Higher Heat Release Rate Research Articles

In-situ generated SiO2 nanoparticles for heat release reduction and smoke suppression in unsaturated polyester composites

Achieving lower heat release rates (HRR) during combustion is one of the key steps toward obtaining flame retardant materials. UPR thermosets, while mechanically strong and chemically durable, show high HRR upon ignition. While most commercial applications focus on blending of metal oxide or other heterogeneous fillers to reduce HRR, they have significant drawbacks like phase segregation, drop in transparency and other features which disfavor their use in UPRs. Herein, a novel, green technique to generate nSiO2 in-situ in UPRs is demonstrated. The method is designed such that the precursors act as nucleating agents covalently bonded to the UPRs and as growth fuel for the nSiO2 production. Apart from major advantages like a uniform phase distribution in the thermoset and transparency, this technique also prevents direct handling of powdered micro or nanoparticles, leading to a safer working environment for the handling of UPRs. The physical, thermal, and mechanical properties analyzed show great promise towards flame retardant composites, as the formed nanocomposite material, with 10 wt% loading of nSiO2 demonstrates a 41% reduction in total heat release (THR) and a 52% reduction in total smoke release (TSR), while retaining optical transmission >90%. On combination with commercial phosphorus containing flame retardant, ammonium polyphosphate (APP), the composite shows an even greater reduction in THR and TSR, while also being self-extinguishing. These compelling features, coupled with the safe nature of generating nanoparticles in-situ, offer substantial benefits of using this nSiO2 approach towards HRR reduction in UPR-based thermosets and advocate for their use in commercial formulations.

Flow structures and combustion regimes in an axisymmetric scramjet combustor with high Reynolds number

This study investigates the flow structures and combustion regimes in an axisymmetric cavity-based scramjet combustor with a total temperature of 1800 K and a high Reynolds number of approximately 1 × 107. The hydroxyl planar laser-induced fluorescence technique, along with the broadband flame emission and CH* chemiluminescence, is employed to visualize the instantaneous flame structure in the optically accessible cavity. The jet-wake flame stabilization mode is observed, with intense heat release occurring in the jet wake upstream of the cavity. A hybrid Reynolds-averaged Navier–Stokes/large-eddy simulation approach is performed for the 0.18-equivalent-ratio case with a pressure-corrected flamelet/progress variable model. The combustion regime is identified mainly in the corrugated or wrinkled flamelet regime (approximately 102 < Da < 104, 103 < Ret < 105 where $Da$ is the Damköhler number and $Re_t$ is the turbulent Reynolds number). The combustion process is jointly dominated by supersonic combustion (which accounts for approximately 58 %) and subsonic combustion, although subsonic combustion has a higher heat release rate (peak value exceeding 1 × 109 J (m3s)−1). A partially premixed flame is observed, where the diffusion flame packages a considerable quantity of twisted premixed flame. The shockwave plays a critical role in generating vorticity by strengthening the volumetric expansion and baroclinic torque term, and it can facilitate the chemical reaction rates through the pressure and temperature surges, thereby enhancing the combustion. Combustion also shows a remarkable effect on the overall flow structures, and it drives alterations in the vorticity of the flow field. In turn, the turbulent flow facilitates the combustion and improves the flame stabilization by enhancing the reactant mixing and increasing the flame surface area.

Effect of pre-chamber volume and nozzle number on turbulent jet combustion characteristics of GDI engines

There are few studies on the effect of turbulent jets on the combustion characteristics of passive pre-chamber (PC) gasoline engines, and their mechanism needs to be elucidated. Therefore, a 3-D simulation was performed using CONVERGE software. The results reveal that a modest expansion in the PC volume contributes to combustion due to the increased jet energy, but when it is too large, the above effect is weakened. In this study, at a smaller 0.8 ml volume, the combustion is still similar to traditional spark plug ignition. At middle 1.6 ml volume, the mixture concentration in the PC increases and the uniformity is better, resulting in the highest jet velocity and shortest jet duration, thus achieving the fastest flame propagation and the highest heat release rate (HRR). However, at a larger 1.8–2.0 ml volume, the mixture concentration near the spark-plug is sharply reduced, thus the reduced combustion rate in the PC leads to insufficient jet energy in the subsequent jets and resulting deterioration in combustion. An appropriate increase in nozzle number also improves combustion by introducing more ignition sources. But more nozzles not always improving the combustion. In the eight-nozzle case, three nozzles are close to the exhaust valve so that the intake is inhibited, resulting in a worsening of the ignition. The combustion under six-nozzle shows the highest HRR and shortest combustion duration. However, the combustion deteriorates at eight-nozzle, since the increase in the ignition point is not enough to compensate for the negative impact of the reduced jet intensity on combustion.

