Constant Heat Release Rate Research Articles

Performance-Based Design Assessment of Temperature Tenability Condition in a Hotel Atrium

Fire safety risk assessment to prevent loss of human life and property is necessary for complex structures where the traditional prescriptive designs are inapplicable. Maintaining tenable temperature conditions is essential for the safe evacuation of building occupants. This study considered British Standards (BS) 7974 and the Code of Practice for Fire Precautions in Buildings to analyze the temperature tenability conditions in the hotel atrium through a performance-based design approach. Further, the Computational Fluid Dynamics (CFD) code, Pyrosim, a Graphical User Interface (GUI) of the Fire Dynamics Simulator (FDS), was utilized to simulate a constant Heat Release Rate (HRR) steady state design fire of 5 Megawatts (MW) igniting from the hotel brasserie (ground floor) within the atrium. The researcher used the big design fire of 5MW to generalize the results to similar fires in similar structures. The objective was to conduct a fire safety risk assessment to prevent loss of property and fatalities by activating a smoke management control system with a ‘what if’ condition when the fire suppression system failed to start. Temperature data was collected through the statistical steady state profile, smoke layer temperatures, thermocouples, and 2-dimensional slice temperature recordings. The ground floor, the fire source, was found to have untenable conditions for human survival with temperatures above 2250C, as confirmed by thermocouple and steady-state temperature profile readings. Other floors demonstrated tenable conditions for human survival with temperatures below 400C due to the effect of natural vents and mechanical extractors, which extracted the hot smoke at a rate of 15m/s. The temperature recordings from this study compared well with those from Chew and Liew’s (2000) Computational Fluid Dynamics results, which had fire igniting within the atrium, without sprinklers, and had mechanical extraction fans and a constant Heat Release Rate of 5 Megawatts (MW). The results indicated that the smoke control management system maintained tenable temperature conditions within the hotel atrium, even without the fire suppression system through sprinklers. Considering the design fire size was 5 MW, which was significantly big, the results could be generalized for other hotels or structures with similar designs.

Numerical study on plug-holing of double fires in tunnel with centralized smoke exhaust

In tunnel fires, smoke is the main fatal factor causing casualties. The technical parameters of tunnel smoke extraction are particularly critical. However, the parameters related to smoke control have rarely been experimentally and quantitatively studied in a tunnel caused by two adjacent fire sources. Numerical simulations were performed to study the plug-holing phenomenon in the centralized smoke exhaust tunnel with multi-fire sources. A 1:10 small-scale tunnel (length 25 m; width 1.2 m; height 0.8 m) was built using FDS. The effects of different fire heat release rates Q̇, fire source separation distances, and smoke exhaust velocities (v) on the plug-holing were considered. Firstly, the smoke layer height beneath the exhaust vent gradually increases as the exhaust velocity becomes higher and then remains almost unchanged until the plug-holing phenomenon occurs. Additionally, the smoke layer height becomes lower as the fire source separation distance increases for the fires with constant heat release rate. For all Q̇ values, the critical plug-holing velocity increases with the increasing separation distance S and Q̇. In addition, by modifying the critical Froude number (Frc), a predictive model of the critical plug-holing velocity considering the dimensionless fire source heat release rate and separation distance is obtained. Furthermore, the modified critical Froude number model, accounting for two adjacent fires with different separation distances, is established. The correlation between the new model and the simulation results shows quite good agreement, indicating that the proposed model can provide a satisfactory prediction for the critical smoke exhaust velocity in plug-holing conditions of double fire sources. This work can provide valuable guidance for tunnel design concerning fire safety.

Investigating the Heat Release Rate of Large-scale Calorimeter using FDS Analysis

This study aims to identify the key design factors of a large-scale calorimeter and evaluate the accuracy of the simulation results using the Fire Dynamics Simulator (FDS) program. The design specifications of a domestic large-scale calorimeter were analyzed to determine the modeling and input conditions for the simulation. The simulation results of temperature, mass flow rate, and oxygen concentration reduction inside the duct were compared with the experimental results for heptane pool fires with diameters of 1.1 m, 1.24 m, and 1.44 m, respectively. To validate the accuracy of the simulation results, the deviations, calculated using FDS for the heat release rate as the experimental value, were found to be 19.12%, 11.86%, and 0.22% for temperature, mass flow rate, and oxygen concentration, respectively. Ultimately, the results of the heat release rate inside the duct obtained by the oxygen consumption method with FDS were found to be consistent with the experimental value, within 2.58%. However, the deviation of oxygen concentration is reduced as the deviation of mass flow rate increases for a constant heat release rate. This implies that for more accurate analysis, the heat loss and shape factors in the duct should be considered.

