Low Flame Research Articles

Heat and fire-resistant nanofiber networks: Towards tailoring the new generation of lightweight intermeshing polymer composite systems

Safe use of materials is a primary focus of emerging low-carbon industry. Catastrophic fire incidents due to high flammability of polymers as versatile materials necessitate developing fire-proof polymer composites. In this study, a novel and robust strategy is implemented to fabricate non-flammable and fire-proof thermoplastics with remarkably lower flame retardant (FR) content leading to outstanding limiting oxygen index (LOI) of 30% and UL 94-V0. This can be achieved using nano-fibrillation by forming networks of heat-resistant polymeric nanofibers (polyphenylene ether (PPE) or polyphenylene sulfide (PPS)) within polystyrene (PS). Formation of heat-resistant nanofibers creates a continuous network-structured layer/shield to preserve the matrix against burning and suppresses dripping by boosting the melt-strength. Nanofibers also lead to promoting a graphitized char layer to thoroughly protect the polymer against fire. These synergistic effects enhance FR efficiency, as demonstrated by a 30% reduction in fire growth rate and peak heat release rate, upon inclusion of 15 wt% PPE nanofibers, compared to an equivalent composite with spherical particles. Only the PS sample containing 25 wt% FR and 15 wt% heat-resistant nanofibers meets UL 94-V0 while presence of a similar content of spherical PPE or PPS, graphene nanoparticles, or carbon nanotubes does not provide this feature. Nanofibers also strengthen energy absorption leading to high impact strength of PS composites (120%). Hence, this novel strategy can be extended to a wide range of polymer systems to fabricate novel generation of fire-proof devices with tunable properties for various potential applications including energy storages packs, electronic equipment, and robotics.

Ammonia-hydrogen engine with reactivity-controlled turbulent jet ignition (RCTJI)

Ammonia (NH3) is a promising fuel for engine carbon neutrality. However, the terrible combustion characteristics substantially restrain the application of NH3 in internal combustion engines (ICE). Hydrogen addition and pre-chamber turbulent jet ignition (TJI) show outstanding abilities to solve the difficult ignition and low flame velocity for ammonia combustion. At present work, a concept of reactivity-controlled TJI (RCTJI) with hydrogen fuel is proposed, and the combustion characteristics of the ammonia-hydrogen engine are investigated. The present study proposes two operating modes of the RCTJI ammonia-hydrogen engine. The controllable pre-chamber reactivity is achieved by varying the hydrogen concentration and/or adjusting the quantity of the pre-chamber mixture. Then, the effects of the pre-chamber properties regarding the pre-chamber nozzle diameter, per-chamber operating mode, and pre-chamber mixture reactivity on the engine performance are analyzed. The results show that adjusting the mixture reactivity in the pre-chamber can effectivity control the ignition ability and engine performance. The better performance of the RCTJI ammonia-hydrogen engine is obtained under the conditions of per-chamber with a 4 mm hole size and hydrogen fuel, and it can further be optimized by operating the pre-chamber in Mode 2 with an extra scavenging process. An operation strategy of the pre-chamber for the RCTJI ammonia-hydrogen engine is proposed: the RCTJI pre-chamber is suggested to operate under Mode 2 and achieve the first scavenging process by stoichiometric hydrogen/air mixture, and the injection quantity of scavenging gas in the pre-chamber should be controlled in the range of 1.0 Mt–2.5 Mt. At the boosting conditions, the power performance and fuel economy of the RCTJI ammonia-hydrogen engine are optimized effectively. The indicated mean effective pressure (IMEP) increases from 6.3 bar to 10.0 bar at λ = 1.0 as the intake pressure increases from 1.0 bar to 1.4 bar. The optimum fuel consumption rate is obtained at the lean condition of λ = 1.4, achieving a 13.3% reduction of the indicated specific fuel consumption (ISFC).

