The cloud interior in all cases remains in saturated, non vaporizing equilibrium at a temperature determined by ambient conditions. Burning occurs at a spherical diffusion flame front outside the cloud. The flame radius to cloud radius ratio is found to be constant and independent of the cloud radius and the droplet radius and number density within the cloud. An external ignition temperature is determined by considering the bifurcation of steady state solutions for single step, irreversible Arrhenius kinetics. At ignition the cloud interior reaches a new equilibrium which is still too cool and rich for single drop ignition. Under conditions of the present analysis a fuel cloud, if it burns at all, will do so with an external diffusion flame.

Differences between determinations of maximum experimental safe gap in Europe and U.S.A.

The Westerberg apparatus is used by Underwriters Labs (USA) for the determination of Maximum Experimental Safe Gap (MESG). The results are smaller than The difference is explained by the small receptor vessel in the Westerberg apparatus, which means that the external ignition takes place in a hot vitia European value, external ignition was probably the result of spontaneous ignition in the vitiated atmosphere.

Neue aspekte der Gerätetechnik und der Methodik zur Laser-mikro-emissionsanalyse

Introduction of variable solid state laser Q-switching, special microscope optics, and triggering of the auxiliary spark excitation by external ignition extends the fields of application and the capabilities of the method. Stable energy output and appropriate sample preparation improve the possibilities of quantitative micro-spectrochemioal analysis using lasers.