Constant Heat Release Research Articles

Influence of the flame jet on heat loss and thermal efficiency of lean burn pre-chamber natural gas engine with various geometrical combustion chambers

Due to relatively high thermal efficiency and low NOx emission, the pre-chamber type lean burn natural gas engine for cogeneration is expected to be spread rapidly in the near future. To offer a guidance for designing the pre-chamber natural gas engines, in the present study, the influence of the flame jets on combustion process and thermal efficiency of pre-chamber type lean burn natural gas engine was investigated with various pre-chamber orifice diameters and angles and piston bowl shapes by numerical simulation. The presented results showed that when the orifice diameter is smaller, it results in higher heat loss with the stronger gas flame jets impinging on piston top and cylinder liner walls, but the higher degree of constant volume heat release can be also obtained. Consequently, there is no significant difference in the thermal efficiency for these four orifice diameters. Increasing the angle of the orifice and the depth of the piston bowl can avoid the heat loss caused by the early impact of flame jets on the piston top wall. In addition, compared to the diameter of piston bowl, the depth of piston bowl, which is related to the distance from the orifice to the piston bowl, should have more effect on the combustion process and thermal efficiency. For wider orifice angle, the heat loss was also increased, particularly to cylinder head. Finally, the optimal thermal efficiency obtained by balancing heat loss and the degree of constant volume heat release is 44.73%.

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.

Mechanism of the reduction in afterburning and thermal efficiency improvement with highly oxygenated fuels in diesel combustion

Highly oxygenated fuels can effectively reduce afterburning in diesel diffusion combustion and improve the degree of constant volume heat release in spite of increases in injection duration due to smaller heating values. The mechanism of afterburning reduction and the structural differences in the diesel fuel spray with changing the oxygen content in the fuel were investigated in a constant volume vessel and analyzed with 3D CFD simulation. The result showed that the equibalance ratio inside the spray decreased with increases in the oxygen content due to lower theoretical air-fuel ratios, promoting the spray combustion after the end of injection. Further, the combustion characteristics and the exhaust gas emissions of the oxygenated fuels were investigated in an experimental single cylinder diesel engine with modern specifications. With increasing oxygen contents, the degree of constant volume heat release increased with reductions in the afterburning, resulting in higher indicated thermal efficiencies. However, the indicated thermal efficiency showed a maximum at around 27 mass% of the oxygen in fuel and further increases in the oxygen contents resulted in lower indicated thermal efficiencies due to larger cooling losses.

Linear Stability of a Combined Convective Flow in an Annulus

Linear stability analysis of a combined convective flow in an annulus is performed in the paper. The base flow is generated by two factors: (a) different constant wall temperatures and (b) heat release as a result of a chemical reaction that takes place in the fluid. The nonlinear boundary value problem for the distribution of the base flow temperature is analyzed using bifurcation analysis. The linear stability problem is solved numerically using a collocation method. Two separate cases are considered: Case 1 (non-zero different constant wall temperatures) and Case 2 (zero wall temperatures). Numerical calculations show that the development of instability is different for Cases 1 and 2. Multiple minima on the marginal stability curves are found for Case 1 as the Prandtl number increases. Concurrence between local minima leads to the selection of the global minimum in such a way that a finite jump in the value of the wave number is observed for some values of the Prandtl number. All marginal stability curves for Case 2 have one minimum in the range of the Prandtl numbers considered. The corresponding critical values of the Grashof number decrease monotonically as the Prandtl number grows.

Performance analysis on the concentrated photovoltaic /thermal air collector with phase change material and vacuum double-glazing for temperature regulation

Although photovoltaic/thermal (PV/T) air collector has simple structure and strong pressure bearing capacity, there are problems such as low thermal efficiency, unstable output temperature, due to low heat transfer performance of air and fluctuating solar irradiation. To address the above issues, a concentrating photovoltaic/thermal air collector with phase change material and vacuum double-glazing (VDG-PCM-CPV/T) is proposed in this paper. The performance of VDG-PCM-CPV/T in three continuous days is studied and compared with the module with PCM and single-glazing (SG-PCM-CPV/T) and the module with single-glazing (SG-CPV/T) by establishing the mathematic model of the daytime and night. It is proven that VDG-PCM-CPV/T has certain advantages in alleviating the downward trend of air temperature caused by the decrease of solar irradiation, due to the constant temperature storage and heat release characteristics of PCM. At night, as the vacuum double-glazing has excellent heat preservation effect, the initial temperature of PCM in VDG-PCM-CPV/T is 5.00 °C higher than that of SG-PCM-CPV/T, enable VDG-PCM-CPV/T to obtain higher thermal efficiency in the next day. While, the electrical power of VDG-PCM-CPV/T is slightly lower than that of SG-PCM-CPV/T and SG-CPV/T. The exergy efficiency of VDG- PCM-CPV/T, SG-PCM-CPV/T and SG-CPV/T at peak is 1.70%, 1.10% and 2.00%, respectively.