Mixing and flame structure study of inverse swirl diffusion flames

Swirling flames appear in many practical applications to enhance flame stabilization. However, relatively few studies have investigated the inverse swirl diffusion flames (ISDFs) in detail. In ISDFs, a central swirling air jet is surrounded by an annular methane fuel jet. In the first part of this work, the stability map of ISDFs is studied. This map shows two distinctive stability regions: a swirling-jet-like region at low swirl and a compact swirling flame region at high swirl intensity. Regardless of the bulk air jet velocity (U), these two regions are separated by an optimum swirl intensity -leading to the highest flame stability. Then across these two regions, the development of the fuel–air mixing and the flame-flow interaction were investigated via acetone-PLIF and simultaneous PIV/OH-PLIF measurements. At the same U, increasing the swirl intensity leads to different mixing patterns. An annular-rich jet exists in the swirling-jet-like region versus a compact short mixing field in the compact flame stability region. Moreover, the development of the fuel–air mixing field downstream of the burner exit impacts the flame-flow interaction. The fast and early fuel–air mixing enhances the mutual interaction between the lower edge of the flame and the wrinkled flame, and the spots of the high heat released from the downstream regions - hence a highly stable flame is obtained. The lower flame edge is seen to track the instantaneous lower stagnation point of the swirling flow, while the increased heat release spots/flame wrinkling track the shear layer vortices. Beyond the optimum swirl intensity, increasing the swirl intensity retarding the fuel–air mixing and weakens the mixture ignitability, straining the flame in the vicinity of the flame edge or the vortices of the shear layer. These results suggest that suitable modifications of the mixing field close to the burner nozzle of ISDFs may increase flame stability.

Multi-functional bio-film based on sisal cellulose nanofibres and carboxymethyl chitosan with flame retardancy, water resistance, and self-cleaning for fire alarm sensors

Flexible and environmentally friendly bio-based films have attracted significant attention as next-generation fire-responsive sensors. However, the low structural stability, durability, and flame retardancy of pure bio-based films limit their application in outdoor and extreme environments. Here, we report the design of a sustainable bio-based composite film assembled from carboxymethyl-modified sisal fibre microcrystals (C-MSF), carboxymethyl chitosan (CMC), graphene nanosheets (GNs), phytic acid (PA), and trivalent iron ions (Fe3+). Cross-linking between Fe3+ and the C-MSF/CMC matrix and the formation of PA–Fe3+ complexes on the surface of the film imparted excellent mechanical properties, chemical stability, self-cleaning ability, and flame retardancy to the bio-film. Furthermore, the bio-film produced a reversible and sensitive response to temperature at 55.3–214.1 °C, and a fire alarm system made from the bio-film had a fire-response time of 4.6 s. In addition, the char layer of the bio-film retained a stable cyclic response to temperature, enabling it to serve as a fire resurgence sensor with a response time of 2.3 s and recovery time of 11.2 s. This work provides a simple pathway for the fabrication of self-cleaning, flame retardant, and water-resistant bio-films that can be assembled into fire alarm systems for the real-time monitoring of fire accidents and resurgence.

Oxygen effects on soot formation in H2/n-heptane counterflow flames

Blending of hydrocarbon fuels with hydrogen is a practically feasible way to rapidly integrate a carbon neutral energy vector in the transport sector and to effectively reduce harmful particulate matter emissions. This work investigates the effects of hydrogen (H2) addition on soot formation in n-heptane in low strain rate counterflow diffusion flames with different oxygen mole fractions (XO2=0.3 ∼ 0.45). Flame temperature, soot volume fraction (fv), monocyclic (MAHs), and polycyclic aromatic hydrocarbons (PAHs) are measured by using OH-2C-PLIF/thermocouple, LII/LE, and PAH-LIF methods, respectively. Measurements of n-heptane flames with addition of helium (He), as an inert gas with a specific heat capacity similar to that of H2, are also carried out and compared. Numerical simulations are then performed using a soot discrete sectional model coupled with detailed gas-phase kinetics to interpret the data obtained. Temperature and soot volume fraction profiles are better predicted by 2D simulations, which account for the non-negligible impact of radial diffusion and buoyancy under low strain rate conditions. Then, it is shown that both the fv and PAH yields almost linearly decrease by increasing H2 or helium (He) addition. The reduction of PAHs and soot is larger in n-heptane/H2 flames due to H2 chemical effects, absent in the n-heptane/He flames, hampering the formation of peri‑condensed structures. The effect of O2 concentration in the oxidizer stream is also studied. Experimental and simulation results show that PAHs and soot increase with XO2 for all flames. Finally, the effects of H2/He addition varying XO2 on soot formation are investigated. With the increase of XO2, the difference in the peak flame temperatures of n-heptane/H2 and n-heptane/He flames decreases. Consequently, compared to the neat n-heptane flame, the reduction of peak fv becomes more and more pronounced in the case of hydrogen addition rather than the helium addition since the H2 soot inhibiting chemical effect prevails over the H2 temperature effect which instead promotes soot formation.

