Hydraulic fluids: An approach to high pressure spray flammability testing based on measurement of heat output

One of the main hazards associated with the use of hydraulic fluids is the accidental release of hydraulic fluid near to a source of ignition. Several tests simulating this hazard have been developed but, in the opinion of the authors, none fulfils all the scriterla required of a flammability test. A new form of test has been developed. A test chamber is ventilated by a smooth flow of air; the hydraulic fluid under test is sprayed into the test chamber and ignited. The temperature rise in the gases leaving the stack and the radiation from the flame are measured at a specified time and from these measurements the heat output of the flame is estimated. Different fluids are then compared on the basis of their heat output values and data are presented in the paper for a variety of fluids.     

An ignition criterion for combustible solids integrating surface temperature and heating rate

Surface ignition temperature has been widely used as an ignition criterion for the piloted ignition of common combustible solids. However, experimental observations have shown that the surface temperature of a solid at ignition varies with external heat flux. In addition, if the external heat flux is smaller than the critical heat flux for ignition, the solid will not ignite while the actual surface temperature may be higher than the defined surface ignition temperature. To overcome these limitations and maintain the simplicity of the surface ignition temperature criterion, a new ignition criterion integrating heating rate and surface temperature is proposed, developed, and validated. Predictions based on the new criterion compare well with experimental results on piloted ignition of a thermoplastic material (black PMMA), a thermoset composite material (E‐glass fiber reinforced polyester composite) and a cellulosic material (Red Oak) subjected to different heat flux levels. Potential factors affecting the accuracy and predictive capability of the new heating rate‐related ignition temperature criterion are discussed. The method and associated procedures to construct the heating rate‐related temperature ignition criterion can be used to obtain the same ignition criterion for other combustible solids. Copyright © 2014 John Wiley & Sons, Ltd.     

Approximate solutions for the ignition of a solid as a function of the Biot number

The ignition of a finite planar 1‐dimensional solid is addressed for constant applied radiant heat flux. An ignition temperature criterion is used, with constant properties, and linearized reradiation. An approximate integral analysis leads to analytic formulas to predict the ignition time in terms of Biot (Bi) number and heat flux. The accuracy of the integral solution is found to be good compared to the exact infinite series solution for the conduction equation. The integral model is then used to assess the accuracy of common ideal thick and thin formulas for ignition. There is a domain of heat flux and Bi where the ideal formulas are not accurate. An example is given where the integral model is accurately applied to ignition data to illustrate the range where the ideal formula is not accurate.     

中国动力煤的着火温度与着火热的分布规律

为了寻求动力煤成分分布与煤质着火及稳燃特性之间的函数关系,根据燃烧学的热力着火理论,对国内大型电站煤粉锅炉燃用的166个典型的煤质分析数据进行了数学分析。分析了固态碳(C_gt)和当量气态碳(C_qt 3.67H_ar)比值随V_daf的分布规律及其对煤质着火的影响;根据文献中77个煤质的一维沉降炉实验数据,拟合出煤粉的着火温度与V_ad及A_ad的函数关系,计算分析了本文大数据样本煤质的着火温度及着火热的分布规律,提出将着火热和着火温度作为煤质着火特性的图像分辨新方法。据此分析了各类煤质的着火与稳燃特性。结果表明,本方法能明确地定量区分不同类煤质和同类煤质的着火特性差异,且在理论上给出符合宏观规律的合理解释。     

Ignition of pyrotechnic mixture by means of a laser diode. Part I: Numerical modelling

A numerical model of the heating and ignition of a reactive solid by a laser beam has been developed. A transient, two-dimensional heat equation was solved numerically using an explicit scheme. A nonlinear source term (Arrhenius equation) complicates the analytical resolution of this type of problem. Laser beam absorption is considered in a few micrometer depth. Influence of depth absorption coefficient is investigated. Influence of laser power density, lasering time and thermal diffusivity on ignition are examined by this model. The developed numerical model has been used to design a laser ignition system for explosive substances. It has been shown that ignition by a 0.6 W laser diode at a fiber optics output is feasible.     

