Flame Propagation Research Articles

Features of the interaction of the combustion front of diluted methane–oxygen mixtures with hollow cylindrical and conical obstacles at low pressures

It was shown that the front of the flame of a well-mixed diluted methane–oxygen mixture at 298 K and 100–300 Torr propagating to the ends of hollow cylindrical and conical obstacles does not form a vortex shedding behind them; however, that instability occurs under the same conditions in the flow of hot products after the obstacles. To find out the reason that vortex shedding is not observed behind the obstacle at flame propagation, but vortex shedding appears in the course of propagation of a reflected stream of hot products, we consider the curved flame front. Let us show that the thermal conductivity should reduce the curvature of the flame and lead to its stabilization. Indeed, the convex areas of the chemical reaction zone in a combustible mixture in relation to the cold ones shall give up more heat than in a flat flame: the heat from these is not only transmitted forward in the direction of flame propagation, but also in the lateral directions. The resulting cooling of the reaction zone will cause the backlog of the areas of the flame that burst forward. The opposite situation will be for concave areas where the temperature rises for the same reasons, reactions rates increase, and they spread forward faster as the flame spreads. Thus, the surface of the curved front of the flame aligns. In other words, the thermal conductivity has a stabilizing effect on the curved flame. This effect is missing in non-reactive gas. The calculations showed that the main observed feature of the flame front propagation against an obstacle in the form of a cylinder is taken into account: vortex shedding is not observed behind the obstacle at flame propagation; the simple consideration was given above. Thus, the qualitative model of compressible non-reactive/reactive Navier–Stokes equations in low Mach number approximation allows obtaining both the mode of the emergence of von Karman instability in chemically inert gas and the absence of the mode for flame propagation.

Assessment of LES-ADM Accuracy for Modelling of Auto-Ignition and Flame Propagation in a Temporally-Evolving Nitrogen-Diluted Hydrogen Jet

Assessment of LES-ADM Accuracy for Modelling of Auto-Ignition and Flame Propagation in a Temporally-Evolving Nitrogen-Diluted Hydrogen Jet

Visualization Study of Methane Deflagration Characteristics in Variable Diameter Pipelines Based on Schlieren Technique

ABSTRACT The phenomenon of pipe diameter change often exists in urban natural gas pipelines. To study the impact of pipe diameter variation on the propagation characteristics of combustible gas deflagration and provide theoretical basis for the prevention and emergency treatment of gas pipeline explosion accidents, this work uses a self-developed circular explosion pipe test bench with a length of 12 m and an inner diameter of 90 mm to study the methane deflagration characteristics in variable diameter pipelines. Under four experimental conditions of variable cross-sectional area ratio (VR) of 1.0, 0.6, 0.4, and 0.2, the schlieren images of the deflagration process of methane/air premixed gas with a methane concentration of 9.5% were captured by a high-speed camera. Combined with the traditional pressure and flame signal point source information, the research results show that the existence of variable diameter pipelines can change the flame structure and shape, causing the flame front to transform into a tulip flame in advance. The flame propagation speed under different experimental conditions is: VR = 0.4 > VR = 0.2 > VR = 0.6. The influence of the variable diameter pipeline on flame velocity depends on the suppression effect of the reflected wave generated by the cross-section area of the variable diameter pipe and the coupling effect of the reduced aperture area of the variable diameter section on the flame acceleration effect. When the reflected wave acts on the flame front, the flame propagation speed decreases, and in severe cases, it will cause flame stagnation and backfire.

