Search Results (3,206)

Hydrogen energy is considered a crucial clean energy carrier for replacing fossil fuels in the future. Liquid hydrogen (LH₂), with its economic advantages and high purity, is central to the development of future hydrogen refueling stations (HRSs). However, leakage poses significant fire and explosion risks, challenging its safe industrial use. In this study, a numerical model of LH₂ leakage at an HRS in Chongqing was established using Computational Fluid Dynamics (CFD) software. The diffusion law of a flammable gas cloud (FGC) was examined under the synergistic effect of the leakage direction, rate, and wind speed of an LH₂ storage tank in an HRS. The phase transition of LH₂ presents dual risks of combustion and frostbite owing to the spatial overlap between low-temperature areas and FGCs. The findings revealed that the equivalent stoichiometric gas cloud volume (Q9) reached 685 m³ in the case of crosswind leakage, with the superimposed effect of reflected waves from the LH₂ transport vehicle resulting in a peak explosion overpressure of 0.61 bar. The low-temperature hazard area and the FGC (with a concentration of 30–75%) show significant spatial overlap. These research outcomes offer crucial theoretical underpinning for enhancing equipment layout optimization and safety protection strategies at HRSs. Full article

This study proposes an equivalent furniture fire model based on standard combustible assembly and verifies its feasibility as a substitute for real furniture through full-scale experiments and numerical simulations. Experiments show that the peak heat release rate and total heat release of the standard combustible assembly are highly consistent with those of the single-seat sofa. The numerical model has been verified by experimental data. The dynamic characteristics of the heat release rate (HRR) curve are consistent with the temperature evolution process, confirming its reliability for the numerical model. The research on optimizing fire extinguishing parameters is carried out based on this numerical simulation. The results show that the response time of the horizontal sprinkler is 22 s shorter than that of the vertical sprinkler, and the fire extinguishing efficiency is improved. Reducing the sprinkler height to 3 m can accelerate activation and reduce CO₂ release. A flow rate of 91.4 L/min can effectively control the fire, but when it exceeds 150 L/min, the fire extinguishing efficiency is significantly reduced. The low response time index sprinkler starts up 88 s faster than the standard type, significantly enhancing the initial fire suppression capability. This scheme provides a safe, economical, and repeatable standardized combustible assembly for fire training and offers theoretical support for the parameter design of intelligent fire extinguishing systems. Full article

The integrity analysis of a combustion chamber that uses Ablative Thermal Protection Systems (ATPSs) is a process that requires the analysis of the thermal and mechanical behavior of the materials involved and their interaction. A 1D thermal model for multilayered combustion chambers of hybrid rocket engines and solid rocket motors is developed, taking into consideration the thermal behavior of charring ATPSs during phase change and the capability of implementing an ablation process. A stress model is also implemented to assess the structural integrity of the combustion chamber that undergoes pressure and thermal loads. A numerical finite-difference model is used to implement analytical models and simulate the behavior of the materials. Bibliographic data and finite element analysis tools are used to evaluate and verify the models developed. Lastly, six different materials are used as a case study, and a parametric optimization is applied to obtain the minimum-mass designs using the materials selected. Full article

Combustion instability poses a significant challenge in aerospace propulsion systems, particularly in afterburners that employ bluff-body flame stabilizers. The flame transfer function (FTF) is essential for characterizing the dynamic response of flames to perturbations, which is critical for predicting and controlling these instabilities. This study experimentally investigates the effect of varying the number of fuel injection holes (N = 3, 4, 5, 6) on the FTF and flame dynamics in a model afterburner combustor. Using acoustic excitations, the FTF was measured across a range of frequencies, with flame behavior analyzed via high-speed imaging and chemiluminescence techniques. Results reveal that the FTF gain exhibits dual-peak characteristics, initially decreasing and then increasing with higher N values. The frequencies of these gain peaks shift to higher values as N increases, while the time delay between velocity and heat release rate fluctuations decreases, indicating a faster flame response. Flame morphology analysis shows that higher N leads to shorter, taller flames due to enhanced fuel distribution and mixing. Detailed examination of flame dynamics indicates that different pulsation modes dominate at various frequencies, elucidating the observed FTF behavior. This research provides novel insights into the optimization of fuel injection configurations to enhance combustion stability in afterburners, advancing the development of more reliable and efficient aerospace propulsion systems. Full article

