Ignition and Fire Development Caused by Leaking Fuels onto Heated Surfaces (original) (raw)
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.
Fire
This research investigated potential fire hazards originating in hidden areas of pressurized sections of aircrafts. The objective was to establish a laboratory-scale flammability test method to predict the behavior of fire propagation under real fire conditions. A confined fire apparatus (CFA) was designed and constructed, and several tests were conducted to better understand the involved mechanisms and their consequences and to estimate flame spreading in hidden-zone fires. The experimental facility and flame-spreading results obtained for a typical material involved in hidden fires, specifically a ceiling panel, were presented and discussed. The experimental facility consisted of a narrow passage where a fire was initiated using a burner on a specimen exposed to a controlled heat flux. Experiments were conducted in the absence of forced airflow. Flame spreading was estimated through visual monitoring of fire development or temperature measurements at specific locations in the spec...
Symposium (International) on Combustion, 1985
A numerical interpretation of thermokinetic interactions leading to oscillatory cool flames and complex, multiple-stage ignitions in acetaldehyde oxidation is presented. The results are well matched to quantitative, experimental measurements in a well-stirred flow reactor; they are the first numerical predictions of oscillatory ignition phenomena in a non-isothermal system with chain branching.
FLAMMABILITY TESTS ON HOT SURFACES FOR INDUSTRIAL FLUIDS
om.ugal.ro
Industrial fluids have to be evaluated not only for their performances as load capacity, durability, but also for their potential risk including ignition. Based on a solid documentation the authors point out the significance of testing the fluid flammability and present some tests related to fluid ignition on hot surfaces. The paper also presents preliminary results on determining the flammability characteristics of fluid when dropping it on a hot surface using an original tester capable of fulfilling the requirements imposed by SR EN ISO 20823:2004 Petroleum and related products. Determination of the flammability characteristics of fluids in contact with hot surfaces.
Chen et al-2014-Fire and Materials
The impact of radiant heat flux on ignition and combustion behavior of typical oils (diesel, lubricating oil, and aviation kerosene) was conducted in a cone calorimeter. A circular steel pan with a diameter of 10 cm was used to contain diesel, lubricating oil, and aviation kerosene without water sublayer. Using the standard oxygen consumption method, we obtained ignition time, heat release rate, mass loss rate, extinction coefficient, CO, and CO 2 yield, and average specific extinction area was calculated from the extinction coefficient. Janssens' method was adopted in this study to deal with ignition time and radiant heat flux under a 0.55 power rule. Results show that the fitting through Janssens' method is good for ignition time of diesel, lubricating oil, and aviation kerosene and radiant heat flux. Moreover, heat release rate, mass loss rate, and CO/CO 2 ratio appear to positively correlate with radiant heat flux, whereas average specific extinction area varies in a certain range.
Laminar burning velocities and Markstein numbers of hydrocarbonair flames
Combustion and Flame, 1993
Effects of positive flame stretch on the laminar burning velocities of hydrocarbon/air mixtures were studied experimentally using outwardly propagating spherical flames. The test conditions included propane, methane, ethane, and ethylene-air flames at various fuel-equivalence ratios and normal temperature and pressure. Karlovitz numbers generally were less than 0.3 so that the flames were remote from quenching conditions. Within this range, the ratio of the unstretched (plane flames) to stretched laminar burning velocities varied linearly with Karlovitz numbers, yielding Markstein numbers that were independent of Karlovitz numbers for a particular reactant mixture. In addition, Markstein numbers varied in a roughly linear manner with fuel-equivalence ratios over the range of the measurements, which were somewhat removed from flammability limits where behavior might differ. Effects of stretch were substantial: Markstein numbers varied from-2.5 to 7.2, yielding corresponding laminar burning velocity variations of 0.4-2,7 times the value for an unstretched (plane) flame over the test range. The ranges of fuel-equivalence ratios for unstable preferential-diffusion conditions (negative Markstein numbers) were as follows: propane, greater than 1.44; methane, less than 0.74; ethane, greater than 1.68; and ethylene, greater than 1.95. Fuel-equivalence ratios for maximum flame temperatures and laminar burning velocities are near unity for the present flames; therefore, neutral preferential-diffusion conditions are shifted toward fuel-equivalence ratios on the unstable side of unity, in qualitative agreement with recent approximate theories treating the effects of stretch on laminar premixed flames.