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Influence of magnetic field on flame dynamics in hydrogen flames: A numerical study 磁场对氢火焰火焰动力学影响的数值研究
IF 5.2 2区 工程技术 Q2 ENERGY & FUELS Pub Date : 2025-01-01 DOI: 10.1016/j.proci.2025.105892
Vaibhav Mysore Natesh, Ivan Langella
Electromagnetic fields influence flame behavior by altering the transport of paramagnetic species such as oxygen and OH radicals in hydrogen flames, affecting reaction pathways and combustion dynamics. This study presents a numerical investigation of the effects of magnetic fields on a premixed swirl-stabilized hydrogen flame using a modified combustion solver in OpenFOAM. Additional body force and diffusion terms were incorporated into the governing equations to model interactions with paramagnetic species, and the solver was validated against experimental data and simulations from the literature. The study focuses on analyzing flame structure, species redistribution, and mixture fraction variations under magnetic conditioning. Large Eddy Simulations (LES) with the Eulerian Stochastic Fields (ESF) method were employed to capture turbulence-chemistry interactions. The results indicate that the presence of a magnetic field induces an upstream-directed force on oxygen, leading to localized changes in mixture fraction and combustion characteristics. A reduction in temperature, heat release rate, and OH concentration was observed, with peak reductions of approximately 2%, 5%, and 6%, respectively. These effects are attributed to the redistribution of oxygen, which makes the flame locally leaner. This study extends the understanding of hydrogen combustion under electromagnetic influence and demonstrates the potential of magnetic fields for controlling the flame behavior. The findings provide new insights into magnetic field-assisted combustion strategies, offering a framework for further research in advanced propulsion and energy applications.
电磁场通过改变顺磁性物质如氧和OH自由基在氢火焰中的输运来影响火焰行为,从而影响反应途径和燃烧动力学。本文采用改进的燃烧溶剂在OpenFOAM中对磁场对预混合旋流稳定氢火焰的影响进行了数值研究。在控制方程中加入了额外的体力和扩散项来模拟与顺磁物质的相互作用,并根据实验数据和文献中的模拟对求解器进行了验证。研究重点分析了磁条件下火焰结构、物质重分布和混合分数的变化。采用大涡模拟(LES)和欧拉随机场(ESF)方法捕捉湍流-化学相互作用。结果表明,磁场的存在对氧产生了上游方向的作用力,导致混合气组分和燃烧特性发生局部变化。观察到温度、放热速率和OH浓度的降低,峰值分别降低了约2%、5%和6%。这些影响归因于氧气的再分配,这使得火焰局部变薄。该研究扩展了对电磁影响下氢燃烧的认识,并证明了磁场控制火焰行为的潜力。这一发现为磁场辅助燃烧策略提供了新的见解,为先进推进和能源应用的进一步研究提供了框架。
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引用次数: 0
A priori analysis of multi-dimensional flamelet effects in a transcritical LOX/GH2 jet flame 跨临界LOX/GH2射流火焰中多维火焰效应的先验分析
IF 5.2 2区 工程技术 Q2 ENERGY & FUELS Pub Date : 2025-01-01 DOI: 10.1016/j.proci.2025.105864
Hanzhang Cao, Wang Han, Yihao Tang, Lijun Yang
Accurate modeling of transcritical combustion is of critical importance for the development of high-efficiency rocket engines. While the one-dimensional flamelet theory has been extensively used in transcritical and supercritical combustion simulations, a comprehensive analysis of multi-dimensional flamelet effects remains scarce. To this end, a priori analysis of multi-dimensional flamelet effects in a transcritical LOX/GH2 jet flame is performed in this work by comparing 1D flamelet solutions with multi-dimensional flamelets extracted from DNS solutions. The results show that while conventional 1D flamelet solutions can provide a good approximation of the jet flame structure, incorporating differential diffusion helps to accurately predict the flame front position. Furthermore, asymptotic scaling analysis and budget analysis of generalized flamelet equations are conducted for the extracted flamelets. It is found that multi-dimensional flamelet effects do have a substantial impact on the jet flame. Nevertheless, flame-normal diffusion is dominant over flame-tangential diffusion. These findings suggest that the 1D flamelet assumption is reasonable for the transcritical LOX/GH2 jet flame and that attention should be paid to incorporating differential diffusion effects in the modeling of transcritical LOX/GH2 jet flames.
