Search Results (299)

The downsized Wankel rotary engine (WRE) fueled with methanol is a promising power source for small unmanned aerial vehicles, owing to its simple structure, high-speed capability, and clean emissions. In general, a well-designed ignition timing (IT) can drastically enhance engine combustion performance. To assess the impact of IT, a numerical simulation study was conducted on a methanol-fueled WRE, analyzing its combustion characteristics and emissions to guide performance optimization. The results indicated that advancing the IT boosted the flame propagation velocity. The peak pressure increased slightly when delaying the IT from −24 °CA to −15 °CA but dropped sharply for −12 °CA at 5000 RPM. This contrasts with the behavior at 11,000 RPM and 17,000 RPM, where peak pressure clearly rose with advanced IT. Indicated thermal efficiency (ITE) decreased with the delay of the IT at 11,000 RPM and 17,000 RPM; the maximum values reached 24.98% and 25.78%, respectively. This contrasted with the trend observed at 5000 RPM, where ITE first increased and then decreased with IT delay. The optimized IT significantly affects pollutant emissions primarily under low-speed conditions (5000 RPM), while exhibiting limited impact at high engine speeds. At 5000 RPM, strategic IT adjustment achieves maximum reductions of 2% in CO emissions and 33% in formaldehyde emissions. Full article

The widespread adoption of lithium-ion batteries (LIBs) in electric vehicles (EVs) and energy-storage systems (ESSs) has raised growing concern about fire hazards caused by thermal runaway (TR). While many studies have examined cell-level TR mechanisms, investigations at the module level remain limited despite their importance for safety design. In this study, TR propagation was experimentally analyzed in a 12-cell (2p6s) pouch-type LIB module with EV-grade cells. The state of charge (SOC) and initiation location were the main variables. TR was initiated by a surface-mounted Kapton heating film, with power increased stepwise from 63 W to 141 W at 5-min intervals. Temperature, voltage, and heat release rate (HRR) were continuously monitored. Results showed that higher SOC led to earlier TR onset, shorter vent-to-ignition delay, and stronger combustion with jet flames. Center initiation produced rapid bidirectional propagation with a peak heat release rate (PHRR) of 590 kW and a propagation time of 107 s, whereas edge initiation caused slower unidirectional spread with a PHRR of 105 kW and a propagation time of 338 s. These results demonstrate that both SOC and initiation location critically control TR severity and propagation, providing essential data for EV fire safety evaluation and module design. Full article

Leveraging catalytic microreactors as compact yet powerful thermal sources represents a promising approach to enable rapid and reliable startup of small-scale solid oxide fuel cell (SOFC) systems. In the present study, the homogeneous–heterogeneous (HH) combustion behavior of a propane/air mixture in a Pt-catalyzed microreactor is investigated using two-dimensional computational fluid dynamic (CFD) simulations. The catalytic reaction kinetics model is integrated into the general module of ANSYSY Fluent via a user-defined function (UDF) interface. By varying the surface area factor, the ignition characteristics of the propane/air mixture under different catalyst activities are systematically explored. Numerical results reveal that the relative catalyst activity range of 0–2 represents a sensitive region for propane/air ignition characteristics, characterized by a 541 K decrease in ignition temperature and a 50% reduction in ignition delay time. Nevertheless, further increases in relative catalyst activity from 2 to 10, yield a much smaller reduction—64 K in ignition temperature and 6.7 s in ignition delay time—indicating a weakly responsive regime. The relative contribution of the heterogeneous reaction (HTR) to the total heat release decreases with higher feed temperatures but increases with enhanced catalyst activity. Regarding the temporal evolution of HTR contribution, the initiation of homogeneous ignition undermines the dominance of HTR contribution. Irrespective of catalytic activity levels, the relative contributions of the two reaction pathways subsequently undergo dynamic redistribution and ultimately stabilize, reaching an equilibrium state within approximately 10 s. These findings provide critical insights into the role of catalyst activity in propane/air mixture ignition and the interplay between homogeneous and heterogeneous reactions in microscale combustion systems. 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

