Search Results (1,459)

Combustion at the meso-scale is constrained by large surface-to-volume ratios that shorten residence time and intensify wall heat loss. We perform steady, three-dimensional CFD of two asymmetric vortex combustors: Model A (compact) and Model B (larger-volume) over inlet-air mass flow rates $\dot{m}$ (40–170 mg s⁻¹) and equivalence ratios ϕ (0.7–1.5), using an Eddy-Dissipation closure for turbulence–chemistry interactions. A six-mesh independence study (the best mesh is 113,133 nodes) yields ≤ 1.5% variation in core fields and ~2.6% absolute temperature error at a benchmark station. Results show that swirl-induced CRZ governs mixing and flame anchoring: Model A develops higher swirl envelopes (S up to ~6.5) and strong near-inlet heat-flux density but becomes breakdown-prone at the highest loading; Model B maintains a centered, coherent Central Recirculation Zone (CRZ) with lower $u_{\theta }$ (~3.2 m s⁻¹) and S ≈ 1.2–1.6, distributing heat more uniformly downstream. Peak flame temperatures (~2100–2140 K) occur at ϕ ≈ 1.0–1.3, remaining sub-adiabatic due to wall heat loss and dilution. Within this regime and $\dot{m}$ ≈ 85–130 mg s⁻¹, the system balances intensity against flow coherence, defining a stable, thermally efficient operating window for portable micro-power and thermoelectric applications. Full article

This study investigates the minimum ignition temperature of smoldering paper scraps with varying bulk densities and lengths under different external airflow rates. Paper scraps of different lengths were compressed to modify the bulk density within the smoldering fuel bed. The ignition tests were performed using a rod-heater with a controlled temperature range of 340–460 °C. Once the rod-heater reached the preset temperature, the current was turned off, and the rod-heater was inserted into the center of the vertically oriented combustion chamber filled with paper scraps. By recording the temperature variations at different locations within the combustion chamber, the ignition limits of smoldering paper scraps with varying bulk densities under different external airflow rates were determined. The results showed that in the absence of external airflow and with a fixed paper scrap length, the ignition limit of smoldering paper scrap exhibits a clear U-shaped trend as bulk density increases. Furthermore, we found that in the absence of external airflow, the length of paper scraps had no significant effect on the ignition limit in the low bulk density range. However, in the high bulk density range, the ignition limit increased with scrap length. As for cases with external air flows, the ignition limit of paper scrap smoldering combustion once again exhibits a U-shaped trend with varying bulk density. Compared with the condition without forced airflow, however, the inflection point of the U-shaped curve shifts toward the higher-density region. Moreover, within the range of externally forced airflow rates examined in the present study, the length of paper scraps had no significant effect on the smoldering ignition limit. Full article

Conical diffusers perform a variety of critical functions in final products (gas, hydraulic, and wind turbines, ejectors, gasifiers, combustion chambers, etc.). The purpose of this study was to experimentally study the flow distribution features in a vertical conical diffuser with different technical air supply methods to find directions for optimal movement organization. The vertical diffuser (apparatus) consisted of a conical section with an opening angle of 30° and a cylindrical section. The scientific results were obtained based on an experimental stand and the thermal imaging method. The article presents simplified equations of continuity and momentum balance for the system under consideration. Two methods of air supply to the diffuser were investigated: air supply through a single duct and air supply through 4 nozzles installed at different angles of 45°, 60°, and 70°. The experiments were carried out for stationary air movement with volumetric flow consumption through the system from 0.0018 m³/s to 0.006 m³/s. The Reynolds number for the air flow at the diffuser inlet ranged from 10,500 to 106,000. Significant differences in the flow structure for air supply to a diffuser through a single duct and nozzles were identified. The possibility of controlling the flow structure in a vertical diffuser by varying the inclination of the supply nozzles was demonstrated. Four characteristic patterns of air distribution in the diffuser were obtained: firstly, a pronounced central flow through the entire apparatus with a noticeable deviation of the flow to the right side; secondly, a local (from 30 to 75% of the apparatus height), central flow in the diffuser; thirdly, active air movement in the lower part of the diffuser with subsequent flow along the side walls of the apparatus; fourthly, multidirectional flow movement throughout the entire volume of the diffuser. Full article