跨临界燃烧的精确建模对高效火箭发动机的研制至关重要。一维火焰理论在跨临界和超临界燃烧模拟中得到了广泛的应用,但对多维火焰效应的综合分析仍然很少。为此,本文通过比较一维小火焰溶液和从DNS溶液中提取的多维小火焰溶液,对跨临界LOX/GH2射流火焰中的多维小火焰效应进行了先验分析。结果表明,虽然传统的一维火焰求解方法可以很好地逼近射流火焰结构,但加入微分扩散有助于准确预测火焰前缘位置。进一步,对提取的小波进行了广义小波方程的渐近尺度分析和预算分析。研究发现,多维火焰效应确实对射流火焰有很大的影响。然而,火焰法向扩散比火焰切向扩散占优势。这些结果表明,对于跨临界LOX/GH2射流火焰,1D小火焰假设是合理的,在跨临界LOX/GH2射流火焰的建模中应注意考虑差分扩散效应。
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引用次数: 0
Large eddy simulation of transient leading edge propagation in a turbulent lifted hydrogen jet flame 湍流提升型氢射流火焰前缘瞬态传播的大涡模拟
IF 5.2 2区 工程技术 Q2 ENERGY & FUELS Pub Date : 2025-01-01 DOI: 10.1016/j.proci.2025.105827
Christoph D.K. Schumann , James C. Massey , Caleb J. Li , Nedunchezhian Swaminathan
A lifted turbulent jet flame involves partial premixing and exhibits a tribrachial flame structure at its leading edge (LE). Its propagation from the initial sparking location towards the final stabilisation height has rich physics. Large eddy simulation (LES) with flamelet-based reaction rate closure for partially premixed combustion is employed to study this propagation. The initial kernel grows radially in the rich region, and it is skewed by the oncoming flow as it is convected downstream. An LE is formed as the flame propagates radially into lean mixtures with low streamwise velocities. This LE encounters the lean limit, while a core flame continues to develop closer to the jet centreline, where the mixture reactivity and flow velocity are significantly large. Eventually, this core flame overtakes the LE in the lean mixture and upstream propagation ensues. The LE propagates mostly in the lean mixture, as the streamwise velocity in the vicinity of the jet core is high, although occasional rapid propagation is observed as the core flame encounters highly reactive mixture due to turbulence. Hence, the two flame branches are competing to form the LE. This behaviour is quite different to propagation in a lifted methane jet flame due to the increased reactivity and wider flammability limits of hydrogen. Turbulence plays a fundamental role during propagation for the formation of new upstream flame kernels, which evolve from pockets of hot reactants and fresh mixture. These kernels may be convected downstream causing the LE to recede. Eventually, the LE reaches a stationary state, and the flame root stabilises at a position where the burning mass flux is balanced by the flame normal advective mass flux. The LE does not encounter the value of the extinction dissipation rate for the mixture fraction during its evolution towards the stabilisation and at this location.
升力湍流射流火焰涉及部分预混,在前缘表现出三臂火焰结构。其从初始火花位置到最终稳定高度的传播具有丰富的物理性质。采用基于火焰的反应速率闭合大涡模拟(LES)对部分预混燃烧的这种传播进行了研究。初始核在富区呈放射状生长,并在向下游对流时被迎面而来的气流扭曲。当火焰沿径向传播成低流速的稀薄混合物时,就形成了LE。当核心火焰继续向靠近射流中心线的地方发展时,这种LE遇到了倾斜极限,在那里混合物的反应性和流动速度都非常大。最终,这个核心火焰在稀薄混合物中超过LE,然后上游传播。由于射流核心附近的流向速度高,LE主要在稀薄的混合物中传播,尽管当核心火焰遇到由于湍流引起的高度反应性混合物时,偶尔会观察到快速传播。因此,两个火焰分支正在竞争形成LE。由于氢气的反应性增加和可燃性限制,这种行为与在提升的甲烷喷射火焰中的传播完全不同。湍流在上游火焰核的形成过程中起着重要的作用,而上游火焰核是由热反应物和新鲜混合物形成的。这些核可能会向下游对流,导致LE后退。最终,LE达到稳态,火焰根部稳定在燃烧质量通量与火焰法向平流质量通量平衡的位置。在趋于稳定的过程中,在这个位置,LE不遇到混合分数的消光耗散率值。
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引用次数: 0
A theoretical study of 1-propanol H-abstractions and successive reactivity 1-丙醇h萃取及连续反应性的理论研究
IF 5.2 2区 工程技术 Q2 ENERGY & FUELS Pub Date : 2025-01-01 DOI: 10.1016/j.proci.2025.105928
Sarah N. Elliott , Maristella Di Teodoro , Simone Vari , Luna Pratali Maffei , Zeynep Serinyel , Océane Clement , Claire Grégoire , Eric L. Petersen , Olivier Mathieu , Guillaume Dayma , Carlo Cavallotti