In this paper, the effect of nozzle height on the combustion dynamics of jet fires in rotating flow fields (JFRFFs) is systematically investigated through experimental and numerical simulations. As the nozzle height increases, the JFRFF flame state transitions from stable rotation (SR) to unstable rotation (USR), and eventually to non-rotation (NR), indicating a weakening interaction between the vortex flow and the jet flame. The radial distribution of tangential velocity gradually deviates from the Burgers vortex model as the nozzle height increases, providing a criterion for distinguishing different flame states. Both vortex intensity and flame length are found to decrease with increasing nozzle height, whereas the maximum flame diameter increases. The relative position of the maximum flame diameter to the whole flame length firstly increases and then decreases to match that of the free jet fires, as the flame evolves from SR to USR and NR. In addition, the air entrainment near the nozzle exit decreases with increasing nozzle height, as evidenced by the gradual rise in lift-off height. These findings establish a theoretical basis for the fire performance design of flares in pipeline retrofitting and process industries. Full article

Fuel combustion is a crucial process in energy utilization. As a key bulk transport mechanism, Stefan flow significantly affects heat and mass transfer during char combustion. However, its physical nature and engineering implications have long been underestimated, and no systematic review has been conducted. This paper presents a comprehensive review of Stefan flow in char combustion, with a focus on its impact on mass transfer and combustion behavior under both air-fuel and oxy-fuel conditions. It also highlights the critical role of Stefan flow in enhancing energy conversion efficiency and optimizing carbon capture processes. The analysis reveals that Stefan flow has been widely neglected in traditional combustion models, resulting in significant errors in calculated mass transfer coefficients (up to 21% in air-fuel combustion and as high as 74% in oxy-fuel combustion). This long-overlooked deviation severely compromises the accuracy of combustion efficiency predictions and model reliability. In oxy-fuel combustion, the gasification reaction (C + CO₂ = 2CO) induces a much stronger outward Stefan flow, reducing CO₂ transport by up to 74%, weakening local CO₂ enrichment, and substantially increasing the energy cost of carbon capture. In contrast, the oxidation reaction (2C + O₂ = 2CO) results in only an 18% reduction in O₂ transport. Stefan flow hinders the inward mass transfer of O₂ and CO₂ toward the char surface and increases heat loss during combustion, resulting in reduced reaction rates and lower particle temperatures. These effects contribute to incomplete fuel conversion and diminished thermal efficiency. Simulation studies that neglect Stefan flow produce significant errors when predicting combustion characteristics, particularly under oxy-fuel conditions. The impact of Stefan flow on energy balance is more substantial in the kinetic/diffusion-controlled regime than in the diffusion-controlled regime. This review is the first to clearly identify Stefan flow as the fundamental physical mechanism responsible for the differences in combustion behavior between air-fuel and oxy-fuel environments. It addresses a key gap in current research and offers a novel theoretical framework for improving low-carbon combustion models, providing important theoretical support for efficient combustion and clean energy conversion. Full article