Adjoint-based optimization methods, that were previously in the realm of computational fluid dynamics (CFD) research, are now available in commercial software. This work explores the use of adjoint-based optimization to maximize mixing and combustion efficiencies for a supersonic combustor. To this end, a two-dimensional combustor was considered with parallel hydrogen injection. Simulations were carried out based on the steady Reynolds-Averaged Navier–Stokes equations and optimization was performed using a simplified passive scalar field instead of the full reactive flow problem. The optimization of a triangle-shaped mixing element is considered in addition to a case allowing the entire bottom of the combustor to deform. The relatively small mixing element could not boost efficiency significantly. By comparison, the optimization of the combustor wall resulted in both mixing and combustion efficiency gains accompanied by total pressure loss penalty. The optimization achieved higher efficiency compared to the baseline by extending the total volume of the reaction zone. The presented proof-of-concept results are relevant for the design of hypersonic vehicle propulsion systems, such as scramjets. Full article

Advancing circular bioeconomy in thermochemical biorefineries requires species-specific data that link biomass composition and thermochemical performance. Here, we provide the first integrated thermochemical dataset for Quercus pubescens bark combining FT-IR, XRD, XRF, TGA, and measured ash fusion temperatures (AFT). The results reveal that bark is enriched in phenolic extractives (21.2%) and inorganics (15%), with calcium oxalate monohydrate (COM) dominating the inorganic fraction, as confirmed by FT-IR and XRD. Thermal decomposition occurs between 150 °C and 690 °C. Pyrolysis follows diffusion-controlled kinetics, with apparent activation energies for bark and its fractions ranging between 70 and 103 kJ mol⁻¹. Extraction increases the activation energy of bark. The ash exhibits a high AFT (softening: 1421 °C, flow: 1467 °C), placing this feedstock within the low-slagging, moderate-fouling range compared to other lignocellulosics. The observed COM-to-CaCO₃/CaO transformation upon heating contributes to the elevated AFT. Reactivity analyses of bark fractions support thermochemical biorefinery routing of fractions: extracted bark (EB) and desuberinised bark (DB) are highly reactive and well-suited to combustion/gasification, whereas raw bark (B) and Klason lignin (KL) exhibit higher thermal stability and yield more persistent char, favoring slow pyrolysis for biochar production. Such routing strategies optimize energy recovery and also enable co-products with environmental co-benefits. Full article

As a carbon-free fuel, ammonia faces challenges in engine applications due to its low flame propagation speed and high ignition energy. The pre-chamber turbulent jet-post spark ignition strategy (TJ-PSI) has been proven effective in accelerating the combustion of stoichiometric ammonia/air mixtures. This study investigates the effects of orifice configuration on the combustion characteristics of stoichiometric ammonia/air premixed mixtures under TJ-PSI mode. Experiments are performed in a constant-volume combustion vessel filled with stoichiometric ammonia/air mixtures, and the spark plug used to trigger the ignition of the mixture in the main chamber is located downstream of the pre-chamber turbulent jet flow. With pre-chamber volume maintained constant, pre-chambers with different orifice numbers (Φ1.4 mm × 1, Φ1.4 mm × 4, Φ1.4 mm × 6) and orifice diameters (Φ4.0 mm × 1) are tested, along with varying time intervals (TI) between the main chamber and pre-chamber spark timings. Experimental results show that the pre-chamber with single large orifice (Φ4.0 mm × 1) produces jet flames but offers limited combustion enhancement. In contrast, a single small orifice (Φ1.4 mm) generates flameless turbulent jets, which reduce combustion duration by 53% compared to the large-orifice case. This improvement is attributed to the pre-chamber jet enhancing turbulence in the main chamber, whereas larger orifices yield lower turbulence intensity. Although multi-orifice configurations provide less pronounced enhancement compared to the single-orifice case, they effectively prevent flame kernel extinction at short TIs (e.g., 10 ms). Consequently, the total combustion duration from pre-chamber spark to the end of main chamber combustion can be significantly shortened. Full article