Patterns of lean methane-air mixtures combustion in piston engine

The article is devoted to the study of the patterns of combustion of lean methaneair mixtures in marine internal combustion engine. Literature review shows that the implementation of combustion technology for a homogeneous lean methaneair mixture will increase the compression ratio, reduce fuel consumption and improve the environmental engine performance. However due to an increase in misfires and a decrease in the speed of flame propagation, the combustion of lean methaneair mixtures remains an unresolved problem. The article studies the influence of the excess air coefficient (from 1 to 1.4) on the turbulent combustion regime (assessed by the Karlowitz and Damkoehler criteria), the completeness and rate of fuel combustion. It was revealed that depletion of the air fuel mixture under conditions of intense turbulence leads to an increase in the Karlowitz criterion and a decrease in the Damköhler criterion. This indicates that the rate of chemical reactions in the flame front decreases, as a result of which the combustion process is characterized by stretching and rupture of the flame front. Therefore, to intensify the combustion of lean methaneair mixtures, it is advisable to increase the average speed of the vortex flow, and not the intensity of turbulence. A study of the influence of the excess air coefficient on the completeness and rate of fuel combustion showed that depletion of the mixture leads to a decrease in the completeness of fuel combustion from 93.5 % (at α=1) to 83 % (at α=1.4). The combustion rates also decrease and their maximum values shift from 13° (at α=1) to 24° (at α=1.4) degrees after top dead center. Therefore for efficient engine operation on lean mixtures, it is necessary to increase the fuel combustion rate through additional swirling of the gasair mixture or the use of combustion promoters.

Effects of injection timing on combustion and mixture formation of a methanol direct injection engine equipped with a small volume passive pre-chamber

The pursuit of high efficiency and cleanliness has always been the focus of engine research. As one of the most promising low-carbon renewable alternative fuel, methanol has gained increasing attention in engine applications. Inspired by the advantages of gasoline direct injection (GDI) in fuel economy, methanol direct injection (MDI) engine has also become a research hot spot. Similar to GDI, the mixture distribution is crucial for MDI engines, especially in the late injection stratified operation mode, an unreasonable mixture distribution of rich and lean regions will result in slow and incomplete combustion, or even flame quenching. Due to the characteristics of multi-point ignition and the high ignition energy, pre-chamber jet flame ignition has the potential to effectively enhance combustion. In this paper, the effect of injection timing on combustion characteristics in a methanol direct injection engine equipped with a small volume pre-chamber are studied experimentally. The mixture formation processes in both the main-chamber and the pre-chamber at different injection timings were also explored through simulations. The research findings indicated that the engine exhibits optimal power performance at the injection timing of − 270 °CA ATDC (after top dead center), primarily attributed to the enhanced volumetric efficiency and improved mixture homogeneity. However, the mixture concentration in the pre-chamber is leaner, resulting in the longest ignition delay period. When the injection timing is located on the middle state of the intake stroke, specifically − 210 °CA ATDC, the ignition delay period is the shortest, indicating that the mixture concentration and temperature in the pre-chamber are conducive to the flame kernel formation and flame propagation. In addition, the volumetric efficiency of this injection case is maximized due to the combined effects of spray-wall interaction, spray-air interaction, and the flow field. When injection occurs on compression stroke, the mixture concentration in the pre-chamber is higher; however, there exists a significant and discontinuous concentration gradient in the main-chamber, which limits the enhancement of the flame propagation speed and the combustion efficiency, especially for − 120 °CA ATDC injection case, the engine exhibits longest combustion duration and the lowest IMEP. The conclusions can provide theoretical basis and empirical data support for enhancing the combustion of methanol direct injection engines equipped with passive pre-chambers.

The suppression and CO elimination performance of Co3O4 dust cloud for methane-air mixture explosion

This paper experimentally studied the effect of Co3O4 dust clouds on the methane-air mixture explosion characteristics and post-explosion CO concentration, aiming to propose a novel method for simultaneously suppressing explosion and eliminating CO product. The Co3O4 catalyst was synthesized utilizing the co-precipitation method. We varied the methane concentration and Co3O4 dust cloud concentration to investigate their effects on the flame propagation behavior, maximum explosion overpressure (Pm), flame combustion time (tc), and the gaseous product concentration. The hazard of the gaseous product was evaluated by the effective escape time (te) based on the Fraction Effective Dose (FED) mathematical model. The results demonstrated that the Co3O4 dust cloud could significantly reduce the explosion severity and CO concentration. Furthermore, the higher the concentration of Co3O4 dust clouds, the more significant the explosion suppression and CO elimination performance, which was as a result of the significant increase in the contact area and collision probability between the Co3O4 particles and the reaction components increased. Compared to traditional inhibitors that only reduce the severity of an explosion, Co₃O₄ could not only significantly reduce the explosion severity, but also quickly eliminate post-detonation CO. The method proposed in this paper could effectively reduce the hazard of methane-air mixture explosion, which was of great practical significance for ensuring the safety of personnel involved in the risk.