Laboratories are complex and dynamic environments where diverse hazards—including toxic gas leakage, volatile solvent combustion, and unexpected fire ignition—pose serious threats to personnel safety and property. Traditional monitoring systems relying on single-type sensors or manual inspections often fail to provide timely warnings or comprehensive hazard perception, resulting in delayed response and potential escalation of incidents. To address these limitations, this study proposes a multi-node laboratory safety monitoring and early warning system integrating multi-source sensing, heterogeneous communication, and cloud–edge collaboration. The system employs a LoRa-based star-topology network to connect distributed sensing and actuation nodes, ensuring long-range, low-power communication. A Raspberry Pi-based module performs real-time facial recognition for intelligent access control, while an OpenMV module conducts lightweight flame detection using color-space blob analysis for early fire identification. These edge-intelligent components are optimized for embedded operation under resource constraints. The cloud–edge–app collaborative architecture supports real-time data visualization, remote control, and adaptive threshold configuration, forming a closed-loop safety management cycle from perception to decision and execution. Experimental results show that the facial recognition module achieves 95.2% accuracy at the optimal threshold, and the flame detection algorithm attains the best balance of precision, recall, and F1-score at an area threshold of around 60. The LoRa network maintains stable communication up to 0.8 km, and the system’s emergency actuation latency ranges from 0.3 s to 5.5 s, meeting real-time safety requirements. Overall, the proposed system significantly enhances early fire warning, multi-source environmental monitoring, and rapid hazard response, demonstrating strong applicability and scalability in modern laboratory safety management. Full article

Utilization of waste tires via pyrolysis is a promising solution. The liquid hydrocarbons generated during this process could be used for enhancing low-reactivity coals for energy application. Current study investigates oxidation and combustion characteristics (including composition of gaseous combustion products) of low-reactivity coal mixed with liquid hydrocarbons from pyrolysis of waste tires with a concentration up to 20%wt at 700 °C. The oxidation tests via TG-analyzer revealed that at heating rates up to 10 °C/min, the process had one stage, associated with combined oxidation of coal-liquid hydrocarbons mixture. Starting from 10 °C/min the second stage occurred at temperature ~400 °C due to evaporation of light components of the mixture. Combustion tests at experimental setup at 700 °C revealed almost linear increase in fuel reactivity, expressed into decline in ignition delay time of mixtures (up to 71.6%) with increasing concentration of liquid hydrocarbons, while flame and diffusion combustion times were, in contrast, increasing (by up to 69.5%). Increasing concentration of additives from 2.5 to 20%wt resulted not only in change in the form of obtained mixture but also changed the combustion mechanism from predominantly heterogeneous smoldering to majorly homogeneous gas-phase ignition and combustion. Gas-phase combustion products concentration curves generally complimented previously observed peculiarities of combustion. Increased CO and NO_x concentrations in combustion products of coal mixed with liquid hydrocarbons revealed necessity in additional tailoring of burner characteristics for mitigating these effects. The compromise composition of mixture was found to include 10%wt of liquid hydrocarbons for enabling quick gas-phase ignition while maintaining moderate level of combustion products emissions. Full article

Hypergolic propellants have long been central to spacecraft propulsion because of their storability, reliability and rapid ignition. Conventional systems such as hydrazine derivatives paired with oxidisers like nitrogen tetroxide deliver ignition delays in the order of a few milliseconds but pose serious risks due to extreme toxicity and handling hazards. The search for safer and environmentally friendlier alternatives has therefore become a priority in recent years. This review examines ignition delay times reported in the literature for both conventional and green propellants under ambient experimental conditions. Data were collected from published studies between 2000 and 2025 using major scientific databases, including Scopus, Web of Science, and Google Scholar, and are compared across three categories of propellants: traditional hydrazine-based systems, self-igniting ionic liquids and amines, and systems enhanced with catalytic or reactive promoters. The analysis shows that while conventional propellants remain benchmarks with ignition delays typically between 1 and 5 ms, some new formulations, particularly those containing reactive additives such as borohydrides or iodide salts, are achieving similar or improved performance in laboratory tests. The review also highlights that variability in reported ignition delays often stems from differences in test methods, droplet size, oxidiser concentration, and diagnostic approaches. Beyond performance considerations, attention is given to safety and environmental aspects since several green candidates reduce acute toxicity but introduce other challenges, such as instability or corrosive byproducts. By bringing together data in a comparative format and emphasising methodological limitations, this review aims to support the future design and evaluation of practical green hypergolic propellants. Full article

To address the challenges of short dwell time near top dead center (TDC) and uneven heat release, this paper presents a comprehensive analysis of the effects of different ignition schemes on combustion characteristics, flame formation and development, and emissions. A three-dimensional model of coupled reaction’s kinetic mechanism was established using Converge 3.0 and validated by experimental data. The results show that ignition position, whether synchronous or asynchronous changes, significantly influence pressure. The pressure in synchronous cases can reach up to 62.5 bar, representing a 10.8% increase, exhibiting a distinct upward trend with advanced ignition position. In asynchronous cases, the pressure variation shows a distinct nonlinear characteristic due to the negative effects of in-cylinder airflow and flame core collision. When the ignition position is advanced, the ignition delay increases for both synchronous and asynchronous strategies. However, for synchronous cases, the combustion duration is reduced by up to 1.5 ms, whereas for asynchronous cases, the reduction is only 0.135 ms. Regardless of the schemes, the layout and the strong counterclockwise swirl lead to the flame core gradually developing from right to left, ultimately engulfing the left-side flame core. Compared then to that case, the left and right flame kernels may collide prematurely, leading to incomplete local combustion and consequently reducing combustion efficiency. Compared to synchronous changes, the emission differences during asynchronous changes are smaller and maintained at a relatively low level. Full article

