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Enhanced methods of energy conversion present a viable solution for addressing energy load challenges. This study introduces a vibrating combustion engine designed to enhance energy conversion efficiency by harnessing flexible dynamics and variable asymmetric motion. However, the consideration of its unique dynamic effects has emerged as a pivotal challenge in fuel-air mixing and combustion research. This study introduces a fuel spray and mixing simulation method that facilitates the reciprocal exchange of coupling parameters between the combustion and dynamics models. It iterates the simulation outcomes of motion and combustion to predict mixture formation. Subsequently, the method is employed to explore the impact of injection position on fuel spray and mixture formation. Results show that there is an optimum injection position for the operation frequency, and retarding or advancing leads to slow compression and weak gas motion for fuel spray and mixing, although retarded injection provides high in-cylinder gas pressure and temperature. The early injection generally causes long penetration, small droplet diameter, slight impingement, and fast evaporation, unless it is too early. The results further indicate that when IAP = 6 mm, a more uniform mixture can be attained at the beginning of combustion, leading to a thermal efficiency of up to 42.9% for the engine. [ABSTRACT FROM AUTHOR]

To explore the combustion characteristics of ammonia‒hydrogen‒air flame, explosion venting experiments of ammonia‒hydrogen‒air mixtures with different equivalence ratios (ϕ), in the range of 0.6–1.7, are carried out in a 2 m long duct. The results show that the pressure‒time histories inside the duct have a three-peak structure (P b , P out , and P ext), which is caused by the burst of the vent cover, venting of burned mixtures, and counterflow flame generated by the external explosion, respectively. P out evolves into three pressure peak types with increasing ϕ. The pressure peak value P e is generated at the pressure measuring point outside the duct because of the external explosion. The change in P e with ϕ is consistent with P out and P ext , all of which increase first and then decrease with increasing ϕ and reach a maximum value at ϕ = 1.3. This study provides basic theoretical support for the promotion and application of ammonia mixed fuel. • The effects of the equivalence ratio, ϕ , on duct-vented ammonia‒hydrogen‒air deflagration were studied. • Counterflow flame generated by the external explosion was observed in all experiments. • The pressure‒time histories inside the duct under each operating condition present had a three-peak structure. • The maximum overpressure inside and outside duct first increased and thereafter decreased. [ABSTRACT FROM AUTHOR]

Ammonia's distinctive chemical makeup, coupled with its ability to combust fully without carbon emissions, position it as a promising carbon-free fuel but requires careful management to mitigate NO x emissions. In practice, supplementing ammonia with hydrogen addresses its slow combustion rate and high ignition energy requirements. Meanwhile, the introduction of a bluff body (BB) within the pipe can alter the way of flame propagation. This study examines the combustion dynamics of the premixed ammonia/hydrogen/air flame in a pipe with a variable cross-section. The experimental findings demonstrate that increasing both equivalence ratio (Φ) and hydrogen volume fraction (α H 2 ) significantly alters the flame front velocity (FFV) and maximum overpressure (P max), while also enhancing the symmetry of the flame across variable cross-section. The addition of BB creates a vortex in the flame, the formation of which intensifies the combustion of the flame behind the BB, which can promote the generation of Helmholtz oscillations, elevate the amplitude of the pressure, improve FFV, and shorten the flame propagation time in the pipe. With the increase of Φ and α H 2 , the time is shortened less. When Φ = 0.8, α H 2 = 40%, the flame propagation time was shortened by 709 ms. When Φ = 1.2, α H 2 = 60%, the flame propagation time was shortened by 5.67 ms only. In addition, P max and maximum flame front velocity (FFV max) are more sensitive to α H 2 than Φ. After the addition of BB, the increase amplitude of P max and FFV max is increased. However, when Φ = 1.0 and Φ = 1.2, the amplitude of FFV max increase decreases with the increase of α H 2 . This study can provide some suggestions for the application of NH 3 /H 2 fuels in variable cross-sections as well as under obstacles. • Ammonia-hydrogen premixed flames were studied. • The BB makes the propagation time is shortened by 709 ms at Φ = 0.8, α H 2 = 40%. • The BB promotes the generation of Helmholtz oscillations. • The addition of BB creates a vortex in the flame, the formation of which intensifies the combustion of the flame behind the BB. • The BB makes the propagation time is shortened by only 5.67 ms at Φ = 1.2, α H 2 = 60%. [ABSTRACT FROM AUTHOR]

The intensification of global warming is leading the exploration of low-carbon fuels, with ammonia emerging as a prominent hydrogen carrier and a research hotspot. This paper summarizes recent literature on turbulent combustion of ammonium-based fuels and analyzes the combustion dynamics, turbulent combustion characteristics and application in industrial facilities. It is found that in turbulent combustion, the simplified mechanism has a wider application. The enhancement of turbulent disturbances leads to intensified molecular diffusion and thermal diffusion in ammonia combustion, resulting in variations in flame surface and differences in heat release rate (HRR) distribution, and impacts on nitrogen oxide (NO x) emissions. Recent advances in the use of ammonia in industrial equipment demonstrate a promising prospect. In future applications, guided by the latest research findings, the combustion efficiency, stability and pollutants reduction of ammonia in industrial equipment can be further enhanced, thereby facilitating the low-carbon transition of industrial systems. • The characteristics and applications of ammonia mechanisms are compared thoroughly. • The effects on turbulent flame structure of ammonia-based fuels are described in details. • Effects of flame structure, molecular distribution and reaction path on NO x are discussed. • Application of ammonia combustion in industry is introduced. [ABSTRACT FROM AUTHOR]

Studying the synergistic effects of dilution gases and hydrogen on the laminar combustion characteristics and NO X -emission concentrations of methane/air can contribute to achieving efficient and clean natural-gas combustion. This study quantitatively analyzes the impact of N 2 and CO 2 as dilution gases on the laminar combustion characteristics and NO X emissions of methane/air under different equivalence ratios. The virtual gases FN 2 and FCO 2 are introduced to distinguish between the physical and chemical effects of the dilution gases. Subsequently, the effect of hydrogen addition on the laminar combustion characteristics and NO X emissions of a methane/5% dilution gas/air mixture is investigated. Finally, the synergistic effects of the dilution gases and hydrogen on the laminar flame speed and NO X -emission concentrations of methane/air under various blending conditions are discussed. The results indicate that CO 2 exhibits a more substantial reduction in laminar flame speed, flame temperature, key radical concentrations, and NO X -emission concentrations than N 2 , primarily because of its physical effects. N 2 has minimal chemical effects, but marginally increases NO X emissions. The addition of hydrogen increases the laminar flame speed and key radical concentrations of the methane/dilution gas/air mixture. however, significant differences in the NO X -concentration trends with increasing hydrogen-blending ratios are observed for the three equivalence ratios (Φ = 0.7,1.0,1.4). Selecting appropriate blending ratios of dilution gases and hydrogen can simultaneously enhance the laminar flame speed of methane/air while reducing the NO X -emission concentrations. This study provides valuable insights into the optimization of the blending ratio of hydrogen-enriched natural-gas engines coupled with exhaust-gas recirculation. • Effects of N 2 and CO 2 on combustion characteristics of CH 4 /air are compared. • Physical and chemical effects of N 2 and CO 2 are distinguishedd. • Coupling H 2 with dilution gases enables clean and efficient combustion of CH 4. • Optimal blending ratios of dilution gases and hydrogen are discussed. [ABSTRACT FROM AUTHOR]

