Experimental study of the combustion characteristics of methanol‐gasoline blends pool fires in a full‐scale tunnel

The combustion characteristics of methanol‐gasoline blends pool fires were studied in a series of full‐scale tunnel experiments conducted with different methanol and gasoline blends. The parameters were measured including the mass loss rate, the pool surface temperature, the fire plume centerline temperature, the ceiling temperature, the smoke layer temperature profile, the flame height, and the smoke layer interface height. The gasoline components were analyzed by GC‐MS. The effects of azeotropism on the combustion characteristics of the different blends were discussed. On the basis of the results of the fire plume centerline temperature, the ceiling temperature, and the flame height, it shows that the tunnel fire regime gradually switches from fuel controlled to ventilation controlled with increasing gasoline fractions in the blends. The fire plume can be divided into 3 regions by the fire plume centerline temperature for the different blends. The N‐percentage rule to determine the smoke layer interface height is found to be applicable for tunnel fires with different blends for N = 26.     

New approaches to determine the interface height of fire smoke based on a three-layer zone model and its verification in large confined space

Large confined space has high incidence of fires, which seriously threatens the safety of people working there. Understanding the distribution of smoke in such large space is critical to fire development prediction and smoke control. Three improved methods for the stratification interface prediction of fire smoke are developed, including of improved intra-variance, integral ratio and N-percentage methods. In these methods, the interface height is determined by the vertical temperature distribution based on a three-layer smoke zone model, which is an improvement of a two-layer zone model. Thereafter, the three improved methods are applied to several typical fire cases simulated CFD to predict the smoke interface, and their applicability and reliability are verified by comparison of the smoke stratification results with the filed simulation results. Results show that the three improved methods can effectively determine the location of the three-layer zone model's interface, and they have the ability to predict smoke interface for fires with different fire source types and ventilation conditions.     

Experimental determination of fire heat release rate with OC and CDG calorimetry for ventilated compartments fire scenario

This research deals with the experimental determination of the heat release rate (HRR) of fires in mechanically ventilated compartments based on oxygen consumption (OC) and carbon dioxide generation (CDG) calorimetry. It proposes formulations for fire in force‐ventilated compartments on the same basis as the relations established for hood calorimetry in an open atmosphere but considering inertia and unsteady behavior of the fire via the time variation mass of O₂ and CO₂ in the compartment. The value of the new formulations of HRR has been tested in two series of propane gas fire experiments performed in a large‐scale facility. The first series involves a fire scenario with one compartment, and the second series, a fire scenario with three compartments connected to each other by doorways. In the first test series, the OC and CDG formulations for HRR are assessed. In the second test series, the OC and CDG formulations are presented with two approaches to definition of the control volume: approach involving three rooms and the flow rate in the ventilation network and approach involving only the fire room and the flow rate through the doorways. On the basis of the fire experiments considered, the most accurate method (accuracy to within 10%) for determining the HRR is the CDG formulation with approach for the control volume without considering the flow rates at the doorways. This analysis points out the different features of each method (OC and CDG) and thoroughly discusses their advantages and drawbacks. The overall analysis allows guidelines to be formulated for fire HRR calculation in confined and ventilated compartments. Copyright © 2013 John Wiley & Sons, Ltd.     

Use of zone models on simulating compartmental fires with forced ventilation

Performance of three fire zone models BR12, CCFM.VENTS and CFAST in simulating forced ventilation fires with low heat release and high ventilation rates were studied experimentally. A fire chamber of length 4.0 m, width 3.0 m height 2.8 m with adjustable ventilation rates was used. Burning tests were carried out with wood cribs and methanol to study the preflashover stage of a compartmental fire and the effect of ventilation. The mass loss rate of fuel, temperature distribution of the compartment and the air intake rate were measured. The heat release rates of the fuel were calculated from the measured mass loss rate. The smoke temperature was used as the validation parameter. A scoring system is proposed to compare the results predicted by the three models. An empirical expression for calculating the smoke temperature is assessed. Lastly, the Computational Fluid Dynamics technique is also used for comparing the simulated fire environment.     

