Combustion and Flame最新文献

{"title":"A general formalism for determining the unburnt composition in multi-stream species transport-based CFD simulations","authors":"Simone Castellani ,&nbsp;Gianmarco Lemmi ,&nbsp;Pier Carlo Nassini ,&nbsp;Roberto Meloni ,&nbsp;Antonio Andreini","doi":"10.1016/j.combustflame.2025.114128","DOIUrl":"10.1016/j.combustflame.2025.114128","url":null,"abstract":"<div><div>The imperative to decarbonise combustion necessitates technical solutions that increasingly rely on the concurrent utilisation of different fuels and/or oxidisers. The complexity of the reactive mixture compositions in such scenarios poses additional challenges from a CFD modelling perspective. While species transport models can generally describe multi-stream combustion problems directly, the definition of turbulence-chemistry interaction closures or the proper comprehension of combustion regimes often requires the reconstruction of the non-reactive mixing field. This work proposes a general comprehensive formalism for determining the unburnt composition in multi-stream combustion environments. The method relies on the elemental mass fraction conservation for the definition of a linear system that can be solved at runtime to retrieve the local unburnt mixture composition. The introduced formalism allows to assess the number of auxiliary stream-tracking scalars <span><math><mrow><mi>a</mi><mo>−</mo><mi>p</mi><mi>r</mi><mi>i</mi><mi>o</mi><mi>r</mi><mi>i</mi></mrow></math></span>, thereby minimising computational efforts and effectively enabling the use of the inherent information within the set of transported species. The study presents an application example where a dual-fuel turbulent combustion scenario is numerically investigated. In this context, the consistency of the method with respect to the use of passive scalars has been discussed with and without the species equi-diffusivity assumption. A procedure for the <span><math><mrow><mi>a</mi><mo>−</mo><mi>p</mi><mi>r</mi><mi>i</mi><mi>o</mi><mi>r</mi><mi>i</mi></mrow></math></span> estimation of the error introduced by the species preferential diffusion has been proposed, providing insights about the expected uncertainty on the predicted mixture composition and the respective flame properties.</div><div><strong>Novelty and Significance Statement</strong></div><div>The determination of the non-reactive mixing field is crucial for understanding reactive CFD simulations based on species transport. Additionally, in turbulent combustion models, knowing the unburnt composition is often a pivotal requirement for the model closure. While recalculated mixture fractions can determine the unburnt composition in dual-stream problems, this approach is inappropriate for multi-stream problems. This research introduces a novel generalised method for determining unburnt mixture composition in multi-stream combustion scenarios using CFD calculations based on species transport. The proposed method minimises the need for additional passive scalars by efficiently utilising existing information from the solved equations and boundary conditions, leveraging elemental mass fraction conservation.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"276 ","pages":"Article 114128"},"PeriodicalIF":5.8,"publicationDate":"2025-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143725034","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"N-containing pollutant formation in pyrrole counterflow diffusion flames","authors":"Bingjie Chen ,&nbsp;Sebastian Faller ,&nbsp;Luna Pratali Maffei ,&nbsp;Andrea Nobili ,&nbsp;Matteo Pelucchi ,&nbsp;Xingcai Lu ,&nbsp;Heinz Pitsch","doi":"10.1016/j.combustflame.2025.114136","DOIUrl":"10.1016/j.combustflame.2025.114136","url":null,"abstract":"<div><div>Biomass conversion through direct combustion (energy production) or pyrolysis (bio-oil production) are novel concepts to reduce CO₂ emission in the energy sector. However, the nitrogen content in biomass feedstocks may result in elevated N-containing pollutants, e.g., NO_x, NH₃, HCN, and nitriles, yet their formation chemistry remains unclear. In this work, we studied N-containing pollutant formation in counterflow diffusion flames fuelled by pyrrole, a biomass tar surrogate component that accounts for the majority of fuel nitrogen. 27 species, including 8 N-containing species, were identified and measured in three flames with designed boundary conditions to reveal the influence of flame temperature and methane addition. Species mole fraction comparisons showed that methane addition and higher flame temperature promoted C₂–C₆ hydrocarbon formation, but mole fractions of N-containing species did not change much, reflecting less dependence on flame temperature or hydrocarbons in the species pool. An existing kinetic model for pyrrole pyrolysis and combustion was developed by updating the formation reactions of N-containing species based on recent literature studies. Numerical simulations using the kinetic model well reproduced mole fractions of most species except for NO and NO₂. Model analyses illustrated the nitrogen conversion pathways from pyrrole to individual N-containing pollutant species, and indicated the possible reactions for underestimated mole fractions of NO and NO₂. This work contributes to a better understanding of the combustion properties of N-containing fuels and N-containing pollutants in the context of biomass energy clean utilization.