A new design of plasma-assisted injector to ignite or stabilize combustion is presented. This design is intended to produce discharges that penetrate the combustion chamber instead of staying at the wall. This plasma-assisted injector, simple and robust, allows compact designs for a weakly intrusive implementation in engines, and is compatible with either air or fuel, depending on the process or application. A prototype was manufactured, implemented and tested with quasi-DC discharges on the LAPCAT2 Dual Mode Ramjet combustor at LAERTE facility in ONERA. Combustion tests showed earlier ignition and increased pressure when the plasma was turned on with a measured plasma power of 1.4 kW. • Presentation of the design and principle of a new plasma assisted injector. • Demonstration of its ability to generate discharges penetrating the flow. • Characterization of the discharge dynamics and its interaction with the gas flow. • Comparison of the discharge behavior in hydrogen vs air. • Ability of the plasma assistance to enhance supersonic combustion. [ABSTRACT FROM AUTHOR]

Hydrogen addition has been widely used to improve the combustion performance of low-reactivity fuels such as NH 3. In this study, a series of two-dimensional NH 3 /H 2 flames in mixing layers were investigated numerically. The aim is to assess and interpret the effects of H 2 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 NH 3 combustion features high heat release rate (HRR), while the two premixed branches are weak. The mixture fraction corresponding to the maximum HRR of NH 3 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 NH 3 , while the other is formed due to the reaction of H 2. 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 (S d ∗) is negatively correlated with the flame stretch (κ) and scalar dissipation rate (χ), with S d ∗ decreasing almost linearly with κ or χ , consistent with previous studies of methane and hydrogen flames. As the H 2 concentration is increased, the values of S d ∗ increase due to the enhanced reactivity. • Effect of H 2 addition on NH 3 flame structure and dynamics in a mixing layer is studied. • Tetrabrachial flame of NH 3 /H 2 combustion is identified for the first time. • Influence of preferential diffusion of H 2 on the structure of NH 3 flame is analyzed. [ABSTRACT FROM AUTHOR]

This study suggests a combustion strategy and introduces a new geometry for the combustor of a micro gas turbine fed by ammonia as fuel. Ammonia is essential for making the energy supply chain more eco-friendly because it is seen as an excellent way to transport green hydrogen and as a renewable, carbon-free fuel. This study has considered different cases with a wide range of overall and primary equivalence ratios to find the optimum geometry regarding lower NO X emission, lower unburned NH 3 , lower unburned H 2 , and temperature distribution. A comprehensive case study of CFD simulation was conducted considering earlier research that showed the NO reduction level in an NH 3 -air swirl burner is dependent on the equivalence ratio of the primary combustion zone. The CFD simulation's boundary conditions were set by running a one-dimensional cycle simulation of the micro gas turbine at various loads. Results indicate that by modifying the geometry to include a staged rich-lean strategy with a primary equivalence ratio of 1.07, the NO mole fraction in the combustor can be reduced to one-third of its original level despite the significantly higher Combustor Inlet Temperature (CIT) compared to previous studies. The study found that the unburnt NH 3 and H 2 levels are low enough in the modified design, which shows the fuel is completely consumed and the overall combustion efficiency is optimized. Also, the analysis of the fluid dynamic behavior of the combustor shows that streamlines are uniform, leading to improved heat transfer and better overall system performance. These findings highlight the staged rich-lean strategy's potential by tuning the combustion stages' equivalence ratio as a promising approach to mitigate NO X emissions in ammonia combustion systems while maintaining high energy efficiency. • Study of ammonia combustion in a 3 kWe MGT's combustor. • Proposing a novel design approach for the combustor. • Higher combustor inlet temperature investigation in smaller combustor. • Implementation of a staged rich-lean combustion strategy to reduce NOx emissions by one-third. • Investigation of various primary ERs and identification of the optimal value at 1.07. [ABSTRACT FROM AUTHOR]

The correction notice for the article "Seismic observation using distributed acoustic sensing around the Tsugaru Strait at the Japan and Kuril Trenches, northeastern Japan" addresses errors in the conversion of DAS original phases to strain rate amplitudes, resulting in corrected figures and equations. The correction does not impact the main results and discussions presented in the original article. The revised graphical abstract, figures, and tables now accurately reflect the corrected data. [Extracted from the article]

The advantage of combustion synthesis is the ability to produce composites from powders in a single technological step, using the heat of an exothermic reaction, in a fast and energy-efficient manner. Ceramic-metal composites TiC–High-Entropy Alloy (HEA) CoCrFeNiMn were fabricated by combustion synthesis from granular mixtures. The content of the metal binder components varied from 10 to 30 wt% and the combustion velocity and temperature gradually decreased as the binder content increased. Scaling up synthesis requires clarification of the parametric range for implementing a safe combustion mode. The impurity gas content and the range of safe conductive combustion were determined from known theoretical models and experimental combustion velocities of samples of granules of 0.6 and 1.1 mm size. The main phases of the product were titanium carbide with up to 3 at. % Cr and HEA CrCoFeNiMn with a reduced Mn content compared to the equimolar composition. The content of secondary phases Cr 7 C 3 and carbon did not exceed 5 wt%. The use of granular mixtures solved the problem of significant sintering of exothermic powder mixtures containing metal binder during combustion. After synthesis, the granules retain their size and do not sinter together, making it easy to grind the sample and obtain a TiC-HEA composite powder. [ABSTRACT FROM AUTHOR]

Aiming at the problem of low turbulent velocity and incomplete combustion in the combustion process of the Wankel rotary engine (WRE), and setting turbulence‐induced blade (TIB) in the combustion chamber recess is an effective means to enhance the turbulent motion and promote combustion. Carifying the optimal arrangement position of TIB can get better combustion performance. Therefore, a computational fluid dynamics (CFD) simulation model of a WRE with TIB was established in this paper. Based on the differential pressure perturbation mechanism, the influence of the arrangement position of the TIB on the flow field and combustion performance were analyzed. The results showed that when the ratio of blade arrangement distance is less than 0.66, the pressure difference between the leading and trailing of the blade is small. At this time, the in‐cylinder flow is mainly disturbed by the forced disturbance of the TIB, the increase of the turbulent velocity is not obvious, and the diffusion velocity of the flame to the rotor direction is small. When the ratio of blade arrangement distance is greater than 0.66, the pressure difference between the leading and trailing of the blade is large. At this time, the In‐cylinder flow is affected by the pressure difference flow in addition to the forced disturbance of the TIB. The turbulent velocity is effectively enhanced, and the flame velocity is fast to the rotor direction. When the ratio of blade arrangement distance is 0.66, it shows the best combustion performance, and the indicated work is the largest. Compared to the scheme without TIB, the indicated work is increased by 16%. [ABSTRACT FROM AUTHOR]

The ignition of spray flames is a process of stochastic nature, especially relevant to the high-altitude relight of aeroengines. The present work aims to quantify the role of spray inhomogeneities in a realistic droplet-laden ignition set-up through Direct Numerical Simulations (DNS). Computations of the ignition process of weakly turbulent ethanol spray flows are performed using complex chemistry, a realistic energy deposition model and a polydisperse description of the spray. A good qualitative agreement of the flame radius evolution is found between the DNS and experiments, and both long-time failure and ignition modes are recovered with comparable radii, hence reproducing the experimentally-observed range of behaviour of ignition kernels. In contrast to experiments where the presence of large droplets at the spark impact both the actual energy deposited in the flow and the local fuel-air equivalence ratio, the effect of both parameters on the ignition outcome are assessed independently in this work by carefully choosing ignition locations in the flow representative of time-wise fluctuations. The minimum ignition energy (MIE) representative of the global flow condition is then evaluated using results from the DNS simulations and flow and spark characteristics. In order to understand the origin of the ignition stochasticity observed experimentally, local values of the fuel-air equivalence ratio $ \Phi _t $ Φt and turbulence level $ u' $ u′ at the spark plug are measured in the simulations using an averaging in volumes of size $ \Delta _b $ Δb. It is found that $ \Phi _t $ Φt best correlates to the MIE at three different locations in the domain for a size around 4 mm, which corresponds approximately to the kernel size at 0.1 ms, that is, the typical time scale of plasma processes and right when the flame becomes toroidal. The results give support to the experimental conjecture that stochasticity is largely due to the spatial fluctuations of $ \Phi _t $ Φt induced by polydispersity and in a lesser extent to those of $ u' $ u′. [ABSTRACT FROM AUTHOR]