Effects of variations in incident heat flux when using cone calorimeter test data for prediction of full‐scale heat release rates of polyurethane foam

The development of methods to predict full‐scale fire behaviour using small‐scale test data is of great interest to the fire community. This study evaluated the ability of one model, originally developed during the European Combustion Behaviour of Upholstered Furniture (CBUF) project, to predict heat release rates. Polyurethane foam specimens were tested in the furniture calorimeter using both centre and edge ignition locations. Input data were obtained using cone calorimeter tests and infrared video‐based flame area measurements. Two particular issues were investigated: how variations in incident heat flux in cone calorimeter tests impact heat release rate predictions, and the ability of the model to predict results for different foam thicknesses. Heat release rate predictions showed good agreement with experimental results, particularly during the growth phase of the fire. The model was more successful in predicting results for edge ignition tests than for centre ignition tests and in predicting results for thinner foams. Results indicated that because of sensitivity of the burning behaviour to foam specimen geometry and ignition location, a single incident heat flux could not be specified for generating input for the CBUF model. Potential methods to determine appropriate cone calorimeter input for various geometries and ignition locations are discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

Heat release and classification of fire retardant wood products

A comparison is presented of cone calorimeter heat release data between fire retardant treated and untreated wood products. The test results show significant differences between these two groups. The parameters included in the comparison are time to ignition, rate of heat release (peak and average values) and total heat release. The wood-based products were also tested in different small-scale national standard fire tests and in the full-scale room fire test. Fire retardant wood products achieve an improved classification both in present national systems and in possible new systems based on the cone calorimeter and the room fire test.     

A mechanistic method for scrutinising LIFT ignition data

The lateral ignition and flame spread test (LIFT) standard (ASTM E 1321‐97a) requires the Thermal Response correlation to be scrutinized for data points that violate the zero heat loss requirement, but the standard gives no guidance on how this should be done. The fundamentals of linear regression were reviewed and an unbiased and mechanistic algorithm for scrutinising LIFT ignition data without human intervention was developed. The algorithm produced reasonable results compared with human interpretation of exemplar test data taken from the literature. Copyright © 2010 John Wiley & Sons, Ltd.     

Ignition performance of new and used motor vehicle upholstery fabrics

This paper examines the standards for fire safety in transport systems and in particular the test method for the flammability of materials within passenger compartments of motor vehicles. The paper compares data from ignition tests conducted in the cone calorimeter and the FIST apparatus with tests conducted using the FMVSS 302 horizontal flame spread apparatus. Ten materials were selected as representative of those used as seat coverings of private and commercial passenger vehicles. The time to ignition of new and used materials subject to exposure heat fluxes between 20 kW/m² and 40 kW/m² was measured. The results from the ignition tests were analysed using thermally thick and thermally thin theoretical models. The critical heat flux for sustained piloted ignition was determined from the time to ignition data using the thermally thin approach. Derived ignition temperatures from both the thermally thick and thermally thin methods were compared with measurements using a thermocouple attached to the back surface of materials in selected tests. The flame spread rates in the FMVSS 302 apparatus were determined and a comparison was made between the performance of the materials in the flame spread apparatus, the cone calorimeter and the FIST. The results suggests that a critical heat flux criterion could be used to provide an equivalent pass/fail performance requirement to that specified by the horizontal flame spread test although further testing is needed to support this. Copyright © 2004 John Wiley & Sons, Ltd.     

Influences of specimen size and heating mode on the ignitability of polymeric materials in typical small‐scale fire test conditions

Small‐scale fire tests including the Underwriters Laboratories 94 (UL94) vertical burning test and the cone calorimeter test are widely used. In this paper, the ignition times of materials heated by the conical heater of a cone calorimeter and the UL94 flame were measured. It was found that for polymer bars heated by the UL94 flame, the ignition time is relatively short and increases with the specimen thickness. But the contribution of the specimen thickness to the delay of the ignition time is limited. The intrinsic properties of materials play a more important role in the ignition time than the specimen thickness. In addition, respectively corresponding to one‐dimensional, two‐dimensional, and three‐dimensional heat transfer, three heating modes of the UL94 flame were presented and compared with the conical heater. It was found that whether the heat source is the conical heater or the UL94 flame, the ignition time depends on the heat flux and the multidimensional heat transfer. The ignition time decreases with the increasing heat flux, and the magnitude order of the ignition time might drop when the heating mode changes from one‐dimensional to multidimensional heat transfer. Copyright © 2011 John Wiley & Sons, Ltd.     