The ablation resistance of silicone-based thermal protection materials in high-temperature, oxygen-rich environments remains insufficiently understood, yet it is critical for the design of thermal management systems in Solid Fuel Ramjets (SFRJs). To address this challenge, we first performed a three-dimensional two-phase flow simulation of an SFRJ combustion chamber under typical flight conditions, obtaining key parameters including temperature, pressure, and oxygen concentration. Based on these thermal boundaries, we developed an advanced ablation simulation device capable of replicating the coupled high-enthalpy oxidative and erosive environment within the chamber. Using this platform, we systematically evaluated silicone rubber composites reinforced with functional fillers and fibers. Results demonstrate that incorporating ZrB₂ significantly enhances thermal stability and promotes the formation of an antioxidative ceramic layer. Furthermore, hybrid composites containing both organic and inorganic fibers exhibit superior erosion resistance due to the formation of a dense and stable char layer with a reinforced skeletal structure. This work not only provides an efficient experimental methodology for screening thermal insulation materials but also offers fundamental insights for the design of advanced ablation-resistant composites tailored to SFRJ applications. Full article

The in situ conversion of oil shale with air injection has the advantage of self-generated heat. The fragmentation degree of oil shale affects the oxidative pyrolysis process. In this paper, the basic properties of oil shale were analyzed, and weight loss observation and high-pressure TGA-DSC (thermogravimetric analysis and differential scanning calorimetry) tests in an air atmosphere were conducted using the cores and particles. The oil shale’s oxidative pyrolysis characteristics and the effect of its particle sizes were evaluated. The results show that the porosity and permeability conditions, TOC (total organic carbon), and inorganic mineral composition of oil shale are highly heterogeneous, with higher permeability and greater TOC along the bedding direction. The derivative of the TGA curve shows a single peak, and the heat flow curve shows a double peak that can be used to determine the oil shale’s oxidation type. The oxidative pyrolysis stage of organic matter can be divided into three temperature ranges, of which the medium temperature range is where the most combustion weight loss and heat release occurs. The activation energy of oxidative pyrolysis, which is affected by factors such as particle size, organic matter content, and pyrolysis temperature, is 46.92–248.11 kJ/mol, indicating the varying degrees of difficulty in initiating the reaction under different conditions. The pre-exponential factor is 3.15 × 10²–6.27 × 10¹¹ 1/s, and the enthalpy value is 2.575–4.045 kJ/g. The combustion indexes and reaction enthalpy under different particle sizes are more correlated with their own organic matter content. As oil shale particle size decreases, the variation law of the activation energy and pre-exponential factor changes with temperature from an initial continuous increase to a decrease, then increases again with the smallest kinetic parameters in the medium temperature zone. A small particle size, high organic matter content, and high pressure are more conducive to initiating the oxidative pyrolysis reaction to achieve in situ conversion of organic matter. Full article

Coal spontaneous combustion causes both human casualties and environmental pollution. Owing to special flow behaviors, foam materials used in fire-fighting technology can effectively bring water and solid non-combustible substances into the fire-fighting area, greatly preventing spontaneous combustion. This paper systematically elucidates three foam materials, three-phase foam, gel foam and curing foam, and analyzes their physical and chemical inhibition mechanisms on coal spontaneous combustion. In particular, the preparation, performance and latest chemical modification methods of the foam materials are summarized in detail. It is found that foam materials with environmental friendliness, economy and excellent anti-fire performance need to be consistently explored. The primary application areas for cement-based foamed materials remain the building materials and civil engineering industries, and their modification should be studied accordingly based on the specific application context. Furthermore, a new component of foam materials, coal gasification slag (a solid waste), is proposed. In addition, the seepage properties of fire-fighting foam in porous media should be fully studied to accurately grasp the dispersion of foam materials in mine goafs. This review provides new insights and guidance for the development of fire-fighting foam materials. Full article

In the context of carbon neutrality, ammonia-coal co-firing is considered an effective way to reduce emissions from coal-fired units. This paper takes a 125 MW tangential combustion boiler as the research object and combines CFD and CHEMKIN models to study the effects of ammonia injection position (L1–L3) and blending ratio (0–30%) on combustion characteristics and NO generation. The results indicate that L1 (same-layer premixed injection) can form a continuous and stable flame structure and maintain low NO emissions. L2 (fuel-staged configuration) shows the highest burnout rate and strong denitration potential under high mixing conditions, while L3 has an unstable flow field and the worst combustion structure. NO emissions show a typical “first rise and then fall” trend with the blending ratio. L1 performs optimally in the range of 15–20%, and L2 peaks at 20%. Mechanism analysis indicates that R430 is the main NO generation reaction, while R15 and R427 dominate the NO reduction process. The synergistic reaction between NH_x free radicals and coke can effectively inhibit the formation of NO and improve combustion efficiency. Full article