To encourage the use of alternative fuels while limiting the use of fossil fuels, researchers have focused on using more environmentally friendly fuels. Furthermore, the goal is to improve engine performance to increase energy efficiency. A four-stroke, single-cylinder, diesel engine with a common rail fuel injection system runs with diesel, biodiesel, and biodiesel–alcohol fuel blends. The tests were performed using a constant engine speed of 2000 rpm and three different gas pedal positions (20%, 50% and 80%). It was found that maximum cylinder gas pressure increased in all test fuels with increased gas pedal position (GPP) and advanced injection start time. In general, the maximum heat release rate increased in blended fuels compared to diesel fuel. In addition, it was seen that advanced injection timings caused an increase in ignition delay in all fuel types. In the same test conditions, it was observed that biodiesel–alcohol fuel blends caused an increase in ignition delay by more than 10% compared to diesel fuel (D100), while shortening combustion duration (CD) by more than 10%. A decreasing trend in CO and HC emissions was observed in the use of biodiesel fuel compared to diesel fuel. With the use of biodiesel–alcohol fuel blends, CO₂ emissions tend to decrease. Advanced injection timings caused high NO emissions. Full article

HTRI xchanger Suite 6.0 software was employed to analyze the thermodynamic performance and thermal resistance distribution of the fuel/lubricating oil heat exchanger A for an aeroengine. Calculated results demonstrated good agreement with experimental results for both heat transfer and flow resistance characteristics. The thermal resistance analysis revealed that the tube-side contribution dominated, accounting for 84.6% of the total resistance. The whole aeroengine test revealed that insufficient tube-side velocity resulted in prolonged fuel filling time, subsequently delaying fuel ignition and affecting aeroengine starting. To address these issues while maintaining lubricating oil cooling requirements, a structural optimization incorporating twisted tape inserts was proposed. It was calculated by HTRI software that when the twist ratio and the thickness of twisted tape inserts was 4 and 0.5 mm, respectively, the optimized fuel/lubricating oil heat exchanger B demonstrated remarkable performance improvements, with an 82.6% reduction in total thermal resistance, a 213% increase in overall heat transfer coefficient, and an 18.0% reduction in total mass. A subsequent whole aeroengine test at the performance evaluation point confirmed that heat exchanger B successfully met all technical requirements of total mass, flow resistance, heat transfer rate, and aeroengine starting, simultaneously. The demonstrated methodology presents significant potential for broader aerospace thermal management applications, such as performance prediction of enhanced heat exchangers, multi-objective optimization of thermal systems, and integrated thermal management solutions. Full article

Xylenes are important components of gasoline fuels, and their hydrogen abstraction reactions are crucial in the consumption pathways of combustion processes. In existing models, rate constants for these reactions are commonly derived by estimation, which can introduce large uncertainties into models and lead to prediction deviations. In this study, the hydrogen abstraction reactions of three xylene isomers (p-xylene, m-xylene, and o-xylene) with hydrogen and hydroxyl radicals were investigated using quantum chemical methods. The high-precision CBS-QB3 method was used to perform a series of calculations, including structure optimization, frequency analysis, and energy calculations. Rate constants for all reactions were obtained using transition state theory with tunneling corrections and fitted to the three-parameter Arrhenius expression. The kinetic parameters of these reactions were updated in existing models of xylene. The integration of the updated rate constants into combustion models generally improves predictive accuracy, particularly for ignition delay times, CO₂ formation, and laminar flame speeds, although discrepancies remain for some species such as CO. Full article

In this study, reaction mechanisms of polytetrafluoroethylene/Al materials under shock compression were investigated. The reaction-induced pressure perturbations in PTFE/Al materials were identified by comparing pressure profiles with those of inert PTFE/LiF counterparts. The pressure rebounded to a range of 10.2–16.9 GPa under an incident shock pressure range of 11.5–22.6 GPa. The pressure perturbation amplitude induced by reaction gradually attenuated with increasing propagation distance. The delay time between the observed pressure perturbations and the incident shock front arrival ranged from 0.84 to 1.71 μs and showed a decreasing trend with increasing incident shock pressure and decreasing aluminum particle size. The results suggest that the reaction ignition and energy release of PTFE/Al materials change from closely following the shock front to being delayed by hundreds of microseconds behind the shock front when shock compression intensity decreases from GPa to MPa levels. Full article