Study of NO emission from CH4-air, oxygen-enriched, and oxy-CH4 combustion under HTC and MILD regimes: Impact of wall thermal condition in different oxidant temperature and dilution level

The present work investigates the effect of wall thermal conditions on the NO emission in the different inlet temperatures and oxidant dilution levels. The studies are performed for the CH4-air, oxygen-enriched, and oxy-CH4 combustion under the HTC and MILD regimes by numerical simulation of the non-premixed furnace and chemical calculations of the WSR reactor. It is found that higher heat loss from the wall and more replacement of CO2 with N2 facilitate the establishment of the MILD regime and significant reduction of NO production. The results show an optimum point for achieving the minimum heat loss and NO emission. Under the MILD regime, dominant mechanisms in the NO emission are prompt through reaction CH + N2⇌HCN + N and thermal routes for the CH4-air condition and N2O-intermediate by reactions N2O + O⇌2NO and N2O + H⇌N2+OH and thermal mechanisms for oxy-CH4 combustion. In both atmospheres, the thermal route plays the main role in the low heat loss from walls, while other routes are more active in the low maximum flame temperature. Reaction N + NO⇌N2+O by supplying O radical from reactions O + CO + M⇌CO2+M and H + O2+M⇌HO2+M is activated by increasing O2 level, while reactions N + NO⇌N2+O and N + OH⇌NO + H show the main contribution in the sensitivity analysis of NO.

Numerical Investigation on the Characteristics of a Novel Multi-Swirl Lean Direct Injection Burner With Large Eddy Simulation-Flamelet Generated Manifold Method

Abstract The lean direct injection (LDI) concept can eventually replace the current combustion systems in aviation engines because of its low NOx emissions without compromising other parameters. A novel multiswirl LDI burner with distributed fuel injection surrounded by air- flow through multiple hexagonal swirlers of vane angle 45 deg was developed. In this study, large eddy simulation (LES), using the dynamic Smagorinsky-Lilly subgrid model together with the flamelet generated manifold (FGM) combustion model, has been used to analyze the correlation between aerodynamics, mixing, and combustion characteristics of the burner. The agreement between the experimental data and the LES simulation was good, and it can accurately predict the trend of variables like velocity, temperature, and mixture fraction at different Reynolds number and equivalence ratios. The LES-FGM results demonstrated the rapid formation of a homogeneous fuel-air mixture over a short distance, which results in excellent flame stability, and it has ultralow NOx emission due to low flame temperature and negligible internal recirculation. It was discovered that going from a global equivalence ratio of 0.7 to 0.9 increases the flame liftoff distance because the high fuel volume flowrate causes the mixing of swirling air and fuel jet to become more and more delayed. The research in this paper provides an insight into the ability of the LES-FGM method to capture the complex flow field structures and the flame behavior globally of a novel low NOx multiswirl burner that might be a competitor in the combustors of commercial gas turbine engines.