Numerical simulation study of hydrogen/air flame propagation and detonation characteristics in an annular cross section of gas turbine combustion chamber

The trends and future directions of hydrogen safety research cannot be separated from the thermodynamic behavior of combustion and explosion, hydrogen spontaneous combustion, flame propagation behavior, thermodynamic mechanisms, and other related topics. In this paper, through the method of numerical simulation, considering the hydrogen flame propagation and detonation characteristics in the annular section of the combustion chamber commonly used in gas turbines, the form of detonation and detonation impact in the channel are evaluated. By discussing the deflagration to detonation transition of hydrogen/air premixed gas and premixed gas under different working conditions, it is found that the flame in the annular channel propagates close to the inner wall and forms a strong expansion and turbulence between the outer wall and the outer wall of the flame. The flame surface and the airflow shear accelerate the detonation of hydrogen. The area close to the wall on the outer side of the flame surface and the tip of the flame surface are prone to set off detonation. The high-pressure area after the detonation mainly acts on the symmetrical end face of the outer wall surface and ignition area. There is a critical working temperature to make the impact strength strongest when the detonation occurs. Reducing the equivalence ratio of the filling gas can significantly reduce the reaction speed and weaken the impact strength of the wall. When the equivalence ratio is less than a certain value, the filling gas is completely consumed in the form of deflagration.

Numerical investigation on the effect of ignition timing on a low-temperature hydrogen-fueled Wankel rotary engine with passive pre-chamber ignition

Adopting the low-temperature hydrogen evaporated from the liquid hydrogen is capable of improving volumetric efficiency for the Wankel rotary engine (WRE). Considering the difficulty in ignition and slow flame propagation of low-temperature hydrogen-air mixtures, the passive pre-chamber is used to improve ignition and combustion. A three-dimensional computational fluid dynamics model for a turbulent jet ignition (TJI) WRE fueled by low-temperature hydrogen was established. The effects of low temperature and TJI on the in-cylinder flow field, combustion, emissions and leakage in the TJI-WRE fueled by low-temperature hydrogen were studied under different ignition timings. The results indicated that low-temperature tends to suppress the flame propagation, whereas TJI can accelerate the flame speed and promote flame propagation to the unburned zone in the combustion chamber. Combining low-temperature hydrogen with the passive pre-chamber can achieve high engine thermal efficiency and power while significantly reducing leakage. With the ignition timing set at 18 °CA before the top dead center, the indicated thermal efficiency reached 39.49% and the indicated mean effective pressure peaked at 0.77 MPa. Compared to the original engine, fresh mixture leakage through spark plug cavities and adjacent chambers was reduced by 72.13% and 78.79%, respectively.

An experimental study on flame propagation and combustion characteristics of multiple emulsified diesel and biodiesel fuel droplets

To unravel the interaction mechanism between droplets that is relevant for practical liquid fueled burners, the flame propagation characteristics of multi-droplet of emulsified diesel and biodiesel (FAME) fuels were studied using a suspended line droplet array. It was found that when S/d0 ≤ 3 (ratio of droplet spacing to initial droplet diameter), the double droplets were ignited simultaneously and surrounded by a single flame, and as the droplet spacing increased, two independent flames were formed around each droplet. The highest flame propagation rate was attained at S/d0 = 3, which was attributed to the consistent values of flame standoff ratio limited by the dominant heat conduction and finite evaporating rate. The droplet interaction, such as oxygen competition effect, enhanced with smaller droplet distance, can result in the reduction in the droplet combustion rate and flame propagation rate; the latter one, however, showed an increasing trend when small droplet or the size non-uniformity of droplet cloud was considered. In addition, the child droplet ejected from the emulsified droplets showed three burning modes and was an important factor promoting the flame spread, and the results showed that compared with the FAME emulsified fuels, the child droplets in diesel cases were more prone to ignition, expanding the burning regime.