The emission of pollutants from ornamental shrubs during forest fires

AbstractThis study investigates the combustion behavior, emissions, and aerosol production of four plant species: Laurus nobilis, Cistus monspeliensis, Photinia fraseri, and Cupressus sempervirens. The Heat Release Rate (HRR) and Smoke Production Rate (SPR) were measured, revealing that Cupressus sempervirens had the highest HRR and longest flame duration due to its higher bulk density. Emission Factors (EFs) for key compounds such as CO₂, CO, NO, and aerosols showed significant variation by species. Aerosol analysis indicated that the combustion of all plants primarily emitted fine particles, with the majority being ultrafine particles (PM0.1), particularly in the 25–130‐nm range. Particle size distributions were bimodal in number but monomodal in volume. These findings highlight the impact of plant characteristics on fire behavior and emissions, with significant implications for understanding fire dynamics in wildland–urban interfaces.

Karakteristik Pembakaran Droplet Campuran Metil Oleat – Etanol dengan Penambahan Multi -Walled Carbon Nanotubes

This research intended to investigate the combustion characteristics of methyl oleic – ethanol blend with OH functionalized multi-walled carbon nanotubes (MWCNT-OH) addition. Methyl oleic is an unsaturated fatty acid methyl ester, which is a constituent of various biodiesels. The observed fuel was a mixture of Methyl oleic with 20% vol of ethanol. MWCNT-OH content was varied by 100 ppm, 200 ppm, 300 ppm, 400 ppm, and 500 ppm (wt based). The presence of ethanol in the droplets is intended to promote the microexplosion phenomenon, generating smaller droplets and a shorter burning time. The experimental results show that the MWCNT-OH addition on the droplet of Methyl oleic – ethanol blend decreased the ignition delay and droplet burning time, while the constant burning rate and droplet temperature (and flame temperature) were increased. Reducing ignition delay time due to the higher thermal conductivity of nanofluid droplets results in more effective heat absorption from the environment and better heat transport inside the droplet. Hence, droplet vaporization, flammable mixture formation and ignition occur in a shorter time. Furthermore, this condition encourages a higher burning rate and a lower droplet burning time. The higher droplet and flame temperatures are related to the higher heating value of the methyl oleic – ethanol – MWCNT-OH mixture and higher droplet burning rate, which results in a higher heat release rate.

Effect of H[formula omitted] addition on NH[formula omitted] flame structure and dynamics in a mixing layer

Hydrogen addition has been widely used to improve the combustion performance of low-reactivity fuels such as NH3. In this study, a series of two-dimensional NH3/H2 flames in mixing layers were investigated numerically. The aim is to assess and interpret the effects of H2 addition on the structure and dynamics of ammonia flames. Detailed chemistry and transport models were considered in the simulations. It was shown that for pure hydrogen or ammonia flames, a classical tribrachial structure was observed. The non-premixed branch in the tribrachial flame of NH3 combustion features high heat release rate (HRR), while the two premixed branches are weak. The mixture fraction corresponding to the maximum HRR of NH3 combustion is significantly lower than the stoichiometric mixture fraction. When blending ammonia with hydrogen, a tetrabrachial flame structure consisting of two premixed branches and two non-premixed branches was observed, where one non-premixed branch corresponds to the reaction of NH3, while the other is formed due to the reaction of H2. It was suggested that the formation of the tetrabrachial flame is related to the preferential diffusion of hydrogen. After decreasing artificially the diffusivity of hydrogen to suppress the preferential diffusion effect, the flame exhibits only three branches with the merging of the two non-premixed branches. By analyzing the flame dynamics at the leading edge, it was found that the flame speed (Sd∗) is negatively correlated with the flame stretch (κ) and scalar dissipation rate (χ), with Sd∗ decreasing almost linearly with κ or χ, consistent with previous studies of methane and hydrogen flames. As the H2 concentration is increased, the values of Sd∗ increase due to the enhanced reactivity.

