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In recent years, the applications of lithium-ion batteries have emerged promptly owing to its widespread use in portable electronics and electric vehicles. Nevertheless, the safety of the battery systems has always been a global concern for the end-users. The separator is an indispensable part of lithium-ion batteries since it functions as a physical barrier for the electrode as well as an electrolyte reservoir for ionic transport. The properties of separators have direct influences on the performance of lithium-ion batteries, therefore the separators play an important role in the battery safety issue. With the rapid developments of applied materials, there have been extensive efforts to utilize these new materials as battery separators with enhanced electrical, fire, and explosion prevention performances. In this review, we aim to deliver an overview of recent advancements in numerical models on battery separators. Moreover, we summarize the physical properties of separators and benchmark selective key performance indicators. A broad picture of recent simulation studies on separators is given and a brief outlook for the future directions is also proposed.

Multifunctional building façades have become an increasingly critical component in modern buildings, especially after the tremendous scrutiny triggered by the utilization of combustible aluminum cladding panels (ACP) in the construction sector. Following the massive effort by both industry and government agencies to reduce the fire risks of combustible façades in recent years, façades with insufficient fire ratings have been continuously causing severe building fires leading to countless human casualties and properties damages. This review aims to provide an in-depth overview of the previous developments and current progress for establishing relevant fire standards with regards to ACPs, from an Australian standpoint. The fire spread mechanisms associate with ACPs, and their potential hazards were discussed. Furthermore, the current building regulations for ACPs have been reviewed, including detailed experimental procedures and rating criterion for all existing international standards. To address the research knowledge gap in terms of the understanding of the cladding fire mechanisms, and combustibility of existing ACP polymer composites, recent advancement in experimental and numerical studies has been summarized and discussed to identify the critical issues and concerns for current ACP products. Future perspectives involving cutting-edge approaches such as computational fluid dynamics (CFD) modeling coupled with artificial neural network (ANN) optimization are advocated in this article. Additionally, fundamental material characterization techniques using molecular dynamics (MD) approaches can be implemented to deliver a better description of the degradation kinetics and smoke/toxicity generations.

Hydrogen-diesel dual direct-injection (H2DDI) is successfully implemented in a compression-ignition engine, which is developed to circumvent the pre-ignition and knocking limitations inherent to port fuel-injection hydrogen engines. An automotive-size single-cylinder common-rail diesel engine was modified to fit an additional high-pressure hydrogen injector in the cylinder head. The engine is operated at intermediate load with constant fuel-energy input using an energy-substitution principle – the diesel injection duration is decreased as the hydrogen amount is increased while adjusting the diesel injection timing to fix the combustion phasing. The results show that, at early hydrogen injection timings, the heat release rate and engine-out emissions show trends indicating premixed combustion whereas later injection timings exhibit hydrogen mixing-controlled combustion behaviour. At 50% hydrogen substitution ratio and optimised direct injection timing of 40 ⁰CA bTDC, the uncompromised indicated efficiency of 47% is achieved while the combustion-induced noise is decreased by 6 dB and the engine-out NOx emission is kept below 11 g/kWh.

Analyzing the heat transfer effectiveness of fire suppression systems at droplet level through experimentation is difficult and costly. To overcome this issue, traditional Eulerian–Lagrangian model has been modified to track droplet histories in association with computational fluid dynamics (CFD) fluid models. This allows a comprehensive description of the flame interaction energy migration process of water droplets. The modified Eulerian–Lagrangian approach is adopted to trace every droplet parcel coupled with the fluid closure. Using the in-house code, the histogram of key parameters (e.g. temperature, velocity, mass, etc.) of droplets on microscopic level during suppression are obtained over time-iterations, then subsequently analyzed by statistical approaches, which made the concept of water utilization rate advocated for the first time. Through combination with other key parameters, this concept can effectively indicate the suppression efficiency at droplet level, and thus provide key insights to the design of water mist or more advanced systems. Among the cases studied, with similar suppression time, it is discovered that the water utilization rate can vary from 10% to 26%, based on different design. Tracing the transient movement and evaporation process of water droplets formulates a new approach to effectively study the heat transfer efficiency of water-based fire suppression systems.

The combustion characteristics and kinetics of microalgae (Chlorella vulgaris) and sub-bituminous coal blends (CCBs) are studied by a thermogravimetric analyzer (TGA), and those of pure Chlorella vulgaris (C. vulgaris) and coal were also taken respectively as control groups. The microalgae to coal blending ratio (MCR) is 3/7, 5/5 and 7/3. The results showed that three stages were observed during the combustion of CCBs. And the main combustion of CCBs was occurred at the second stage ranged from 254.6 ~ 389.4°C to 698.7 ~ 741.0°C. Both of the ignition temperature (Ti) and the final temperature detected when stabilization of samples mass occurred (Tf) were decreased as the C. vulgaris content increased in the CCB. The maximum combustion rate (Rmax) of C. vulgaris was maximum. The average reaction rate (Rv) was firstly decreased, and then increased as the content of C. vulgaris in CCBs increasing. With the increasing content of C. vulgaris, both of the ignition index (Di) and the comprehensive combustion characteristic index for the blends (SM) were increased. Some deviations from their expected characteristics indicate interaction. As the heating rate (β) increases, Ti, the peak temperature (Tp), the reaction rate at the peaks (Rp), Rv and Tf were all increased significantly, while the residual mass (Mr) was first increased, and then decreased. For CCBs, the activation energy (E) was the first decreased, and then increased, and the minimum E was obtained as MCR = 5/5. Among all the samples, E of pure coal was the minimum one. Finally, kinetic triplets were determined by the Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), and master-plots method, they are respectively E = 62.90, 108.99, 85.28, 92.27, 104.98 kJ/mol, the reaction order (n) = 1.4, 4.1, 2.7, 3.2, 4 and the frequency factor (A) = 6.38 × 105, 1.05 × 106, 2.29 × 104, 8.73 × 104, 2.93 × 106 min−1 for the coal, blends with MCR of 3/7, 5/5, 7/3 and C. vulgaris combustion at β = 20°C/min.