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"276 ","pages":"Article 114136"},"PeriodicalIF":5.8,"publicationDate":"2025-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143725033","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A data-driven method to optimize soot kinetics based on uncertainty quantification and the active subspace approach","authors":"Xingyu Su ,&nbsp;Andrea Nobili ,&nbsp;Feixue Cai ,&nbsp;Alberto Cuoci ,&nbsp;Alessio Frassoldati ,&nbsp;Hua Zhou ,&nbsp;Matthew J. Cleary ,&nbsp;Zhuyin Ren ,&nbsp;Assaad R. Masri ,&nbsp;Tiziano Faravelli","doi":"10.1016/j.combustflame.2025.114137","DOIUrl":"10.1016/j.combustflame.2025.114137","url":null,"abstract":"<div><div>This paper introduces a novel approach integrating uncertainty quantification (UQ) and data-driven techniques that aim to optimize soot particle size distributions (PSDs) using an existing soot kinetic model. Leveraging the active subspace (AS) method, the influential parameters governing the overall soot production and several representative PSDs are identified. Gradient descent techniques are employed to optimize the kinetic parameters simultaneously with reference to experimental measurements of burner stabilized stagnation (BSS) flames. The optimization process is rigorously validated against experimental data and the response surface predictions, demonstrating robustness and generalization capabilities across different cases. It is found that while the soot volume fraction was adequately predicted, the iterative UQ-assisted gradient descent technique can improve the prediction of PSDs but fails to fully reproduce the experimentally observed bimodality. This confirms the need for future improvements in the sectional kinetics model. In this regard, the analysis performed points at the need of distinguishing the coagulation kinetics of liquid-like and solid primary particles. With such future improvements, whose implementation is guided by the combined UQ and data-driven approach, soot modeling may advance into a data-driven era, minimizing reliance on expert knowledge alone.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"276 ","pages":"Article 114137"},"PeriodicalIF":5.8,"publicationDate":"2025-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143714497","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Investigation of combustion instability caused by different fuels combustion induced backpressure in a scramjet engine","authors":"Guangming Du ,&nbsp;Erda Chen ,&nbsp;Changchun Yan ,&nbsp;Yitong Zhao ,&nbsp;Yueqian Zhou ,&nbsp;Ye Tian ,&nbsp;Jialing Le","doi":"10.1016/j.combustflame.2025.114142","DOIUrl":"10.1016/j.combustflame.2025.114142","url":null,"abstract":"<div><div>The study examines the influence of kerosene and ethylene fuels on combustion instability characteristics at various equivalence ratios, with the objective of investigating supersonic combustion instability induced by combustion-induced backpressure. It was revealed that flow separation, triggered by this backpressure, plays a crucial role in combustion instability. The propagation of flow separation upstream can be classified into three typical flow states, with the timing between these states dependent on the fuel type and equivalence ratio. Hysteresis effects were noted during the flow separation propagation in both upstream and downstream directions. Different fuels and equivalence ratios have a direct impact on the magnitude of combustion-induced backpressure. Lower backpressure is linked to decreased combustion intensity and a flame front position closer to the upstream region, resulting in distinct combustion instability characteristics. Spectral analysis indicated that low-frequency oscillations (100–200 Hz) are associated with flame flashback and blowoff, while mid-to-low frequency oscillations (300–1000 Hz) originate from oscillations between the upstream and downstream regions of the combustor and the cavity shear layer. High-frequency oscillations (1000–3000 Hz) are connected to acoustic self-excited oscillations within the cavity. Correlation analysis was performed between the flame luminosity intensity in different combustor regions and the total luminosity intensity to clarify the oscillation characteristics of the cavity recirculation zone and the cavity shear layer. A method was developed using a weighted Damköhler number to evaluate combustion stability, taking into account the contributions of the cavity recirculation zone stabilized mode and the cavity shear layer stabilized mode. The results of this method regarding flame stability are in good agreement with the experimental observations.