A mechanistic understanding of alcohol pyrolysis and oxidation is critical to their effective integration into the fuel industry. 1-propanol (1-C3H7OH) is a promising biofuel and, moreover, its mechanism is a foundation for that of larger alcohols. As part of a combined modeling-experimental-theoretical investigation into 1-C3H7OH, we explore the H abstractions from 1-C3H7OH with ab initio transition state theory-based master equation (AI-TST-ME) evaluations for the two abstractors, OH and H, that are influential during 1-C3H7OH combustion. We report branching fractions between the resulting C3H7O radicals (i.e., at 1500 K, for the OH abstractor: 0.40, 0.27, 0.24, and 0.09 to α-, β−, γ−, and ο−C3H7O; for the H abstractor: 0.80, 0.14, 0.06, and 0.00). The sensitivity to level of theory as well as the influence of multidimensional torsional effects are evaluated for the abstractions by OH. Notably, the correction for torsional coupling for the α−C3H7O is about half of that as for the β−C3H7O – fully neglecting the multidimensional effect, then, would lead to significantly different branching fractions. The subsequent dissociation of the C3H7O radicals to nine products, including CH3, OH, ethene, ethyl radical, and H is also reported with AI-TST-ME computations. We find, however, that at relevant temperatures and pressures, very little 1-C3H7OH + OH collisionally stabilizes to thermalized C3H7O radicals (i.e., 7 % at 1 atm and 1500 K). Instead, the abundant, rovibrationally excited populations of C3H7O radicals promptly dissociate to the products. In the first exploration of the influence of non-thermal effects on the branching fractions to dissociation products, we find that H production enhances significantly (i.e., more than a factor of 2) at the cost of OH production.
了解酒精热解和氧化的机理对其有效整合到燃料工业至关重要。1-丙醇(1-C3H7OH)是一种很有前途的生物燃料,而且,它的机理为大醇的机理奠定了基础。作为1-C3H7OH的建模-实验-理论联合研究的一部分,我们利用基于过渡态理论的从头算主方程(AI-TST-ME)对影响1-C3H7OH燃烧过程的OH和H这两个抽象因子进行了评价,探讨了1-C3H7OH中H的抽象。我们报告了生成的C3H7O自由基之间的分支分数(即,在1500 K下,OH萃取剂:0.40,0.27,0.24和0.09到α-, β -, γ -和ο - C3H7O;对于H萃取剂:0.80,0.14,0.06和0.00)。评价了OH对理论层次的敏感性以及多维扭转效应对抽象的影响。值得注意的是,α - C3H7O的扭转耦合修正量约为β - C3H7O的一半,因此,完全忽略多维效应将导致明显不同的分支分数。随后的C3H7O自由基解离为九种产物,包括CH3, OH,乙烯,乙基自由基和H,也报道了ai - sts - me计算。然而,我们发现,在相应的温度和压力下,很少有1- c3h7oh + OH碰撞稳定为热化的C3H7O自由基(即在1atm和1500k时为7%)。相反,大量的、振动激发的C3H7O自由基迅速解离到产物上。在第一次探索非热效应对分支馏分对解离产物的影响时,我们发现以OH生产为代价,H的生产显著增加(即超过2倍)。
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引用次数: 0
Investigation of hot-spot-induced pre-ignition in methanol- and hydrogen-fueled spark-ignition engines 甲醇和氢燃料火花点火发动机的热点诱导预点火研究
IF 5.2 2区 工程技术 Q2 ENERGY & FUELS Pub Date : 2025-01-01 DOI: 10.1016/j.proci.2025.105932
D. Golc , S. Esposito , M. Khosravi , J. Beeckmann , H. Pitsch
The transition of the transport sector towards more sustainable propulsion requires the adoption of alternative fuels. Methanol and hydrogen are promising options because of their possible renewable production pathways, low to zero carbon content, low pollutant emission, and potential for reaching higher thermal efficiencies. A drawback is that hydrogen and methanol are more prone to hot-spot-induced pre-ignition (PI) due to their lower minimum ignition energy compared to conventional fuels. Hot-spot-induced PI can occur in engines due to hot surfaces acting as ignition points, which is a limiting factor for operation, safety and efficiency. Although undesirable in spark ignition engines (SI), hot-spot-induced ignition can facilitate the use of low-cetane fuels such as methanol and hydrogen in compression ignition engines (CI). Understanding