Performance evaluation of bromofluoropropene in extinguishing liquid fuel spray fires

Liquid fuel spray fires emit high radiation heat fluxes, posing great threat to humans. The study of suitable agents and techniques for extinguishing this particular type of fire is of great importance. In this study, degradable 2‐bromo‐3,3,3‐trifluoropropene (BTP), a new clean fire extinguishing agent, was tested for its effectiveness in extinguishing three types of liquid fuel spray fires, namely diesel, gasoline, and ethanol. Bench‐scale experiments were conducted in a 6 × 5 × 3 m compartment with natural ventilation. The liquid fuels sprayed at varying pressures were ignited by a small open flame and then extinguished by a portable BTP extinguisher. Results showed that BTP of less than 60.0 g could extinguish all liquid fuel spray fires of 0.20 to 1.0 MPa in less than 2.0 s. The results also showed that when compared with fire sparked by gasoline and diesel, it is significantly easier to put out ethanol spray fires because of its high flame temperature and low flame power. Based on well‐established fire suppression theories and experimental results, the detailed mechanism of how BTP functions as an extinguishing agent in the suppression of liquid fuel spray fires will be discussed. Copyright © 2013 John Wiley & Sons, Ltd.     

Horizontal cable tray fire in a well‐confined and mechanically ventilated enclosure using a two‐zone model

Electrical cable trays are used in large quantities in nuclear power plants (NPPs) and are one of the main potential sources of fire. A malfunction of electrical equipment due to thermal stress for instance may lead to the loss of important safety functions of the NPPs. The investigation of such fires in a confined and mechanically ventilated enclosure has been scarce up to now and limited to nuclear industry. In the scope of the OECD PRISME‐2 project, the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) conducted more than a dozen fire tests involving horizontal electrical cable trays burning either in open atmosphere or inside mechanically ventilated compartments to investigate this topic. A semi‐empirical model of horizontal cable tray fires in a well‐confined and mechanically ventilated enclosure was developed. This model is partly based on the approach used in FLASH‐CAT and on experimental findings from IRSN cables fire tests. It was implemented in the two‐zone model SYLVIA. The major features of the compartment fire experiments could then be reproduced with acceptable error, except for combustion of unburned gases. The development of such a semi‐empirical model is a common practice in fire safety engineering concerned with complex solid fuels.     

Prediction of Layer‐Inversion Behavior of Down‐Flow Binary Solid‐Liquid Fluidized Beds

The layer‐inversion behavior of down‐flow binary solid‐liquid fluidized beds is predicted using the property‐averaging approach. The binary pair in this case consists of a larger solid species which is also heavier than its smaller counterpart, while both are lighter than the fluidizing medium. The model is based on using the generalized Richardson‐Zaki correlation for evaluation of the bed void fraction wherein mean values of particle properties are used. However, unlike the maximum bulk density condition for the conventional up‐flow binary solid fluidized bed, the model is based on a minimum bulk density condition for occurrence of layer inversion. This is due to the fact that the volume contraction phenomenon associated with the mixing of unequal solid species leads to a decrease in bulk density of the bed. Model predictions are also compared using the limited data available in the literature. Predictions are consistent with the observed mixing behavior.     

The Performance of SOFC Model Under Different Three‐phase Load Conditions

In this paper, the dynamic performance of a modified thermal based dynamic model of a solid oxide fuel cell (SOFC) is presented under different three‐phase load conditions. The modified thermal based fuel cell model contains ohmic, activation and concentration voltage losses, thermal dynamics, methanol reformer and fuel utilization factor limiting stage. SOFC model and the power conditioning unit (PCU), which consists of a DC‐DC boost converter, a DC‐AC inverter, their controller, transformer and filter, are developed on Matlab/Simulink environment. The simulation results show that the real and reactive power management of the inverter is performed successfully in an AC power system with the proposed thermal based SOFC model under three‐phase load conditions such as ohmic loads, switched ohmic−inductive loads and a three‐phase induction motor. Finally, the three‐phase induction motor is performed both no load and load conditions. The simulation results show that the modified thermal based fuel cell model provides an accurate representation of the dynamic and steady state behavior of the fuel cell under different three‐phase load conditions.     