This paper focuses on a dual-fuel injector to characterize the ignition delay time (IDT), flame propagation, and flame spectral distribution of diesel and methane combustion. To gain an insight into the combustion characteristics of diesel pilot-ignited methane dual-fuel combustion with a high-pressure direct injection (HPDI) strategy under various conditions, the ignition and combustion processes are obtained by a high-speed color camera. The variables such as diesel injection pressure (DIP), diesel injection duration (DID), fuel relative injection interval time (RIT), ambient temperature (AT), and ambient pressure (AP) are varied according to engine-like conditions for a better understanding of the relation between the operating conditions and combustion characteristics. The results show that methane jets inhibited the IDT of diesel, while the conditions and ignition of diesel also determined the ignition of methane. Premixed flame always exists at the initial combustion, the development of the flame propagation indicates that the entrainment between diesel and methane plays a crucial role in the flame velocity and combustion intensity. According to sensitivity analysis, the IDT, Flame tip penetration (P), Flame tip velocity (V), and Flame area (FA) are most sensitive to the AT, and at least 4, 3, 2, and 7 times to the other variables each. However, the area ratio of chemiluminescence to soot incandescence (B/R) is most sensitive to AP, which is at least 14 times the other variables. • The effects of 5 variables on diesel ignition high-pressure methane combustion characteristics are studied. • A segmentation method for chemiluminescence and soot incandescence has been proposed. • The sensitivity of combustion characteristic parameters to variables is quantitatively analyzed. [ABSTRACT FROM AUTHOR]

In this study, we used the numerical simulation tool FLUENT to numerically simulate the combustion of ammonia-hydrogen fuel in the combustion chamber of a 9E heavy-duty gas turbine, and analysed the effects of different hydrogen blending ratios on the stability of ammonia combustion and NOx emissions. We found that an increase in the hydrogen mixing ratio in the fuel during the ammonia-hydrogen mixture combustion process contributes to the reduction of NOx emissions and has a positive effect on combustion stability. The key highlights of our research include. (see Fig. 3–6 and 10 and 11) • Ammonia-hydrogen combustion simulation of the 9E heavy duty gas turbine. • Increase in the proportion of hydrogen leads to an increase in the maximum temperature produced by combustion. • The high temperature zone moves closer to the fuel inlet as hydrogen increases. • The increase in hydrogen has little effect on the flow field in the combustion chamber. • Increased hydrogen ratio effectively reduces NOx emissions. [ABSTRACT FROM AUTHOR]

The vehicle sector has seen an upsurge in energy demand due to population expansion. Due to the escalating costs and exhaustion of fossil fuels, researchers are now dedicating more of their endeavors to exploring other options. The objective of this investigation, which is being conducted on a single-cylinder DI diesel engine propelled by hydrogen and diesel, is to optimize engine load. We evaluated the investigation on hydrogen/diesel composites against unadulterated diesel (D100). Different variations of fuels with varying percentages of hydrogen supplementation, viz., DH5 (diesel and 5% hydrogen), DH10 (diesel and 10% hydrogen), and DH15 (diesel and 15% hydrogen), were analyzed. In the experimental investigation, we used an injection pressure of more than 220 bar at 18:1 compression ratio for load optimization, and we used a single fuel injector with a diameter of 0.25 mm, The results showd improved brake thermal efficiency of 1.8% for DH5, 5.2% for DH10, and 17.6% for DH15, along with a drop in fuel consumption of 1.7% for DH5, 14.5% for DH10, and 31.6% for DH15. In addition, the addition of hydrogen to diesel demonstrates a promising reduction in smoke emissions of 10.5%, carbon monoxide (CO), and hydrocarbon (HC) emissions by DH15 under full load conditions. The results were subjected to regression analysis using an artificial intelligence network (ANN), to enhance the performance and reduce emissions of fuel mixtures. The ANN proves to be a very good method for the regression of data and prediction. The ANN provides an excellent fit for all the parameters, with a fitting value of more than 99%. [Display omitted] • Diesel-H2 mixes outperformed pure diesel fuel in terms of BTE. • Blends of diesel with H2 lowered BSFC and smoke emissions. • NOx emissions are increased by diesel-H2 mixes. • The engines performance and emission characteristics were predicted using ANN. [ABSTRACT FROM AUTHOR]

For hydrogen internal combustion engines (H 2 ICEs), the existing researches mainly focus on their thermodynamic aspects, while the engine acoustics are paid less attention. The objective of this research is to investigate the combustion noise characteristics of H 2 ICEs and find the biggest lever for combustion noise mitigation. Based on the data from previous thermodynamic measurements of various H 2 ICEs, the influences of different parameters for the combustion noise and knocking are studied with sensitivity analysis and machine learning based method. The results show that increasing Air–fuel equivalence ratio (λ), ignition delay and exhaust-gas recirculation rate (EGR) are acoustically beneficial, where λ is the most effective one with possible noise reduction up to 20 dB. Further, the comparison results between the H 2 ICEs and conventional engines indicates that the combustion noise of the H 2 ICE is kept at similar level as the respective gasoline variant if the H 2 ICE is operated withλ >2. [ABSTRACT FROM AUTHOR]

Hydrogen is a promising zero-carbon fuel, and its application in the micro-combustor can promote carbon reduction. The structural design of micro-combustors is crucial for combustion characteristics and thermal performance improvement. This study investigates the premixed combustion characteristics of hydrogen/air in a micro-cylindrical combustor with double ribs, using an orthogonal design method to assess the impact of various geometric parameters on thermal performance. The results indicate that the impact of rib height, rib position, and inclined angle is greater than rib width and their interactions, while their influence decreases in that order. Increased rib height improves mean wall temperature and exergy efficiency due to an expanded recirculation region and increased flame–wall contact, but negatively affects temperature uniformity and combustion efficiency. Although double ribs enhance performance, placing them too close may reduce heat transfer due to the low-temperature region between the ribs. When the double ribs are positioned at the axial third equinoxes of the micro-combustor, the highest mean wall temperature is achieved. Meanwhile, with a rib height of 0.3 and an inclined angle of 45°, the micro-combustor achieves optimal thermal performance, with the mean wall temperature increasing by 61.32 K. [ABSTRACT FROM AUTHOR]

Blending gasoline with hydrogenated catalytic biodiesel has the potential to improve combustion problems of gasoline direct-injection compression combustion, and the spray characteristics of the blending fuel can directly affect the combustion effect. In order to understand the spray characteristics of a gasoline–hydrocatalyzed catalytic biodiesel mixture, a numerical spray model of constant volume combustion chamber was established, and the accuracy of the model was verified by experimental data in the literature. Based on this model, the spray penetration, sauter mean diameter, spray velocity field and concentration field of gasoline–hydrocatalyzed catalytic biodiesel at different blending ratios were studied. The results show that under the conditions of 850 K ambient temperature, 5 MPa ambient pressure, and 80 MPa injection pressure, as the proportion of hydrogenated catalytic biodiesel in the blending fuel increases, the spray penetration increases, the sauter mean diameter decreases slightly, and the area of high velocity and high concentration at the spray center increases. The results of this study will contribute to the development of blended fuels for superior combustion performance and reduced pollutant emissions at appropriate blending ratios. [ABSTRACT FROM AUTHOR]