Experimental Study of Turbulent Premixed Flames of Gas-to-Liquids (GTL) Fuel in a Fan-Stirred Combustion Bomb

This study experimentally investigates the turbulent flame speeds (St) of Gas-to-Liquids (GTL) fuel and a 50/50 blend with diesel across turbulence intensities (u') ranging from 0.5 to 3.0 m/s and equivalence ratios (Φ) from 0.7 to 1.3. Experiments were conducted using a cylindrical fan-stirred combustion bomb at an initial temperature (Ti) of 463 K and atmospheric pressure under near homogeneous and isotropic turbulence (HIT) conditions. A pressure transducer measured the St of the propagating GTL flame. High-speed imaging reveals that changes in flame brightness are associated with variations in flame temperature and soot incandescence. Compared to diesel, stoichiometric GTL and the 50/50 diesel-GTL blend showed peak combustion pressure reductions of 8.9% and 4.9%, respectively. Rich diesel fuel and lean GTL exhibited higher pressure rise rates, flame propagation, and St due to their Lewis numbers (Le) being less than one, enhancing flame-turbulence interaction. At u` of 0.5, 1.5, and 3.0 m/s, St for GTL increased by approximately 3.6%, 5.3%, and 2.8%, respectively, when compared to diesel, with these increases observed at Φ < 1.1. Transition from wrinkled to corrugated flamelets with increasing u` supports models predicting flame stability and potential industrial combustion efficiency improvements. Comparisons with numerical St results using the Zimont Turbulent Flame Speed Closure (Zimont TFC) model showed good agreement at lower (u' = 0.5 m/s) and mid-range (u' = 2.0 m/s) turbulence intensities but discrepancies at higher intensities (u' = 3.0 m/s), highlighting the need to refine numerical models for more accurate predictions across all turbulence levels.

Strategic optimization of dual-fuel diesel/gas engines by numerical approach for environmental and economic benefits

The study introduces a framework for optimizing eco-friendly dual-fuel engines, combining CFD and ANN, to reduce carbon emissions and improve sustainable transportation.We achieved optimal performance with a 52–65 % NG substitution ratio. SOI timing had a big effect on NOx emissions; later injection decreased NOx formation because it made the mixture more homogeneous. We developed a radial basis function neural network model to predict engine performance and emissions with 99 % accuracy. The study examines the effect of fuel droplet spraying on cylinder walls on engine performance and emissions, utilizing response surface methodology to create engine maps. Numerical experiments revealed that a lowered natural gas replacement ratio of less than 50 % resulted in decreased flame propagation and the attainment of a burn mixture mode. The decrease in flame propagation speed during CA10 led to a fivefold increase in CO emissions. As the NG substitution ratio exceeded 50 %, the air/fuel ratio neared equilibrium, resulting in a reduction in NOx emissions and in-cylinder combustion temperature. Nevertheless, the highest RoHR level decreased by 25 %. The downward trend proceeded until the natural gas substitution ratio reached to 90 %. The TOPSIS method was utilized to identify optimal operating conditions for DFDI engines, offering valuable insights for efficiency and emissions reduction.

Experimental Study on Overpressure and Flame Characteristics of Hydrogen-methane mixture

In order to evaluate the consequences of hydrogen-methane mixture explosion accidents in open space and confined space, large-scale (8m3) open space and confined space (55m3) hydrogen-methane mixture explosion experiments were carried out to study the effects of hydrogen-doped ratio and equivalent ratio on hydrogen-methane mixture explosion characteristics. In the open space experiments, within the equivalence ratio range of 0.9 to 1.3, the overpressure measured at an equivalence ratio of 1.1 is the highest. When the equivalent ratio is 1.1, the higher the hydrogen blending ratio, the higher the overpressure peak and the farther the action distance. The overall overpressure increased significantly when the hydrogen blending ratio increased from 20% to 30%. When the hydrogen ratio is 30%, the flame propagation speed is as high as 20 m/s, which is about twice the flame propagation peak speed when the hydrogen ratio is 10%-20%. Therefore, from the angle of overpressure and flame development, the step point of overpressure harm can be obtained by a hydrogen mixing ratio of 20%. The overall trend of external overpressure change in confined and open spaces is consistent; both decrease with the increase in distance. However, the external overpressure in confined space is more significant than in open space, and the flame propagation speed is much higher than in open space. When the hydrogen mixing ratio is 5%, 10%, 15%, and 30%, the Outdoor flame propagation speed of 62.129/85.332/40.091/52.364 m/s, respectively. Compared with open space, the harm range of confined space is more extensive. This study provides an experimental basis for the safety assessment of hydrogen-methane mixture and the formulation of safety protection measures.