Driven by the “dual carbon” goal, virtual power plants (VPPs) are the core vehicle for integrating distributed energy resources, but the multiple uncertainties in wind power, electricity/heat load, and electricity price, coupled with the impact of carbon-trading cost, make it difficult for traditional scheduling methods to balance the robustness and economy of VPPs. Therefore, this paper proposes an oxy-fuel combustion capture (OCC)-VPP architecture, integrating an OCC unit to improve the energy efficiency of the system through the “electricity-oxygen-carbon” cycle. Ten typical scenarios are generated by Latin hypercube sampling and K-means clustering to describe the uncertainties of source and load probability distribution, combined with the polyhedral uncertainty set to delineate the boundary of source and load fluctuations, and the stepped carbon-trading mechanism is introduced to quantify the cost of carbon emission. Then, a three-stage stochastic–robust scheduling model is constructed. The simulation based on the arithmetic example of OCC-VPP in North China shows that (1) OCC-VPP significantly improves the economy through the synergy of electric–hydrogen production and methanation (52% of hydrogen is supplied with heat and 41% is methanated), and the cost of carbon sequestration increases with the prediction error, but the carbon benefit of stepped carbon trading is stabilized at the base price of 320 DKK/ton; (2) when the uncertainty is increased from 0 to 18, the total cost rises by 45%, and the cost of purchased gas increases by the largest amount, and the cost of energy abandonment increases only by 299.6 DKK, which highlights the smoothing effect of energy storage; (3) the proposed model improves the solution speed by 70% compared with stochastic optimization, and reduces cost by 4.0% compared with robust optimization, which balances economy and robustness efficiently. Full article

This study aimed to investigate the effects of diesel/ethanol/n-butanol mixed fuel on the marine diesel engine combustion and emissions at different ethanol blending ratios, different single injection times, and pre-injection times. In addition, this study takes the injector fault phenomenon as an example, simulates the three fault phenomena of the injector, and uses a variety of algorithms to optimize the probabilistic neural network model to achieve the fault state identification and diagnosis of the injector. The results of research showed that, with the increase in the ethanol blending ratio, the peak cylinder pressure shows a decreasing trend. The ignition delay period is extended, and the peak instantaneous heat release rate increases. Compared with D100, the nitrogen oxide (NO_x) emissions of D50E40B10 mixed fuel are reduced by 12.3%, soot emissions are reduced by 29.18%, and carbon monoxide (CO) emissions are increased by 5.7 times. With the injection time advances, the peak values of cylinder pressure and heat release rate show an increasing trend, soot emissions gradually decrease, and NO_x and CO emissions gradually increase. The peaks of the cylinder pressure and heat release rate in the pilot injection stage gradually decrease as the pilot injection time advances, while the peak heat release rate in the main injection stage increases. In terms of emissions, NO_x emissions first decrease and then increase as the pilot injection time advances, while soot emissions gradually increase. The average accuracy of the PSO-PNN neural network model reaches 90%, and the average accuracy of the WOA-PNN neural network model reaches 95%. Therefore, the WOA-PNN neural network model is determined to be the optimal injector fault diagnosis model, which can be applied to the identification and diagnosis of injector fault states of diesel engines. Full article

Accurate temperature control across different zones during the combustion and heat exchange stages is crucial for both the economic efficiency of municipal solid waste incineration (MSWI) power plants and the consistent achievement of environmental targets. To address limitations in existing research, such as single-point temperature prediction models and the difficulty in characterizing the correlation mapping between adjacent zones, this article proposes a multi-point serial temperature prediction modeling method for the combustion and heat exchange stages of the MSWI process. Firstly, based on identifying five key temperature points across different zones in these stages, the Pearson correlation coefficient (PCC) is utilized for regional feature selection targeting each individual temperature point. Subsequently, multiple single temperature point prediction models based on a linear regression decision tree (LRDT) are constructed using the selected feature variables. Finally, considering the mutual influence between temperatures in neighboring zones, a serial multi-point temperature prediction model is built by using the knowledge transfer. To our knowledge, this is the first interpretable multi-point temperature prediction model for the MSWI process. It can assist in precise temperature control across different zones during the combustion and heat exchange stages in future studies. Validation results demonstrate that the minimum MSE attained 0.0238, the minimum MAE reached 0.1223, and the maximum R² achieved 0.9985 across multiple temperature points. The proposed method is validated using actual operational data from an MSWI power plant in Beijing. Full article