This study explores the combined effects of fuel composition and injection angle on the combustion behavior of an NH 3 / H 2 / N 2 jet in an air crossflow by means of high-fidelity Large Eddy Simulations (LESs). Four distinct fuel mixtures derived from ammonia partial decomposition, with hydrogen concentrations ranging from 15% to 60% by volume, are injected at angles of 90 ° and 75 ° relative to the crossflow, and at operating conditions frequently encountered in micro-gas turbines. The influence of strain on peak flame temperature and NO formation in non-premixed, counter-flow laminar flames is first examined. Then, the instantaneous flow features of each configuration are analyzed focusing on key turbulent structures, and time-averaged spatial distributions of temperature and NO in the reacting region are provided. In addition, statistical analysis on the formation pathways of NO and H 2 is performed, revealing unexpected trends: in particular, the lowest hydrogen content flame yields higher temperatures and NO production due to the enhancement of the ammonia-to-hydrogen conversion chemical mechanism, thus promoting flame stability. As the hydrogen concentration increases, this conversion decreases, leading to lower NO emissions and unburned fuel, particularly at the 75 ° injection angle. Flames with a 90 ° injection angle exhibit a more pronounced high-temperature recirculation zone, further driving NO production compared with the 75 ° cases. These findings provide valuable insights into optimizing ammonia–hydrogen fuel blends for high-efficiency, low-emission combustion in gas turbines and other applications, highlighting the need for a careful balance between fuel composition and injection angle. [ABSTRACT FROM AUTHOR]

High-temperature furnaces and coal-fired boilers are widely employed in the petrochemical and metal-smelting sectors. Over time, the deterioration, corrosion, and wear of pipelines can lead to equipment malfunctions and safety incidents. Nevertheless, effective real-time monitoring of equipment conditions remains insufficient, primarily due to the interference caused by flames generated from fuel combustion. To address this issue, in this study, a through-flame infrared imager is developed based on the mid-wave infrared (MWIR) radiation characteristics of the flame. The imager incorporates a narrowband filter that operates within the wavelength range of 3.80 μm to 4.05 μm, which is integrated into conventional thermal imagers to perform flame filtering. This configuration enables the radiation from the background to pass through the flame and reach the detector, thereby allowing the infrared imager to visualize objects obscured by the flame and measure their temperatures directly. Our experimental findings indicate that the imager is capable of through-flame imaging; specifically, when the temperature of the target exceeds 50 °C, the imager can effectively penetrate the outer flame of an alcohol lamp and distinctly capture the target's outline. Importantly, as the temperature of the target increases, the clarity of the target's contour in the images improves. The MWIR through-flame imager presents considerable potential for the real-time monitoring and preventive maintenance of high-temperature furnaces and similar equipment, such as detecting the degradation of refractory materials and damage to pipelines. [ABSTRACT FROM AUTHOR]

Oxy-steam combustion is a new oxy-fuel combustion technology. This paper focuses on the NO emission characteristics during the combustion of SF (Shen Fu) coal in O2/N2 and O2/H2O mixtures. Experiments were performed in a drop-tube furnace. Combustion tests were carried out in O2/N2 and O2/H2O atmospheres for various O2 concentrations (21%, 30%, 40%, and 60%) at different temperatures (1173 K, 1273 K, and 1373 K). In addition, combustion experiments at different excess oxygen ratios (λ) were conducted in O2/N2 and O2/H2O atmospheres. The influences of the atmosphere, oxygen concentration, temperature, and excess oxygen ratio on NO emissions were analyzed. The results show that the NO concentrations of SF coal combustion in the 21% O2/79% H2O atmosphere were much lower than those in the 21% O2/79% N2 atmosphere at the three temperatures considered. This was because a large amount of NO was decomposed during the SF coal combustion in the O2/H2O atmospheres. The reasons for the decomposition of NO include the selective non-catalytic reaction (SNCR) mechanism and char's important role as a catalyst for the destruction of NO, either directly or by reacting with CO or H2. In oxy-steam combustion, the NO concentrations significantly increased with the increase in the oxygen concentration from 21 vol.% to 60 vol.% and the temperature from 1173 K to 1373 K. The excess oxygen ratio (λ) slightly impacted the NO emissions in the O2/H2O atmosphere. [ABSTRACT FROM AUTHOR]

In this study, free‐standing composites consisting of 90 wt% nanoenergetic mesoparticles are fabricated and their combustion characteristics are investigated. The findings reveal that the integrity of the mesoparticles remains intact during the printing process and a reduction in sintering is observed for the composite of mesoparticles compared to the physical mixture. However, the composite of mesoparticles exhibits noncontinuous and oscillating propagation behavior at a steady frequency of ≈5 Hz. This is attributed to insufficient heat feedback from the flame to the unburnt material. To address this issue, carbon fiber (C.F.) is introduced into the composite to enhance heat feedback to the reaction front by intercepting hot agglomerates near the burning surface. Incorporating C.F. leads to steady propagation of the composite. Agglomerate residence time and characteristic heat transfer time analysis near the burning surface indicate that while the composite without C.F. has agglomerate residence time on the same order of magnitude as the characteristic heat transfer time, the composite with C.F. has significantly increased overall agglomerate residence time compared to the characteristic heat transfer time. This confirms the enhanced heat feedback through C.F. inclusion. This study demonstrates the crucial role of heat feedback in the combustion behavior of energetic composites. [ABSTRACT FROM AUTHOR]

While there are numerous results on minimizers or stable solutions of the Bernoulli problem proving regularity of the free boundary and analyzing singularities, much less is known about critical points of the corresponding energy. Saddle points of the energy (or of closely related energies) and solutions of the corresponding time‐dependent problem occur naturally in applied problems such as water waves and combustion theory. For such critical points u$u$—which can be obtained as limits of classical solutions or limits of a singular perturbation problem—it has been open since (Weiss, 2003) whether the singular set can be large and what equation the measure Δu$\Delta u$ satisfies, except for the case of two dimensions. In the present result we use recent techniques such as a frequency formula for the Bernoulli problem as well as the celebrated Naber–Valtorta procedure to answer this more than 20 year old question in an affirmative way: For a closed class we call variational solutions of the Bernoulli problem, we show that the topological free boundary ∂{u>0}$\partial \lbrace u > 0\rbrace$ (including degenerate singular points x$x$, at which u(x+r·)/r→0$u(x + r \cdot)/r \rightarrow 0$ as r→0$r\rightarrow 0$) is countably Hn−1${\mathcal {H}}^{n-1}$‐rectifiable and has locally finite Hn−1${\mathcal {H}}^{n-1}$‐measure, and we identify the measure Δu$\Delta u$ completely. This gives a more precise characterization of the free boundary of u$u$ in arbitrary dimension than was previously available even in dimension two. We also show that limits of (not necessarily minimizing) classical solutions as well as limits of critical points of a singularly perturbed energy are variational solutions, so that the result above applies directly to all of them. [ABSTRACT FROM AUTHOR]

Core–shell fuel@oxidizer nanocomposite can combust in oxygen‐starved environment. A ferrimagnetic reactive particle, being successfully engineered, allows for manipulation using an external magnetic field and facilitates target heat or gas production. This research reports on interesting flame dynamics of newly synthesized core–shell Al@Fe3O4 nanoparticles under the influence of a magnetic field. Serving as an oxidizer and a functional ferrimagnetic component, iron oxide nanoparticles (IONPs) are grown in situ on nano‐sized Al (n‐Al) particles. Electron microscopic images demonstrate nearly monodispersed IONPs ≈7 nm decorating the surface of n‐Al. X‐ray diffractogram and X‐ray photoelectron spectroscopy confirm the formation of Fe3O4. Thermal analysis suggests the as‐prepared core–shell particles predominantly go through a solid‐state reaction mechanism that exhibits 30% lower activation energy compared to physically‐mixed nanocomposite (215.0 vs 310.8 kJ mol−1). The core/shell particles can be ignited and combust under laser irradiation with or without the effect of a magnetic field. When suspended in the middle of the tube by the magnetic field, an interesting combustion process is observed, highlighting a grow‐shrink‐grow flame resulted from the interactions between the combustion products and the external magnetic field, as well as backfiring at the bottom of the sample without major changes in burning rate and ignition delay. [ABSTRACT FROM AUTHOR]