This experimental study aims to evaluate the engine performance and emissions when exhaust gas recirculation (EGR) and e-boosting are used in a gasoline compression ignition (GCI) engine operating at 2000 rpm and 800-900 kPa indicated mean effective pressure (IMEP) conditions. In an automotive size common-rail diesel engine architecture, a partially premixed charge-based GCI combustion was realized implementing triple injections with a split ratio of 50%, 10%, and 40% and injection timings of 170, 40, and 9-6 crank angle degrees (°CA) before top dead center (bTDC). The previous tests performed in the same engine suggested this injection strategy could achieve further nitrogen oxides (NOx) reduction if EGR is utilized with the help of intake air boosting to compensate for the loss in power output and engine efficiency. In the present study, the GCI engine is set up with a conventional EGR system and a supercharger driven by an electric motor (or an e-booster). Each EGR and e-boosting effect was systematically evaluated, and the tests were repeated not only for GCI combustion but also diesel combustion, as a reference case. This study found that the charge dilution and reduced combustion temperature due to 16% EGR achieve over 50% NOx reduction and 5% noise reduction, but only at the expense of reduced engine efficiency and increased emissions of unburnt hydrocarbon (uHC), carbon monoxide (CO), and smoke. The test on e-boosting showed that the efficiency loss caused by EGR could be fully recovered with only 10 kPa of intake air boosting. At higher boosting pressure of 30 kPa, GCI combustion achieved not only 11% efficiency improvement but also 75% NOx and 5.6% noise reduction compared with no EGR and no e-boosting baseline condition. This was significant because uHC and CO emissions were also reduced due to enhanced oxidation. It was found that the sensitivity to charge dilution with EGR and e-boosting is much higher for GCI combustion than that for diesel combustion.

The evolution and combustion of H2 jets were investigated in an optically-accessible constant-volume chamber under simulated direct-injection (DI) compression-ignition (CI) engine conditions. The parameters varied include injection pressure (84–140 bar) and ambient temperature (1000–1140 K). A detailed characterization of the injector system and the ensuing jet penetration process is reported first. High-speed schlieren imaging, OH∗ chemiluminescence imaging and pressure trace measurements were subsequently used to investigate the auto-ignition and combustion of the H2 jets. The results show that the ignition delay of H2 jets under such conditions is sensitive to ambient temperature variations, but not to injection pressure. Optical imaging reveals that the combustion of H2 jets mostly initiated from a localized kernel, before spreading to engulf the whole jet volume downstream of ignition location. The imaging also indicates that after ignition, the flame recesses back towards the nozzle and appears to attach to the nozzle to form a diffusion flame structure.

Gasoline compression ignition (GCI) engines have potential to improve fuel economy and reduce emissions harmful to health and the environment compared with conventional diesel combustion engines. The underpinning knowledge of key phenomena of fuel-air mixture formation, ignition, combustion, and pollutant formation, however, is lacking at present. This work investigated the ignition and combustion interaction processes between two consecutive jets of iso-octane (gasoline surrogate) and n-heptane (diesel surrogate) inside a quiescent steady environment with an ambient density of 22.8 kg/m3, an O2 concentration of 21 vol % but with ambient temperatures of 950 and 780 K, respectively. Three injection schedules were tested, consisting of a double injection that follows a pilot-main injection duration (2.6 ms/6.5 ms) with dwell times of 0.2, 0.7, and 1.2 ms, in addition to single injections with long (9.1 ms) and short (2.6 ms) injection durations as reference cases. Combined high-speed schlieren imaging, pressure trace measurements, combustion luminosity detection using photodiode and closed-homogeneous reactor simulations revealed that under the 950 K condition for iso-octane and 780 K condition for n-heptane, pilot-injection-induced local temperature and flame intermediate changes can considerably affect the preignition reactions of the main injections that followed. It is also found that the interaction effects are dependent on the ignition and combustion characteristics of the fuels involved as well as the temporal separation between the injections.

A numerical study of the fire whirl formation under symmetrical and asymmetrical entraining configuration is presented. This wok aims to assess the effect of eddy-generation configuration on the evolution of the intriguing phenomenon coupled with both flow dynamics and combustion. The numerical framework implements large-eddy simulation, detailed chemistry to capture the sophisticated turbulence-chemistry interaction under reasonable computational cost. It also adopts liquid-based clean fuel with fixed injection rate and uniformed discretisation scheme to eliminate potential interference introduced by various aspects of uncertainties. The result reveals that the nascent fire whirl formulates significantly rapidly under the symmetrical two-slit configuration, with extended flame height and constrained vortex structure, compared with the asymmetrical baseline. However, its revolution orbit gradually diverges from domain centreline and eventually stabilises with a large radius of rotation, whereas the revolution pattern of that from the baseline case is relatively unchanged from the inception of nascent fire whirl. Through the analysis, the observed difference in evaluation pathway could be explained using the concept of circular motion with constant centripetal force. This methodology showcases its feasibility to reveal and visualise the fundamental insight and facilitate profound understanding of the flaming behaviour to benefit both research and industrial sectors.

With recent developments in the design and manufacturing process of water-based fire suppression systems, more advanced technologies such as water mist systems have expanded in their building application. In this article, the critical fire suppression mechanisms of water mist systems and conventional fire sprinklers are investigated and compared, with emphasis on the influence of water droplet sizes on the fire suppression mechanisms. Applying computational fluid dynamics (CFD), a fully ventilated fire compartment room has been considered where a methane pool fire was placed at the centre. The considered fire suppression systems were placed directly upon the fire. Thermocouple and gas probes were applied in the computational domain to identify different stages of the fire suppression process, as well as to evaluate the suppression performance. The velocity field was analyzed to examine the penetration effect of suppression systems. Relative humidity and oxygen concentration data obtained by gas analyzers were also studied to further understand the droplet/fire interaction behavior. It was found that latent cooling, volumetric displacement, and dilution of oxygen and fuel were the main suppression mechanisms for water mist systems, as smaller droplets evaporate more efficiently compared to larger ones. On the other hand, for sprinklers, heat extraction by water droplets from the fire was found to be the main suppression mechanism, and the evaporation effect is not as significant as in water mist systems. According to in-depth parametric studies of water droplet sizes, recommendations for the optimal running conditions have been provided for both systems.