Formation of a conductive network in urea−formaldehyde/carbon nanotube composite foams for electromagnetic shielding

AbstractDue to advantages of low cost and intrinsic flame retardancy, urea−formaldehyde (UF) foams with electromagnetic shielding function present a promising application prospect in the fields of construction, transportation and electronics. In this study, by using carbon nanotubes (CNTs) as conductive filler and thermo‐expandable microspheres (EMs) as physical foaming agent, a series of UF/CNT composite foams with perfect and polygonal closed cellular structure were prepared for electromagnetic shielding. By adding 6 wt% EMs, the composite foam exhibited a uniform cell wall thickness, while the local accumulation of CNTs was inhibited and CNTs were distributed evenly within the cell walls. With increasing CNT content the dispersion of CNTs transformed from a scattered and ‘island‐like’ structure to an interconnected structure, and for samples with CNT content higher than 1.34 vol% a continuous conductive network was constructed within the cell walls, thus significantly improving the electrical conductivity and electromagnetic shielding effectiveness for the foams, which reached 34.5 dB and satisfied the requirement of commercial applications. Moreover, the contribution of absorption to the electromagnetic shielding effectiveness was much larger than that of reflection for composite foams, indicating that absorption was the dominant shielding mechanism. © 2023 Society of Industrial Chemistry.

Microstructure and Tribo-Behavior of WC–Cr3C2–Ni Coatings by Laser Cladding and HVAF Sprayed: A Comparative Assessment

SK5 steel is the base material used for the preparation of the wrinkle scraper, whose service life strongly affects the working efficiency and economic benefits. In this work, WC-Cr3C2-Ni coating was deposited on the SK5 steel substrate by using High-velocity air fuel spray (HVAF) and Laser cladding (LC) processes respectively, named HVAF-WC coating and LC-WC coating. The microstructure and wear resistance of both coatings were analyzed, and were compared with the substrate sample. Results showed that the coatings were adhesive well onto the substrate. More WC with fine crystals is retained in HVAF-WC coating due to low flame flow temperature, while WC of LC-WC coating is characterized by columnar crystals. The wear rate of HVAF-WC and LC-WC coating was 4.00 × 10-7 mm3/(N•m) and 3.47 × 10-6 mm3/(N•m), respectively, which was two and one orders of magnitude lower than SK5 steel with 3.54 × 10-5 mm3/Nm. HVAF-WC coating exhibited the best wear resistance because of significant fine grain strengthening, which wear mechanism is mainly dominated by abrasive wear. Thus, it was thought that HVAF-WC coating is more effective ways to improve the wear resistance of SK5 steel, comparing with LC-WC coating.

Performance and Microstructure Characterizations of Halloysite Nanotubes Composite Flame Retardant–Modified Asphalt

To solve the problems of low flame retardant efficiency and weak low-temperature performance of asphalt modified by conventional flame retardants (CFR), in this study, halloysite nanotubes (HNTs) and CFR were used to prepare nanocomposite flame retardants (NCFR) to modify asphalt. A fluorescence microscope (FM), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope/energy dispersive spectrometer (SEM/EDS) were used to characterize the microstructure of NCFR-modified asphalt. An oxygen index meter, Cleveland open cup, and cone calorimeter were used to test the flame retardant properties of the asphalt. A dynamic shear rheometer, bending beam rheometer, and force ductility tester were used to test the rheological properties of asphalt. At the same time, flame retardant–modified asphalt mixtures were prepared to verify the flame retardancy and road performance of the flame retardant–modified asphalt. The research results showed that the asphalt modified with 8% CFR and 1% HNTs (MA/CFR/1% HNTs) showed better dispersibility. The increase of limiting oxygen index and self-ignition temperature and the decrease of heat release rate and smoke production rate of MA/CFR/1% HNTs indicated that it has good flame retardancy. At 64°C, compared with modified asphalt (MA), the rutting factor of MA/CFR/1% HNTs increased by 88.17%, the creep recovery increased, and the irreversible creep decreased, indicating that its high-temperature performance improved significantly. At −18°C, compared with that of MA/CFR, the low-temperature creep stiffness of MA/CFR/1% HNTs decreased by 36 MPa and the creep rate of MA/CFR/1% HNTs increased by 0.034, indicating that only 1% HNTs can improve the effect of degraded CFR on the low-temperature performance of MA. Simultaneously, MA/CFR and MA/CFR/1% HNTs can improve the high-temperature performance and water stability of asphalt mixtures. Adding 1% HNTs to a MA/CFR-modified asphalt mixture can improve the low-temperature performance of the asphalt mixture to the level of the low-temperature performance of the modified asphalt mixture. In summary, the modification of asphalt with 1% HNTs and 8% CFR can effectively improve the flame retardant efficiency and significantly improve the road performance of asphalt.