Comparative study on the influence of chemical reaction mechanisms on turbulent jet flame

Abstract This paper focus on the influence of chemical reaction mechanisms on the simulation of turbulent jet flame of 11 different chemical reaction mechanisms. These mechanisms are mainly selected from GRI series and their reduced mechanisms, and their reaction kinetics were analyzed. This paper uses LES-TPDF method to simulate Sandia Flame D turbulent jet flame and then analyze the difference of time-averaged temperature, heat release rate and species concentration results in different mechanisms. The results show that the kinetic performance of different chemical mechanisms is very different. The ignition delay time of JL4, SMOOKE and z42 mechanisms are either overestimated or underestimated due to the omission of multi-carbon species and other important species. The differences of the LES results in different mechanisms increase along the axis. The differences near the fuel inlet are mainly due to the difference of kinetic performance, while the difference away from the fuel inlet is more due to the different species and elementary reactions involved in different chemical reaction mechanisms. For all chemical mechanisms, there is a tendency that the more species used in the chemical reaction, the more concentrated the region of high heat release rate, the shorter the flame length, and the higher the maximum temperature throughout the field.

Investigation of [formula omitted] formation in non-premixed, swirl-stabilised, wet hydrogen/air gas turbine combustor

In line with the Paris Agreement and the United Nations Sustainable Development Goals, the use of fossil fuels is to be phased out in the coming decades. Fossil-free hydrogen is a promising candidate for decarbonising the energy sector. However, hydrogen combustion is known to produce undesirable emissions such as nitrogen oxides (NOx) and calls for mitigation measures such as steam-diluted hydrogen combustion, which is known to reduce the NOx emissions. This study focuses on improving the understanding of NOx formation in a swirl-stabilised, steam-diluted, non-premixed hydrogen/air combustion using high-fidelity large eddy simulation (LES) and zero-dimensional (0D) perfectly stirred reactors (PSR). The LES results are used to identify four salient points in the domain where the NOx chemistry is analysed in detail. These points are chosen in the main flame, flame tail, post-flame and central recirculation regions. Note, the high heat release rate (HRR) region is referred to as the main flame while the flame tail denotes the low-HRR and V-shaped flame region adjacent to the main flame. Based on the LES data at these chosen points, the contribution of the major NO production pathways such as the Zeldovich mechanism, extended Zeldovich mechanism, N2O route and the NNH route are studied and reveal different rates of production of NO (i.e. ROPNO). Also, the role of individual reactions in NO production and consumption is investigated. Furthermore, reaction pathway diagrams illustrating the chemical pathways leading to NO are visualised. The sensitivity of NO to each reaction is also reported. These analyses provide insights into the NO chemical pathways observed at the salient points across the domain. The dominance of the Zeldovich mechanism remains but is much less compared to that in dry hydrogen combustion as its contribution to ROPNO is less than 20% at all the points considered. However, the extended Zeldovich mechanism is significant at all the points. The NNH route is observed to be important in the flame regions. The major NNH reaction contributing to ROPNO in the flame regions is NNH+O⇌NH+NO. Furthermore, the complex NO chemistry at all the identified points is presented in great detail using the above-mentioned analyses and illustrations. This work highlights the possibility of combining a high-fidelity simulation and a simple 0D ideal reactor to decipher the nuances of NO chemical pathways in a practical swirl-stabilised gas turbine combustor and provide new understanding for assisting engineers in designing clean burners.