the effects leading to hot-spot-induced pre-ignition is essential for both suppressing the phenomenon in SI engines and leveraging it in CI engines. This study investigates hot-spot-induced PI phenomena using an SI single-cylinder research engine featuring a prototype glow-plug equipped with an integrated thermocouple in order to create a controlled hot spot inside the combustion chamber. Methanol has been introduced in the combustion chamber with a direct injection (DI), while hydrogen with a port fuel injector (PFI). A parametric study was conducted using methanol and hydrogen to identify dependencies of PI events linked to certain engine operating parameters. A comprehensive data analysis featuring 3D Reynolds averaged Navier Stokes (RANS) and chemical kinetics simulations were conducted to explain the main mechanisms responsible for PI. Generally, hydrogen requires a higher hot-spot temperature to achieve pre-ignition compared to methanol. For methanol, this study provides insights into the dependencies of various parameters on the ignition timing in CI applications, allowing potentially to achieve a controllable CI combustion with glow-plug assistance. An important finding is that while methanol combustion can be effectively controlled through glow-plug temperature, the study demonstrates that such controllability is more challenging for hydrogen. Indeed, numerous parameters influencing hot-spot-induced ignition were identified. In particular, the local mixture composition near the glow-plug and elevated pressures were found to significantly impact the onset of PI, with higher pressures effectively suppressing pre-ignition. This counterintuitive behavior is explained by the inverse pressure dependence of ignition delay times for hydrogen and analyzed with reaction pathway analysis. Overall, it was observed that by adjusting the operating parameters, the potential hot-spot temperature required to trigger PI could be optimized, allowing for an increase of up to 100K. These insights are essential for developing s
运输部门向更可持续推进的过渡需要采用替代燃料。甲醇和氢气是很有前途的选择,因为它们可能的可再生生产途径,低至零碳含量,低污染物排放,以及实现更高热效率的潜力。与传统燃料相比,氢和甲醇的缺点是由于其最低点火能量较低,因此更容易发生热点诱导预点火(PI)。在发动机中,由于热表面充当着火点,可能会产生热点诱发PI,这是一个限制运行、安全和效率的因素。虽然在火花点火发动机(SI)中是不可取的,但热点诱发点火可以促进在压缩点火发动机(CI)中使用低十六烷燃料,如甲醇和氢。了解导致热点诱导预点火的影响对于抑制SI发动机中的现象和在CI发动机中利用它至关重要。为了在燃烧室内产生可控的热点,本研究使用SI单缸研究发动机来研究热点诱导的PI现象,该发动机具有配备集成热电偶的原型发光塞。甲醇通过直接喷射(DI)进入燃烧室,而氢气通过端口喷油器(PFI)进入燃烧室。使用甲醇和氢气进行了参数研究,以确定PI事件与某些发动机运行参数相关的依赖关系。采用三维雷诺平均纳维斯托克斯(RANS)和化学动力学模拟的综合数据分析来解释PI的主要机制。一般来说,与甲醇相比,氢气需要更高的热点温度来实现预点火。对于甲醇,这项研究提供了对CI应用中各种参数对点火时间的依赖关系的见解,从而有可能在辉光塞辅助下实现可控的CI燃烧。一个重要的发现是,虽然甲醇燃烧可以通过辉光塞温度有效地控制,但研究表明,这种可控性对氢气来说更具挑战性。事实上,确定了影响热点点火的许多参数。特别是,在辉光塞附近的局部混合物成分和高压被发现对PI的发生有显著影响,高压有效地抑制了预点火。用氢气点火延迟时间的逆压力依赖性解释了这种违反直觉的行为,并用反应路径分析对其进行了分析。总的来说,观察到通过调整操作参数,可以优化触发PI所需的潜在热点温度,允许增加高达100K。这些见解对于制定控制或防止PI的策略至关重要,以便在未来的发动机中更安全,更有效地使用甲醇和氢气。该实验研究为今后的工作和数值模型的验证提供了坚实的数据集。
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引用次数: 0
Super-resolution reconstruction of scalar fields from the pyrolysis of pulverised biomass using deep learning 基于深度学习的生物质粉状热解标量场的超分辨率重建
IF 5.2 2区 工程技术 Q2 ENERGY & FUELS Pub Date : 2025-01-01 DOI: 10.1016/j.proci.2025.105982
A. Shamooni , R. Cheng , T. Zirwes , O.T. Stein , A. Kronenburg