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"276 ","pages":"Article 114142"},"PeriodicalIF":5.8,"publicationDate":"2025-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143714499","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A Fundamental investigation of the pyrolysis chemistry of oxymethylene ethers. Part II: Experiments and comprehensive model analysis","authors":"Kevin De Ras ,&nbsp;Olivier Herbinet ,&nbsp;Frédérique Battin-Leclerc ,&nbsp;Andreas Eschenbacher ,&nbsp;Marvin Kusenberg ,&nbsp;Robin J. Varghese ,&nbsp;Thomas Panaget ,&nbsp;Oğuzhan Akin ,&nbsp;Yann Fenard ,&nbsp;Luc-Sy Tran ,&nbsp;Guillaume Vanhove ,&nbsp;Joris W. Thybaut ,&nbsp;Kevin M. Van Geem","doi":"10.1016/j.combustflame.2025.114122","DOIUrl":"10.1016/j.combustflame.2025.114122","url":null,"abstract":"<div><div>Oxymethylene ethers (OMEs) form a high-potential family of synthetic chemicals to replace fossil-based fuels. These alternative liquid energy carriers can contribute to a circular carbon economy when synthesized through carbon capture and utilization technology using renewable electricity, so-called e-fuels. Despite the potential to significantly reduce greenhouse gas and particulate matter emissions and their favorable ignition characteristics, the radical decomposition chemistry of long-chain OMEs remains largely unexplored. Pyrolysis of small OMEs is well understood. Still, there is limited data available for long-chain OMEs, such as oxymethylene ether-3 (OME-3), oxymethylene ether-4 (OME-4), and oxymethylene ether-5 (OME-5). In this study, the pyrolysis of these long-chain OMEs is investigated by combined experimental and kinetic modeling work. Six new datasets are acquired from experimental units with tubular and jet-stirred reactors. The thermal decomposition is examined across a broad range of reaction conditions, which enables studying both the primary and secondary decomposition chemistry. At low temperatures, smaller OMEs and formaldehyde are the major decomposition products, whereas at high temperatures H₂, CO, and methane become the dominant products. The yield of species with carbon-carbon bonds remains low. The kinetic model based on first principles from Part I, consisting solely of elementary reaction steps, is validated against the newly acquired experimental datasets. This new model outperforms literature models and predicts experimental trends of important products, on average, within the experimental uncertainty margin without fitting model parameters. Comprehensive model analysis by means of rate of production and sensitivity analyses indicates that formaldehyde elimination reactions, which yield smaller OMEs, dominate the thermal decomposition.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"275 ","pages":"Article 114122"},"PeriodicalIF":5.8,"publicationDate":"2025-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143714940","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Investigation of the pure ammonia flames in a novel two-stage burner","authors":"M. Srinivasarao ,&nbsp;Giancarlo Sorrentino ,&nbsp;Mara de Joannon ,&nbsp;V. Mahendra Reddy","doi":"10.1016/j.combustflame.2025.114131","DOIUrl":"10.1016/j.combustflame.2025.114131","url":null,"abstract":"<div><div>Ammonia's slow chemical kinetics and fuel-bound NOx emissions present challenges for combustion applications. However, its carbon-free nature, easy storage and transport, and high hydrogen content have attracted growing research interest. To improve the burning efficiency of pure ammonia flames, this study introduces a novel burner design with two reactor sets, aimed at achieving stable ammonia-air flames with reduced NOx zero NH₃ slip. Experiments are conducted and successfully stabilised the pure ammonia flames under the wide range of global equvalence ratios (0.3-1.3) and thermal intensities (∼1.5 MW/m³ to ∼9.2 MW/m³). Emissions of NH₃, NO, and NO₂, along with temperatures at various combustor levels, are measured. Computational simulations using Large Eddy Simulation (LES) are conducted to study flame dynamics and mixing in pure ammonia flames. The results indicated that the new burner design enhanced flame stability (0.3-1.3), improved mixing, achieved nearly zero NH₃ slip, and reduced NOx levels in non-premixed ammonia-air flames. Both experimental and predicted data revealed that higher thermal intensities are key to reducing NH₃ and NOx emissions across all equivalence ratios. At lower thermal outputs (10 kW and 20 kW), minimal NH₃ emissions were noted at rich conditions (1.3), while higher thermal outputs completely eliminated NH₃ emissions. The burner's air staging and recuperative design resulted in lower NO emissions compared to previous studies, with the lowest NO levels (420, 302, 390, and 299 ppm) at 10, 20, 40, and 60 kW, respectively, without NH₃ emissions. Rich conditions produced well-distributed flames at 40 kW and 60 kW. A chemical reaction network (CRN) analysis showed the influence of O₂ availability and thermal intensities on NO emissions, confirming that uniform mixing from tangential air inlets effectively controlled ammonia consumption.