A LES study on the instantaneous H2 jet-ignited combustion characteristics of H2/NH3 mixtures

This paper presents a Large Eddy Simulation (LES) study investigating jet flame ignition characteristics to achieve stable ammonia combustion for novel applications in gaseous ammonia/hydrogen-fueled engines with an active prechamber. The study investigated three cases with initial global equivalence ratios of 0.6, 0.8, and 1.0. Two main ignition modes were proposed, and five stages of coupled flame propagation processes were identified. The oscillation of supersonic hydrogen jet flame was investigated. The modes of flame-vortex interaction including vortex ring formation, along with the mechanism of highly reactive zone formation, were proposed. The effects of reactivity and turbulence transition on piloted ammonia flame were investigated to attain stable ammonia combustion and achieve a high heat release rate. The results showed that oscillations in the jet flame were strengthened at low global equivalence ratios with high hydrogen mass ratios. Enhancing propagation of initial and secondary vortex rings broadened highly reactive zones. Vorticity dissipated more rapidly at low equivalence ratios, leading to a stratified structure and enhanced piloted spherical flame. The Unsteady Flamelet Ignition Prediction (UFIP) sub-model of combustion was verified for the piloted ammonia flame, enabling a more comprehensive discussion of flame propagation tendencies.

Simulation of lithium-ion battery thermal runaway considering active material volume fraction effect

The multi-physics solver BatteryFOAM couples with the side reaction model for thermal runaway (TR) simulations, including the electrolyte decomposition (E) and solid electrolyte interface layer decomposition (SEI), and the reaction of the electrolyte with graphite intercalated lithium (NE-E) and the reaction of positive electrode active material with the electrolyte (PE-E). This solver is used to study the lithium-ion battery (LIB) TR at different conditions. The published experimental results are used to validate the effectiveness and practicability of BatteryFOAM in predicting the temperature under constat high temperature. We also discuss the reactant concentration, reaction rate, and heat release rate during the LIB TR. The influences of the external factor of the equal equivalent heat transfer (h) on the battery TR is considered, and the sequence in which the battery reaches the critical temperature rising rate (RTR, 60 K/min) and the separator failure temperature (Tsep) is predicted. The results demonstrate that overall the exothermic reaction peaks arise sequentially from SEI decomposition, PE-E reaction, NE-E reaction, and electrolyte decomposition, and NE-E reaction has three exothermic peaks induced by other three side reactions. PE-E reaction contributes more heat for fuse energy to trigger TR, but the NE-E reaction and electrolyte decomposition mainly accounts for the runaway energy. In addition, increasing SEI and electrolyte decomposition intensity is found no effect on the TR temperature. Besides, the rapid reaching to RTR is caused by the high heat release rate of positive electrode active material with electrolyte. Results further show that reducing the fNE−E within 5.0 % will significantly reduce TR risk.

A Comprehensive Study on <i>Calophyllum inophyllum</i> Biodiesel and Dimethyl Carbonate Blends: Performance Optimization and Emission Control in Diesel Engines

The rising fuel demand, driven by expanding logistical infrastructure, transportation sector growth, and the need for faster transport modes, has led to significant urban sprawl and vehicle emissions, posing serious threats to air quality and human health. Chronic exposure to vehicle emissions is linked to severe health issues such as lung cancer, asthma, cardio-respiratory problems, hypersensitivity, and hypertension. In response, the quest for alternative fuels from renewable resources, particularly biodiesel, has gained momentum. Biodiesel, derived from waste seed oil, animal fat, and vegetable oil, presents a promising substitute for traditional diesel fuel. This study investigates the effects of bl enhances diesel with up to 20% Dimethyl Carbonate (DMC), an oxygenated additive, to enhance ignition properties. Engine performance and emissions were assessed under standard operational conditions. Results indicated that pure biodiesel achieved a maximum cylinder pressure 1.73% higher than diesel. Increasing DMC content in the biodiesel blend resulted in a 21.54% higher Heat Release Rate (HRR) and a 17.75% improvement in brake thermal efficiency compared to pure biodiesel at higher loads. However, the higher DMC blend also increased NOx emissions by 4.2% while significantly reducing smoke, hydrocarbon (HC), and carbon monoxide (CO) emissions by 32.5%, 36.36%, and 35.65% respectively, compared to diesel at maximum load.