Comparative Analysis of Flame Propagation and Flammability Limits of CH4/H2/Air Mixture with or without Nanosecond Plasma Discharges

This study investigates the kinetic modeling of CH4/H2/Air mixture with nanosecond pulse discharge (NSPD) by varying H2/CH4 ratios from 0 to 20% at ambient pressure and temperature. A validated version of the plasma and chemical kinetic mechanisms was used. Two numerical tools, ZDPlasKin and CHEMKIN, were combined to analyze the thermal and kinetic effects of NSPD on flame speed enhancement. The addition of H2 and plasma excitation increased flame speed. The highest improvement (35%) was seen with 20% H2 and 1.2 mJ plasma energy input at ϕ = 1. Without plasma discharge, a 20% H2 blend only improved flame speed by 14% compared to 100% CH4. The study found that lean conditions at low flame temperature resulted in significant improvement in flame speed. With 20% H2 and NSPD, flame speed reached 37 cm/s at flame temperature of 2040 K at ϕ = 0.8. Similar results were observed with 0% and 5% H2 and a flame temperature of 2200 K at ϕ = 1. Lowering the flame temperature reduced NOx emissions. Combining 20% H2 and NSPD also increased the flammability limit to ϕ = 0.35 at a flame temperature of 1350 K, allowing for self-sustained combustion even at low temperatures.

Ammonia and hydrogen blending effects on combustion stabilities in optical SI engines

Ammonia is a promising energy carrier and carbon-free fuel, which is getting more attention today when fossil energy is increasingly exhausted. However, ammonia combustion in the IC engine suffers from combustion instabilities and misfiring issues. Hydrogen is also carbon-free energy and can be directly obtained by ammonia catalytic reforming. The addition of a small amount of hydrogen can effectively alleviate the weakness of ammonia combustion, while ammonia and hydrogen blending effects on combustion stabilities and their critical conditions remain unclear. In this work, the effects of hydrogen addition on ammonia combustion characteristics were experimentally investigated in an optical SI engine with high compression ratios. The results show that the indicated thermal efficiency first increases and then decreases with the elevation of hydrogen-ammonia energy ratios (χ), with an optimal value at χ≈7.5 %. Further hydrogen addition can aggravate indicated thermal efficiency due to the large heat transfer loss caused by high-temperature hydrogen combustion. Combustion visualizations show that there is a critical threshold of hydrogen-ammonia energy ratio (χ=10.0–12.5 %), around which engine combustion characteristics are changed significantly. When χ < 10 %, the effect of hydrogen addition on the ammonia flame speed becomes more pronounced since the hydrogen substantially improves the stability of the early-stage combustion. When χ > 12.5 %, hydrogen shows an obvious influence on the initial flame formation of ammonia, which is attributed to the low flame stretch sensitivity, facilitating early flame development. In addition, flame propagation when χ < 10 % is more sensitive to temperature than flame propagation with χ > 12.5 %. The current research demonstrates that proper ammonia-hydrogen energy ratios are important for stable combustion and thermal efficiency improvement.

