Ignition and Fire Development Caused by Leaking Fuels onto Heated Surfaces (original) (raw)
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Flame spread on aviation fuels
Fire Safety Journal, 1997
Flame spread rates and flame spread induction times have been measured for JP-5, JP-8 and mixtures of these fuels over the temperature range 10-90°C. The flame spread data were correlated on the basis of the initial liquid temperature relative to the closed cup flashpoint. Liquid-phase-controlled flame spread is observed for liquid temperatures <15°C above the closed cup flashpoint and the flame spread rate ranges from 3 to 12 cm/s depending on the liquid temperature relative to the flashpoint. For liquid temperatures > 15°C above the closed cup flashpoint, flame spread is via gas-phase-controlled flame spread and flame spread rates range from 12 to 160 cm/s. The transition at V = 12 cm/s and the maximum flame spread rate are consistent with present knowledge of gas-phase flame spread and burning velocities. Differences between the present data and other available data from the literature are the result of differences in flashpoint interpretation for hydrocarbons versus alcohols and the use of very narrow flame spread pans by early investigators. The use of pans of only 1-6 cm causes large changes in flame spread rate with temperature which are not observed in wider pans. Therefore the use of narrow tray flame spread experiments gives an incorrect indication of the flame spread rate to be expected in large-scale (realistic) conditions. Pan widths of at least 20 cm are required to avoid these small-pan-width effects. Variations in the flashpoint of mixtures of JP fuels were successfully predicted using the method of Affens and McLaren by treating each JP fuel as a single fuel characterized by a single vapour pressuretemperature relation and assuming that mole fractions in the liquid phase may be approximated by the volume fraction of the JP fuel. Flame spread induction times were shown to be a function of the liquid * Author to whom all correspondence should be addressed. D. White et al. temperature relative to the closed cup flashpoint. The induction time was also shown to be dependent on the strength and nature of the ignition source. ~ 1997 Elsevier Science Ltd.
Journal of Energy Conservation
Critical conditions are usually obtained for ignition in a self-heating solid system consisting of two components generating heat independently, one component being inexhaustible and the other exhaustible by either simple first order or autocatalytic reaction. Ignition depends upon whether the exhaustible component can cause a temperature rise in excess of the upper stationary, but unstable, value possible for the inexhaustible component reacting alone. The system provides a theoretical model for some commonly occurring examples of self-heating and ignition in porous solids containing oxidisable oils. It is shown that: (a) the ignition criterion of the model, which involves a nonarbitrary critical temperature increase, has a high degree of physical reality; (b) the model is, in principle, capable of predicting ignition from primary kinetic and thermal data; (c) it is likely to be possible often to make a reliable prediction of critical size for self-ignition in a two-component syste...
Revue Roumaine de Chimie
Computed burning velocities of C2H6-air, C2H4-air and C2H2-air stoichiometric flames with variable initial pressure and temperature obtained by a detailed numerical modeling are compared to those measured or previously reported burning velocities obtained from transient pressure-time records during explosions in spherical vessels with central ignition. Correlations in the form of S-u/S-u.ref = (p/pref)(v)(T-u/T-u,T-ref)(mu)describe well the burning velocity dependence on pressure and temperature of all mixtures, for both experimental and computed data. The bane coefficient, v, was further used for calculation of the overall reaction order, n, found to vary within 1.3 and 1.8 for the examined hydrocarbons. The burning velocity dependence on the average flame temperature was used to calculate the overall activation energy of the oxidation, E-a,specific for each flame. The change of flame initial conditions (pressure and temperature) was found to determine important changes of the flam...
Kerosene Ignition and Combustion: An experimental and modelling study
The ignition delay time of two JET-A samples obtained at random at two locations (Haifa and Stuttgart) have been investigated in parallel, by two groups of researchers. The experiments carried out in two different shock tube devices covered a temperature range of 1100 to 1900 K at pressures between 2.4 and 6 bar. The four sets of experiments consisting of almost 400 shocks are analyzed, statistically evaluated, and compared with ignition delay experiments for decane. Computer simulation of two surrogate fuel models (i) pure n-decane, (ii) a mixture of 70% n-decane, 30% propylbenzene, are compared to the experimental data. It was found that all measured ignition delay time data can be represented by a single statistical fit. Furthermore, predictions by using pure n-decane as the surrogate fuel match the statistical fit obtained for all the experiments, and explicitly the Stuttgart experiments. A. Introduction Kerosene is the main fuel for all aircrafts, civil and military. Kerosene is a complex fuel containing about 180 individual chemicals. Furthermore, their concentrations and identity change not only according to the source of the fuel, but also according to the refinery where the fuel was distilled. However, in order to cope with the demands of international civil and military aviation, kerosene is the only fuel produced under very strict physical standards defined as Jet-A, Jet A1 and for American Military as JP-4, JP5 etc. (Ranges of boiling point, freezing point, viscosity, polarity, minimum ignition temperature etc. are defined). The chemical composition is not a part of these standards. The physical standards take care of the transport and flow of the jet fuel in the jet aircraft, but the combustion is a function of the chemical components of the fuel. In Fig 1 we present schematically a jet engine combustor. The compressed air at 600 K is flown together with a spray of fuel. The spray vaporizes at very high velocity, within a short time to the gas phase where it is combusted. This information is trivial for aeronautical engineers, but chemists and mechanical engineers have only recently addressed to it [34]. The understanding of how fuels burn and having a computer simulator for the way they release energy is a very important tool in the hands of designers of car and jet engines, rocket engines etc. Without these tools, pollution reduction and increase of efficiencies is problematic. The facts of the real combustion devices are usually not taken into account. Fig 1. Schematic diagram of a jet engine combustion chamber. 400% air flows into the engine at high altitude. The air is compressed aerodynamically by the compressor and its temperature reaches 600 K. 300% of the air flows around the combustion chamber for cooling purposes. Only 100% of the needed air for full combustion of the kerosene enters the combustion chamber at different stages. 12% enter primarily with the fuel spray and causes it to heat and start to evaporate. The droplets travel at high speed and have to fully evaporate before the end of the combustion zone. Droplets that manage to go out of the combustion chamber will hit the turbine and damage it.