Study of air supplement velocity by thermal stack effect and critical velocity under longitudinal ventilation in the uniclinal V-shaped tunnel

This research focuses on the specific uniclinal V-shaped tunnel during a fire, studying the air supplement triggered by the thermal stack effect and further examining the control mechanism of upstream smoke. It revealed how the air supplement velocity generated by the thermal stack effect, influenced by longitudinal ventilation, varied in the tunnel. It also established a prediction model for the critical velocity based on different geometric tunnel parameters. Results indicate that internal longitudinal velocity enhances air entrainment, lowers the temperature field, and significantly reduces the stack effect. As longitudinal velocity increases, the air supplement velocity exhibits an exponential decay, with a decay coefficient identified as 3.22. Higher heat release rates and slope heights increase the internal temperature and height differences, promoting air supplementation. Combining air supplement velocity with the critical velocity prediction for horizontal tunnels, the study quantifies the critical velocity in uniclinal V-shaped tunnels under varying conditions. It introduces a P parameter to decide on the necessity of external mechanical ventilation for smoke control. P ≥ 1 indicates that mechanical ventilation is unnecessary; P < 1 suggests the opposite. These findings offer significant insights into the dynamics of smoke and air in tunnels, providing valuable guidance for tunnel fire smoke management.

Study on the lower head failure in severe accidents Part II: Thermal-mechanical coupling behavior analysis on CAP1400 reactor lower head

Under severe accident conditions with core meltdown, large amounts of molten material relocate to the lower head at high temperatures. Significant thermal and mechanical loads may lead to failure of the reactor pressure vessel (RPV) lower head, spreading radioactive fission products. Lower head failure time and location are crucial for accident mitigation and consequence assessment. This study developed a thermodynamic failure analysis model for the lower head by investigating material failure mechanisms, coupling this into an Integrated Severe Accident Analysis code (ISAA), and conducting experimental validation and applied research. Part I mainly introduces the thermodynamic analysis module development, validation against OLHF experiments, and preliminary failure criteria analysis. Results indicate the model accurately predicts lower head failure behavior, and Larson-Miller life fraction and Hedl-Dorn parameter criteria accurately assess lower head integrity. Part II presents applied research after validation and preliminary analysis. Using the improved ISAA, melt pool behavior and lower head thermal–mechanical response were analyzed for a CAP1400 small break loss-of-coolant accident (SBLOCA), assuming multiple safety system failures. Results indicate the bottom of the lower head melt pool didn’t form a hard shell due to high heat release rate, only an oxide shell layer around the second layer. Decay heat from melt pool components cannot be dissipated, leading to lower head failure. Further External Reactor Vessel Cooling (ERVC) heat transfer model analysis and research are needed in ISAA. The two developed mechanical analysis models predict material failure at high temperatures, and the timing and location of lower head failure are consistent, at approximately 16,000 s at 25.38°±5.47° on the lower head. The predicted failure mode is similar to Part I validation, indicating both Larson-Miller life fraction and Hedl-Dorn parameter criteria provide consistent lower head integrity judgments.

The application of UHPC on the monolithic part of the Štvanice footbridge

The use of UHPC with fibers is becoming an increasingly common topic in the world. This material is used for its superior mechanical and physical properties and long service life. However, the production cost is high, hence UHPC is used for special applications or for smaller prefabricated parts. This paper focuses on UHPC application for the construction of the Štvanice Footbridge, Prague, the Czech Republic. A monolithic part of the structure was made of UHPC from fresh transport concrete, which was produced by Skanska Transbeton. The special feature is that about 126m3 of fresh concrete was industrially prepared. This concrete achieved the properties of SCC and the final 28 day compressive strength was 120MPa with tensile strength of 18.6 MPa. Due to high hydration heat release rate, an internal water cooling system was designed and sucessfully appled using water from Vltava River.