Numerical investigation and optimization of the ammonia/diesel dual fuel engine combustion under high ammonia substitution ratio

This study investigated the effects of initial temperature, equivalence ratio, and diesel injection timing on engine combustion and emission characteristics at high ammonia substitution ratios. Increased compression temperature and pressure significantly reduce ignition delay, enhance combustion speed and efficiency, and decrease N2O and unburned NH3 emissions. A strong correlation exists between the amount of N2O produced and the mass of unburned NH3 when ammonia combustion efficiency is high. The N2O distribution is concentrated near the cylinder walls and the bottom surface of the piston platform, in areas with high concentrations of unburned NH3. As the equivalence ratio increases from 0.6 to 0.75, flame propagation speed and indicated thermal efficiency (ITE) increase, while NOx, N2O, and unburned NH3 emissions decrease. The combustion performance and emissions were optimized by advancing the diesel injection timing and increasing the equivalence ratio to accelerate the combustion speed. This adjustment increases ITE to 47.6% at an 80% ammonia energy ratio. Post-optimization results show a reduction in unburned NH3 emissions from 51.7 g/kW·h to 5.9 g/kW·h and a decrease in N2O emissions from 0.930 g/kW·h to 0.370 g/kW·h, culminating in a 60.4% reduction in greenhouse gas (GHG) emissions.

Enhancement of calcium alginate and urea in gel-modified dry water inhibition of methane-air explosion

Methane has a wide range of applications in several industries. However, it also exhibits flammable and explosive properties, which pose a potential hazard. This study used calcium alginate to make ordinary dry water powder have a stable network gel structure, and urea was added to enhance further dry water powder’s chemical inhibition. A visual test system verified the explosion suppression effect of gel-modified dry water powder on the methane-air explosion. The results show that the optimal parameters for Ordinary dry water preparation were as follows: mass ratio of SiO2 to H2O = 9:100, stirring speed = 5000 r/min, stirring time = 240 s. The powder concentration for the best explosion suppression effect is 0.52 g/L. 10 mass% Urea-modified dry water, which achieves high explosion suppression efficiency in the methane-air explosion system by cooling and endothermic suppressing the explosion reaction. The spatial distribution of Calcium alginate gel urea modified dry water hinders the propagation of the flame. Urea continuously produces nitride at different temperatures, and nitride competes for O2 and OH· Free radicals, thus destroying the methane-air explosion chain reaction. Calcium alginate gel urea (10 mass%) modified dry water of 0.52 g/L has the best explosion suppression efficiency, which reduces the flame propagation velocity of methane-air explosion system by 42.48 %, the suppression efficiency of flame temperature reaches 40 %, and the suppression effect on explosion relief pressure reaches 16 %. Calcium alginate gel urea modified dry water, a new explosion suppression material, significantly improve the explosion suppression effect of methane-air explosions, which can not only improve the industrial safety of methane-containing processes, extend equipment life, and reduce production costs but also help improve environmental protection and resource utilization efficiency by inhibiting methane explosions. This study helps to promote the development of gas explosion suppression materials and has practical significance for safe energy utilization and industrial methane applications.