Experimental analysis and performance of refinery fuel gas on lean and rich fuel–air premixed combustion

Refinery fuel gas (RFG) is a blend of gas streams produced as by-products in various refinery processes. Large amounts of RFG are burning around the clock in the air with thermal energy waste and adverse effects on the environment. The present work investigates experimentally the performance of different compositions of RFG from lean to rich fuel–air premixed combustion, with focus on an efficient and low-emission combustion for its heat recovery. Radiant and porous media burners are the combustion technologies used. For the radiant burner, fuel compositions are propane and ethane with an average ethane ratio of 5%, 10%, and 15% (E05, E10, E15 respectively), which are contrasted with pure propane and liquefied petroleum gas (LPG). The pure gases fluxes are fixed as 1 and 2 m3/h for low and high flame configurations, respectively. The lean fuel–air flames investigated are stable for all ethane ratios with low carbon monoxide (CO) and nitrate oxides (NOx) emissions. Maximum temperature is given by pure propane flame (besides LPG), followed by E05, E10 and E15, for both flame configurations. Then, the radiation heat flux of ethane mixtures exhibits a reduction in comparison with LPG. For the porous media burner, lean and rich fuel–air mixture composed by natural gas (NG, 97% methane) and representative flue samples of 55% (C1) and 70% (C2) methane concentration are tested. The C1 and C2 flue samples present high combustion temperatures, showing a positive swap from NG. The NG rich-fuel combustion exposes high hydrogen conversion (27%) at high equivalence ratio (ϕ=1.8). Finally, for both burners lean fuel–air premixed combustion shows high combustion efficiencies, 74.8% with E05 and 80.7% with C1 flue sample.

A Computational Study on the Influence of the Hydrous Ethanol Water Content in Spark-Ignition Engine Performance and in Flame Development

A multidimensional numerical model was developed to simulate the operation of one cylinder of a 1.4-liter flex-fuel spark-ignition engine. Hydrous ethanol with 4.3%, 7.5%, 10%, 15%, and 20% water volumetric contents were the considered fuels for the engine. The full load engine operating point was analyzed at 3,875 rpm with a relative air-fuel ratio of 0.9 and a fixed ignition delay. A Grid Convergence Index study was conducted to guarantee the accuracy of the obtained numerical solutions. A six consecutive mechanical cycle simulation was performed for hydrous ethanol with 4.3% water content, and experimental data were used for validation purposes. Turbulent flame speeds were also evaluated and analyzed. Numerical results showed that 10% water content led to the highest engine-generated power output and flame propagation speeds and to the lowest CO and unburned ethanol emissions among the tested fuels. The flame shape and encompassed volume were also analyzed. The results also showed that the high swirl in the in-cylinder flow affects the initial development of the flame for all water contents considered. Fuels leading to lower flame distortions early after ignition showed higher reaction rates and better performance.

Experimental Study of Effect of Injection Timing on Port Fuel Injection Gasoline, Port Fuel Injection Compressed Natural Gas, and Direct Injection Compressed Natural Gas Engine Performance, Combustion, and Emissions Characteristics

Abstract Compressed natural gas (CNG) has gained popularity due to its wide availability, higher efficiency, and lower emissions compared to gasoline. However, the lower flame speed characteristics of CNG with conventional port injection reduce the CNG engine volumetric efficiency and power output. CNG's lower gas jet momentum during a low load operation creates a non-uniform air-fuel mixture that affects ignition and combustion quality. Direct injection of CNG with optimum injection timing is expected to improve volumetric efficiency, ignition quality, and combustion process. In this study, a comparative study on the effect of end-of-injection (EOI) timing on volumetric efficiency, thermal efficiency, combustion duration, and emissions was carried out in a single-cylinder port fuel injection (PFI) spark-ignition engine using gasoline and CNG, and direct injection (DI) spark ignition engine using CNG. The experiments were performed at two-part load operations of 20% and 40% throttle at 900 and 1500 rpm. Experimental results indicate that the PFI CNG engine is more influential in EOI timing than gasoline engines. The performance of the PFI CNG engine is improved when the injection occurs during the intake valve open period compared to the closed valve period with higher thermal efficiency, volumetric efficiency, and indicated mean effective power (IMEP). A shorter flame development angle and combustion duration were observed when EOI timing was in the open intake valve condition. DI CNG improved volumetric efficiency at advanced EOI timing compared to the PFI CNG engine. However, the combustion process is critically dependent on injection timing and air-fuel mixing duration. A three-dimensional computational fluid dynamics simulation was conducted to evaluate the effect of advanced and retarded EOI timing on DI CNG engine's in-cylinder turbulent kinetic energy development and in-cylinder equivalence ratio near the ignition point. An excess advanced EOI timing resulted in stratified rich and retarded EOI timing results in loss of turbulence energy, leading to a slightly rich and lean mixture for advanced and retarded EOI timing, respectively. Hence, an optimum EOI timing provides a conducive environment to initiate the combustion and flame front propagation. Further, advanced EOI timing was required at higher throttle opening and engine speed. The emissions in DI CNG were also greatly affected by EOI timing.