Core-shell structured α-AlH3/Fe2O3 thermite with improved heat-release and combustion performance

Thermites are widely used in propellants, explosives and ignition materials because of their high heat release rate and good combustion efficiency. Structural control over thermites to achieve improved performance leads to a promising research area. Among these, core-shell structured composites have attracted wide attention due to their excellent properties and close contact among components. Herein, core-shell structured α-AlH3/Fe2O3 thermites were prepared, which exhibit high heat-release and excellent combustion performance. At an equivalence ratio of 2.0, the core-shell structured α-AlH3/Fe2O3 has the most heat release (1213.8 J/g) and the lowest reaction activation energy (147.5 kJ/mol). The ignited combustion performance of α-AlH3/Fe2O3 was notably strengthened by the shorter ignition delay period (11 ms). Interestingly, the core-shell structured α-AlH3/Fe2O3 was less sensitive to electrostatic discharge, which suggests that the core-shell structured α-AlH3/Fe2O3 reaches the goal of high energy release and electrostatic safety. The core-shell thermite system with α-AlH3 as metal fuel could provide an efficient alternative to hunt for thermites with high reactivity.

Investigations on a Spark Ignition Engine, Part II: Impact of Hydrogen Addition and Compression Ratio on a Biogas-Fuelled Engine

Performance, emissions and combustion were studied using a spark ignition engine modified from a single-cylinder diesel engine with varying compression ratios and hydrogen addition. When the compression ratio increases, there is a slight increase in brake power and thermal efficiency. There is a small increase in brake power and brake thermal efficiency when the compression ratio is above 13:1. Increased emissions of nitric oxide, hydrocarbon, and carbon monoxide were observed at compression ratios above 13:1. Leaner mixtures, brake power and brake thermal efficiency are lowered. Spark timing is retarded as the compression ratio rises which results in high peak pressure and rate of heat release. At a compression ratio of 13:1, a small amount of hydrogen (15% on an energy basis) was added along with biogas. The lean limit of biogas combustion and the combustion rate are greatly increased by the addition of hydrogen. In addition, there was a rise in brake power and thermal efficiency. The levels of hydrocarbons were significantly reduced. Nitric oxide emissions did not rise as a result of the use of the retarded ignition timing. The effect of two throttle conditions on spark ignition engines using biogas as fuel is presented as Part I of this study.

Study on fire characteristics of lithium battery of new energy vehicles in a tunnel

In order to explore fire safety of lithium battery of new energy vehicles in a tunnel, a numerical calculation model for lithium battery of new energy vehicle was established. This paper used eight heat release rate (HRR) for lithium battery of new energy vehicle calculation models, and conducted a series of simulation calculations to analyze and compare the fire development characteristics of fuel vehicles and new energy vehicles with different HRR in a tunnel. This paper investigated temperature distribution below the ceiling and smoke diffusion in a tunnel, as well as the distribution of CO2 and CO concentrations, to explore the spread of lithium battery of new energy vehicle fires in a tunnel. Then, the accuracy of the numerical simulation was verified through comparison with existing examples. The results showed that there is a correlation between the temperature distribution below the ceiling in a tunnel and the HRR of lithium battery of new energy vehicle fires, with higher HRR and higher temperature below the ceiling in a tunnel. In addition, the heat release of fuel vehicles in a tunnel is lower than that of lithium battery of new energy vehicles. The analysis of the ceiling temperature of new energy vehicles in tunnels after a fire showed that for different HRR, the temperature below the ceiling increases with the increase of HRR. In tunnel fires, lithium battery of new energy vehicles generate higher temperature, smoke, and CO emission concentrations than fuel vehicles. Therefore, the risk of fire for lithium battery of new energy vehicles in tunnels is higher than that of fuel vehicles, and their fire safety needs to be paid more attention.

Evaluations of the effects of different flame retardants combinations on particleboards produced using urea–formaldehyde resin