Both NH3 and H2 are considered to be carbon-free fuels, and their mixed combustion has excellent performance. Considering the laminar burning velocity as a key characteristic of fuels, accurately predicting the laminar burning velocity of NH3/H2/Air is crucial for its combustion applications. The study made improvements to the XGBoost model and developed NH3/H2/Air Laminar Burning Velocity Net (NHLBVNet), which adopts a composite hierarchical structure to connect the functions of feature extraction, feature combination, and model prediction. The dataset consists of 487 sets of experimental data after the exclusion of outliers. The correlation coefficient ( R 2 > 0.99) of NHLBVNet is higher than that of the XGBoost model ( R 2 > 0.93). Robustness experiment results indicate that this model can obtain more accurate prediction results than other models even under small sample datasets. [ABSTRACT FROM AUTHOR]

Blowoff limits are essential in establishing the combustor operating envelope. Hence, there is a great demand for practical aero-engines to extend the blowoff limits further. In this work, the behavior of non-premixed swirling flames under fuel flow rate oscillations was investigated experimentally close to its blowoff limits. The methane flame was stabilized on the axisymmetric bluff body and confined in a square quartz enclosure. External acoustic forcing at 400 Hz was applied to the fuel flow to induce a fuel mass flow rate fluctuation (FMFRF) with varying amplitudes. A high-speed burst-mode laser and cameras ran at 20 kHz for OH*-chemiluminescence (CL), CH2O-, and SO2-PLIF measurements, offering the visualization of the two-dimensional flame structure and heat release distribution, temporally and spatially. The results show that the effect of FMFRF is predominantly along the central axis without altering the time-averaged flame structure and blowoff transient. However, the blowoff limits are extended due to the enhanced temperature and longer residence time induced by FMFRF. This work allows us to explore the mechanism of flame instability further. [ABSTRACT FROM AUTHOR]

The usage of biomass can reduce vast amounts of fossil resource dependence. Rice husk is attractive due to its calorific value and high silica content in ash. In order to produce amorphous silica in ash, rice husk was combusted with temperatures below 700°C and this can be realized in a suitable furnace type, i.e. suspension furnace. This study began with rice husk ignition test in a fixed bed furnace. The ignition temperature was observed above (428 ± 8)oC. Combustion was then performed in a suspension furnace. Rice husk was semi-continuously fed when it attained the ignition temperature with total air to biomass ratio of 8.5. The mass flowrates of rice husk were set at 9.27, 20.23, 25.20, 31.36, and 42.51 kg/h. The feeding was stopped until it reached 2500 g for the first 4 variations and 500 g for the last variation. From this study, the flaming combustion lasted for 15–30 min and then continued with glowing combustion which plays an important role in the successful conversion to ash. The highest temperatures of combustion were 552–560°C. Besides, the yield of produced ash was 18.94–23.68%-wt with silica content therein of 88.29–89.15%-wt. Ash was acquired in the amorphous silica phase with unburnt carbon content of 5.11–23.27%-wt. [ABSTRACT FROM AUTHOR]

This research work emphasizes on the development aspects of a cartridge cable cutter for helicopter application. This cartridge is used to rescue hoist system during emergency for helicopter application under adverse conditions. It is an electrically initiated cartridge in which two electrical squibs are used with specified current and voltage. As the cartridge is initiated, the squib gets incandescent and initiates an explosive train. A cartridge cable cutter is a propellant actuated device (PAD) that generates hot combustion gases having high temperature and pressure on burning of gun powder and propellant inside the cartridge case. The cable cutter cartridge under study is filled with energetic materials (EM) such as propellants and gun powder. It releases the energy very quickly which acts on the projectile i.e. the cutter in actual system. A projectile velocity measurement was carried out using Doppler RADAR (radio detection and ranging). To assess the projectile velocity is the unique design feature in armament field. It is responsible for the measurement of the projectile velocity at the muzzle end of velocity test rig (VTR). The minimum and maximum projectile velocities were experimentally measured in between 70 ms−1 and 150 ms−1. The projectile velocity measurement is an evaluation methodology as performance parameter of this cartridge. The cartridge under study has been developed meeting structural, functional and mechanical requirements. The cartridge has undergone various exhaustive qualification tests during development phase. The cartridge was thus designed, qualified and validated through rigorous development trials. The main objective of this article is to address development aspects of the cartridge cable cutter for helicopter application. In conclusion, after successful design, development and qualification trials, the cartridge was found to meet all the functional and operational requirements considering the end use. [ABSTRACT FROM AUTHOR]

The present work proposes the application of CH 4 and H 2 synergy to improve the performance of the Wankel rotary engine (WRE). The whole work was experimentally conducted at 1500 r/min. The results indicate that CH 4 WRE can achieve similar power and significantly higher thermal efficiency than gasoline WRE based on quantitative control, with a maximum absolute efficiency improvement of 11.4%. At the same time, it also can achieve 64% and 77% maximum reduction of CO and NO emissions, respectively. CH 4 –H 2 synergy can further improve the performance of CH 4 -fueled WRE, which can broaden the lean flammability limits and make qualitative control application possible. Compared with CH 4 WRE with quantitative control, qualitative control hybrid fuel WRE can achieve a maximum relative improvement of 6.54% in brake thermal efficiency and significantly reduced NO and CO emissions. However, the extent of qualitative control is limited by cyclic variation. Overall, CH 4 –H 2 synergy can be a potential alternative to elevate the performance of WRE, the key to which is the reasonable match of synergy level and qualitative control extent. • Comparison of performances between CH4 and gasoline Wankel rotary engines. • CH4 has significant advantages in efficiency, CO and NO emission than gasoline. • CH4–H2 synergy can further improve the performance of the CH4 Wankel rotary engine. • Blending H2 coupling qualitative control is a good load control model in CH4 WRE. [ABSTRACT FROM AUTHOR]

The issue of spontaneous ignition has become a bottleneck for hydrogen applications. This comprehensive review delves into the intricate mechanisms governing the spontaneous ignition of pressurized hydrogen released through tubes. Beginning with an exploration of fundamental concepts, including the properties of hydrogen and various theoretical frameworks, the study meticulously examines the development of diffusion ignition theory. Methodologically, both experimental and simulation approaches are scrutinized for their contributions to understanding this complex phenomenon. Moving deeper into the core of the investigation, the review dissects the spontaneous ignition mechanisms occurring inside pipes, unraveling the influence of different initial conditions as well as the impact of varying pipe structures. Subsequently, the review shifts its focus to the flame morphology at the pipe exit, analyzing combustion behavior, shock wave dynamics, flow structures, and the formation of jet flames, while exploring influential factors affecting combustion. Through a comprehensive synthesis of findings, this review provides valuable insights into the spontaneous ignition dynamics of pressurized hydrogen within tube systems, offering a foundation for future research and engineering applications in safety and energy sectors. • Introduced theories of self-ignition and development of diffusion ignition theory. • Summarized ignition mechanisms of pressurized hydrogen released inside pipes. • Summarized flame morphology at pipe exit based on vortex position. • Identified deficiencies in reviewed studies and areas needing further research. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive theoretical analysis of the interaction between two quasi-steady burning droplets with differing temperatures, sizes and distances, building upon the mass-flux-potential model and flame-sheet assumption. In contrast to existing research, this study introduces a fresh perspective on droplet interactions by considering the different temperatures of the droplets. Utilizing the bispherical coordinate approach, theoretical solutions for the Stefan flow, scalar fields, droplet evaporation/burning rates, interaction coefficients and flame positions have been derived successfully. A comparison with extensive numerical simulations indicates a good agreement between the analytical and numerical results under a variety of conditions. It is revealed that proximity between the droplets causes non-uniform evaporation rates on their surfaces, and in some cases, leads to condensation on the cooler droplet. Notably, when the temperatures of the two droplets differ, this results in an uneven temperature distribution across the flame surface, and increasing the temperature of one droplet substantially elevates the temperature of the nearby flame. This study also establishes a criterion for the transition between different combustion modes, specifically between group and separated combustion. The findings of this study are crucial in deepening our understanding of evaporation and combustion processes, as well as the dynamics of flame spreading, local ignition, and extinction in systems involving multiple droplets. [ABSTRACT FROM AUTHOR]