Numerical Simulation of Ammonia Combustion at Different Hydrogen Peroxide Concentrations

Ammonia (NH3) is a promising carbon-free fuel. However, modifying its high ignition temperature and low flame speed remains challenging. In this study, NH3 combustion was numerically investigated using hydrogen peroxide (H2O2) of different concentrations as the oxidizer to overcome these limitations. Adiabatic, free-propagating laminar burning velocities for NH3/H2O2/H2O mixtures were examined using a detailed chemical model. The maximum flame temperature between equivalence ratios is not considerably different at high concentrations of H2O2 (&gt;80%), because the heat release is dominated by H2O2 decomposition. The equivalence ratio does not significantly affect the flame speed when the H2O2 concentration is less than 50%. The impact of H2O2 on the burning velocity at low concentrations is mainly attributed to the chemical effect. The chemical effect gradually decreases and the thermal effect increases because of the high heat release at high H2O2 concentrations. Moreover, the different concentrations of H2O2 consequently divide the flame into two sections. The first section is dominated by H2O2 reactions and the second by NH3 reactions. However, when the H2O2 concentration is 90 or 100%, flames do not appear in both sections. Finally, a quasilinear relationship between the flame speed and (NH2+OH)max mole fraction is identified.

Premixed combustion and emission characteristics of methane diluted with ammonia under F-class gas turbine relevant operating condition

Ammonia has been used on a small scale in other industrial equipment, such as gas turbines, as a carbon-free fuel. However, ammonia fuel suffers disadvantages such as high ignition temperature, low flame velocity and high NOx emissions. Doping with ammonia using a more reactive fuel, such as methane, can solve the above problems. Therefore, under the relevant operating conditions of the gas turbine (T = 723 K, p = 16.5 atm), the effect of ammonia content on the combustion and emission characteristics of laminar premixed methane flames was numerically investigated. This research uses the PREMIX code from ANSYS CHEMKIN-PRO 2020 and Okafor chemical kinetic mechanisms and provides a reference for our subsequent analysis of gas turbine operating conditions. Firstly, the emission data of major pollutants under different ammonia content (XNH3 = 0–1.0) and equivalent ratio (Φ = .6–1.4) were calculated. Then, the laminar premixed flame structure is analyzed under the lean fuel conditions associated with gas turbines (Φ = .6, .8). Finally, the effect of ammonia addition on the chemical reaction path of NO and CO emission was studied. The results show that ammonia/methane mixture fuel is more suitable for combustion at .6 &amp;lt; Φ &amp;lt; .8 under high temperature and pressure. High ammonia content (XNH3 &amp;gt; .6) and low equivalent ratio can reduce NO and CO emissions. The molar fractions of H, O, and OH radicals and flame temperature decreased with the increase in ammonia content. In addition, high temperature and high pressure conditions and ammonia content greatly influence the reaction path of NO and CO production. The increase in pressure resulted in a change in the primary reaction that produced NO. In conclusion, this study guides reducing the emission of NO and CO from lean side of gas turbine plants.