Nowadays, using flame-retardant chemicals is gaining importance in chipboard production. Melamine resins to produce chipboard are preferred to provide flame retardancy properties with a cost of approximately 2.5 times the urea–formaldehyde (UF) resin. In this study, the UF resin to produce the chipboard was preferred due to its economical availability. To improve the flame retardancy properties of the chipboard, phosphate-based and inorganic flame retardants were used in the chipboards. In chipboard production, oak, pine, poplar, sawdust, urea–formaldehyde resin as adhesive, flame retardant chemicals like triphenyl phosphate (TPP), ammonium polyphosphate (APP), and calcium gluconate (CaG) were used. Flame retardant chemicals were added to chipboards in single and double compositions and prepared by pressing method. Mechanical (tensile, bending, and surface strength), physical (humidity, density, formaldehyde emission), and fire (limiting oxygen index (LOI), cone calorimeter, and UL-94 vertical) tests were performed on wooden boards. It has been observed that the use of different types of flame retardant and their combinations in chipboard does not significantly change the mechanical properties. It was seen that the free formaldehyde emission rate decreased by using flame retardant added compared to the control sample. The chipboard samples with added flame-retardant chemicals have entered the V-0 rating in the UL-94. LOI values of the chipboard samples containing 50% CaG-50% APP and 50% TPP—50% CaG were observed as 29.7% and 29.8%, respectively. Besides, the highest heat release rate (HRR) reduction was obtained in the chipboard sample containing 50% CaG—50% APP.

Cage Nanofillers' Influence on Fire Hazard and Toxic Gases Emitted during Thermal Decomposition of Polyurethane Foam.

Polyurethane (PUR), as an engineering polymer, is widely used in many sectors of industries. However, the high fire risks associated with PUR, including the smoke density, a high heat release rate, and the toxicity of combustion products limit its applications in many fields. This paper presents the influence of silsesquioxane fillers, alone and in a synergistic system with halogen-free flame-retardant compounds, on reducing the fire hazard of polyurethane foams. The flammability of PUR composites was determined with the use of a pyrolysis combustion flow calorimeter (PCFC) and a cone calorimeter. The flammability results were supplemented with smoke emission values obtained with the use of a smoke density chamber (SDC) and toxicometric indexes. Toxicometric indexes were determined with the use of an innovative method consisting of a thermo-balance connected to a gas analyzer with the use of a heated transfer line. The obtained test results clearly indicate that the used silsesquioxane compounds, especially in combination with organic phosphorus compounds, reduced the fire risk, as expressed by parameters such as the maximum heat release rate (HRRmax), the total heat release rate (THR), and the maximum smoke density (SDmax). The flame-retardant non-halogen system also reduced the amounts of toxic gases emitted during the decomposition of PUR, especially NOx, HCN, NH3, CO and CO2. According to the literature review, complex studies on the fire hazard of a system of POSS-phosphorus compounds in the PUR matrix have not been published yet. This article presents the complex results of studies, indicating that the POSS-phosphorous compound system can be treated as an alternative to toxic halogen flame-retardant compounds in order to decrease the fire hazard of PUR foam.

Flame evolution and pressure dynamics of premixed stoichiometric ammonia/hydrogen/air in a closed duct

Ammonia is regarded as a promising energy carrier due to its zero-carbon emissions and its suitability for long-distance, large-scale storage, and transportation. Ammonia/hydrogen mixed combustion is an important way to solve the problem of high ignition temperature and low flame speed in the process of ammonia combustion. This study systematically investigates the evolution of flames and pressure dynamics in a closed duct for ammonia/hydrogen/air mixtures with varying hydrogen blending ratio (0–100 %). Simultaneously, the study assesses the impact of flame instability and heat release on the evolution of ammonia/hydrogen/air flames and pressure dynamics. The results show that the flame tip speed and overpressure increase with the increase of hydrogen blending ratio and initial pressure, and when the hydrogen blending ratio is more than 25 %, the growth range of flame tip speed peak and overpressure peak value increases significantly. At the same time, the flame thickness decreases after hydrogen blending, the hydrodynamic instability increases, and the degree of wrinkles on the flame surface increases, which promotes flame acceleration. The Froude number increases significantly, the influence of buoyancy instability gradually weakens, and the flame core does not undergo significant displacement. In the later stage of flame propagation, both the flame front propagation velocity and pressure show significant pulsation phenomena. The heat release calculation results show that hydrogen blending significantly increases the adiabatic flame temperature. Consistent with the evolution law of overpressure, when the hydrogen blending ratio is greater than 25 %, the net heat release increases significantly. The elementary reaction with the highest heat release rate changes from the chain termination reaction R41 to the chain termination reaction R3. The research results can provide theoretical basis and experimental data support for the formulation of safety standards during the regulation and utilization of the combustion structure of ammonia/hydrogen/air mixtures.