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Flame Front (flame + front)
Selected AbstractsCorrelations between pyrolysis combustion flow calorimetry and conventional flammability tests with halogen-free flame retardant polyolefin compoundsFIRE AND MATERIALS, Issue 1 2009Jeffrey M. Cogen Abstract Seven halogen-free flame retardant (FR) compounds were evaluated using pyrolysis combustion flow calorimetry (PCFC) and cone calorimetry. Performance of wires coated with the compounds was evaluated using industry standard flame tests. The results suggest that time to peak heat release rate (PHRR) and total heat released (THR) in cone calorimetry (and THR and temperature at PHRR in PCFC) be given more attention in FR compound evaluation. Results were analyzed using flame spread theory. As predicted, the lateral flame spread velocity was independent of PHRR and heat release capacity. However, no angular dependence of flame spread velocity was observed. Thus, the thermal theory of ignition and flame spread, which assumes that ignition at the flame front occurs at a particular flame and ignition temperature, provides little insight into the performance of the compounds. However, results are consistent with a heat release rate greater than about 66kW/m2 during flame propagation for sustained ignition of insulated wires containing mineral fillers, in agreement with a critical heat release rate criterion for burning. Mineral fillers can reduce heat release rate below the threshold value by lowering the flaming combustion efficiency and fuel content. A rapid screening procedure using PCFC is suggested by logistic regression of the binary (burn/no-burn) results. Copyright © 2008 John Wiley & Sons, Ltd. [source] Dimensionality estimate of the manifold in chemical composition space for a turbulent premixed H2 + air flame,INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2004Shaheen R. Tonse The dimensionality () of manifolds of active chemical composition space has been measured using three different approaches: the Hausdorff geometrical binning method, Principal Component Analysis, and the Grassberger-Procaccia cumulative distribution method. A series of artificial manifolds is also generated using a Monte Carlo approach to discern the advantages and limitations of the three methods. Dimensionality is quantified for different levels of turbulent intensity in a simulation of the interactions of a 2D premixed hydrogen flame with a localized region of turbulence superimposed over the cold region upstream of the flame front. The simulations are conducted using an adaptive mesh refinement code for low Mach number reacting flows. By treating the Ns species and temperature of the local thermo-chemical state as a point in multidimensional chemical composition space, a snapshot of a flame region is mapped into chemical composition space to generate the manifold associated with the 2-D flame system. An increase in was observed with increasing turbulent intensity for all three methods. Although each method provides useful information, the Grassberger-Procaccia method is subject to fewer artifacts than the other two thereby providing the most reliable quantification of . © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 326,336, 2004 [source] Geometric features of the flame propagation process for an SI engine having dual-ignition systemINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2002Atilla Bilgin Abstract Flame front surface area and enflamed volume (the volume enclosed with flame front) is theoretically analysed for a spark-ignition engine, having cylindrical disc-shaped combustion chamber with two spark plugs located axisymmetrically on cylinder head, between cylinder axis and cylinder wall. Spherical flame front assumption is used. A computer code is developed based on purely geometric consideration of the flame development process in combustion chamber, and is used to investigate the effects of variations of spark plugs' locations on geometric features of the flame front. A comparison has also been made with a spark-ignition engine having one spark plug at the same location. Copyright © 2002 John Wiley & Sons, Ltd. [source] Gasification of char particles in packed beds: analysis and resultsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 12 2001S. Dasappa Abstract In this paper a packed bed of char particles is considered for experimental study and analysis. The packed char bed is modelled by extending the single-particle analysis (Dasappa et al., 1994a, Chem. Eng. Sci.49,2:223,232. Dasappa et al., 1994b, Twenty-fifth Symposium (International) on Combustion, pp. 1619,1628. Dasappa et al., 1998, Twenty-seventh Symposium (International) on Combustion, pp. 1335,1342.). All the reactions related to gasification are introduced into the reaction system as in Dasappa et al. (1998). The propagation of the reaction front into the packed char bed against the air stream is modelled. The results are compared with the experimental data on a model quartz