Combustion-generated soot particles is a subject of great interest due to its existing and future use in research and industrial sectors. An in-house Direct Quadrature Method of Moments (DQMOM) based population balance model is constructed to investigate the evolution of soot particulate. Most numerical models assume the particle size to be monodispersed, while the proposed model enables the evaluation of real-time soot particle size distribution which further enhances prediction accuracies. The proposed model is fully coupled with all essential fire sub-modelling components and is specifically constructed for low-speed buoyant flames. Additionally, to better describe the combustion process of parental fuel, ethylene, the strained laminar flamelet model considering detailed chemical reaction mechanisms is adopted. Numerical simulation with the implementation of the proposed population balance soot model has been validated against an in-house co-flow burner experimental study and been compared with other numerical studies. The results demonstrated that the improved DQMOM soot model has significant improvement to the accuracy of simulation when compared to Moss-Brookes soot model. It was also discovered that by employing Moss nucleation law, modified NSC oxidation law and adopting fractal dimension value of 2.0, the DQMOM model produces the results with the best agreement against experimental data.

This paper numerically examines the characterisation of fire whirl formulated under various entrainment conditions in an enclosed configuration. The numerical framework, integrating large eddy simulation and detailed chemistry, is constructed to assess the whirling flame behaviours. The proposed model constraints the convoluted coupling effects, e.g., the interrelation between combustion, flow dynamics and radiative feedback, thus focuses on assessing the impact on flame structure and flow behaviour solely attribute to the eddy-generation mechanisms. The baseline model is validated well against the experimental data. The data of the comparison case, with the introduction of additional flow channelling slit, is subsequently generated for comparison. The result suggests that, with the intensified circulation, the generated fire whirl increased by 9.42% in peak flame temperature, 84.38% in visible flame height, 6.81% in axial velocity, and 46.14% in velocity dominant region. The fire whirl core radius of the comparison case was well constrained within all monitored heights, whereas that of the baseline tended to disperse at 0.5 m height-above-burner. This study demonstrates that amplified eddy generation via the additional flow channelling slit enhances the mixing of all reactant species and intensifies the combustion process, resulting in an elongated and converging whirling core of the reacting flow.

Magnetorheological (MR) fluid is a smart material fabricated by mixing magnetic-responsive particles with non-magnetic-responsive carrier fluids. MR fluid dampers are able to provide rapid and reversible changes to their damping coefficient. To optimize the efficiency and effectiveness of such devices, a computational model is developed and presented where the flow field is simulated using the computational fluid dynamics approach, coupled with the magnetohydrodynamics model. Three different inlet pressure profiles were designed to replicate real loading conditions are examined, namely a constant pressure, a sinusoidal pressure profile, and a pressure profile mimicking the 1994 Northbridge earthquake. When the MR fluid damper was in its off-state, a linear pressure drop between the inlet and the outlet was observed. When a uniform perpendicular external magnetic field was applied to the annular orifice of the MR damper, a significantly larger pressure drop was observed across the annular orifice for all three inlet pressure profiles. It was shown that the fluid velocity within the magnetized annular orifice decreased proportionally with respect to the strength of the applied magnetic field until saturation was reached. Therefore, it was clearly demonstrated that the present model was capable of accurately capturing the damping characteristics of MR fluid dampers.

© Asia-Pacific Conference on Combustion, ASPACC 2019.All right reserved. Experiments were performed to investigate lift-off length instability reported in previous work for iso-octane (i.e. gasoline surrogate) combustion under compression ignition engine conditions. Iso-octane was injected into a quiescent steady environment inside a constant-volume combustion chamber with 22.8 kg/m3 ambient gas density and 21 vol.% O2 concentration. High-speed shadowgraph imaging was performed to access the combustion characteristics of iso-octane flames under ambient gas temperature 800 K condition. An injection duration of 10 ms was used to avoid end-of-injection transient effect on the results. Measurements were also performed under 900 and 1000 K ambient temperature conditions for refence purposes. From high-speed shadowgraph images, isolated ignition kernels were observed to form at locations upstream of main combustion regions under 800 K ambient temperature condition. Flame stabilization locations appeared to be shifted upstream after the ignition kernels merged with downstream established combustion regions. Flame stabilization locations at the end of fuel injection remained inconsistent among runs. Ignition kernels were not observed in the cases under ambient temperature 900 and 1000 K conditions, in which the flame stabilization distances were relatively consistent after initiation of ignition.

© 2019 Elsevier Ltd The authors regret in reference, ‘[52] Yang W, Tawiah B, Yu C, Qian Y-F, Wang L-L, Yuen AC-Y, et al. mechanical and flame retardant properties of poly(lactic acid) biocomposites based on calcium magnesium phytate and carbon nanotubes’ should be revised to ‘[52] Yang W, Tawiah B, Yu C, Qian Y-F, Wang L-L, Yuen AC-Y, et al. Manufacturing, mechanical and flame retardant properties of poly (lactic acid) biocomposites based on calcium magnesium phytate and carbon nanotubes’. The authors would like to apologise for any inconvenience caused.

In this article, the evolution of in-flame soot species in a slow speed, buoyancy-driven diffusion flame is thoroughly studied with the implementation of the population balance approach in association with computational fluid dynamics (CFD) techniques. This model incorporates interactive fire phenomena, including combustion, radiation, turbulent mixing, and all key chemical and physical formation and destruction processes, such as particle inception, surface growth, oxidation, and aggregation. The in-house length-based Direct Quadrature Method of Moments (DQMOM) soot model is fully coupled with all essential fire sub-modelling components and it is specifically constructed for low-speed flames. Additionally, to better describe the combustion process of the parental fuel, ethylene, the strained laminar flamelet model, which considers detailed chemical reaction mechanisms, is adopted. Numerical simulation is validated against a self-conducted co-flow slot burner experimental measurement. A comprehensive assessment of the effect of adopting different nucleation laws, oxidation laws, and various fractal dimension and diffusivity values is performed. The results suggest the model employing Moss law of nucleation, modified NSC law of oxidation, and adopting a fractal dimension value of 2.0 and Schmidt number of 0.9 yields the simulation result that best agreed with experimental data.