Recently, advanced deep-learning techniques have been successfully applied as deconvolution operators to super-resolve the low-resolution data in large-eddy simulation (LES). The super-resolution (SR) operator provides an approximate inverse to the filter operators in LES such that the under-resolved and un-resolved sub-grid information can be reconstructed from the resolved scales. In this work, a particle-aware attention-based conditional super-resolution generative adversarial network (PACASRGAN) is proposed for the fourfold SR of gas field scalars which are generated by the pyrolysis process in a hot turbulent flow laden with pulverised biomass particles. Multiple carrier-phase direct numerical simulations (DNS) of two-way coupled particle-laden flows with heat and mass transfer, that mimic the near-burner field of pulverised biomass combustion (PBC) systems, are carried out to build the training/testing datasets. The model performance is assessed in an a priori manner by investigating statistical quantities of interest for the modelling in LES of PBC. The results show that the proposed model can super-resolve the temperature and mixture fraction fields to a good accuracy and outperforms unconditional GAN models. Particles create localised sources/sinks via two-way coupling which sharpen scalar gradients in the subgrid. The particle mask and feature vector encode this localisation to improve the predictions of the generator. The scalar spectra, the conditional average of unresolved scalar variances, the probability density function (PDF), and the conditional average of the square of the mixture fraction gradient from the reconstructed fields follow the DNS values well. Slight deviations are observed at rich conditions in conditional statistics and at the tail of the PDFs. Nonetheless, the results demonstrate that SR is applicable to two-way coupled particle-laden flows with heat and mass transfer, providing reasonably accurate high-resolution information for both the entire gas field and particle positions.
近年来,先进的深度学习技术已成功地作为反卷积算子应用于大涡模拟(LES)中低分辨率数据的超分辨。超分辨率(SR)算子提供了一种近似逆的滤波算子,可以从已分辨的尺度重构出未分辨和未分辨的子网格信息。在这项工作中,提出了一种基于粒子感知注意力的条件超分辨率生成对抗网络(PACASRGAN),用于在充满颗粒状生物质颗粒的热湍流中热解过程产生的气田标量的四倍SR。通过模拟生物质燃烧(PBC)系统的近燃烧器场,对双向耦合颗粒负载流进行多载波相位直接数值模拟(DNS),以建立训练/测试数据集。通过调查PBC的LES建模感兴趣的统计量,以先验的方式评估模型性能。结果表明,该模型可以超分辨温度场和混合分数场,且精度较高,优于无条件GAN模型。粒子通过双向耦合创建局部源/汇,从而在子网格中锐化标量梯度。粒子掩模和特征向量对这种定位进行编码,以提高生成器的预测能力。重构场的标量谱、未解析标量方差的条件平均值、概率密度函数(PDF)和混合分数梯度平方的条件平均值与DNS值吻合较好。在条件统计的丰富条件下和pdf的尾部观察到轻微的偏差。尽管如此,结果表明,SR适用于具有传热传质的双向耦合颗粒负载流动,为整个气田和颗粒位置提供了相当准确的高分辨率信息。
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引用次数: 0
Full-spectrum fitting method applied to YAG:Dy : Impact of oxygen content and laser fluence on wall-temperature phosphor thermometry for combustion 应用于YAG:Dy的全光谱拟合方法:氧含量和激光辐照量对燃烧用壁温荧光粉测温的影响
IF 5.2 2区 工程技术 Q2 ENERGY & FUELS Pub Date : 2025-01-01 DOI: 10.1016/j.proci.2025.105845
Tobias Guivarch , Hugo Samson , Jérôme Bonnety , Jessy Elias , Sébastien Ducruix , Clément Mirat , Christopher Betrancourt , Guilhem Dezanneau , Ronan Vicquelin
Achieving the European net-zero greenhouse gas emissions target requires the development of sustainable combustion processes across various industrial sectors. These promising alternatives introduce new challenges, such as modifying wall heat transfer. Accurate surface temperature measurements are essential for understanding these effects. Laser-Induced Phosphorescence (LIP) provides a semi-invasive method that exploits the temperature-dependent phosphorescence spectra of thermographic phosphors. YAG:Dy is a thermographic phosphor that emits a phosphorescence signal over the range of 300 K to 2000 K. However, its poor sensitivity with the intensity ratio method and its low sensitivity at lower temperatures with the lifetime method limit its use to high-temperature combustion applications. Additionally, its