On the Thermal Ignition of Combustible Materials
Formulas are derived for the time to achieve the ignition temperature as a function of the incident heat flux and the various thermophysical material parameters for thermally thick, thermally thin and thermally intermediate solid combustibles. Predictions are compared with recent experimental data for various natural wood species and wood products, and to previous data for wood and thermoplastics. The correlations are excellent when (1) the physical parameters used as the axes of the plots are chosen consistent with those of the theoretical formulas and (2) the experiments and the materials do not violate any of the restrictions imposed by the theory. From these plots it is easy to estimate the minimum heat flux for ignition, which is of great importance both in practice and for making theoretical predictions.
The role of liquid-fuel vaporization and oxygen diffusion in lagging fires
1998
Experimental and numerical studies have been performed to establish how liquid and vapor distributions of flammable liquids within an insulation matrix and that of residual oxygen may affect the propensity for spontaneous ignition to occur when the insulation is exposed to elevated external temperatures.
The principal investigators directing this effort were Professors Irvin Glassman, William A. Sirignano and Martin summerfield. The overall program was divided into three major parts: flame spreading across liquid pools, ignition of pools, and a theoretical effort on flame spreading and projectile ignition. As a matter of administrative convenience to the sponsoring agency, a small study on ignition of solid propellants directed by Professor Summerfield was added to the program under the same contract. Considering the scope of the effort, it was deemed most logical to write this report in four separate parts which would inclbde each of the major aspects of the flame study and the solid propellant study. Each part is written as if it were a separate document and includes its own table of contents, text, references and figures. Co-authors who have contributed to the program are listed at the beginning of each part. Following the accepted practice for research, the feedback of information from the experiments to the model showed that there were *A 3.6 mm thick layer of kerosene was floated on a 15.3 mm layer of water in an aluminum tray, 48 inches long, 6 inches wide and 1 inch deep. " *; '-' 10. AVAILABILITY/LIMITATION NOTICES: Enter any limitations on further dissemination of the report, other than those G'O 64. 551 Secutity Classification
Detailed investigation of ignition by hot gas jets
Proceedings of the Combustion Institute, 2007
Experimental and numerical investigations of the ignition of hydrogen/air mixtures by jets of hot exhaust gases are reported. An experimental realisation of such an ignition process, where a jet of hot exhaust gas impinges through a narrow nozzle into a quiescent hydrogen/air mixture, possibly initiating ignition and combustion, is studied. High-speed laser-induced fluorescence (LIF) image sequences of the hydroxyl radical (OH) and laser Schlieren methods are used to gain information about the spatial and temporal evolution of the ignition process. Recording temporally resolved pressure traces yields information about ambient conditions for the process. Numerical experiments are performed that allow linking these observables to certain characteristic states of the gas mixture. The outcome of numerical modelling and experiments indicates the important influence of the hot jet temperature and speed of mixing between the hot and cold gases on the ignition process. The results show the quenching of the flame inside the nozzle and the subsequent ignition of the mixture by the hot exhaust jet. These detailed examinations of the ignition process improve the knowledge concerning flame transmission out of electrical equipment of the type of protection flameproof enclosure.
Flow, Turbulence and Combustion, 2018
Airworthiness standards require a fire resistance demonstration for aircraft or helicopter engines to obtain a type certificate. This demonstration relies on tests performed with prototype engine parts in the late stages of the development. In hardest tests, a kerosene standardized flame with imposed burnt gas temperature and heat flux is placed next to the engine casing during a given time. The aim of this work is to provide a better characterization of a kerosene/air certification burner in order to reach a better understanding of the thermal environment during fire tests. To this purpose, Large-Eddy Simulation (LES) of the certification burner is carried out. Spray combustion, forced convection on walls and conduction in the solid parts of the burner are coupled to achieve a detailed description of heat transfer. In a first place, physical aspects involved inside the burner in an adiabatic case are described. Then, differences that exist with a conjugate convective and conductive heat transfer case are analyzed. To a larger extent, the aim is to have a better characterization of the flow impinging the casing and to progress on fire test modeling so as to minimize the risks of test failure.
Fuel Pool Ignition Caused by a Pyrotechnic Device
WIT Transactions on the Built Environment, 2005
Safety protocols on both military and commercial aircraft rely on knowledge of fire dynamics, temperature distributions and thermal mass transfer of specific chemical components. Indeed, the temperature field associated within an incendiary flash has numerous implications, particularly in the aircraft survivability arena. Present knowledge is limited when it comes to determining the local; temperature field around a burning incendiary and although there are full-scale experimental facilities these are often too expensive to perform all the parameters that are necessary to understand this type of event. Furthermore, if a fire has been initiated due to the instigation of a short duration pyrotechnic event then the scenario is further complicated, and is even more so if the event is in close proximity to a pool of fuel. Indeed, the ignition of a fuel pool by an incendiary device, such as a armour-piercing incendiary (API), has not been exhaustively covered, and it is widely accepted th...