Temperature of post‐flashover compartment fires—Calculations and validation

This paper describes and validates by comparisons with tests a one‐zone model for computing temperature of fully developed compartment fires. Like other similar models, the model is based on an analysis of the energy and mass balance assuming combustion being limited by the availability of oxygen, ie, a ventilation‐controlled compartment fire. However, the mathematical solution techniques in this model have been altered. To this end, a maximum fire temperature has been defined depending on combustion efficiency and opening heights only. This temperature together with well‐defined fire compartment parameters was then used as a fictitious thermal boundary condition of the surrounding structure. The temperature of that structure could then be calculated with various numerical and analytical methods as a matter of choice, and the fire temperature could be identified as a weighted average between the maximum fire temperature and the calculated surface temperature of the surrounding structure as a function of time. It is demonstrated that the model can be used to predict fire temperatures in compartments with boundaries of semi‐infinitely thick structures as well as with boundaries of insulated and noninsulated steel sheets where the entire heat capacity of the surrounding structure is assumed to be concentrated to the steel core. With these assumptions, fire temperatures could be calculated with spreadsheet calculation methods. For more advanced problems, a general finite element solid temperature calculation code was used to calculate the temperature in the boundary structure. With this code, it is possible to analyze surrounding structures of various kinds, for example, structures comprising several materials with properties varying with temperature as well as voids. The validation experiments were accurately defined and surveyed. In all the tests, a propane diffusion burner was used as the only fire source. Temperatures were measured with thermocouples and plate thermometers at several positions.     

Characterization of the fire environments in central offices of the telecommunications industry

Eight free burning and two sprinklered fire tests were performed with electrical cable trays and live digital switch racks in a large enclosure to simulate telecommunications central office (TCO) fires started by electrical overheating. Very‐slow‐growing (non‐flaming), slower‐growing (partially flaming) and low‐intensity‐faster‐growing (flaming) fires releasing gray‐white, gray, and black smoke, respectively, were observed in the tests. Under quiescent conditions present in the unvented enclosure fire tests for cables, very‐slow‐growing fires were detected in about 1452 s, whereas the slower‐growing fires were detected in about 222 s by commercial fire detectors. Under ventilation conditions typical of TCOs, detection times were very similar for the five types of commercial TCOs fire detectors used in the tests. The average detection times for slower‐growing fires (cable fires) and low‐intensity‐faster‐growing fires (digital switch rack fires) were 242±17% and 249±11%s respectively. The TCO procedures to reduce smoke damage from fires (on fire detection, inlet ventilation flow is turned off and exhaust flow is turned on) were found to be beneficial. The extent of smoke damage decreased significantly with an increase in the exhaust flow rate. The chloride ion mass deposition suggested that equipment recovery would be possible in the smoke environment if the cable vapor concentration could be reduced below about 3 g/m³. The metal corrosion rate was found proportional to the 0.6th power of the smoke concentration, similar to that found for the corrosion of metal surfaces exposed to aqueous solutions of HCl and HNO₃ and for acid rain with no protective layer at the surface. Sprinkler water was found to wash down the smoke deposits on the surfaces with little indication of corrosion enhancement. Copyright © 2003 John Wiley & Sons, Ltd.     

Predicting HCl concentrations in fire enclosures using an HCl decay model coupled to a CFD‐based fire field model

The amount of atmospheric hydrogen chloride (HCl) within fire enclosures produced from the combustion of chloride‐based materials tends to decay as the fire effluent is transported through the enclosure due to mixing with fresh air and absorption by solids. This paper describes an HCl decay model, typically used in zone models, which has been modified and applied to a computational fluid dynamics (CFD)‐based fire field model. While the modified model still makes use of some empirical formulations to represent the deposition mechanisms, these have been reduced from the original three to two through the use of the CFD framework. Furthermore, the effect of HCl flow to the wall surfaces on the time to reach equilibrium between HCl in the boundary layer and on wall surfaces is addressed by the modified model. Simulation results using the modified HCl decay model are compared with data from three experiments. The model is found to be able to reproduce the experimental trends and the predicted HCl levels are in good agreement with measured values. Copyright © 2006 John Wiley & Sons, Ltd.     

Characterization of the combustion products in large‐scale fire tests: comparison of three experimental configurations

The storage of large amounts of polymers and other bulk chemicals is a potential hazard in the case of fire. There is at present a lack of knowledge about the implications of such fires. In particular the role of the ventilation conditions on fire chemistry has warranted investigation. A set of indoor, large‐scale combustion experiments, conducted on five different materials is described in this article. The main test series was conducted using the ISO 9705 room, where both well‐ventilated and under‐ventilated conditions were attained by restricting the opening of the room. The degree of ventilation was determined using a phi meter. Furthermore, in addition to measuring the traditional fire‐related parameters, extensive chemical characterization of the combustion products was made. Two additional series of experiments were also performed. In one series of tests the size of the enclosure was increased and the fuel was placed in a storage configuration to simulate a real storage situation. In the other test series, three of the materials were tested as large‐scale open pool fires. The results from the three configurations are compared regarding yields of combustion products as a function of the degree of ventilation. For a number of toxic combustion products a clear dependence of the production on the equivalence ratio was found. Further, placing the fuel in a storage configuration did not significantly change the outcome of the combustion. Thus, the ISO 9705 room is of a size and scale that can be taken as a model for representing real‐scale fires. Additionally it has been demonstrated that an advantage of the ISO 9705 room is the ability to alter the ventilation conditions. Copyright © 2001 John Wiley & Sons, Ltd.     