sensitivity to ambient oxygen reduces the accuracy of those methods. This study evaluates the performance of the Full-Spectrum Fitting (FSF) method, developed by the EM2C Laboratory in Lechner et al. (2022), when applied to YAG:Dy. The method leverages the phosphor’s spectral temperature dependence over a wide range (303 to 1773 K), achieving an accuracy of 0.3 K and a precision of 8.4 K under given experimental conditions. It is observed that there is a laser fluence threshold above which temperature determination using the FSF method becomes independent of laser fluence. The impact of YAG:Dy’s sensitivity to oxygen concentration on temperature measurement is quantified. In the worst case, uncertainty in oxygen concentration can introduce a temperature error ranging from 7 to 19 K. Guidelines are provided to help mitigate these sensitivities in combustion applications.
实现欧洲温室气体净零排放目标需要在各个工业部门开发可持续燃烧过程。这些有希望的替代方案带来了新的挑战,例如修改壁面传热。精确的表面温度测量对于理解这些影响至关重要。激光诱导磷光(LIP)提供了一种半侵入性的方法,利用热成像荧光粉的温度依赖性磷光光谱。YAG:Dy是一种热成像荧光粉,在300k到2000k的范围内发出磷光信号。然而,强度比法灵敏度较差,寿命法在较低温度下灵敏度较低,限制了其在高温燃烧应用中的应用。此外,它对环境氧的敏感性降低了这些方法的准确性。本研究评估了由Lechner等人(2022)的EM2C实验室开发的全谱拟合(FSF)方法在应用于YAG:Dy时的性能。该方法利用荧光粉在宽范围内(303至1773 K)的光谱温度依赖性,在给定的实验条件下实现了0.3 K的精度和8.4 K的精度。我们观察到存在一个激光通量阈值,超过这个阈值,用FSF方法测定温度就与激光通量无关了。定量分析了YAG:Dy对氧浓度的敏感性对测温的影响。在最坏的情况下,氧浓度的不确定性会导致7到19k的温度误差。提供了指南,以帮助减轻燃烧应用中的这些敏感性。
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引用次数: 0
Single-step flame synthesis of surface-disordered titania nanoparticles in Hencken-supported hydrogen premixed flames hencken负载氢预混火焰中一步火焰合成表面无序纳米二氧化钛
IF 5.2 2区 工程技术 Q2 ENERGY & FUELS Pub Date : 2025-01-01 DOI: 10.1016/j.proci.2025.105944
Hu Meng , Yuhao Nie , Junqing Chen , Yun Huang , Yihua Ren
Surface-disordered TiO2 nanoparticles exhibiting various colors including grey, yellow, blue, and black have attracted considerable attention owing to their outstanding photocatalytic activity, attributed to their narrow bandgap and thus enhanced absorption of solar energy. In this study, we have successfully synthesized TiO2 nanoparticles with tailored surface-disorder structures using a well-controlled H2/O2/N2 premixed Bunsen flame supported by multi-element diffusion flames in a single step. To systematically examine the influence of gas composition on surface-disorder layer formation, we designed four distinct flame conditions maintaining consistent flame structures, adiabatic temperatures, and precursor concentrations while varying the atmospheric composition. In-situ OH-planar laser induced fluorescence (PLIF), spontaneous Raman scattering (SRS), and 2D phase-selective laser-induced breakdown spectroscopy (PS-LIBS) has been employed to characterize the flame structures, temperature profiles, atmospheric conditions, and particle volume fraction across all flame conditions. The in-situ diagnostic results verify that the designed flame conditions have identical particle formation and growth route in flames but with varying gas-particle interactions under different post-flame atmospheres. Ex-situ characterization through high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) of the synthesized nanoparticles demonstrates that TiO2 nanoparticles with surface disorder structure and rutile phase are more preferentially formed under reducing atmospheric condition. Furthermore, both ex-situ UV-Vis spectra and in-situ PS-LIBS indicated that a higher H2 mole fraction in the post-flame region can enhance the light absorption of the synthesized nanoparticles attributed their stronger surface disorder structures.