Recent high-profile building fires involving highly-combustible external cladding panels in Australia as well as Dubai, China, and the United Kingdom have created a heightened awareness by the public, government, and commercial entities to act on the risks associated with non-compliant building structures. In this paper, a database of fire events involving combustible aluminium composite panels was developed based on (i) review of relevant major fire events in Australia and other countries, and (ii) numerical simulation of the ignitability, fire spread, and toxic emissions associated with composite panels. Through the application of large-eddy-simulation (LES)-based computational fire field models, the associated risks for a standardized two-storey building with external cladding was considered in this study. A total of sixteen simulation cases with different initial sizes of the fire and different air cavity widths in the exterior cladding assembly were examined to investigate the tolerable situations and their influences. It was discovered that for most cases, with an initial fire size greater than 400 kW/m−2, the fire will spread from the first to second floor before the allowed egress time period.

Boron nitride nanosheets (BNNSs) were prepared via the exfoliation of hexagonal boron nitride in isopropyl alcohol. Extremely stable BNNSs dispersions were obtained after the ultrasonication in pectin aqueous suspensions, and the bio-composite aerogels were fabricated via the freeze-drying process. The digital photographs of pectin/BNNSs aqueous suspensions and Fourier-transform infrared spectroscopy results showed that there was a strong interfacial interaction between BNNSs and pectin macromolecular chains. Owing to the excellent dispersion and intensive interaction, the thermal stability, compressive strength and flame retardant properties of pectin/BNNSs bio-composite aerogels were significantly improved. Compared to neat pectin aerogel, pectin/BNNSs-2 (mass ratio of pectin and BNNSs, 10/1) possessed improved onset thermal decomposition temperature (by 9 °C), enhanced compressive strength (by 119%), reduced peak heat release rate (by 45%) and peak CO2 production (by 53%) at cone radiation intensity of 60 kW/m2. Residue analysis indicated that the presence of BNNSs promoted the carbonization of pectin aerogels.

The scenario of fuel injected into hot surrounds is found in a range of practical combustion applications. These flame conditions have been emulated using a jet-in-hot-coflow-burner using prevaporised n-heptane and mixtures of n-heptane and toluene, relevant to gasoline and diesel fuel surrogates. This paper reports measurements of six lifted, turbulent flames, with a constant jet flow of a prevaporised fuel/N2 mixture at 380 K into various hot and vitiated coflow conditions. Five of these flames issued into coflows generated by the combustion of different mixtures of ethylene/air and one had a coflow from a natural gas/air flame. Two n-heptane/toluene fuel blends were also measured to study the effect of soot propensity. Gas sampling, non-linear excitation regime two-line atomic fluorescence (NTLAF) and laser-induced incandescence (LII) were used to characterise the flames, investigate the mixing between the hot coflow and the surrounding air, and measure the flame temperature for the different coflow configurations. A comparison of results of the flames issuing into hot coflows is presented, indicating that the hottest flame is not associated with the coflow containing the highest concentration of O2, but with the minimum soot loading and, consequently, the minimum radiative heat loss. Subsequent numerical simulations of canonical opposed-flow flames demonstrate that the soot loading in the downstream region of the flames is strongly dependent on PAH formation in the hot coflow region and further analyses reveal the chemical pathways which are most impacted by small variations in hot coflow composition.

In this study, a Large Eddy Simulation (LES) based fire field model was applied to numerically investigate the effectiveness of smoke control using smoke vents and curtains within a large-scale atrium fire. Two compartment configurations were considered: the first case with no smoke curtains installed, while the second case included a smoke curtain at the centre of the compartment to trap smoke. Based on the thermocouple results, it was found that the model predicted the gas temperature near the fire particularly well. The time development and heat transfer of the gas temperature predictions were in good agreement with the experimental measurements. Nevertheless, the gas temperature was slightly under-predicted when the thermocouple was further away from the flaming region. Overall, it was discovered that the combination of a smoke curtain and ceiling vents was a highly effective natural smoke exhaust system. However, under the same vent configuration, if the smoke curtain height is not adequate to completely block the spread of smoke, it significantly reduces the pressure differential between the compartment and the exterior, causing reduced flow rates in the outlet vents.

A paradigm shift towards the utilization of carbon-neutral and low emission fuels is necessary in the internal combustion engine industry to fulfil the carbon emission goals and future legislation requirements in many countries. Hydrogen as an energy carrier and main fuel is a promising option due to its carbon-free content, wide flammability limits and fast flame speeds. For spark-ignited internal combustion engines, utilizing hydrogen direct injection has been proven to achieve high engine power output and efficiency with low emissions. This review provides an overview of the current development and understanding of hydrogen use in internal combustion engines that are usually spark ignited, under various engine operation modes and strategies. This paper then proceeds to outline the gaps in current knowledge, along with better potential strategies and technologies that could be adopted for hydrogen direct injection in the context of compression-ignition engine applications-topics that have not yet been extensively explored to date with hydrogen but have shown advantages with compressed natural gas.

Fabricating high-performance MXene-based polymer nanocomposites is a huge challenge because of the poor dispersion and interfacial interaction of MXene nanosheets in the polymer matrix. To address the issue, MXene nanosheets were successfully exfoliated and subsequently modified by long-chain cationic agents with different chain lengths, i.e., decyltrimethylammonium bromide (DTAB), octadecyltrimethylammonium bromide (OTAB), and dihexadecyldimethylammonium bromide (DDAB). With the long-chain groups on their surface, modified Ti3C2 (MXene) nanosheets were well dispersed in N,N-dimethylformamide (DMF), resulting in the formation of uniform dispersion and strong interfacial adhesion within a polystyrene (PS) matrix. The thermal stability properties of cationic modified Ti3C2/PS nanocomposites were improved considerably with the temperatures at 5% weight loss increasing by 20 °C for DTAB-Ti3C2/PS, 25 °C for OTAB-Ti3C2/PS and 23 °C for DDAB-Ti3C2/PS, respectively. The modified MXene nanosheets also enhanced the flame-retardant properties of PS. Compared to neat PS, the peak heat release rate (PHRR) was reduced by approximately 26.4%, 21.5% and 20.8% for PS/OTAB-Ti3C2, PS/DDAB-Ti3C2 and PS/DTAB-Ti3C2, respectively. Significant reductions in CO and CO2 productions were also obtained in the cone calorimeter test and generally lower pyrolysis volatile products were recorded by PS/OTAB-Ti3C2 compared to pristine PS. These property enhancements of PS nanocomposites are attributed to the superior dispersion, catalytic and barrier effects of Ti3C2 nanosheets.