Effects of passenger blockage on smoke flow properties in longitudinally ventilated tunnel fires

This paper investigates the effects of passenger blockage on smoke flow properties in longitudinally ventilated tunnel fires. A series of numerical simulations were conducted in a 1/5 small-scale tunnel with the different heat release rates (50-100 kW), longitudinal ventilation velocities (0.5-1 m/s), passenger blockage lengths (2-6 m), and ratios (0.17-0.267). The typical smoke flow properties in different tunnel fire scenarios are analyzed, and the results show that under the same heat release rate and longitudinal ventilation velocity, the smoke back-layering length, maximum smoke temperature, and downstream smoke layer height decrease with increasing passenger blockage length or ratio. The Li correlations can well predict the smoke back-layering length and maximum smoke temperature in tunnel fire scenarios without the passenger blockage. When the passenger blockage exists, the modified local ventilation velocity that takes the blockage length and ratio into account has been proposed to correct the Li correlations. The smoke back-layering length and maximum smoke temperature with the different blockage lengths and ratios can be predicted by the modified correlations, which are shown to well reproduce the simulation results.     

Designing an experimental rig for developing a fire severity model using numerical simulation

In this study, an experimental rig representing a deep enclosure was designed to be used to validate a CFD‐based fire model in predicting the outcome. The model then can be used for further study to investigate physical phenomenon within a deep enclosure and to develop an engineering fire severity (heat release rate, HRR, vs time vs position [1]) model. Two empirical models (the VU model [1] and Kawagoe model [2]) were used along with Fire Dynamics Simulator (FDS) in designing the experimental rig. For a specific‐sized enclosure, when the HRR was prescribed to the FDS as input from the VU model, it was accurately reproduced, while the HRR from the Kawagoe was used as the input, the FDS calculated much lower value. The experimental rig of that specific size was then built, and various parameters were measured from the tests with liquid fuel fire within this experimental rig. The measured HRR was prescribed into the FDS, and the FDS could reproduce HRR values well. However, the predicted temperature and radiation flux was not as good, especially when the flames were near the opening. This may be due to the tendency of flames over‐projecting outside the opening in FDS simulations.     

Validation of the lumped parameter code COCOSYS against large‐scale OECD PRISME 2 fire experiments

Fire safety analysis is a major issue for nuclear power plants (NPPs) in the context of deterministic safety assessments as well as of probabilistic safety analyses. Oil reservoirs and cables represent major fire loads. Therefore, simulations of oil and cable fires are of interest for quantifying the risk of such internal hazards in NPPs. To investigate the applicability of lumped parameter (LP) modelling, validations against fire experiments are required. In this way, results obtained with the LP code COCOSYS for simulations of oil and cable fire experiments conducted in the OECD PRISME 2 Project are presented. The PRISME 2 VSP (vertical smoke propagation) tests involving oil fires in a confined and mechanically ventilated facility were used to assess the ability of the LP code to simulate smoke propagation through a horizontal opening from the fire compartment to a compartment on top of it. As it was already identified in the “International Collaborative Fire Modelling Project (ICFMP),” this type of opening might cause problems in fire simulations, particularly for zone or LP fire models. In these simulations, attention has been paid to the coupling between the fire and the surrounding environment due to the decrease of oxygen concentration. Furthermore, different cable materials have been tested in the PRISME 2 CORE (completing and repeating) test campaign. By simulating the CFS‐3 (cable fire spreading) test with confined underventilated conditions, the applicability of the COCOSYS cable fire model with input parameters deduced from open atmosphere fire tests (CORE‐2) was analysed. Results show that the applicability of a LP fire model to predict the pyrolysis rate is partly limited for both oil and cable fires, in confined environment. However, simulations with prescribed pyrolysis rates show encouraging results in good agreement with the experimental data and underline the capability of the LP code COCOSYS to simulate the interaction between the thermal hydraulics inside compartments and the fire source.     