Chemistry of Ammonia/Hydrogen and Ammonia/n-Heptane Fuels: Reaction Mechanism Updating and Chemical Kinetic Analysis

For spark ignition and compression ignition ammonia engines, a typical approach to ensure stable operation involves the blending of ammonia with hydrogen and diesel, respectively. For the ammonia/hydrogen fuel, in this study a comprehensive comparison was conducted firstly for the differences among existing chemical mechanisms according to the experimental data of ignition, oxidation, and flame propagation. The result indicates that the current reaction mechanisms for ammonia/hydrogen fuel exhibit high prediction accuracy only within limited condition ranges. Subsequently, considering the completeness of combustion reaction pathways for ammonia/hydrogen fuel, a chemical mechanism of ammonia and ammonia/hydrogen fuel was developed and optimized in this study, and the comprehensive validation demonstrates the accuracy of the developed mechanism. On this basis, the ammonia mechanism was integrated with the detailed n-heptane mechanism to derive a mechanism for ammonia/diesel fuel that includes 1351 species and 6227 reactions. The good performance of this mechanism was demonstrated in terms of the experimental data of ignition and oxidation. In addition, the ignition sensitivity and reaction pathways of ammonia/hydrogen fuel were investigated based on the constructed mechanism, and the significance of C3–C7/N reactions was also analyzed for the ammonia/diesel fuel ignition process.

Combustion characteristics of Ammonia/Air mixture ignited by flame jet with and without hydrogen injection in Pre-Chamber

Ammonia is one of the important fuels that can promote the achievement of carbon neutrality, but its combustion characteristics are not conducive to its application in engines. Injecting hydrogen in the pre-chamber to form a flame jet to ignite the ammonia/air mixture is a method to improve the combustion of ammonia. This ignition method was investigated with the constant volume combustion chamber, high-speed video camera observation and the main-chamber pressure analysis. The flame behavior and combustion characteristics were compared with those ignited by the ammonia flame jet. Hydrogen flame jet significantly enhanced the combustion of the mixture and extended the lean flammability limit. Under conditions of hydrogen injection, the pressure rise delay and combustion duration became shorter, the average heat release rate became higher, and the combustion process was more stable. The hydrogen flame jet rapidly penetrated the main-chamber and impinged on the lower surface, generating intense turbulence. As a result, the combustion pressure took less time to rise from 10% to 50% than it did to go from 50% to 90%. This was different from the situation without hydrogen injection, where time required for both was similar. The hydrogen flame jet was shuttle-shaped when touching the lower surface owing to the rapid combustion speed of hydrogen, while the ammonia flame jet was spindle-shaped with the flame kernel in the center. The combustion process of the flame jet igniting the mixture exhibited two peaks in the heat release rate, reflecting two combustion stages dominated by the flame jet and flame propagation.

The influence of radiative heat transfer on flame propagation in dense iron-air aerosols

It is demonstrated that in the (near) zero-gravity experiments conducted by Tang et al. (Combust. Flame; 2009, 2011) iron powder aerosols created using the finest powders are optically thick, implying that radiative heat transfer between particles should not be neglected. To test this concept, an iron particle oxidation model has been implemented in OpenFOAM, including a coupling with the P1-model for radiative heat transfer.For flame simulations in which radiation is not included, obtained flame propagation velocities deviate less than 8% with results obtained using Chem1D-Fe and also show a good correspondance with algebraic models for optically thin aerosols. No significant difference in predicted flame propagation velocity is observed between 1D and 3D simulations: contrary to what is seen in gaseous flames, including the curvature of the flame does not increase predicted flame speeds substantially. However, measured flame propagation velocity values exceed numerically obtained predictions excluding thermal radiation by a factor of three to four. To the authors’ knowledge, this discrepancy is exemplary for the difference between experimentally obtained values for flame propagation velocities, and predictions made using numerical simulation tools neglecting radiative heat transfer.Accounting for radiation increases predicted flame propagation velocities, in the absence of confining boundaries, by approximately a factor of 10 which is in line with algebraic models for optically thick aerosols. In 3D simulations for the two finest iron powders in the experiments, including radiation and accounting for the presence of the confining tube wall results in an error of 11% and 35% with respect to measured flame propagation velocities, significantly smaller than predictions obtained excluding thermal radiation. Although these flames are not purely radiation-driven, inclusion of particle-to-particle radiative heat transfer enhances flame propagation velocities in simulations to values that correspond much better with experimental values than if radiation would not be taken into account.