As a key precursor of tropospheric ozone and secondary particulate matter, nitrogen oxides (NO_x) exert significant impacts on air quality. Traffic emissions represent a dominant source of near-surface NO_x. The widespread adoption of new energy vehicles (NEVs) has progressively transformed the automobile fleet composition, leading to measurable reductions in NO_x emissions. This study developed a NO_x emission inventory model to quantify the impact of NEV penetration on emission trends in Guangdong (2013–2022), under the assumption that the emission shares of internal combustion engine vehicles (ICEVs) and NEVs have no significant change in adjacent years. Results demonstrate that total vehicular NO_x emissions peaked in 2019 at 55.69 × 10⁴ tons (a 16.6% increase from 2018), followed by a consistent decline. ICEVs exhibited a declining emission share from 0.037 × 10⁴ tons/year in 2013 to 0.022 × 10⁴ tons/year in 2019—a 40.5% reduction, attributable to progressive technological advancements. Following a marginal increase (2019–2021), the emission share declined significantly to 0.019 × 10⁴ tons/year in 2022. In contrast, NEVs contributed to emissions reduction, with maximal mitigation observed in 2021 (−0.241 × 10⁴ tons). ICEVs initially demonstrated emission reductions (2014–2017), succeeded by a transient increase (11.7 × 10⁴ tons through 2021) before resuming decline in 2022. The NEV-driven mitigation effect intensified progressively from 2018 to 2021, with modest attenuation in 2022. Full article

The utilization of ammonia as a fuel for gas turbines involves practical challenges due to its low reactivity, narrow flammability limits, and slow laminar flame propagation. One of the potential solutions to enhance the combustion reactivity of ammonia is co-firing with syngas. This paper presents an experimental and numerical investigation of the laminar burning velocity (LBV) of ammonia/syngas/air mixtures under elevated pressures (up to 10 bar) and temperatures (up to 473 K). Experiments were conducted in a constant-volume combustion chamber with a total volume of 11 L equipped with a dual-electrode capacitive discharge ignition system. A systematic sensitivity analysis was conducted to experimentally evaluate the system performance under various syngas compositions and equivalence ratios from 0.7 to 1.6 and ultimately identify the factors with the most impact on the system. As a complement to the experiments, a detailed numerical simulation was carried out integrating available kinetic mechanisms—chemical reaction sets and their rates—to support advancements in the understanding and optimization of ammonia/syngas co-firing dynamics. The sensitivity analysis results reveal that LBV is significantly enhanced by increasing the hydrogen content (>50%). Furthermore, the LBV of the gas mixture is found to increase with the use of a rich flame, higher mole fractions of syngas, and higher initial temperatures. The results indicate that higher pressure reduces LBV by 40% but at the same time enhances the adiabatic flame temperature (by 100 K) due to an equilibrium shift. The analysis was also extended to quantify the impact of syngas mole fractions and elevated initial temperatures. The kinetics of the reactions are analyzed through the reaction pathways, and the results reveal how the preferred pathways vary under lean and rich flame conditions. These findings provide valid quantitative design data for optimizing the combustion kinetics of ammonia/syngas blends, offering valuable design data for ammonia-based combustion systems in industrial gas turbines and power generation applications, reducing NOₓ emissions by up to 30%, and guiding future research directions toward kinetic models and emission control strategies. Full article

Advancements in battery technology, marked by reduced costs and enhanced efficiency, are steadily making electric vehicles (EVs) more accessible to consumers. This trend is fueling global growth in EV fleet sizes, allowing EVs to compete directly with internal combustion engine vehicles. However, this rapid growth in EV numbers is likely to introduce challenges to the power grid, necessitating effective load management strategies. This work proposes an optimization method where EV load management is integrated into the Transmission Constrained Unit Commitment Problem (TCUCP). A Differential Evolution (DE) variant, enhanced with heuristic repair sub-algorithms, is employed to address the TCUCP. The heuristic sub-algorithms, adapted from earlier approaches to the simpler Unit Commitment Problem (UCP), are updated to incorporate power flow constraints and ensure the elimination of transmission line violations. Additionally, new repair mechanisms are introduced that combine priority lists with grid information to minimize violation. The proposed formulation considers EVs as both flexible loads and energy sources in a large urban environment powered by two grid nodes, accounting for the vehicles’ daily movement patterns. The algorithm exhibits exceptionally fast convergence to a feasible solution in fewer than 150 generations, despite the nonlinearity of the problem. Depending on the scenario, the total production cost is reduced by up to 45% within these generations. Moreover, the results of the proposed model, when compared with a MILP algorithm, achieve values with a relative difference of approximately 1%. Full article