表面无序的TiO2纳米颗粒呈现出灰色、黄色、蓝色和黑色等多种颜色,由于其窄小的禁带隙,从而增强了对太阳能的吸收,因此具有出色的光催化活性,引起了人们的广泛关注。在这项研究中,我们利用控制良好的H2/O2/N2预混本生火焰,在多元素扩散火焰的支持下,一步成功地合成了具有定制表面无序结构的TiO2纳米颗粒。为了系统地研究气体成分对表面无序层形成的影响,我们设计了四种不同的火焰条件,在改变大气成分的同时保持一致的火焰结构、绝热温度和前驱体浓度。采用原位oh -平面激光诱导荧光(PLIF)、自发拉曼散射(SRS)和二维相位选择激光诱导击穿光谱(PS-LIBS)表征了所有火焰条件下的火焰结构、温度分布、大气条件和颗粒体积分数。现场诊断结果验证了所设计的火焰条件具有相同的颗粒在火焰中的形成和生长路线,但在不同的火焰后气氛下,气-颗粒相互作用不同。通过高分辨率透射电镜(HRTEM)和x射线衍射(XRD)对合成的纳米颗粒进行了离地表征,结果表明,在还原大气条件下,TiO2纳米颗粒更倾向于形成具有表面无序结构和金红石相的纳米颗粒。此外,非原位UV-Vis光谱和原位PS-LIBS均表明,火焰后区域H2摩尔分数越高,合成的纳米颗粒的光吸收能力越强,这是由于其表面无序结构越强。
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引用次数: 0
Turbulence-flame interactions in high-Karlovitz-number lean premixed hydrogen piloted jet flames 高karlovitz数稀薄预混氢操纵射流火焰的湍流-火焰相互作用
IF 5.2 2区 工程技术 Q2 ENERGY & FUELS Pub Date : 2025-01-01 DOI: 10.1016/j.proci.2025.105868
G.S. Russell , T.L. Howarth , A.W. Skiba , C.D. Carter , A.J. Aspden
Turbulence is known to exaggerate the thermodiffusive response in lean premixed hydrogen flames. The mean local flame speed has been demonstrated to increase with Karlovitz number, but the range of validity has not been established; furthermore, several studies observed a decrease in turbulent/local flame speed at moderately-high Karlovitz numbers. All of the aforementioned DNS studies were conducted in the canonical flame-in-a-box (FIAB) configuration. To investigate these observations further and to establish whether similar behaviour is observed in realistic configurations, six DNS have been conducted to reproduce a laboratory piloted jet flame. The jet internal diameter was 7.04 mm, with bulk inflow velocities from 6 m/s to 192 m/s (increasing in factors of 2), corresponding to jet Reynolds numbers of 2,500 to 80,000; the reactants had an equivalence ratio of φ  =  0.32 at atmospheric conditions. Complementary turbulent FIAB simulations are used to compare the realistic configuration with the canonical abstraction. The mean local flame speed is found to peak in the 48 m/s case, after which a decrease is observed; the transition is found to occur at slightly higher Karlovitz number in the FIAB configuration. A key difference between the two configurations is shown to be that the jet flames are effectively unconfined, whereas the turbulent FIAB area confined by the periodic boundary conditions (so there is a limit on how much flame surface area can be generated in a given volume). Finally, at the highest inflow speed, the jet flame appears to become lifted (there is a significant region near the inlet with little-to-no heat release), and turbulence-flame interaction is shown to be distinctly different to that at lower Karlovitz numbers; the thermodiffusive response is suppressed without the flame becoming fully distributed.