Experimental study, dimensional analysis and an integral model for horizontal buoyant turbulent jet fires under opposing wind

This work demonstrates a comprehensive model for horizontal turbulent jet flame geometries under opposing wind, for which few data or models can be found in the literature. This situation can be a practical scenario of offshore drilling platform with a horizontal flare under opposing wind. The opposing wind pushes the jet flame back, which eventually turns around and upwards, pointing finally downstream in the windward direction. The flame geometries are characterized by four parameters including horizontal length and vertical height from nozzle exit to the location of farthest point that flame envelope could reach before the flame turns around as well as horizontal length and vertical height from nozzle exit to the location of flame tip. Experiments are carried out for horizontal jets discharged from circular nozzles having diameters of 3, 5, 7 and 9 mm and employing propane as fuel with opposing wind speeds from 0.35 to 1.08 m/s. The locations of flame tip and the flame farthest point decrease with increasing opposing wind for a constant heat release rate. Dimensional analysis is derived from a physical model considering the momentum of fuel jet, flame buoyancy due to the flame temperature rise, opposing wind momentum and normalized flow rate at stoichiometric conditions at flame tip. The normalized flame geometry parameters based on the proposed model are well represented by two characteristic length scales derived by accounting for the interaction between excess jet-wind momentum and flame buoyancy as well as that between opposing wind momentum and flame buoyancy. In addition, the normalized mass flow rate at stoichiometric conditions determines the total length of flame trajectory. Moreover, an integral model is deduced by an air entrainment model and top hat profiles for the mass and momentum conservations to predict well the flame geometries of horizontal jet fires under opposing wind.

Numerical Investigation of the Effect of Sloped Terrain on Wind-Driven Surface Fire and Its Impact on Idealized Structures

In this study, a time-dependent investigation has been conducted to numerically analyze the impact of wind-driven surface fire on an obstacle located on sloped terrain downstream of the fire source. Inclined field with different upslope terrain angles of 0, 10, 20, and 30° at various wind-velocities have been simulated by FireFoam, which is a large eddy simulation (LES) solver of the OpenFOAM platform. The numerical data have been validated using the aerodynamic measurements of a full-scale building model in the absence of fire effects. The results underlined the physical phenomena contributing to the impact of varying wind flow and terrain slope near the fire bed on a built area. The findings indicated that under a constant heat release rate and upstream wind velocity, increasing the upslope terrain angle leads to an increase in the higher temperature areas on the ground near the building. It is also found that raising the inclined terrain slope angle from 0 to 30°, results in an increase in the integrated temperature on the surface of the building. Furthermore, by raising the terrain slope from 0 to 30°, the integrated temperature on the ground for the mentioned cases increases by 16%, 10%, and 13%, respectively.

Numerical Study on Natural Ventilation around a Burning Car inside a Tunnel

This study aimed to analyse the flow and temperature fields around a car on fire inside a medium-size tunnel under natural ventilation. The study used the fire dynamics simulator (FDS), which is an open-source software package, to simulate the thermo-fluidic characteristics inside the tunnel. A constant heat release rate (HRR) was assumed to ensure the release of consistent heat from the car while varying the speed of the mass flux natural ventilation. A medium-size tunnel and scaled car were modelled to simulate a realistic field environment; the car was assumed to have its primary components, including the body frame, tyres, seats, and other flammable materials. The constant HRR was set at 3.8 , which was measured in a field experiment using a cone calorimeter. The closed car windows were set to break when the temperature around them reached 600°C. Additionally, natural ventilation was one of the parameters used in the calculation; it was assigned as an inlet condition, referred to as the steady longitudinal inlet velocity, and ranged from 1.8 to 3.0 m/s. Based on the ventilation velocities, the variations of the flow characteristics, temperature field, turbulence kinetic energy levels, and vortex structure inside the tunnel were investigated. Additionally, the critical longitudinal velocity for natural ventilation was estimated by performing the current simulation under different ventilation velocities. Given that the thermo-fluidic parameters and geometry information are all similar, the FDS results were compared to those from three semi-empirical models for predicting critical ventilation velocities from previous studies.