Driven by the global energy transition and the dual carbon goals, developing low-carbon and zero-carbon alternative fuels has become a core issue for sustainable development in the internal combustion engine sector. Ammonia is a promising zero-carbon fuel with broad application prospects. However, its inherent combustion characteristics, including slow flame propagation, high ignition energy, and narrow flammable range, limit its use in internal combustion engines, necessitating the addition of auxiliary fuels. To address this issue, this paper proposes a composite injection technology combining “ammonia duct injection + hydrogen cylinder direct injection.” This technology utilizes highly reactive hydrogen to promote ammonia combustion, compensating for ammonia’s shortcomings and enabling efficient and smooth engine operation. This study, based on bench testing, investigated the effects of hydrogen direct injection timing (180, 170, 160, 150, 140°, 130, 120 °CA BTDC), hydrogen direct injection pressure (4, 5, 6, 7, 8 MPa) on the combustion and emissions of the ammonia–hydrogen engine. Under hydrogen direct injection timing and hydrogen direct injection pressure conditions, the hydrogen mixture ratios are 10%, 20%, 30%, 40%, and 50%, respectively. Test results indicate that hydrogen injection timing that is too early or too late prevents the formation of an optimal hydrogen layered state within the cylinder, leading to prolonged flame development period and CA10-90. The peak HRR also exhibits a trend of first increasing and then decreasing as the hydrogen direct injection timing is delayed. Increasing the hydrogen direct injection pressure to 8 MPa enhances the initial kinetic energy of the hydrogen jet, intensifies the gas flow within the cylinder, and shortens the CA0-10 and CA10-90, respectively. Under five different hydrogen direct injection ratios, the CA10-90 is shortened by 9.71%, 11.44%, 13.29%, 9.09%, and 13.42%, respectively, improving the combustion stability of the ammonia–hydrogen engine. Full article

Lubrication oil consumption (LOC) is one of the major sources of emissions from internal combustion (IC) engines; yet, analyzing and predicting it through modeling is challenging due to its multi-physics nature, which spans different time and length scales. In this work, a digital twin model is developed to simulate oil transport in the piston ring pack of IC engines and predict the resulting oil consumption with all major physical mechanisms considered. Three main contributors to LOC, namely, top ring up-scraping, oil vaporization on the liner, and reverse gas flows through the top ring gap, are included in the model. It was found that their behaviors are heavily dependent on the arrangement of the piston ring gaps. Therefore, with the ring rotation behavior still not resolved, the current model can predict the LOC range of a given engine profile. Results show that the predicted range can well encapsulate the experimentally measured LOC value. Full article

Hydrogen-based technologies, prominently fuel cells, are emerging as strategic solutions for decarbonization. They offer an efficient and clean alternative to fossil fuels for electricity generation, making a tangible contribution to the European Green Deal climate objectives. The primary issue is the production and transportation of hydrogen. An on-site hydrogen production system that includes CO₂ capture could be a viable solution. The proposed power system integrates an internal combustion engine (ICE) with a steam methane reformer (SMR) equipped with a CO₂ capture and energy storage system to produce “blue hydrogen”. The hydrogen fuels a high-temperature polymer electrolyte membrane (HT-PEM) fuel cell. A battery pack, incorporated into the system, manages rapid fluctuations in electrical load, ensuring stability and continuity of supply and enabling the fuel cell to operate at a fixed point under nominal conditions. This hybrid system utilizes natural gas as its primary source, reducing climate-altering emissions and representing an efficient and sustainable solution. The simulation was conducted in two distinct environments: Thermoflex code for the integration of the engine, reformer, and CO₂ capture system; and Matlab/Simulink for fuel cell and battery pack sizing and dynamic system behavior analysis in response to user-demanded load variations, with particular attention to energy flow management within the simulated electrical grid. The main results show an overall efficiency of the power system of 39.9% with a 33.5% reduction in CO₂ emissions compared to traditional systems based solely on internal combustion engines. Full article