A green synthesis strategy for liquid microcapsule flame-retardant polyurethane foam: Lowering consumer health risks from flame retardant inhalation and ensuring long-lasting fire safety

Dimethyl methylphosphonate (DMMP), is widely used in the production of commercial flexible polyurethane foam due to its excellent fire-retardant properties and the low addition levels required. However, in daily use, the volatility and migration of this liquid fire retardant reduce its fire safety performance and pose significant health risks. To address this issue, we employed interfacial polymerization facilitated by ultraviolet light-induced triallyl isocyanurate (TAIC) cross-linking at the water-oil interface to rapidly encapsulate DMMP. Incorporating TAIC@DMMP microcapsules into FPUF composites effectively suppressed DMMP emissions, maintaining low health and fire safety risks. These microcapsules act as sprinkler heads within each FPUF cell, rupturing during flame propagation. This release of phosphorus-containing radicals significantly enhances fire safety, reducing the peak heat release rate (PHRR) and total heat release (THR) by approximately 47% and 33%, respectively. The TAIC@DMMP microcapsule FPUF composite material exhibited excellent fire safety performance after 28 years of long-term aging simulated in an oven, passing the vertical burning test. In an environment simulating a 60 °C heat source, the TAIC@DMMP microcapsule FPUF composite material significantly reduced the release of DMMP, lowering the carcinogenic risk and non-carcinogenic risk by approximately 80 times and 100 times, respectively. This study presents a method for preparing FPUF composites that balance fire safety and environmental health, offering a valuable reference for further research on flame-retardant materials in environmental safety.

Experimental investigation on the regulation of methane addition for multi-stage combustion of lean ammonia/air mixtures using jet ignition

The effect of methane content on the flame structure, flow field and pressure characteristics of lean premixed ammonia/air gas combustion was systematically investigated in a constant volume chamber (CVC) under different methane content with a pre-combustion chamber (PCC). The results show that the auto-ignition locations of the CH4/NH3/Air dilute fuels begin at the top of the MCC and propagate from top to bottom, which is different from the auto-ignition at the bottom of the lean methane mixtures. Moreover, with the increase of ammonia content, the flame propagation time induced by jet ignition becomes longer, and the first derivative of the pressure changes from bimodal to unimodal, where the amplitude of the first peak gradually decreases and the second peak gradually dominates. Finally, chemical kinetic analysis combined with flame dynamics analysis showed that a reduction in fuel activity resulted in a shift in the heat release rate. Initially, the heat release rate was mainly dominated by the jet ignition. Subsequently, the auto-ignition became the dominant factor. This shift led to a shorter flame propagation time caused by auto-ignition, which increased the heat release rate in the auto-ignition stage.

Combustion characteristics of ammonia-hydrogen mixture with turbulent jet ignition

Ammonia and hydrogen are promising zero-carbon fuels that can help combustion engines achieve the zero-carbon emissions target. However, ammonia features high ignition energy demand and slow flame propagation speed. Pre-chamber turbulent jet ignition, with high ignition energy and enhanced in-cylinder turbulence, shows potential for achieving efficient and stable engine combustion with low-reactivity fuels. The optical constant volume combustion chamber simulates the process of pressure environment in the engine cylinder during the compression stroke to push the unburned gas into the pre-chamber, and simulates the process of jet ignition during the pressure environment in the main combustion chamber at the end of the compression stroke. The effects of different parameters such as ambient pressure, hydrogen fraction, and orifice diameter on the turbulent jet ignition combustion were investigated. The results indicate that jet ignition is a more effective means than spark ignition to accelerate the ammonia-hydrogen mixture combustion. A hot jet carrying heat and active radicals is injected into the main chamber due to the pressure difference, and then ignites the ammonia-hydrogen mixture. With increased hydrogen volume fraction, the ignition process is advanced due to the earlier formation and higher reactivity of the hot jet. Meanwhile, the enhanced fuel reactivity and turbulent disturbance accelerate turbulent flame propagation with increased hydrogen addition. The ignition delay time and jet flame axial development are accelerated with increase in equivalence ratio from 0.6 to 1.0. With increased orifice diameter, the pre-chamber jet flame is observed due to the weakened quenching effect, leading to shortened ignition delay and extended combustion duration.