Simulation on smoke re-circulation transition in an urban street canyon for different fire source locations with cross wind

When a fire occurs inside an urban street canyon, the pollutant evolution is particular as a result of the fire-induced high buoyancy. Controlled by the competition of cross wind inertia force and fire plume buoyancy, the presence of fire smoke re-circulation in the street canyon has significant threat on human safety. Previous research mostly reported the re-circulation when fire locates in the center position, but the fire location variation effect has not been taken into consideration. In this paper, a street canyon model of 18 m wide and 18 m high is built with a constant heat release rate of 5 MW, while ten fire distances to the leeward building from 3 to 15 m are simulated. Results show that the smoke re-circulation is distinguished into three regimes for different fire locations. The re-circulation does not exist at the first regime, but it appears with its critical wind velocity slightly increases at the second regime, then the critical velocity increases sharply at the third regime. Besides, the flow patterns, and CO concentrations are presented and discussed as references to such re-circulation transition. Correlations are proposed to predict the critical wind velocity and the corresponding Froude Number for various fire locations.

Simulation investigation on the smoke spread process in the large-space building with various height

In this paper, the fire growth and smoke spread process in Large-space building have been investigated through the Fire Dynamics Simulator (FDS). What's more, the alarm process of the Line-type Infra-red Beam Smoke Fire Detector (LSD) and the Aspirating Smoke Detection System (ASD) have discussed, some valuable results have been obtained. The results indicated that the raise of the difference between the two height, and the smoke spread process is becoming slower at the constant heat release rate. The set of fire alarm system in large-space should be consider the “height advantage”, as the higher set of the smoke decent responding earlier than the lower ones. What's more, referring to the ASD system the aspirator samplers close to the building's edge should be affected by the edge. For the LSD system should determine the parameter of install by the numerical or experimental test to optimizing the performance of the LSD, which has been proposed in the paper. In summary, the research investigates the basic fire alarm process for the LSD and the ASD System in the large-space buildings, and these are valuable for the selecting and setting of fire alarm system in the large-space buildings.

Investigation of terrain slope effects on wind enhancement by a line source fire

Wind enhancement triggered by fire-wind interaction can potentially pose significant damage to structures built in bushfire prone areas. The effect of terrain slope is one of the parameters contributing to the enhancement of wind by fire that needs to be taken into account. This study employs a validated model of Computational Fluid Dynamics to assess the effects of terrain slope on this phenomenon. A module was developed and appended to the FireFOAM solver to output individual component of flow acceleration. Multiple analyses were used to explain the effects of terrain upslope and downslope on the phenomenon. The results reveal that although the enhancement of wind velocity due to fire increases with an increase in terrain upslope, a terrain downslope reduces flow enhancement by fire. The results also established that while an upslope terrain reinforces the Coanda effects and intensifies attachment of the plume to the ground, the downslope condition mitigates Coanda effects and reduces the flow's tendency to attach to the ground downstream of the fire source. Furthermore, under a constant heat release rate and upstream wind velocity, the maximum magnitude of wind enhancement linearly increases with the increase of upslope angle.

Combustion of straight algae oil in a swirl-stabilized burner using a novel twin-fluid injector

The current study investigates the combustion performance of straight algae oil (AO) in a 7-kW lab-scale gas turbine burner enabled by a novel twin-fluid injector, named Swirl-burst (SB) injector. The chemical structure (fatty acid profile), the physical, and chemical properties of AO are acquired to understand the combustibility of the oil as a potential biofuel. Effects of equivalence ratio (ER) and atomizing air to liquid mass ratio (ALR) across the injector on the global combustion characteristics are investigated at a constant heat release rate for the oil. The features of interest include visual flame images, product gas temperature, emissions of carbon monoxide (CO), and nitrogen oxides (NOx) at the combustor exit. Results show that mono-unsaturated fatty acid is predominant in the composition of the oil, suggesting possibly short ignition delay. AO has a heating value comparable to that of diesel but with a high kinematic viscosity (approximately 16 times more viscous than diesel). Clean combustion highly depends on fine sprays that lead to fast fuel pre-vaporization, thorough fuel-air mixing, and thus clean premixed combustion. Conventional injectors such as air blast (AB) atomizers cannot finely atomize viscous oils for clean combustion due to the low viscosity tolerance. Fortunately, with the SB injection, clean, complete, and lean-premixed combustion of straight AO has been successfully achieved without fuel preheating at most of the investigated cases, reasonably reflecting the fine atomization capability of the SB injector even for the viscous oil. The blue flames, overlapping temperature profiles, and low emissions of CO and NOx consistently show the clean lean-premixed AO flames. Stable and clean flames are obtained at ERs of 0.60–0.75 (with the optimum ER identified at 0.65, in terms of flame stability and low emissions), and a blow-out limit at the ER of about 0.55. At the ER of 0.65, clean and lean-premixed flames are also acquired for all the tested ALRs (2.0–5.0). Increase in ALR varies the SAA and spray behavior of the SB injection as well as the aerodynamic interaction between fuel and oxidizer. The increasing ALR results in dominantly blue flames and decrease in CO and NOx concentrations, less than 10 ppm at ALRs > 2.5, due to finer atomization and better fuel-air mixing at the higher ALRs, and thus enhanced premixed combustion. Overall, clean and stable lean-premixed combustion of straight AO is achieved without fuel preheating using the novel SB injector despite the high fuel viscosity. The SB injection potentially enables AO itself as a cost-effective and near-zero-emission biofuel.