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.

Heat transfer in BCC lattice materials: Conduction, convection, and radiation

Research studies have recently been conducted on heat transfer in architected materials. As a type of rationally-designed lightweight material, lattices have received much attention in the past few years due to their multifunctional properties, mainly realized by the application of 3D printing techniques. In the present research, fluid flow and conduction, convection, and radiation heat transfer in three-dimensional periodic BCC lattices, as a topologically cubic example among a myriad of cellular architectures, are studied for a wide range of porosity (0.7–0.99) and Reynolds numbers (1–150) via a CFD analysis. The steady and incompressible flow of cool fluid with constant thermophysical properties inside a unit cell or an assembly of unit cells is simulated using the Fluent software. First, the hydrodynamic behavior of the fluid flow in the unit cell without a thermal gradient is studied. In the absence of radiation, conduction and convection heat transfer are explored under two different thermal conditions, namely Constant temperature at solid struts and Constant heat release from solid struts. The numerical results show that cell temperature increases for the constant temperature boundary condition and decreases for the constant heat release when the cell porosity decreases at the same Reynolds number. By considering radiation mechanism via the Discrete Ordinates Method, it is observed that radiative thermal conductivity increases by increasing the porosity. The increase, linearly correlated with the cell size, slightly enhances by increasing the solid radiative emission coefficient and the applied temperature difference. At lower porosities, the heat conduction, and at higher porosities, the radiation heat transfer plays a significant role in the effective thermal conductivity. At the average cell temperature of 1800 K, the ratio of radiative thermal conductivity to the effective thermal conductivity is 95% for the porosity of 0.99 and is 12% for the porosity of 0.7. After examining all three modes of heat transfer at the constant heat release thermal condition, it is found that the temperature of solid struts increases by decreasing the Reynolds number, leading to an increase of the ratio of radiation heat transfer to the total heat transfer (the ratio rises six times as the Reynolds number decreases from 150 to 1.5625 for the porosity of 0.99). For the constant heat release thermal condition, radiation heat transfer in BCC lattices can not be ignored when the porosity is high or the thermal conductivity of constitutive solid and the flow Reynolds number are low.

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.

Predicting transient building fire based on external smoke images and deep learning

A real-time evaluation of fire severity inside a building could facilitate decision-making in firefighting and rescue operations. This work explores the real-time prediction of transient fire scenarios by using external smoke images and deep learning algorithms. A big database of 1845 simulated compartment fire scenarios is formed. Three input parameters (constant fire heat release rate, opening size, and fuel type) are paired with the external smoke images, and then trained by Convolutional Neural Network (CNN) model. Results show that by training either the front-view or side-view smoke images, the artificial intelligence (AI) method can well identify the transient fire heat release rate inside the building, even without knowing the burning fuels, and the error is no more than 20%. This work demonstrates that the deep learning algorithms can be trained with simulated smoke images to determine the hidden fire information in real-time and shows great potential in smart firefighting applications.

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.

LES analysis of fire source aspect ratio effects on fire-wind enhancement

Enhancement of wind by bushfire, referred to as bushfire-wind enhancement phenomenon, causes damages to buildings located in bushfire-prone areas by increasing pressure load around the structures. This study focuses on the effects of point source aspect ratio (AR) on the wind enhanced by fire. FireFOAM solver of OpenFOAM platform is used to perform Large Eddy Simulation analysis for different fire source aspect ratios under two different fire source conditions: (i) identical fire intensity (fire heat release rate per unit area) and (ii) identical fire heat release rate conditions. Simulations were performed for three different fire source aspect ratios under these fire source boundary conditions. An appropriate normalization group based on fire source hydraulic diameter was introduced for fire-induced pressure gradient to explain the variation of wind enhancement with fire source aspect ratio. The results reveal that under a constant fire intensity condition, increasing the fire source aspect ratio causes a higher normalized fire-induced pressure gradient which leads to more intensified wind enhancement. In contrast, the increase of fire source aspect ratio while fire heat release rate is kept constant culminates in a reduction in the normalized fire-induced pressure gradient, reducing wind enhancement. Moreover, with the increase of the fire source aspect ratio, the area of counter-rotating vortices (CRV) where maximum wind enhancement occurs is expanded. The results also show that with the increase of fire source aspect ratio, the length of flame attachment to the ground immediately downstream of fire increases. In addition to the longitudinal wind enhancement, the effects of fire source aspect ratio on vertical velocity were also analyzed based on the Richardson number defined by hydraulic diameter and flow reference velocity. The effects of the aspect ratio on flame length were also studied. It was shown as a result of the increase of aspect ratio for one unit, flame length increases by approximately 14% and reduces by 7% under constant fire intensity and constant fire heat release rate condition, respectively.