Based on a pre-constructed simplified chemical reaction mechanism for afterburning in exhaust plumes, this study integrates a gas–solid two-phase combustion flow model with numerical radiative transfer calculations to systematically explore the optimization of computational domains for exhaust plume simulations and reveal the regulatory mechanisms of flight parameters affecting on plume evolution. The results demonstrate that as altitude increases, the plume expands overall, the afterburning zone shifts rearward, and the peak radiation brightness is delayed but with a slight enhancement. Conversely, increasing flight velocity leads to axial elongation and radial compression of the plume, reduced afterburning intensity, and an overall decrease in radiative intensity. This study establishes a correlation between solid rocket motor flight parameters and plume dynamics, providing theoretical and practical guidance for suppressing infrared signature signals in solid rocket motors and designing multifunctional propellant formulations. Full article

Carbon dioxide (CO₂) is the primary component contributing to anthropogenic greenhouse gas emissions, necessitating the adoption of effective mitigation strategies to promote environmental sustainability. Among the various carbon capture methodologies, chemical absorption is acknowledged as the most scalable solution for post-combustion applications. This investigation presents a thorough, comparative, and scenario-based evaluation of both singular and blended amine solvents for CO₂ capture within packed absorption–desorption columns. A validated rate-based model employing monoethanolamine (MEA) functions as the benchmark for executing process simulations. Three sequential scenarios are meticulously examined to switch the solvents and see the results. In the preliminary scenario, baseline performance is assessed by applying MEA to achieve the designated 73% removal target. Then the implementation of alternative solvents is examined—piperazine (PZ), a combination of methyldiethanolamine (MDEA) and PZ, and a blend of MEA and PZ—under uniform design parameters to ascertain their relative effectiveness and performance. In the second scenario, the design of the system is changed to reach a CO₂ removal efficiency for MEA of 90%, and then MEA is switched to other solvents. In the final scenario, critical design parameters, including column height and diameter, are adjusted for each solvent system that did not meet the 90% capture efficiency in Scenario 2 to achieve 90% CO₂ capture. A comprehensive sensitivity analysis is subsequently conducted on the adjusted systems to evaluate the influence of critical operational variables such as temperature, flue gas and solvent flow rates, and concentrations. Importantly, the MEA + PZ blend also demonstrated the lowest specific reboiler duty, as low as 4.28 MJ/kg CO₂, highlighting its superior energy efficiency compared to other solvents in the condition that the system in this study is pilot-scale, not commercial-scale, and due to this reason, the energy consumption of the system is slightly higher than the reported value for the commercial-scale systems. The results yield invaluable insights into the performance trade-offs between singular and blended amines, thereby facilitating the development of more efficient CO₂ capture systems that function within practical constraints. Full article

In the present study, a recently developed improved Self-Adaptive Turbulence Eddy Simulation (SATES) turbulence model (marked as SATES-Mixed), is validated for the simulation of complex multiple swirling turbulent flows. The new SATES-Mixed method aims to enhance both the performances in the wall region as well as the free shear layer region. For comparisons, the Large Eddy Simulation (LES) with WALE and Smagorinsky sub-grid model is also conducted with the same numerical setups. Compared with the original widely used SATES model, the SATES-Mixed model inherits the low grid sensitivity and high accuracy for free turbulence while improving the calculation accuracy in the near-wall regions. Therefore, the prediction ability of the SATES-Mixed model is validated in challenging complex swirling flows encountered in multi-stage swirl combustion chambers. Good overall agreement between SATES-Mixed and experiments is observed with relatively coarse mesh, which is even better than the LES-WALE results. The SATES-Mixed model accurately captures the typical single-vortex tube PVC evolution characteristics in a double swirling combustor (GTMC) and effectively models the complex interactions between single/double vortex tubes in a three-stage swirling combustor, including their intertwined twisting motions and mutually evolving processes. Full article