A fire code has been developed for the purpose of modelling wildland fires via Large Eddy Simulation (LES) and the use of the level-set approach to track the flame front. Detailed chemical kinetics have been considered via the strained laminar flamelet approach for the combustion process which included the consideration of the yields of toxic volatiles such as CO, CO2 and soot production. Numerical simulations have been validated against an experimental study on the fire spread on a pine needle board under different slope angles. Peak temperatures and occurrence times during the propagation process were predicted with an overall average error of 11% and 3% respectively. This demonstrates that the flaming behaviour could be well predicted under different slope conditions. By incorporating the level set with the gas phase models, information including temperature field, toxic volatiles and soot particle concentrations can be realised in comparison to empirical fire spread models.

Gold nanoparticle (GNP) aggregation has a strong influence on the plasmonic resonance and hence the effectiveness in various photothermal applications. In relation to this, a comprehensive numerical model is developed to simulate and characterize the GNP aggregation process at various particle volume fractions and base fluid pH levels. Computational fluid dynamics techniques are utilized to model the base fluid, whereas discrete phase modeling is adopted in determining the nanoparticle trajectories. Two-way coupling is implemented to handle the particle-fluid interactions. Discrete dipole approximation approach is utilized to further examine the absorption and scattering efficiency of various GNP aggregate structures. At lower particle volume fraction, short chain-like structures are formed in the particle aggregation process, with a more complex interconnected "particle network" structure formed at higher particle volume fractions. With the three base fluid pH levels investigated, GNP aggregates are more compact with larger fractal dimensions and higher mean coordination numbers at pH = 3.5, whereas a more "loose" structure formed at pH = 6.7 and 9.4 because of larger electrostatic repulsive forces as a result of changes in the zeta potential and Debye length of the GNPs. Among the typical GNP aggregate structures characterized in this paper, the chain-like tetramer demonstrates the highest absorption efficiency of 1.83 at 700 nm wavelength - comparable to the plasmonic resonance of a nanorod - which lies in the optical window of biological tissue. Predictions of GNP optical properties are found to be in good agreement with the published experimental data.

Hydroxyapatite (HAP) nanorods were synthesized via a facile hydrothermal method, which were used as nanoadditives to prepare the flame-retardant microcrystalline cellulose (MCC) composite aerogels. Flame-retardant and thermal properties of MCC/HAP composite aerogels were evaluated. When tests were performed at room temperature, the composite aerogels exhibited enhanced thermal stability and low thermal conductivity but more rapid thermal dynamic transfer rate during heating and thermal dissipation rate during cooling compared to pure MCC aerogel. The MCC aerogel containing 50 wt % HAP yielded a reduction of 93.7% in peak heat release rate (PHRR), and the smoldering occurred when exposed to a flame or the cone heater. The remarkable improvement in the flame-retardant properties of MCC/HAP should be attributed to these possible mechanisms: (i) the increased thermal dynamic transfer performance during heating has an adverse effect on the increment in time to ignition and time to PHRR; (ii) the nonflammable HAP-backbone aerogel-like residual char with lower thermal conductivity coefficient, which is in situ formed along the temperature gradient during the thermal degradation and combustion processes, exhibits a positive effect on slowing the diffusion of heat and mass as well as the adsorption of smoke. These mechanisms interact as well as compete with others during the thermal degradation or combustion processes.

Porous media combustion (PMC) is characterized by intense heat exchange from the combustion gases to the solid media, enabling higher temperatures at the outer surface of the solid matrix. This paper, for the first time, experimentally investigates how to control combustion inside a porous media matrix to take advantage of its hot outer surface for active emission to a thermophotovoltaic (TPV) system. This ‘coupled porous media combustion-based thermophotovoltaic (PMC-TPV) system’ requires a stable flame over (only) the narrow height where the photovoltaic cells are mounted. Thus, this study reports a systematic flame stability analysis for lean Air/methane mixtures to optimize the radiant performance of three different porous media combustor designs for thermophotovoltaic applications. In this study, the equivalence ratio was set at 0.7 and the firing rates were varied in order to find the stable and unstable regimes of each reactor. Results indicate that the use of a radiant reflector shifts the stable flame regimes and increases the radiant efficiency to 63% at an operating temperature of 1356 °C. Superadiabatic conditions were also found to be possible in this system, with a maximum temperature of 1538 °C, which improves the radiant emission spectrum for the photovoltaic (PV) cells. These fundamental combustion findings will help to define the operating parameters and improve the electrical conversion efficiency in future PMC-TPV systems.

A novel three-dimensional (3D) epoxy/graphene nanosheet/hydroxylated boron nitride (EP/GNS/BNOH) hybrid aerogel was successfully fabricated in this study. This was uniquely achieved by constructing a well-defined and interconnected 3D network architecture. The manufacturing process of EP/GNS/BNOH involved a simple one-pot hydrothermal strategy, followed by the treatment of freeze-drying and high-temperature curing. In comparison with EP/GNS-3, EP/GNS/BNOH-3 demonstrated improvement of 97% for compressive strength at 70% strain. Through compression tests, fracture occurred for EP/GNS-3 at ninth compression cycles, whereas EP/GNS/BNOH-3 retained its original form after twenty compression cycles, with a residual height of 97% (i.e., only 3% reduction). By the addition of BNOH in the polymer matrix, the dynamic heat transfer and dissipation rates of EP/GNS/BNOH aerogels were also considerably reduced, indicating that the aerogel with BNOH additive possessed excellent thermal insulation properties. Thermogravimetric analysis results revealed that the thermal stabilities of EP/GNS and EP/GNS/BNOH aerogels were improved with increasing loading of EP, and EP/GNS/BNOH aerogels exhibited a better thermal stability at high temperatures. Through the elevated levels attained in the compressive strength, superelasticity, and thermal resistance, EP/GNS/BNOH aerogels has the great potential of being a very effective thermal insulation material to be utilized across a board range of applications in building, automotive, spacecraft, and mechanical systems.