High impedance grounding faults (HIGFs) are a common yet difficult-to-detect issue in distribution networks. Characterized by low fault currents and prolonged durations, they pose a significant risk of triggering secondary hazards such as wildfires. Existing HIGF prevention and control technologies face challenges in effectively addressing arc ignition, fault current limitation, and wildfire mitigation. To tackle these limitations, this paper proposes a novel asymmetric operational structure incorporating a single-phase isolation transformer and supplementary edge-phase capacitance. Through theoretical modeling and simulation analysis, the interrelations among fault current, phase voltage, zero-sequence voltage, and HIGF characteristics are systematically explored. A coordinated control strategy is developed to optimize three-phase voltage distribution within the distribution network. Simulation results demonstrate that the proposed configuration significantly reduces edge-phase voltages, suppresses fault current levels, prevents arc initiation, extends arc ignition delay times, and consequently mitigates wildfire risk. This study presents a new technical pathway for HIGF prevention and control, offering both practical engineering value and theoretical insight. Full article

The ammonia-n-heptane reaction mechanism is essential for simulation of the in-cylinder process for diesel-ignited ammonia engines. To gain insight into the differences in predictive performance among various ammonia-n-heptane reaction mechanisms, four mechanisms were comprehensively evaluated and analyzed based on the modeling of ignition, oxidation, laminar flame propagation and in-cylinder combustion processes. The result shows that only under high ammonia blending ratios and elevated temperatures are discrepancies in predicted ignition delay times observed among the studied reaction mechanisms. Regarding the oxidation process, on the whole, the concerned mechanisms can reasonably predict concentrations of reactants and complete combustion products. However, significant discrepancies exist among the mechanisms in predicting concentrations of intermediate species and other products. For laminar burning velocity, the modeled values from the studied mechanisms are consistent with experimental results under both fuel-lean and -rich conditions. The Wang mechanism exhibits significant deviations from the other three mechanisms in predicting reaction pathways of ammonia and n-heptane. From the perspective of reaction class, the studied mechanisms are similar to each other, to some extent, in the key reactions governing consumption of ammonia and n-heptane. For the engine simulation, the predicted in-cylinder pressure and temperature profiles show minimal variations across different reaction mechanisms. In conclusion, the Fang mechanism can be selected to understand more accurately ignition, oxidation and flame characteristics of ammonia-n-heptane mixtures, while to reduce the engineering computational cost of the engine simulation, the Wang mechanism tends to be a good choice. Full article

This paper presents a detailed analysis of the thermal and flammability properties of polylactide- (PLA) and poly(ethylene terephthalate)- (PET) based polymer blends with biofillers, such as calcium lignosulfonate (CLS), lignosulfonamide (SA) and lignosulfonate modified with tannic acid (BMT) and gallic acid (BMG). Calorimetric studies revealed the presence of two glass transitions, one cold crystallization temperature, and two melting points, confirming the partial immiscibility of the PLA and PET phases. The additives had different effects on the temperatures and ranges of phase transformations—BMT restricted PLA chain mobility, while CLS acted as a nucleating agent that promoted crystallization. Thermogravimetric analyses (TGA) analyses showed that the additives significantly affected the thermal stability under oxidizing conditions, some (e.g., BMG) lowered the onset degradation temperature, while the others (BMT, SA) increased the residual char content. The additives also altered combustion behavior; particularly BMG that most effectively reduced flammability, promoted char formation, and extended combustion time. CLS reduced PET flammability more effectively than PLA, especially at higher PET content (e.g., 65% reduction in PET for 2:1/CLS). SA inhibited only PLA combustion, with strong effects at higher PLA content (up to 76% reduction for 2:1/SA). BMT mainly reduced PET flammability (48% reduction in 1:1/BMT), while BMG inhibited PET more strongly at lower PET content (76% reduction for 2:1/BMG). The effect of each additive also depended on the PLA:PET ratio in the blend. FTIR analysis of the char residues revealed functional groups associated with decomposition products of carboxylic acids and aromatic esters. Ultimately, only blends containing BMT and BMG met the requirements for flammability class FV-1, while SA met FV-2 classification. BMG was the most effective additive, offering enhanced thermal stability, ignition delay, and durable char formation, making it a promising bio- based flame retardant for sustainable polyester materials. Full article