Evaluation of Oxygen Reduction System (ORS) in Large-scale Fire Tests

An oxygen reduction system (ORS) is a fire prevention system that uses a low-oxygen environment to reduce, if not eliminate, the potential for ignition and fire propagation in a protected space. The key parameter for ORS design is the limiting oxygen concentration (LOC), defined as the lowest O2 concentration that can support combustion for a given fuel. The present work examines LOCs of solid fuels at large scale in a configuration representative of a rack-storage and discusses the results in relation to the design concentration for ORS.To simulate ORS applications in engineering practice, a two-tier fuel array of standard commodities in rack storage configuration was set up in an enclosure. A constant N2/Air mixture flow was supplied to the enclosure at a desired oxygen concentration. The oxygen concentration was varied from 9% up to 17%. A premixed flame with a constant heat release rate was used as the ignition source to maintain repeatable test conditions. This premixed flame ignitor represents potential heat sources such as electric arc and hot work that are not sensitive to oxygen level. The tested materials included five standard commodities: Class 3, Cartoned Unexpanded Plastic (CUP), Cartoned Expanded Plastic (CEP), Uncartoned Unexpanded Plastic (UUP) and Uncartoned Expanded Plastic (UEP). This paper reports detailed test results at different oxygen levels only for Class 3. The impact of the test conditions on fire propagation was examined and the results showed that the oxygen concentration was the major parameter to control fire propagation. When successful flame spread is initiated by the igniter, the fire size tends to be larger as the igniter is sustained for a longer time. The results of fire propagation success were obtained for the five standard commodities under different oxygen concentrations with a sustained igniter (hard limits) and without a sustained igniter (soft limits). The LOC was defined as an oxygen concentration at 0.05 probability of flame spread by using statistical analysis. The resulting LOC values measured for different commodities in a two-tier rack storage are:• Cartoned (Class 3, CUP and CEP) – hard limit 11.1%,• Uncartoned (UUP and UEP) – hard limit 13.0%,• Cartoned (Class 3, CUP and CEP) – soft limit 13.8%,• Uncartoned (UUP and UEP) – soft limit 14.7%.These LOCs are generally lower than the oxygen design concentrations recommended by existing standards including VdS 3527 and EN 16750 due to different test conditions. The hard limits resemble fundamental LOC for gases and vapors and do not depend significantly on the ignition duration and array size, while the soft limits vary significantly with the size and configuration of the fuel array and ignition duration. It is concluded that the hard limits are more suitable for ORS design purposes.

Numerical Investigation of Critical Velocity in Reduced Scale Tunnel Fire with Constant Heat Release Rate

When a fire occurs in a tunnel in the absence of sufficient air supply, large quantities of smoke are generated, filling the vehicles and any space available around them. Hot gases and smoke produced by fire form layers flowing towards extremities of the tunnel which may interfere with person’s evacuation and firefighter’s intervention. This paper carries out a numerical simulation of an unexpected fire occurring in a one-way tunnel in order to investigate for the critical velocity of the ventilation airflow; this one is defined as the minimum velocity able to maintain the combustion products in the downstream side of tunnel. The computation is performed successively with two types of fuels representing a large and a small heat release rate, owing to an open source CFD code called ISIS, which is specific to fires in confined and nonconfined environments. It is indicated that, after several computations of full-scale fires of 43.103 and 19.103 kJ/kg as heat release rate, the velocities satisfying the criterion of healthy environment in the upstream side of the tunnel are 1.34 m/s and 1.12 m/s, respectively.