The present study explores the effect of in-cylinder generated non-thermal plasma on hydroxyl and soot development. Plasma was generated using a newly developed Microwave Discharge Igniter (MDI), a device which operates based on the principle of microwave resonation and has the potential to accentuate the formation of active radical pools as well as suppress soot formation while stimulating soot oxidation. Three diagnostic techniques were employed in a single-cylinder small-bore optical diesel engine, including chemiluminescence imaging of electronically excited hydroxyl (OH), planar laser induced fluorescence imaging of OH (OH-PLIF) and planar laser induced incandescence (PLII) imaging of soot. While investigating the behaviour of MDI discharge under engine motoring conditions, it was found that plasma-induced OH∗ signal size and intensity increased with higher in-cylinder pressures albeit with shorter lifetime and lower breakdown consistency. Results also indicated that a decreasing pressure gradient extends the lifetime of plasma-induced OH∗ signals while an increasing pressure gradient suppresses plasma-induced OH∗ formation and increases the rate of signal decay. Studies on the effect of MDI at the start of high temperature reaction when plasma is discharged during the ignition delay phase were also carried out. Despite plasma-induced OH∗ signals being detected from the motoring experiments, no significant difference in OH∗ or OH-PLIF signals were observed under fuel injected conditions in comparison to the baseline case. However, PLII imaging revealed that discharging the MDI during the sooting period of combustion resulted in both suppressed formation and enhanced oxidation of soot. This effect became more prominent with the implementation of multiple pulse MDI discharge strategies, leading to significantly reduced soot over all crank angles.

This study applies particle image velocimetry (PIV) to an optical spark-ignition direct-injection engine in order to investigate the effects of fuel-injection on in-cylinder flow. Five injection timing combinations, each employing a stoichiometric 1:1 split ratio double-injection strategy, were analysed at an engine speed of 1200 RPM and an intake pressure of 100 kPa. Timings ranged from two injections in the intake stroke to two injections in the compression stroke, resulting in a variety of in-cylinder environments from well-mixed to highly turbulent. PIV images were acquired at a sampling frequency of 5 kHz on a selected swirl plane. The flow fields were decomposed into mean and fluctuating components via two spatial filtering approaches — one using a fixed 8 mm cut-off length, and the other using a mean flow speed scaled cut-off length which was tuned in order to match the turbulent kinetic energy (TKE) profile of a 300 Hz temporal filter. From engine performance tests, the in-cylinder pressure traces, indicated mean effective pressure (IMEP), and combustion phasing data showed very high sensitivity to injection timing variations. To explain the observed trend, correspondence between the measured flow and these performance parameters was evaluated. An expected global trend of increasing turbulence with retarded injection timing was clearly observed; however, relationships between TKE and burn rate were not as obvious as anticipated, suggesting that turbulence is not the predominant factor associated with injection timing variations which impacts engine performance. Stronger links were observed between bulk flow velocity and burn rate, particularly during the early stages of flame development. Injection timing was also found to have a significant impact on combustion stability, where it was observed that low-frequency flow fluctuation intensity revealed strong similarities with the coefficient of variance (CoV) of IMEP, suggesting that these fluctuations are a su

High-performance poly(1,4-butylene terephthalate) (PBT) nanocomposites have been developed via the consideration of phosphorus-containing agents and amino-carbon nanotube (A-CNT). One-pot functionalization method has been adopted to prepare functionalized CNTs via the reaction between A-CNT and different oxidation state phosphorus-containing agents, including chlorodiphenylphosphine (DPP-Cl), diphenylphosphinic chloride (DPP(O)-Cl), and diphenyl phosphoryl chloride (DPP(O3)-Cl). These functionalized CNTs, DPP(Ox)-A-CNTs (x = 0, 1, 3), were, respectively, mixed with PBT to obtain the CNT-based polymer nanocomposites through a melt blending method. Scanning electron microscope observations demonstrated that DPP(Ox)-A-CNT nanoadditives were homogeneously distributed within PBT matrix compared to A-CNT. The incorporation of DPP(Ox)-A-CNT improved the thermal stability of PBT.Moreover, PBT/DPP(O3)-A-CNT showed the highest crystallization temperature and tensile strength, due to the superior dispersion and interfacial interactions between DPP(O3)-A-CNT and PBT. PBT/DPP(O)-A-CNT exhibited the best flame retardancy resulting from the excellent carbonization effect. The radicals generated from decomposed polymer were effectively trapped by DPP(O)-A-CNT, leading to the reduction of heat release rate, smoke production rate, carbon dioxide and carbon monoxide release during cone calorimeter tests.

Post injection is a multiple-injection strategy that is commonly used as a particulate matter control measure to reduce soot emissions, yet the mechanisms and the interactions between the main and post injections are only vaguely understood. For this work, experiments were performed to assess the effects of varying dwell time between the main and post injections in a compression-ignition (CI) engine environment simulated using a constant-volume combustion chamber. The ambient density, bulk temperature, and oxygen concentration used for this work were controlled at 19.4 kg/m3, 900 K, and 15 vol % O2, respectively. A canola oil-based biodiesel was tested and injected at a fixed injection pressure of 100 MPa into the simulated CI engine environment. A mass ratio of 80%-20% was maintained between the main and post injections, with the dwell time between the injections varied from 1.5 to 2.5 ms. Comparative measurements were performed using the same fuel and injection schedules, but at a higher ambient gas temperature condition of 1100 K. Optical diagnostics methods, including diffused-back illumination and high-speed flame luminosity imaging, were used to assess the spray and combustion processes of the post injection test case. Under the conditions of this work, it was found that the ignition delays, ignition locations, and flame lift-off lengths of the post injection flames are consistently shorter than those of the main injections, with the variations influenced by the extent of the interaction of the post injection with the combustion products from the main injection. A two-color pyrometry technique was also used to measure the soot temperature and soot concentration factor information on the main-post injection cases. The data revealed a greater interaction between the main and post injections resulted in a more rapid development of the soot zone of the post injection with higher temperature after ignition. The distribution of the most probable soot concentration f

This paper aims to improve a knowledge base of methyl decanoate, a long alkyl-chain biodiesel surrogate fuel gaining popularity in engine combustion research. To this end, a comparative study on diesel and methyl decanoate combustion has been conducted with a focus on high temperature flame structures and soot distributions in an optically accessible single-cylinder light-duty common-rail diesel engine. The in-cylinder pressure trace and apparent heat release rate curves were well matched for both fuels when the same amount of fuel energy was supplied, which confirmed very similar combustion phasing. Planar laser induced fluorescence of hydroxyl radicals (OH-PLIF) and planar laser induced incandescence (PLII) as well as line-of-sight integrated chemiluminescence imaging of cool-flame signals and electronically excited OH (OH∗) were performed for various crank angles to capture the temporal and spatial development of diesel and methyl decanoate flames. The results show that both the cool-flame and OH radical signals are higher during methyl decanoate combustion with their wider distributions and larger in-cylinder volume fraction when compared to that of diesel, suggesting enhanced low- and high-temperature reactions due to oxygen in fuel. The oxygenated methyl decanoate with no aromatics in its molecular structure shows a lower soot formation rate than diesel as evidenced by delayed appearance of LII signals and lower overall intensity. This difference is significant even if the lower sooting propensity of methyl decanoate and thus less attenuation in the laser beam is considered. The rate of soot oxidation is also higher for methyl decanoate not only due to oxygen in fuel but also higher OH radicals surrounding smaller soot pockets compared to diesel.