在稀薄的预混氢火焰中,湍流被认为会夸大热扩散反应。局部平均火焰速度随Karlovitz数的增加而增加,但其有效范围尚未确定;此外,一些研究发现,在中等高的卡洛维茨数下,湍流/局部火焰速度会下降。前面提到的所有DNS研究都是在典型的FIAB配置中进行的。为了进一步研究这些观察结果,并确定是否在实际配置中观察到类似的行为,进行了6次DNS来重现实验室驾驶射流火焰。射流内径为7.04 mm,整体入流速度为6 ~ 192 m/s(增加2倍),对应的射流雷诺数为2500 ~ 80000;在常压条件下,反应物的等效比为φ = 0.32。利用互补湍流FIAB模拟,比较了实际构型与规范抽象的异同。局部平均火焰速度在48 m/s时达到峰值,之后开始下降;在FIAB结构中,这种转变发生在略高的Karlovitz数处。两种结构之间的一个关键区别是,射流火焰实际上是无限制的,而湍流FIAB区域受到周期性边界条件的限制(因此在给定体积内可以产生多少火焰表面积是有限制的)。最后,在最高入流速度下,射流火焰出现升腾(在入口附近有一个明显的区域,几乎没有热量释放),湍流-火焰相互作用与较低Karlovitz数时明显不同;在火焰没有完全分布的情况下,热扩散响应被抑制。
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引用次数: 0
Hydrogen fluoride emissions from lithium-ion batteries during induced thermal runaway via in situ laser spectroscopy 锂离子电池在诱导热失控过程中的氟化氢排放
IF 5.2 2区 工程技术 Q2 ENERGY & FUELS Pub Date : 2025-01-01 DOI: 10.1016/j.proci.2025.105800
Yi Yan, Nicolas S.B. Jaeger, R. Mitchell Spearrin
Improved understanding of hydrogen fluoride (HF) emissions from lithium-ion battery fires, including the temporal dynamics, is needed to optimize fire response and protection. Due to the high polarity of HF and its associated surface adsorption and reactivity, most traditional sensing methods are prone to error and slow response due to issues with sampling or surface interactions. To address these limitations, an in situ tunable diode laser absorption spectrometer is developed to achieve real-time measurements of HF emissions during dynamic battery fires with a temporal resolution of milliseconds, and with detection limits of single parts per million along with several orders of magnitude of dynamic range. The laser spectrometer is used in situ to perform measurements near the fire source so that the fire dynamics and the transient behavior of HF emissions can be more accurately characterized. Thermal runaway and fire/explosion conditions of model 18650 lithium-ion batteries are simulated in a conical radiative heater, and HF measurements are performed online via an optical access port in the effluent exhaust. By varying the radiative heating flux of the conical heater and the initial state of charge of the batteries, different characteristics of the safety venting and thermal runaway behavior of lithium-ion batteries and the corresponding emissions of toxic HF gas are measured. These findings provide valuable insights into the dynamics of lithium-ion battery fires and will aid in the development of strategies to mitigate their associated risks.
需要更好地了解锂离子电池火灾产生的氟化氢(HF)排放,包括时间动态,以优化火灾响应和保护。由于HF的高极性及其相关的表面吸附和反应性,大多数传统的传感方法容易由于采样或表面相互作用的问题而产生误差和缓慢的响应。为了解决这些限制,开发了一种原位可调谐二极管激光吸收光谱仪,以实现动态电池火灾期间高频辐射的实时测量,时间分辨率为毫秒,检测限为百万分之一,动态范围为几个数量级。激光光谱仪用于火源附近的原位测量,以便更准确地表征火灾动力学和HF发射的瞬态行为。在锥形辐射加热器中模拟了18650型锂离子电池的热失控和火灾/爆炸条件,并通过排气口的光学接入端口在线进行了高频测量。通过改变锥形加热器的辐射热流密度和电池的初始充电状态,测量了锂离子电池安全排气和热失控行为的不同特征以及相应的有毒HF气体排放。这些发现为了解锂离子电池火灾的动态提供了有价值的见解,并将有助于制定减轻相关风险的策略。
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引用次数: 0
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Proceedings of the Combustion Institute
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