Modeling carbon monoxide spread in underground mine fires

Carbon monoxide (CO) poisoning is a leading cause of mine fire fatalities in underground mines. To reduce the hazard of CO poisoning in underground mines, it is important to accurately predict the spread of CO in underground mine entries when a fire occurs. This paper presents a study on modeling CO spread in underground mine fires using both the Fire Dynamics Simulator (FDS) and the MFIRE programs. The FDS model simulating part of the mine ventilation network was calibrated using CO concentration data from full-scale mine fire tests. The model was then used to investigate the effect of airflow leakage on CO concentration reduction in the mine entries. The inflow of fresh air at the leakage location was found to cause significant CO reduction. MFIRE simulation was conducted to predict the CO spread in the entire mine ventilation network using both a constant heat release rate and a dynamic fire source created from FDS. The results from both FDS and MFIRE simulations are compared and the implications of the improved MFIRE capability are discussed.

Q.C.M.

Nowadays many research efforts are focused on the study and development of new combustion modes, mainly based on the use of locally lean air–fuel mixtures. This characteristic, combined with exhaust gas recirculation, provides low combustion temperatures that reduces pollutant formation and increases efficiency. However these combustion concepts have some drawbacks, related to combustion phasing control, which must be overcome. In this way, the use of a spark plug has shown to be a good solution to improve phasing control in combination with lean low temperature combustion. Its performance is well reported on bibliography, however phenomena involving the combustion process are not completely described. The aim of the present work is to develop a detailed description of the spark assisted compression ignition mode by means of application of UV–Visible spectrometry, in order to improve insight on the combustion process.Tests have been performed in an optical engine by means of broadband radiation imaging and emission spectrometry. The engine hardware is typical of a compression ignition passenger car application. Gasoline was used as the fuel due to its low reactivity. Combining broadband luminosity images with pressure-derived heat-release rate and UV–Visible spectra, it was possible to identify different stages of the combustion reaction. After the spark discharge, a first flame kernel appears and starts growing as a premixed flame front, characterized by a low and constant heat-release rate in combination with the presence of remarkable OH radical radiation. Heat release increases temperature and pressure inside the combustion chamber, which causes the auto-ignition of the rest of the unburned mixture. This second stage is characterized by a more pronounced rate of heat release and a faster propagation of the reactions through the combustion chamber. Moreover, the measured UV–Visible spectra show some differences in comparison with the other stages. The relative intensities in of spectra from different combustion radicals have also been related to the different combustion phases.

Characterizing Heat Release Rates Using an Inverse Fire Modeling Technique

A ubiquitous source of uncertainty in fire modeling is specifying the proper heat release rate (HRR) for the fuel packages of interest. An inverse HRR calculation method is presented to determine an inverse HRR solution that satisfies measured temperature data. The methodology uses a predictor-corrected method and the Consolidated Model of Fire and Smoke Transport (CFAST) zone model to calculate hot gas layer (HGL) temperatures in single compartment configurations. The inverse method runs at super-real-time speeds while calculating an inverse HRR solution that reasonably matches the original HRR curve. Examples of the inverse method are demonstrated by using a multiple step HRR case, complex HRR curves, experimental temperature data with a constant HRR, and a case with an experimentally measured HRR. In principle, the methodology can be applied using any reasonably accurate fire model to invert for the HRR.

CFD Study of Huge Oil Depot Fires - Generation of Fire Merging and Fire Whirl in (7 x 7) Arrayed Oil Tanks

One of the largest disasters on industrial fires may exist in oil tank depots which store much amount of oil. Many previous studies on the fire safety of oil tank depots have been related to the fire propagation from one single oil tank fire to the adjacent tank via radiation. However, single oil tank fire may cause a fire whirl in windy conditions, entraining much more ambient air and enhancing flame radiation, which may increase the possibility of fire propagation toward the neighbors. In addition, when an oil depot storing large amount of oil in tanks is subject to destructive earthquakes, merging fires and fire whirls may be generated, leading to disastrous consequences. In this work, the authors examined the fire merging and fire whirl behaviors in multiple huge oil tank fires by CFD simulations, by FDS-4. The constant heat release rate model was employed and the effects of tank-to-tank distance, wind speed and heat release rate were examined. It was found that these parameters are important to cause the fire merging and fire whirls, and at the same time, the conditions to cause fire merging and fire whirls lie in a limiting range. Some relevant correlations were established. The results are expected to be useful for mitigating the disasters due to fire merging and fire whirls.