Alternative fuels will come from a variety of feed stocks and refinement processes. Understanding the fundamentals of combustion and pollutants formation processes of these fuels will be useful for their implementation in different combustion systems. In this work, optical diagnostics were performed to waste cooking oil (WCO) and canola oil (CAO) based biodiesel sprays to assess their combustion and soot formation processes. Conventional diesel was used as a reference fuel for comparison with the biodiesels. The experiments were conducted in an optically-accessible constant-volume combustion chamber (CVCC) with simulated compression-ignition engine conditions, with different degree of exhaust gas recirculation. The liquid length and lift-off length results indicate that there was no significant interaction between the liquid phases of the fuels and their combustion regions. The flame lift-off lengths were found to be affected by both the chemical and physical properties of the fuels. It was observed that a larger difference between the lift-off length and the first-luminosity distance was correlated with lesser downstream soot formation, although the molecular structure of the fuel was found to affect the process too. Assessing the sooting and combustion characteristics of the biodiesel and diesel flames across the varied ambient O atmospheres revealed that the estimated soot contents of the biodiesel and diesel flames peaked at 15 and 21 vol.% O concentration, respectively. The peak soot contents of the WCO and CAO biodiesel flames were found be comparable, but lower than that of diesel, across the various O environment. The results also demonstrated that the biodiesels have higher normalized peak pressure values than diesel at all O conditions. Two-color pyrometry data demonstrated that the measured soot temperature and soot KL factors of the flames were similar at 15 and 21 vol.% O , but varied with further reduction of ambient O concentration. Variations in the

A new in-flame particulate sampling method has been developed and implemented in a direct-injection petrol engine to better understand the original causes of engine-out particulate emissions that have recently become a subject of regulations. The sampling probe has been designed to hold a transmission electron microscope (TEM) grid slightly above the piston top where wall-wetting induced pool fire and diffusion flame was expected. The particulates deposition was expected due to thermophoretic force between hot particulates within the flame and the cold TEM grid surface. The sampled particulates were imaged using a TEM and the images were post-processed to determine particulate size and fractal dimension. Of particular interest is how inherent engine cyclic variations impact the particulate morphology as the first evaluation of the newly developed sampling method. Results show that the increasing in-cylinder pressure conditions tend to increase the particulate number counts, especially small and compact ones. The measured mean primary particle diameters were ranged from 24.09 nm to 24.93 nm, and the aggregate radius of gyration was spanned from 61.34 nm to 68.47 nm depending on the test runs. The fractal dimensions were measured at 1.59 ~ 1.75. However, none of these fluctuations show a good correspondence with the measured in-cylinder pressure for various engine runs, suggesting that the engine cyclic variations do not make a significant impact on key morphology parameters of the sampled particulates.

Particle image velocimetry (PIV) was applied to an optical spark-ignition direct-injection (SIDI) engine in order to analyse various turbulent properties of the flow-field. The engine was motored at 1200 RPM with an intake pressure of 100 kPa, while PIV images were acquired on the horizontal (swirl) plane. The flow was decomposed into mean and fluctuating components via spatial filtering with an 8-mm cut-off length. Five dual-injection timing strategies were analysed, ranging from two injections early in the intake stroke to two injections during the compression stroke. The in-cylinder pressure traces, indicated mean effective pressure (IMEP), and combustion phasing data suggested that engine performance is incredibly sensitive to relatively minor changes in injection timing. An expected global trend of increasing turbulence with retarded injection timing was clearly observed. Relationships between turbulent kinetic energy (TKE) and burn rate were present, but not as obvious as anticipated, as total kinetic energy (KE) and variations in large-scale flow structures were also found to play a significant role.

There is a strong motivation for alternative energy sources, such as fuel technologies based on the use of sustainable biomass feedstocks, due to increasing pressure to conserve ever diminishing fossil fuel resources and to reduce greenhouse gas emissions. Microalgae and oil shale are two promising potential alternative energy sources. In this work, an assessment of nitrogen oxides (NOx) and sulfur dioxide (SO2) emission characteristics of a species of microalgae (i.e. Chlorella vulgaris) under conditions that are relevant to large-scale use of biomass for heat and other products is performed. The pollutant emission characteristics of the microalgae samples, when blended with different catalyst materials (SiC, ZnCl2, MgO, and CuCl2) and different oil shale content, are also measured. The microalgae biomass samples are observed to display variation in the devolatization and char oxidation characteristics at different furnace operating temperature conditions. In this work, the reduction in the peak NOx and SO2 emissions are found to decrease in the order of CuCl2 > SiC > ZnCl2 > MgO, and MgO > SiC > ZnCl2 > CuCl2 as the added catalyst, respectively. The co-combustion of microalgae biomass and oil shale is also found to affect the NOx and SO2 emission profiles, which is most likely caused by the inhibitory effects on mass transfer caused by the very high ash content in the oil shale samples used in this work.

An in-house large eddy simulation (LES) based fire field model has been developed for large-scale compartment fire simulations. The model incorporates four major components, including subgrid-scale turbulence, combustion, soot and radiation models which are fully coupled. It is designed to simulate the temporal and fluid dynamical effects of turbulent reaction flow for non-premixed diffusion flame. Parametric studies were performed based on a large-scale fire experiment carried out in a 39-m long test hall facility. Several turbulent Prandtl and Schmidt numbers ranging from 0.2 to 0.5, and Smagorinsky constants ranging from 0.18 to 0.23 were investigated. It was found that the temperature and flow field predictions were most accurate with turbulent Prandtl and Schmidt numbers of 0.3, respectively, and a Smagorinsky constant of 0.2 applied. In addition, by utilising a set of numerically verified key modelling parameters, the smoke filling process was successfully captured by the present LES model.