Experimental assessment of bench‐scale ignitability parameters

This work aims to explore possible ways of improving the precision of ignition measurements in the cone calorimeter. Both inherent repeatability of parts of the testing equipment and operator‐dependent variations are considered. Inherent repeatability is indicated to be slightly improved if the test samples used are circular rather than square. Operator‐dependent variation is discussed in terms of the method used for determining ignition. Four procedures are compared, namely, visual observation, usage of a light sensor, and looking at the peak of the second and first derivatives of the mass loss and heat release curves, respectively. Results indicate that the preferable operator‐independent method depends on the test conditions; the derivative of the heat release rate is an alternative to the mass loss rate derivative when the scale is of standardised quality. A light sensor for ignition time observation is a good option when the surrounding light is not changed during the test.     

A milligram-scale flame calorimeter pyrolyzer system used to emulate burning of nonthermally thin solid samples

A new Milligram-scale Flame Calorimetry (MFC) pyrolyzer system was developed to approximate heating conditions experienced by material samples in gram-scale tests, such as cone calorimetry. The main features of this pyrolyzer system are a miniature flat heating coil embedded into a platform supporting the sample crucible. The use of a constant power rather than a constant heating rate operation mode distinguished the new MFC from the other mg-scale flammability test method—microscale combustion calorimetry (MCC). A series of tests was carried out using the new MFC, cone, and MCC on five synthetic polymers representing a wide range of flammability behavior. All methods produced similar solid residue yields. The MFC peak heat release rate (HRR) was found to correlate linearly with the cone peak HRR (R² = 0.93). The MCC peak HRR did not exhibit a strong correlation with the corresponding cone data. The new MFC was found to produce heat of combustion (HOC) values nearly identical to those measured in cone calorimetry. The MCC had a tendency to produce higher heats of combustion. Both MFC and MCC measured sample ignition temperatures that showed some correlation with the square root of the time to ignition measured in a cone calorimeter. The MFC airborne particular yield was found to correlate well (linear R² = 0.91) with the average specific extinction area measured in the cone tests. It was concluded that the newly designed MFC can deliver relatively accurate flammability measurements similar to cone calorimetry while using three orders of magnitude smaller samples.     

Polymer surface reflectance-absorptance characteristics

During an investigation of the time for ignition of polymeric materials under the influence of radiant heating, it was found that the polymer surface reflectance-absorptance characteristics were a major factor in the variance of the ignition times. A subsequent research study was made of the reflectance-absorptance characteristics of those polymers used in the ignition testing. Reflectance values were obtained over the wavelength of 0.3 to 2.5 microns using a double-beam Cary model 14 spectrophotometer with an integrating sphere reflectometer and over the wavelengths of 1.0 to 10.0 microns using a Gier-Dunkle Hohlraum with a Perkin-Elmer spectrophotometer. Absorptance values were obtained by means of Kirchoff's Law, Drawings and graphs are included which illustrate the test apparatus and type of data collected. A table of average absorptances of several polymers are given and listed according to the particular type of heat source used. Average absorptances of the polymers over the monochromatic wavelength span of the heat sources were calculated using the equation Mathematical analyses were developed and are presented for both the integrating sphere reflectometer and Gier-Dunkle Hohlraum unit. Drawings and graphs are included which illustrate the test apparatus and type of data collected. A table of average absorptances of several polymers are given and listed according to the particular type of heat source used.     

A theoretical basis for flammability properties

Theoretical formulations are presented for the fire growth processes under external radiant heating. They included ignition, burning and energy release rate, and flame spread. The behaviour of these processes with external heating is described along with the critical conditions that limit them. These include the critical heat fluxes for ignition, flame spread and burning rate. It is shown how these processes and their critical conditions depend on a limited number of properties measurable by a number of standard test methods. The properties include heat of combustion, the heat of gasification, ignition temperature and the thermal properties of the material. Alternatively, the properties could be related to parameters easily found from data; namely: (1) the critical heat flux (CHF) for ignition; (2) the slope of the energy release rate with externally imposed flux, defined as heat release parameter (HRP); and (3) the ignition parameter, defined as thermal response parameter (TRP). It is further shown that the flame heat flux differences between small laminar flame ignition sources and larger turbulent flames can affect flame spread due to heat flux and ignition length factors. Finally, it is found that the critical energy release rates theoretically needed for ignition, sustained burning, and turbulent upward flame spread are roughly 13, 52, and 100 kW/m², respectively, and independent of material properties. Copyright © 2005 John Wiley & Sons, Ltd.     