reactor using charcoal. Experimental data of propagation of the reaction front through the packed bed from the present study and of Groeneveld's charcoal gasifier are used for comparison. Using the analysis of Dosanjh et al. 1987 (Combust. Flame68:131,142), it is shown that heat loss dominates the heat generation at the quench condition. It is also shown that increasing the oxygen fraction in air has resulted in flame front to propagate into the char bed. The critical air mass flux for peak propagation rate in a bed of char is found to be 0.1 kg m,2 s. Copyright © 2001 John Wiley & Sons, Ltd. [source] RANS-simulation of premixed turbulent combustion using the level set approachPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2005A. Kurenkov A model for premixed turbulent combustion is investigated using a RANS-approach. The evolution of the flame front is described with the help of the level set approach [1] which is used for tracking of propagating interfaces in free-surface flows, geodesics, grid generation and combustion. The fluid properties are conditioned on the flame front position using a burntunburnt probability function across the flame front. Computations are performed using the code FASTEST-3D which is a flow solver for a non-orthogonal, block-structured grid. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Predicting deflagration to detonation transition in hydrogen explosionsPROCESS SAFETY PROGRESS, Issue 3 2008Prankul Middha Abstract Because of the development in computational resources, Computational Fluid Dynamics (CFD) has assumed increasing importance in recent years as a tool for predicting the consequences of accidents in petrochemical and process industries. CFD has also been used more and more for explosion predictions for input to risk assessments and design load specifications. The CFD software FLACS has been developed and experimentally validated continuously for more than 25 years. As a result, it is established as a tool for simulating hydrocarbon gas deflagrations with reasonable precision and is widely used in petrochemical industry and elsewhere. In recent years the focus on predicting hydrogen explosions has increased, and with the latest release the validation status for hydrogen deflagrations is considered good. However, in many of these scenarios, especially involving reactive gases such as hydrogen, deflagration to detonation transition (DDT) may be a significant threat. In previous work, FLACS was extended to identify whether DDT is likely in a given scenario and indicate the regions where it might occur. The likelihood of DDT has been expressed in terms of spatial pressure gradients across the flame front. This parameter is able to visualize when the flame front captures the pressure front, which is the case in situations when fast deflagrations transition to detonation. Reasonable agreement was obtained with experimental observations in terms of explosion pressures, transition times, and flame speeds. The DDT model has now been extended to develop a more meaningful criterion for estimating the likelihood of DDT by comparison of the geometric dimensions with the detonation cell size. This article discusses the new models to predict DDT, and compare predictions with relevant experiments. © 2007 American Institute of Chemical Engineers Process Saf Prog 2008 [source] Deflagration and detonation of ethylene oxide vapor in pipelinesPROCESS SAFETY PROGRESS, Issue 3 2000Paul Thibault Pure ethylene oxide (EO) vapor may propagate decomposition flames through pipe above certain minimum conditions of temperature, pressure and pipe diameter. Flame propagation was studied in both closed and vented 5 cm (2-inch) pipe and closed 30 cm (12-inch) pipe. Flame progression in closed pipe was irregular and proceeded in pulsed stages. A possible mechanism involves preferential flame propagation at the pipe roof accompanied by periodic autodecomposition of EO accumulated in hot products behind the flame front, such accumulation probably being augmented by liquid EO condensed on the pipe walls ahead of the expanding flame system. Flames propagated 15 m (50 ft) through horizontal 5 cm pipe at 70°C and initial pressures , 4.3 bar (62 psia). In a series of 30 cm pipe tests employing low-energy ignition and otherwise increasingly severe conditions, a deflagration-to-detonation transition (DDT) occurred, partially destroying the test equipment. A new test facility was set up to confirm the ability of EO to propagate detonations in 30 cm pipe and to further investigate the phenomenon. Two EO detonations at 2.9 bar and one at 3.5 bar were directly initiated via the strong shocks from hydrogen-oxygen detonations. Based on a spectrum analysis of the pressure histories, the two detonations at 2.9 bar were probably marginal and propagated in a single spin detonation mode. At 3.5 bar, the pressure history suggests that the detonation propagated in a two-head detonation mode near the end of the 24 m test section. [source] | |||||||||||||