Assessments of air quality in industrial cities are receiving much attention, especially in regions sensitive to the ecological and climate changes. The atmospheric aerosol loading was studied in the city of Novy Urengoy during the summer–autumn of 2023. Particle number concentration and the mass concentration of particles with a size less than 10 µm (PM10) and 2.5 µm (PM2.5), as well as black carbon (BC), were measured by the mobile Aerosol Complex. The portion of fossil fuel combustion (FF%) and biomass burning (BB%) was estimated using the aethalometer model. BC concentrations increased during pollution episodes recorded at the end of June (I) and July (II) and, in the beginning of August (III) and September (IV), doubled on average in comparison with the level of urban emissions. During episode IV of maximum pollution, the ВС concentration and its impact on PM2.5 increased 4 and 5 times, respectively. At that time, the portion of fossil fuel combustion FF% approached 96%. Cluster analyses of ВС dependence on the wind speed and direction revealed the sector of high concentration source. FF% indicated the direction of the emissions from the biggest industrial enterprise of the Urengoy oil and gas condensate field. Wildfire plume was identified by ВВ% from the south of Siberia. [ABSTRACT FROM AUTHOR]

Alloys of Ni–25Cr–(2Mn–1Si) under mixed deposits of ash + (0, 10, 50 and 90) wt% sulphate were exposed to an Ar–60CO2–20H2O gas at 650 and 750 °C for up to 300 h, forming both protective chromia and regions of Ni-rich oxide. The presence of ash + sulphate mixtures improved Ni–25Cr alloy protection, increasing surface coverage by thin, protective chromia compared with the deposit-free condition. Increasing sulphate proportions in these mixtures led to an accelerated chromia scale growth and reduced internal oxidation zone (IOZ). These beneficial effects were more significant at 750 °C, where surface coverage by the protective scale was increased, and a chromia band was formed beneath nonprotective regions at the IOZ-substrate interface. Alloy additions of Mn and Si generally slowed the growth of outer NiO and IOZ but did not lead to exclusive chromia scale formation. [ABSTRACT FROM AUTHOR]

The use of wheat straw as a renewable energy source is essential from both energy production and environmental points of view. It has a great energy potential that can be generated either by combustion or anaerobic digestion. However, there are some limitations during its conversion to energy in both techniques. Therefore, the current study investigated the effect of physical and chemical treatments on the characteristics of wheat straw as fuel for energy applications. Water washing of wheat straw and mixing with KOH solution were applied for physical and chemical treatments. Physical, chemical, and thermal characteristics of wheat straw were investigated before and after the treatments. It was found that the wheat straw has high carbon (44.8%) and volatile contents (87.1%), making it an excellent source for energy production. The physical treatment showed a positive impact on reducing the ash content (by 14.9%) and undesirable compounds, such as K and Cl, which were reduced by 46.4% and 57.0%, respectively. Moreover, it reduced sintering formation through combustion. In contrast, the chemical treatment resulted in 9.3% lignin removal and destroyed the complex lignocellulosic structure, thereby increasing the cellulose accessibility and enhancing the anaerobic digestion process. Therefore, the applied treatments showed attractive options to solve problems related to straw energy generation. [ABSTRACT FROM AUTHOR]

The challenge of paper sludge disposal has become an important environmental issue; therefore, the combustion characteristics of paper sludge need to be examined. In this paper, the combustion of paper sludge particles under different atmospheres was analysed and investigated using a flat flame burner and optical observation techniques under fast temperature rise conditions. The combustion of paper sludge could be divided into a preheating stage, volatile combustion stage, and coke combustion stage. The changes in oxygen content had different effects on the different stages of combustion. The increase in oxygen content had no significant impact on the ignition time of the sludge particles; however, the flame brightness significantly increased. The CH* free radical appeared in the most intense stage of combustion and was depleted before the volatile flame disappeared. A higher oxygen content correlated to a faster CH* depletion. The influence of the oxygen content on the combustion rate and burnout degree of the sludge particles was investigated by comparing mass loss data and heating data. The maximum temperature and heating rate also increased with increasing oxygen content. The reduced oxygen concentration could not fully penetrate the ash layer on the surface of the particles and react with the interior sludge, resulting in a lesser degree of sludge particle burnout. [ABSTRACT FROM AUTHOR]

A meticulous definition of the residence time (also referred to as the fluid age) in the context of auto-ignition in a thermally stratified gas has demonstrated that the age can be considered as a level-set function, which allows the tracking of a self-ignition front propagating. In order to avoid the difficulty of defining the boundary and initial conditions for this age, which can be seen as fluid birth, a normalized age is introduced. Meticulous derivation of the equation revealed additional terms related to the scalar dissipation rates and the gradient in the composition space of the auto-ignition delay. To validate this model equation, two canonical configurations were proposed: one representing a hot spot self-igniting with significant thermal diffusion and the other where a self-ignition front propagates at an almost constant speed. The analysis, based on the normalized age of the particles, reveals the impact of thermal diffusion on the acceleration or deceleration of particle aging. In certain instances, a particle rejuvenation mechanism through thermal diffusion has been identified. Furthermore, this work demonstrates the capacity of the normalized residence time field to map transitions between auto-ignition and laminar flame. Finally, the different cases studied were classified in an auto-ignition/diffusion diagram based on three non-dimensional characteristic numbers, which highlighted five combustion regimes. [ABSTRACT FROM AUTHOR]

The supersonic inflow passes through the shock train in the isolator of the scramjet to complete deceleration and pressurization, followed by combustion and energy release, providing strong thrust. When the back pressure generated by combustion is disturbed forward, the location of shock train leading edge (STLE) will also change accordingly. Once it moves to the entrance of the isolator, it will cause unstart. Accurately detecting STLE in the isolator of a scramjet is crucial for controlling the shock train and preventing the inlet from unstart. Therefore, based on the sparse reconstruction of compressive sensing and sensor compression coupling, a supersonic flowfield reconstruction model (POD-STLE) based on proper orthogonal decomposition (POD) was constructed to reconstruct the supersonic flowfield and detect the location of STLE in the supersonic isolator. The experiments were conducted on the shock oscillation under variable Mach numbers and back pressures, to construct the experimental dataset. Combining supersonic flowfield reconstruction and matrix decomposition, different sensor layouts were constructed, which can ensure accuracy and stability while saving sensor resources. The POD-STLE was applied to the flowfield reconstruction of the supersonic isolator, and the location of STLE was detected under variable and constant conditions, ultimately achieving the expected reconstruction effect and detection accuracy. This study provides a new research method for detecting the location of STLE in the supersonic isolator of a scramjet and provides technical for exploring supersonic flowfield. [ABSTRACT FROM AUTHOR]