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.

Influence of shape and heat release of thermal passenger manikins on the performance of displacement ventilation in a train compartment

The influence of sensible heat release on the performance of displacement ventilation was studied in a generic laboratory representing the lower cabin of the German Aerospace Center (DLR)’s Next Generation Train. Tests at variable mean cabin temperatures were conducted with human subjects, thermal manikins and heating mats at different but constant heat release rates. Moreover, tests with thermal manikins and an adaptive heat release rate were performed. Flow fields, surface temperature distributions as well as local temperatures and velocities were evaluated. The study revealed that the shape of the heat sources is negligible if only global quantities, such as the global enthalpy flux or the heat removal efficiency, are evaluated. The latter was found to be independent of the amount of released heat. However, it strongly reacts to the choice of probe positions used for the mean cabin temperature. Regarding the comfort-relevant flow parameters, both the shape and the heat release rate are highly relevant to temperature stratifications and flow fields in the passenger zone. The manikins with adaptive heat release proved to be a major improvement in terms of realistic simulation of the human metabolism for investigations regarding the performance of ventilation systems. However, the determination of the mean cabin temperature receives increased relevance as it is prone to limit the closeness to reality.

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.

Thermal efficiency improvement with super-charging and cooled exhaust gas recirculation in semi-premixed diesel combustion with a twin peak shaped heat release

Thermal efficiency–related parameters in semi-premixed diesel combustion with a twin peak shaped heat release were experimentally investigated in a 0.55-L single-cylinder diesel engine. Here, the first heat release peak is realized with the premixed combustion at top dead center after the end of the first fuel injection with a sufficient ignition delay. The fuel injection quantity for the first combustion was maximized in a range to limit the rate of pressure rise below 0.6 MPa/°CA at 0.4 MPa IMEP, 0.8 MPa/°CA at 0.8 MPa IMEP, and 1.0 MPa/°CA at 1.3 MPa IMEP to ensure the large degree of constant volume heat release and to suppress smoke emissions. The second heat release peak is formed from the rate-controlled combustion with the second fuel injection immediately after the end of the first combustion. The influence of the intake oxygen concentration and the intake gas pressure on the thermal efficiency and the exhaust gas emissions was systematically examined at three load conditions (indicated mean effective pressure ≈0.4, 0.8, and 1.3 MPa). The results with two types of combustion chambers, a toroidal chamber expecting smaller cooling losses with weaker in-cylinder gas motion, and with a re-entrant chamber expecting better air utilization with stronger in-cylinder gas motion are compared. At the medium load, a significantly high indicated thermal efficiency exceeding 50% is established with a reduction in the intake oxygen concentration due to the smaller cooling loss. The indicated thermal efficiency improves with a decrease in the intake oxygen concentration as the reduction in the cooling loss is more significant than the increase in the exhaust loss. However, an excessive reduction in the intake oxygen concentration results in a deterioration in the indicated thermal efficiency due to a reduction in the combustion efficiency. At low load conditions, the indicated thermal efficiency is lower than at the medium load due to lower combustion efficiency and the improvement in the indicated thermal efficiency with reductions in the intake oxygen concentration is not significant as the combustion efficiency decreases with the decrease in the intake oxygen concentration. At the high load condition, the indicated thermal efficiency is lower due to a larger exhaust loss than at the low and medium load conditions and the indicated thermal efficiency decreases with the decrease in the intake oxygen concentration. With an increase in the intake gas pressure, the indicated thermal efficiency increases consistently mainly due to the reducing cooling loss. In comparison with the re-entrant combustion chamber, the indicated thermal efficiency with the toroidal combustion chamber is 1% higher due to a smaller cooling loss at the low load, almost comparable at the medium load and 1.2% lower at the high load due to the larger exhaust loss.

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.