Effect of the nature of fuel on the characteristics of fully developed compartment fires

The coupling between the constituent reactions of a burning process, namely pyrolysis, combustion of volatiles, and (possibly) oxidation of char, is on the whole quite different for fires occurring in the open and for those that develop in an enclosure. Consequently, knowledge of the characteristics of free burning fires is of only limited value in studies related to compartment fire. Since the singe-rout communication between the fire compartment and its environment, always assumed in classical fire studies, is not at all common in real world fires, great sophistication in the mathematical modeling of classical fires is rarely warranted. An examination of pool-like fires and pile fires of noncharring fuels has shown that the severity of such fires in the fire compartment, as characterized by the so-called ‘fire severity product’, decreases slightly with an increase in ventilation. The principal danger presented by these fires, however, is not so much to the fire compartment itself as to the surrounding spaces. An interesting feature of fires involving charring fuels, cellulosies in particular, is that the rate of consumption of fuel, the so-called ‘rate of burning’, is practically independent of all process variables except ventilation. The severity of fires of cellulosics is, as a rule, much higher than that of fires of noncharring fuels. It exhibits a maximum at relatively low ventilations. From the point of view of spread of fire to the surrounding spaces, cellulosics are generally less dangerous than noncharring plastics. Fires involving cellulosics mixed with smaller amounts of noncharring plastics can be characterized as basically cellulosics fires, with a superimposed initial period of very high spread liability.     

An efficient approach to improving fire retardancy and smoke suppression for intumescent flame‐retardant polypropylene composites via incorporating organo‐modified sepiolite

In this work, an efficient approach to improving the fire retardancy and smoke suppression for intumescent flame‐retardant polypropylene (PP) composites is developed via incorporating functionalized sepiolite (organo‐modified sepiolite [ONSep]). The PP composites with different amounts of intumescent flame retardants and ONSep were prepared by melt compounding. The morphology, thermal behavior, fire retardancy, smoke suppression, and mechanical property of flame‐retardant PP composites were studied. The results indicate an appropriate amount of ONSep in the flame‐retardant PP composites can increase thermal degradation temperature and char formation as well as a reduction of the peak heat release rate and total heat release; moreover, the addition of ONSep significantly decreases the CO production, total smoke production, smoke production rate, and smoke temperature. Simultaneously, the impact strength of intumescent flame‐retardant PP composite is also maintained by introducing an appropriate amount of ONSep as compared with that without ONSep.     

Fire calorimetry relying on the use of the fire propagation apparatus. Part II: burning characteristics of selected chemical substances under fuel rich conditions

The paper focuses on the detailed characterization of ventilation controlled fires of industrial products that are likely to govern accidental fire scenarios in fire resistant enclosures. Results regarding under‐ventilated fires of substances that are not polymers are presented to illustrate the capability of the fire propagation apparatus (FPA) to qualify such types of fires. Based on results from heptane fire tests in both well‐ and under‐ventilated fire conditions, a set of recommendations was previously provided in order to check the validity of the experimental results. The application of these recommendations is illustrated for the selected liquid substances containing hetero‐atoms. It emerges that the fire propagation apparatus assesses quite easily the performance of well‐controlled fires in both well‐ and under‐ventilated conditions. Another major outcome of our work is that the potential of the FPA has the capability to address fire issues outside the conventional use of the equipment, in particular to qualify the burning behaviour of chemicals on the full spectrum of ventilation conditions. Copyright © 2005 John Wiley & Sons, Ltd.     

Reducing the energy demand of corn‐based fuel ethanol through salt extractive distillation enabled by electrodialysis

The thermal energy demand for producing fuel ethanol from the fermentation broth of a contemporary corn‐to‐fuel ethanol plant in the U.S. is largely satisfied by combustion of fossil fuels, which impacts the possible economical and environmental advantages of bioethanol over fossil fuels. To reduce the thermal energy demand for producing fuel ethanol, a process integrating salt extractive distillation—enabled by a new scheme of electrodialysis and spray drying for salt recovery—in the water‐ethanol separation train of a contemporary corn‐to‐fuel ethanol plant is investigated. Process simulation using Aspen Plus® 2006.5, with the electrolyte nonrandom two liquid Redlich‐Kwong property method to model the vapor liquid equilibrium of the water‐ethanol‐salt system, was carried out. The integrated salt extractive distillation process may provide a thermal energy savings of about 30%, when compared with the contemporary process for separating fuel ethanol from the beer column distillate. © 2011 American Institute of Chemical Engineers AIChE J, 2012