This paper describes two-dimensional numerical simulations of pulsed injection to a hydrogen-fueled air-breathing ramjet using the Reynolds-averaged Navier–Stokes method. We analyze the effects of sinusoidal pulsed injection on the start-up ignition time, start-up ignition range, combustion efficiency, and flow field evolution of the ramjet and compare the performance with that of steady injection. The results show that pulsed injection shortens the ignition time and optimizes the ignition equivalence ratio of hydrogen. Pulsed injection also improves the combustion efficiency of hydrogen, increasing the thrust of the engine by 7.79% compared with steady injection under the same equivalence ratio. We find that pulsed injection can cause oscillations in the ramjet combustion flow field, and show that the oscillation frequency is affected by the pulsed injection frequency. [ABSTRACT FROM AUTHOR]

This work aimed to investigate combustion mode conversions by rapid variation of the fuel flow rate in a cavity-based scramjet combustor. The experiments were carried out on a direct-connected facility with an inflow condition of Mach number 2.52, a total pressure of 1.35 MPa, and a total temperature of 1650 K. The fuel injector consisted of two injection ports: fuel was continuously injected from one port while the other controlled the fuel flow for mode conversions by switching it on or off. Simultaneous schlieren and CH* imaging techniques were used to characterize the dynamics of combustion mode conversions. It was recognized that the combustion modes characterized by different flow field structures and heat release distributions can be classified into three types: the shear-layer mode, the transition mode, and the jet-wake mode. During the combustion mode conversion, the mixing region of the transverse jet and air became thicker with the increase in fuel flow rate, and the gradient of the flow field density and the flame area increased, making the flame more likely to propagate upstream. The combustion suppression induced by rapid fuel addition was observed at low equivalence ratios. It was speculated that the weak heat supply was insufficient to provide adequate heat for the rapid ignition of the added fuel. Furthermore, it was found that the flame-flow matching process with frequent flame propagation upstream occurred during the combustion mode conversion. This process was attributed to the mismatch between the increasing heat release and the original flow field structure. [ABSTRACT FROM AUTHOR]

In recent years, physics-informed neural networks (PINNs) have shown potential as a method for solving combustion physics. However, current efforts using PINNs for the direct predictions of multi-dimensional flames only use global reaction mechanisms. Considering detailed chemistry is crucial for understanding detailed combustion physics, and how to accurately and efficiently consider detailed mechanisms under the framework of PINNs has not been explored yet and is still an open question. To this end, this paper proposes a PINN/flamelet/progress variable (FPV) approach to accurately and efficiently solve combustion physics, considering detailed chemistry. Specifically, the combustion thermophysical properties are tabulated using several control variables, with the FPV model considering detailed chemistry. Then, PINNs are used to solve the governing equations of continuity, momentum, and control variables with the thermophysical properties extracted from the FPV library. The performance of the proposed PINN/FPV approach is assessed for diffusion flames in a two-dimensional laminar mixing layer by comparing it with the computational fluid dynamics (CFD) results. It has been found that the PINN/FPV model can accurately reproduce the flow and combustion fields, regardless of the presence or absence of observation points. The quantitative statistics demonstrated that the mean relative error was less than 10%, and R 2 values were all higher than 0.94. The applicability and stability of this model were further verified on other unseen cases with variable parameters. This study provides an efficient and accurate method to consider detailed reaction mechanisms in solving combustion physics using PINNs. [ABSTRACT FROM AUTHOR]

Existing research on reflux self-excited oscillating nozzles (RSONs) has primarily focused on flow drag reduction and combustion mixing, with relatively little investigation of their impact on cavitation. This study employs the large-eddy simulation framework to conduct numerical simulations of the three-dimensional cavitating jet generated by an RSON. We analyze the impact of vortex dissipation and the nozzle throat structure on the cavitation phenomena and the evolution of vortex structures. Further analysis examines the impact pressure, pulse frequency, cavitation phenomena, and distribution patterns of vortex structures in the flow field for RSONs and an organ pipe nozzle under inlet pressures of 7, 14, and 21 MPa. The results show that the dissipation of spanwise vortices is jointly determined by the shape of the nozzle outlet and the intensity of vortex structures, with nozzles featuring a reflux structure producing faster dissipation. The main frequency of jet pulsation initially increases and then decreases with the development of the jet. The impact pressure of the jet is closely related to the intensity of the cavitation cloud and the location of its collapse. The RSON with a throat structure produces the maximum impact pressure near the nozzle outlet. This study deepens our understanding of the RSON flow field characteristics and provides a scientific basis for RSON applications in a broad range of fields. [ABSTRACT FROM AUTHOR]

The increasing energy shortage and environmental pollution make the use of clean and efficient alternative fuels an effective way to solve the emission problem. Diesel from indirect coal liquefied (DICL) is a clean and efficient alternative fuel for diesel engines. The composition and chemical kinetics mechanism of DICL research contributes to a better understanding of combustion and pollutant formation process. The components of DICL were analysed by gas chromatography-mass spectrometry (GC-MS). The proportion of normal alkanes contained in DICL is particularly high, 93.82%, which proves that its reactivity is particularly good. The mixture of n-dodecane and iso-octane was selected as the surrogates of DICL. The oxidation process of DICL surrogates was examined by a jet-stirred reactor (JSR) over the temperature range of 500–890 K. A detailed kinetic mechanism of surrogates encompassing 1356 species and 6008 reactions was constructed. The critical reactions associated with the reactivity of surrogates were adjusted by the sensitivity analysis method to increase the accuracy of mechanism prediction. The predicted value of the improved mechanism is in good agreement with the experimental value. The improved mechanism can reasonably predict the oxidation process and the ignition characteristics of DICL and the improved mechanism can provide a good reference value for the subsequent analysis of combustion and emission problems of DICL. Abbreviations: C/H, C/H ratio; CN, cetane number; DDCL, direct coal liquefy diesel; DICL, Diesel from indirect coal liquefied; GC-MS, gas chromatography-mass spectrometry; HMN, 2,2,4,4,6,8,8-heptamethylnonane; HXN, n-hexadecane; IDT, ignition delay time; JSR, jet-stirred reactor; LHV, low heating value; LLNL, Lawrence Livermore National Laboratory; NSRL, National Synchrotron Radiation Laboratory; NTC, negative temperature coefficient; PICS, photoionization cross section; PRF, gasoline substitute; PSR, perfectly stirred reactor; SVUV-PIMS, Synchrotron VUV photoionization mass spectrometry; TOF-MS, time-of-flight mass spectrometer [ABSTRACT FROM AUTHOR]

Large eddy simulations (LES) with flamelet and presumed filtered density function closure are used to simulate turbulent premixed and partially premixed hydrogen flames. Different approaches to model differential diffusion are investigated and compared. In particular, two existing models are extended to the LES framework to correct the resolved diffusive flux of the controlling variables due to differential diffusion. A lean premixed turbulent hydrogen flame in a slotted burner configuration is simulated first to compare the capability of the considered models in capturing local mixture fraction redistribution, super-adiabatic temperatures and thermo-diffusive instabilities. Results show that both models describe the formation of cellular burning structures. Next, a partially premixed lifted hydrogen flame in vitiated hot coflow is simulated to gain insight on the relevance of differential diffusion modelling at a higher turbulence level, a different combustion mode and in the presence of a complex stabilisation mechanism. Good predictions of the turbulent mixing and temperature fields are observed. Moreover, results show that the flame lift-off height has an appreciable sensitivity to the differential diffusion model. When differential diffusion is included only in the thermochemistry database, only mild effects on the predicted temperature fields, mixing and flame height are observed. On the contrary, a considerable shift of the flame base is observed when corrections are applied in the LES at the resolved level, depending on what controlling variables are considered. Further analyses reveal how the corrections of diffusive fluxes in the thermochemistry and at the LES level affect differently the flame burning mode, whose details are given throughout the paper. [ABSTRACT FROM AUTHOR]