Thermal Decomposition and Ignition of PBXN‐110 Plastic‐Bonded Explosive

Due to safety requirements, insensitive behavior in slow or fast thermal heating (cook‐off) conditions is a desired behavior for today’s munitions. The ignition time of munitions under slow or fast cook‐off conditions is an important parameter in the design of insensitive munitions. The critical temperature, which mainly depends on the chemical, physical, and the geometrical properties of the energetic material, is the determining factor whether the material will end up with thermal initiation or not, when it is exposed to an external heat source. In this study a slow cook‐off test setup is designed and developed and the tests for a generic munition containing PBXN‐110 plastic‐bonded explosive are performed in order to obtain temperature distribution in the test item, ignition time, ignition temperature, and ignition location. In this paper the development procedure and the experimental results of the slow cook‐off tests are explained. Moreover, the kinetic parameters such as activation energy and pre‐exponential factor for the plastic‐bonded explosive obtained from the TGA tests are presented.     

Measurement of dynamic heat fluxes by gauges with sensitive elements on their surfaces

A new algorithm is proposed for processing the results of direct measurements, which allows one to change the requirements to the gauge construction. An automated system has been developed for the measurement of pulsed heat fluxes in the ignition and combustion of condensed substances. Sergiev Posad. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 5, pp. 38–45, September–October, 1993.     

A sample holder for determining material properties

The determination of material properties, such as thermal conductivity, for use in fire models requires precise knowledge of all heat losses. For example, the ignition and subsequent burning of solid samples is sensitive to heat losses from the rear surface of the tested sample. The heat loss depends on the sample holder and its environment. Theoretical predictions of ignition and pyrolysis in standard flammability apparatuses show that the construction of the sample holder has a surprisingly large effect on measured properties especially for thermally thin samples. This makes flammability measurements and inferred thermal properties apparatus dependent. For example, ignition measurements of 6.4 mm (1/4″) plywood samples show a 40% reduction in the critical heat flux for ignition. The back and sides of the sample were sealed by wrapping it with aluminium foil tape. Heat losses from the sample were minimized by placing it on a sample holder having four layers of 3.2 mm (1/8″) thick insulating ceramic paper surrounded by an outer layer of aluminium tape. A detailed mathematical model is developed to fully characterize the thermal response of a sample to a prescribed heat flux in a standard flammability apparatus. The model is used to estimate the residual heat losses not eliminated by the sample holder. Model predictions accurately track the temperature response of blackened brass plates of different thicknesses exposed to several different incident heat fluxes. Brass, of course, has well known thermophysical properties; so, it also provides an excellent means for in situ calibration of the incident heat fluxes. Copyright © 2000 John Wiley & Sons, Ltd.     

纯氧换热转化合成甲醇新工艺

纯氧换热转化合成甲醇工艺是国内首创，并在国际上首先实现工业化。文中阐述该新工艺的节能原理、工艺流程和技术难点：（１）引燃；（２）传热强化与膨胀差；（３）纯氧部分氧化的超温。还介绍了难点的突破办法。     

A simplified model for predicting the ignition of FRP composites with validation using intermediate‐scale fire experiment data

This study presents a simplified theoretical model to predict the ignition of FRP composites of general thermal thickness (GTT) subjected to one‐sided heating. A simplified GTT heat transfer model to predict the surface temperature of GTT composite panels was developed, and the exposed surface temperature was used as ignition criterion. To validate the GTT model, intermediate scale calorimeter fire tests of E‐glass fiber reinforced polyester composite panels at three heat flux levels were performed to obtain intermediate‐scale fire testing data in a controlled condition with well‐defined thermal boundary conditions. The GTT model was also verified by using results from finite element modeling predictions. This model can be used to estimate the surface temperature increase, time‐to‐ignition, and mass loss of FRP composites for fire safety design and analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Simulation of the process of coal dust ignition in the presence of metal particles

A mathematical model was developed for the gas-phase ignition of a layer of the dust of typical 2B brown coal by a metal particle heated to high temperatures (above 1100 K) under ideal thermal contact conditions. This model took into account the heating and thermal decomposition of ground coal upon the cooling of a local source, the yield of volatile components, and the formation, heating, and ignition of the gas mixture. The effect of heat source parameters (shape and dimensions) on the fundamental process characteristic—the delay time of ignition—was found. A relationship of the ignition zone position near a hot particle with the heating intensity of a gas mixture of volatile substances and an oxidizing agent was revealed. The results of numerical studies are consistent with well-known experimental data on the conditions and characteristics of ground coal burning on local heating by sources of limited energy capacity.