In fire simulations, it is essential to include detailed chemical kinetics for the description of the combustion process where intermediate chemical products are formed through a series of elementary reactions. A novel in-house fire field model based on Large Eddy Simulations (LES) approach incorporating fully coupled subgrid-scale (SGS) turbulence, combustion, soot formation and radiation models for the interactive and non-linear nature of the turbulent reacting flow in compartment fire phenomena has been developed in this article. It uniquely embraces the detailed reaction mechanisms for the chemical processes involved during combustion. Since the modelling of hydrocarbons by-products are enabled when considering the full chemical profile, the formation of soot particles can be related to the concentration of main incipient such as acetylene, which provides an appropriate representation of nucleation, surface growth processes. The significance of the improvement of soot particles modelling had been numerically investigated applying three different two-equations semi-empirical soot models: (i) Moss model (simplified model taken the fuel as the soot precursor); (ii) Moss-Brookes model (considers acetylene as the soot precursor) and (iii) Moss-Brookes-Hall model (considers acetylene, benzene ring and phenyl radical as the soot precursors). Comprehensive temperature and soot measurements from fire tests in a full-scale ISO compartment constructed purposely with a small opening gap to create the under-ventilated fire condition with which the effect of soot particles generation would be more significant. The computed results were compared with measured results for validation of the implemented soot models.

An experimental investigation was performed to assess the combustion characteristics of a waste cooking oil (WCO) biodiesel fuel under simulated compression-ignition engine conditions. A conventional diesel was used as a base fuel for comparison purpose. The fuels were injected into the quiescent steady environment inside a constant-volume combustion chamber (CVCC) of 19.4 kg/m ambient density, 6 MPa ambient pressure, and 1100 K bulk temperature. A range of optical diagnostics were performed, to compare the fuels over ambient O concentrations of 10-21 vol.%, and injection pressures of 70-130 MPa. The results reveal that for the investigated test conditions (i) the lift-off lengths and the first soot distances of the biodiesel are consistently longer than that of diesel; (ii) the peak soot level of the flame increases with the relative distance between the first soot formation and flame liftoff; and (iii) the WCO biodiesel has a lower soot formation propensity than diesel. The fuel liquid lengths were also measured to be shorter than their lift-off distances, indicating no interaction between their spray and combustion processes. 3 2

The influence of unresolved turbulent fluctuations on radiation heat transfer and formation of NO and soot in an n-dodecane spray flame (Spray A) under diesel engine conditions was investigated. The transported probability density function model including the effect of turbulent fluctuations in temperature and composition were compared with the well-mixed model to separate and quantify the relative influence of turbulence-chemistry interactions radiation heat transfer and turbulence-radiation interaction. At Spray A conditions the contribution to the Planck mean absorption coefficient from gas-phase species (mainly CO2 and H2O) was comparable to the one of soot which plays an important role for the radiation reabsorption in the periphery of the jet. Radiation reduced the flame temperature by 10 K-20 K with a consequent reduction of the total NO mass by approximately 5%-10%. However neglecting turbulent fluctuations resulted in an increase of the NO mass by a factor of two. Minimal effect of radiation on soot formation was observed.

The planar laser-induced fluorescence of fuel and hydroxyl and incandescence of soot together with morphology and nanostructure information of soot particles sampled via thermophoresis were analyzed to investigate the in-cylinder soot processes under the influence of jet-to-jet interactions. The experiments were conducted in a single-cylinder small-bore optical diesel engine fuelled by a low-sooting methyl decanoate fuel for diagnostic purposes. Two different nozzle configurations of one hole and two holes were used to simulate isolated single-jet and double-jet conditions respectively. Results demonstrated that fuel-rich mixture formed in the jet?jet interaction region caused faster initial growth of soot that persists for a longer period of time compared to the soot formed in the wall-impingement region of the single jet. These soot particles affected by the jet?jet interaction displayed larger aggregates composed of larger primaries and the nanoscale internal structures revealed higher carbon fringe-to-fringe separations. These indicated higher particle reactivity and the formation stage of soot.

The thermophoretic sampling of particulates from hot media, coupled with transmission electron microscope (TEM) imaging, is a combined approach that is widely used to derive morphological information. The identification and the measurement of the particulates, however, can be complex when the TEM images are of low contrast, noisy, and have non-uniform background signal level. The image processing method can also be challenging and time consuming, when the samples collected have large variability in shape and size, or have some degree of overlapping. In this work, a three-stage image processing sequence is presented to facilitate time-efficient automated identification and measurement of particulates from the TEM grids. The proposed processing sequence is first applied to soot samples that were thermophoretically sampled from a laminar non-premixed ethylene-air flame. The parameter values that are required to be set to facilitate the automated process are identified, and sensitivity of the results to these parameters is assessed. The same analysis process is also applied to soot samples that were acquired from an externally irradiated laminar non-premixed ethylene-air flame, which have different geometrical characteristics, to assess the morphological dependence of the proposed image processing sequence. Using the optimized parameter values, statistical assessments of the automated results reveal that the largest discrepancies that are associated with the estimated values of primary particle diameter, fractal dimension, and prefactor values of the aggregates for the tested cases, are approximately 3, 1, and 10 %, respectively, when compared with the manual measurements.

This study aims to provide a preliminary insight into the effect of injection timing and spark timing on flame propagation in a wall-guided spark-ignition direct-injection (SIDI) optical engine. High-speed imaging of natural combustion luminosity was performed for various injection timings and spark timings while other operating conditions were fixed. Injection timings have been selected based off our previous study using the same engine which compared the mixture formation properties of flash-boiling sprays to non-flash boiling sprays. Spark timings were also varied to investigate its influence on the ignition kernel development and flame propagation. Results have shown that later injections tend to create a richer region surrounding the spark plug, which leads to more rapid initial kernel development. The data also suggests that varying the spark timing has an effect on flame propagation speed such that earlier spark timing leads to earlier and faster flame propagation. This is likely due to the associated changes in piston speed and in-cylinder pressure.