This work proposes a numerical model to estimate the radiant heat feedback from the flame of a burning aluminium particle. The objective is to evaluate its role on the burning time. It rests on a detailed combustion simulation of a single particle coupled with a simple two-flux approximation for the radiant flux emitted from the oxide smoke. Radiated flux from the flame is found to be around 1 MW/m $ ^2 $ 2 for atmospheric pressures, going up to more than 5 MW/m $ ^2 $ 2 for higher pressures (30 bar). Parametric simulations show that aluminium size has a small effect while oxygen-rich atmospheres can double the radiated flux. Overall, the role of flame radiation on aluminium burning rate is calculated to lie roughly between 1 and 25%, depending on conditions. This is the first study that clearly evaluates the role of flame radiation on aluminium combustion ; in most configurations, this effect, however, remains limited. [ABSTRACT FROM AUTHOR]

The paper focuses on modelling the heat flux through the isothermal wall boundary in premixed turbulent combustion. In a statistically stationary configuration, the distorted flames, advected by the incoming flow toward the wall, can be either head-on or entrained. The wall heat flux model with respect to the head-on and entrained parts are constructed differently to describe their distinct behaviours. In model validation, to exclude the interference from various inaccuracies, either numerically or experimentally, the filtered three-dimensional direct numerical simulation (DNS) fields are adopted as benchmark. Results justify that the newly proposed model is able to capture the wall heat flux statistics. The predictions are consistently satisfactory at different filter widths, performing clearly better than direct evaluation from the filtered temperature gradient and effective diffusivity. In addition, it is also straightforward to integrate this model together with existing flow solvers. [ABSTRACT FROM AUTHOR]

This paper examines a new Conditional Source-term Estimation (CSE) implementation in which an integral inversion is performed for species mass fractions without any chemistry tabulation. To tackle the numerical stiffness due to chemistry, a constant-pressure chemical reactor is considered in conditional space. The objective of this work is to investigate this new method in CSE by comparing its numerical performance (accuracy of predictions and computational efficiency) with previous CSE implementations using tabulated chemistry. For the first time, the constraints for mass and mixture fraction conservation in conditional space are included in the inversion process. The investigation is performed in a Reynolds Averaged Navier-Stokes (RANS) framework using a well-documented turbulent flame with detailed measurements in conditional and physical spaces for many reacting scalars. A chemical mechanism including 16 species and 35 reactions is incorporated. CSE predictions of conditional and Favre averaged temperature and different species mass fractions are analysed. CSE with full chemistry performs as well as CSE with tabulated chemistry, if not slightly better. Numerical errors are discussed. The new CSE implementation is made possible by the proposed numerical treatment of stiffness due to chemistry and first-order Tikhonov regularisation technique with additional physical constraints. The new approach is found to be more CPU intensive than CSE with a pre-tabulation technique, but as a preliminary analysis, the computational cost of CSE with direct integration of a chemical mechanism appears to be much smaller than the run time associated with CMC for a similar set-up. Further investigation is required to refine this initial conclusion. These results open new opportunities towards CSE simulations that involve fuel blends and more complex operating conditions for example with spray and multi-stream inlets with non-uniform compositions for which accurate chemistry tabulations are difficult to generate. [ABSTRACT FROM AUTHOR]

The combustion cycle‐to‐cycle variations (CCV) are the typical combustion phenomena in the internal combustion engine, which will not only affect the combustion efficiency, heat‐work conversion process, and emission formation in the cylinder, but also cause the output torque and power fluctuation, resulting in unstable and even misfire. These phenomena are particularly evident in the spark ignition (SI) engine, especially at idle, acceleration, and high exhaust gas recirculation conditions. Consequently, it is quite important to explore the internal relationship and correlation mechanism between the CCV and the affecting factors. This paper comprehensively reviewed the fundamental reasons and mechanisms of CCV of the SI engine. In addition, the characteristic parameters and characterization methods of the CCV, the laws and influencing factors of the CCV, and the numerical simulation methods of the CCV were introduced in detail to quantitatively analyze the performance, combustion, and emissions characteristics of the SI engine. Each research direction is discussed in detail in various sections. The research status of the CCV of the SI engine from the experimental and numerical simulation aspects was also presented and discussed. Lastly, effective methods and strategies were proposed to improve the combustion process and fuel economy, and reduce exhaust emissions of the SI engine for high efficiency and clean combustion. [ABSTRACT FROM AUTHOR]

In recent years, international energy cooperation has become more extensive, and the safe and reliable transportation of oil and gas resources has become increasingly important. However, storage and transportation sites can have confined spaces in engineering practice, which can lead to safety problems. There is a risk of gasoline–air mixture explosions in confined spaces such as pump rooms, valve operation rooms, and inspection wells, particularly in Class B and Class C pipeline trench areas that utilize non-sand-filled trenches or where the local depth exceeds 2.0 m. These locations are equipped with doors, manholes, or ventilation openings for personnel access within oil storage zones. To investigate the combustion characteristics of gasoline–air mixture explosions in such confined spaces, experimental research was conducted on a simulation platform (L/D = 15, V = 0.015 m3). The findings reveal the following: (1) the most hazardous initial gasoline–air mixture volume fraction for ignition at the upper ignition point is 1.7%; (2) the morphology of the internal flame evolves through four distinct stages, with the post-explosion flame shapes resembling "brush-like" and "mushroom cloud" formations; (3) low YCH = 1.1%, medium YCH = 1.7%, and high YCH = 2.3% volume fractions of hydrocarbons were selected to analyze the progression of the explosion development process; (4) the external overpressure distribution during venting explosions, with varying initial gasoline–air mixture volume fractions, conforms to the function y = ae−bx as the distance L varies, with venting pressure waves exhibiting a trend of exponential decay. [ABSTRACT FROM AUTHOR]

This article utilizes the combustion characteristics of combustible materials to investigate the fire mechanisms and extinguishing technologies in substations. Experimental and simulation analyses have revealed patterns in heat release rates, flame heights, flame temperatures, flame resistance, and particulate ash. A modular solution employing a novel hot aerosol fire suppression system has been introduced. This system integrates independently manufactured alarm devices, initiation devices, sensors, and fire suppression equipment, offering either semi-automatic or fully automatic functionality. It serves both targeted fire suppression and complete immersion scenarios. By developing an integrated fire suppression and database alert system, enhanced intelligent fire protection has been attained, thereby advancing the sophistication of substation fire safety and the digitization of power networks. [ABSTRACT FROM AUTHOR]

It has been found out that Pd-Co-based catalyst, supported on anodized aluminum, possesses very high activity in combustion reactions of C1–C6 alkanes and toluene. The catalyst characterization has been made by N2-pysisorption, XRD, SEM, XPS, FTIR, TEM, and EPR methods. In view of the great interest, methane combustion was investigated in detail. It is ascertained that the complete oxidation of methane proceeds by dissociative adsorption on PdO and formation of hydroxyl and methyl groups, the former being highly reactive, and it undergoes further reaction to oxygen-containing intermediates, whereupon HCHO is one of them. The presence of Co2+ cations promotes greatly oxygen adsorption. The dissociative adsorption is favored on neighboring Co2+ cations, leading to the formation of bridging peroxides. Further, the oxygen dissociates on the nearest Pd2+ cations. According to the results from the experimental data, instrumental methods, and the observed kinetics and DFT model calculations, it can be concluded that the reaction pathway over Pd+Co/anodic alumina support (AAS) catalyst proceeds most probably through Mars–van Krevelen. The obtained data on the kinetics were used for simulation of the methane combustion in a full-scale adiabatic reactor. [ABSTRACT FROM AUTHOR]