High-performance wood scrimber prepared by a roller-pressing impregnation method

Wood scrimber is a wood-based composite material with high mechanical strength and large size, which can potentially replace the use of steel and cement in various fields. However, its poor dimensional stability and low flame retardancy limit its use in outdoor construction projects and fire-prone areas. To solve this, here we report a roller-pressing impregnation method to realize the deep penetration of resin using mechanical compression and low-pressure adsorption. Microstructural imaging by SEM and 3D ultra-deep field microscopy shows the phenol formaldehyde(PF) resin distribution of the roller-pressed wood scrimber (R-WS) is deeper and more uniform, which increases the flatness and crystallinity. The R-WS showed greatly improved dimensional stability, with 63 % and 35 % lower thickness swelling rate (TSR) and width swelling rate (WSR) compared with the traditional wood scrimber (T-WS). In terms of flame retardancy, the smoke production rate (SPR) and heat release rate (HRR) of R-WS decreased by 32.7 % and 52 %, respectively. The R-WS at 800 °C formed a dense char that content increased by 20 %, helping to inhibits combustion. The mechanical properties of R-WS were also improved, and the modulus of rupture (MOR), modulus of elasticity (MOE) and short-beam strength (SS) of R-WS increased by 31.2 %, 7.4 %and 26.7 %, respectively. The R-WS suffer toughness failure and wood-to-wood failure under bending and shear scenarios, respectively, indicating that the roller-pressing impregnation treatment enhanced toughness and bonding strength. In addition, the use of a rotating roller is expected to realize the continuous production of the dipping link, saving drying energy consumption and improving production efficiency. These properties are expected to promote the outdoor utilization and continuous production of wood scrimber.

Thermal Management Techniques for Lithium-Ion Batteries Based on Phase Change Materials: A Systematic Review and Prospective Recommendations

Thermal management systems for lithium-ion batteries based on the cooling and heating of phase change materials have become a popular research topic. However, the low thermal conductivity, flame resistance, high and low temperature adaptability of phase change materials, as well as the thermal runaway mechanisms and lightweight design of phase change material-based systems remain to be explored. The aim of this paper is to conduct a publication-wide macro bibliometric review on thermal management systems for lithium-ion batteries based on phase change material to date. Total of 583 associated publications were retrieved from the Web of Science Core Collection database for the period 2006–2022. A bibliometric study was conducted through the visualization software VOSviewer. The findings were derived from annual publication trends, geographical and institutional distribution, authors and their collaborative networks, keyword network analysis and analysis of highly cited publications as well as reference co-citation analysis. The findings provide a comprehensive overview of the evolution of research hotspots in the field and can help researchers who would like to work in the field to quickly grasp the research frontiers and the overall picture. Furthermore, some suggestions for future work are summarized.

Phosphonate-Functionalized Ionic Liquid Gel Polymer Electrolyte with High Safety for Dendrite-Free Lithium Metal Batteries.

The conventional lithium-ion battery technology relies on the liquid carbonate-based electrolyte solution, which causes excessive side reactions, serious risk of electrolyte leakage, high flammability, and significant safety hazards. In this work, phosphonate-functionalized imidazolium ionic liquid (PFIL) is synthesized and used as a gel polymer electrolyte (GPE) to replace the organic carbonate-based electrolyte solution. The as-prepared ionic liquid-based gel polymer electrolyte (IL-GPE) shows low crystallinity, flame retardance, and excellent electrochemical performance. Thanks to the fast double channel transport of lithium ions in the IL-GPE electrolyte, a high ionic conductivity of 0.48 mS cm-1 and a lithium-ion transference number of 0.37 are exhibited. Symmetrical lithium cells with IL-GPE retain stable cycling even after 3000 h under 0.1 mA cm-2. IL-GPE exhibits good compatibility toward lithium metal, yielding excellent long-term electrochemical kinetic stability. IL-GPE induces the formation of a uniform and robust SEI layer, inhibiting the growth of lithium dendrites and improving the rate performance and cycle stability. Furthermore, Li/LiFePO4 cells exhibit a specific capacity of 63 mA h g-1 after 150 cycles at 5.0 C, with a capacity retention of 90.2%. It is foreseen that this GPE is a promising candidate to enhance the safety of high-performance lithium metal batteries.