Micro-combustion-powered thermoelectric generators (μ-CPTEGs) combine the high energy density of hydrocarbons with solid-state conversion, offering compact and refuelable power for long-endurance electronics. Such characteristics make μ-CPTEGs particularly promising for aerospace systems, where conventional batteries face serious limitations. Their achievable performance hinges on how a swirl-stabilized flame transfers heat into the hot ends of thermoelectric modules. This study uses a conjugate CFD framework coupled with a lumped parameter model to examine how input power and equivalence ratio shape the flame/flow structure, temperature fields, and hot-end heating in a swirl combustor-powered TEG. Three-dimensional numerical simulations were performed for the swirl combustor-powered TEG, varying the input power from 1269 to 1854 W and the equivalence ratio from φ = 0.6 to 1.1. Results indicate that the combustor exit forms a robust “annular jet with central recirculation” structure that organizes a V-shaped region of high modeled heat release responsible for flame stabilization and preheating. At φ = 1.0, increasing Q_in from 1269 to 1854 W strengthens the V-shaped hot band and warms the wall-attached recirculation. Heating penetrates deeper into the finned cavity, and the central-plane peak temperature rises from 2281 to 2339 K (≈2.5%). Consistent with these field changes, the lower TEM pair near the outlet heats more strongly than the upper module (517 K to 629 K vs. 451 K to 543 K); the inter-row gap widens from 66 K to 86 K, and the incremental temperature gains taper at the highest power, while the axial organization of the field remains essentially unchanged. At fixed Q_in = 1854 W, raising φ from 0.6 to 1.0 compacts and retracts the reaction band toward the exit and weakens axial penetration; the main-zone temperature increases up to φ = 0.9 and then declines for richer mixtures (peak 2482 K at φ = 0.9 to 2289 K at φ = 1.1), cooling the fin section due to reduced transport, thereby identifying φ = 0.9 as the operating point that best balances axial penetration against dilution/convective-cooling losses and maximizes the TEM hot-end temperature at the fixed power. Full article

Particulate matter (PM2.5) is a critical indicator of air quality and has significant health implications. This study presents the development and evaluation of a custom-built PM2.5 device, named the P-Tracker, designed to offer an accessible alternative to commercially available air quality monitors. This paper presents the design framework used to address the requirements of a low-cost, accessible device which meets the performance of existing commercial systems. Step-by step build instructions are provided for hardware and software development and connection to the P-tracker open access website which displays the data and interactive map. To demonstrate the performance, the P-Tracker was compared against leading consumer devices, including the AtmoTube Pro by AtmoTech Inc., Flow by Plume Labs, View Plus by Airthings, and the Smart Citizen Kit 2.1 by Fab Lab Barcelona, across four controlled tests. The tests included: (1) a controlled paper combustion test in which all devices were exposed to combustion aerosols in a sealed environment alongside the DustTrak 8530 (TSI Incorporated, Shoreview, MN, USA), used as the gold standard reference, where the P-Tracker achieved a Pearson correlation of 0.99 with DustTrak over the final measurement period; (2) an outdoor test comparing readings with a stationary reference sensor, Osiris (Turnkey Instruments Ltd., Rudheath, UK), where the P-Tracker recorded a mean PM2.5 concentration of 3.08 µg/m³, closely aligning with the Osiris measurement of 3.53 µg/m³ and achieving a Pearson correlation of 0.77; (3) a controlled indoor air quality assessment, where the P-Tracker displayed stable readings with a standard deviation of 0.11 µg/m³, comparable to the AtmoTube Pro; and (4) a real-world kitchen environment test, where the P-Tracker effectively captured fluctuations in PM2.5 levels due to cooking activities, maintaining a consistent response with the DustTrak reference. The results indicate varied degrees of agreement across devices in different conditions, with the P-Tracker demonstrating strong correlation and low error margins in high-pollution and controlled scenarios. This research underscores the potential of open-source, low-cost, custom-built air quality sensors which may be developed and deployed by communities to provide hyperlocal measurements of air pollution. Full article