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"276 ","pages":"Article 114131"},"PeriodicalIF":5.8,"publicationDate":"2025-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143714496","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Insights into the scalar structures in turbulent diffusion flames with progressive H2 addition using 1D spontaneous Raman scattering and simultaneous PIV-OH PLIF","authors":"Kuppuraj Rajamanickam ,&nbsp;Ariff Magdoom Mahuthannan ,&nbsp;Corine Lacour ,&nbsp;Said Idlahcen ,&nbsp;Armelle Cessou ,&nbsp;David Honoré ,&nbsp;Bertrand Lecordier","doi":"10.1016/j.combustflame.2025.114129","DOIUrl":"10.1016/j.combustflame.2025.114129","url":null,"abstract":"<div><div>This paper examined the effect of H₂ enrichment in a primary fuel (CH₄) on turbulent flame features using 1D spontaneous Raman scattering (SRS) and simultaneous particle Image Velocimetry (PIV), OH-Planar Laser Induced Fluorescence (PLIF) measurements. The experiments are conducted in a canonical non-premixed bluff body burner operating under typical central fuel jet-dominated flow mode. Downstream of the bluff body, the flow exhibits complex patterns, and it can be globally categorized into three successive zones: recirculation, neck, and jet-like zones. The flame undergoes local extinction in the neck zone, where the local flow-induced hydrodynamic strain rate (κ_hyd) is much higher than the flame extinction strain rate (κ_ext). It is well known that H₂ enrichment increases κ_ext and thus modifies the probability of localized flame extinctions in the neck zone. Additionally, recent studies have shown the significance of preferential diffusion effects of H₂ in H₂ + CH₄ bluff body stabilized premixed and turbulent jet diffusion flames. Although 1D SRS measurements in canonical jet and bluff body stabilized non-premixed flames were studied extensively, to the best of our knowledge, differential diffusion has not been reported earlier in the non-premixed bluff body burner fueled with progressive H₂ addition. To better understand this phenomenon, five H₂ enrichment levels are considered: 0 %, 10 %, 30 %, 50 % and 80 % (in vol.). The simultaneous PIV and OH-PLIF measurements revealed the presence of local extinctions in the cases of H₂ enrichment ≤ 30 %, while local extinctions are not witnessed for H₂ = 50, 80 %. The conditional PDFs of the temperature in mixture fraction space obtained from the 1D SRS further confirmed this observation. Furthermore, the local instantaneous hydrogen/methane mass fraction ratio has been estimated to evaluate the differential diffusion effects. The results showed the dominance of the differential diffusion in the burner's near field, while the strong turbulence mixing effect weakens the differential diffusion in the far field.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"276 ","pages":"Article 114129"},"PeriodicalIF":5.8,"publicationDate":"2025-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143714500","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Panoramic vision analysis of burning aluminum droplet and oxide cap with 360-degree microscopic photography","authors":"Yu Wang ,&nbsp;Yang Zhang ,&nbsp;Hang Zhang ,&nbsp;Shixi Wu ,&nbsp;Weiqiang Xiong ,&nbsp;Wen Ao ,&nbsp;Dongping Chen ,&nbsp;YingChun Wu ,&nbsp;Xuecheng Wu","doi":"10.1016/j.combustflame.2025.114108","DOIUrl":"10.1016/j.combustflame.2025.114108","url":null,"abstract":"<div><div>The aluminum agglomerate surfaces serve as the essential interfaces for heat and mass transfer processes during combustion, with the attached oxide cap exerting a significant effect on the asymmetrical spatial distribution of agglomerate physical properties. Therefore, understanding the surface characterization and its dynamic evolution during aluminum combustion is important. However, significant challenges exist in visualizing and measuring agglomerate surfaces due to the micrometer-scale size, extremely rapid dynamic evolution, asymmetric three-dimensional morphology, and complex combustion behaviors. Traditional methods are limited in providing three-dimensional, in situ measurements of agglomerate surfaces under the propellant-burning environment. Thus, a panoramic vision analysis method is proposed to achieve 360-degree visualization and measurement of agglomerate surfaces. A high-speed panoramic microscopic imaging system up to 30 kHz is established, composed of two high-speed cameras positioned opposite each other to capture the panoramic view of agglomerates. A data processing pipeline, incorporating an artificial intelligence segmentation algorithm and an ellipsoid geometric model, is developed to reconstruct three-dimensional models of agglomerates with varying diameters over time. The oxide cap distributions and dynamic behaviors, such as rotation and drift on the droplet surface, are visualized. Quantitative measurements of oxide cap and droplet areas are also obtained, with oxide cap area ratios ranging from 10% to 40%. This study provides a method for visualization and quantitative measurement of agglomerate surfaces, offering a tool for further research on the mechanism of oxide cap dynamics on surfaces.</div><div><strong>Novelty and significance statement</strong></div><div>The novelty of this work lies in proposing a 360-degree panoramic vision analysis method, which enables three-dimensional surface visualization and quantitative measurement of burning droplets and oxide caps. A high-speed panoramic microscopic imaging system, operating at up to 30 kHz, is established by positioning two high-speed cameras opposite each other to capture the front and back sides of the agglomerates simultaneously. The experimental results demonstrate that the proposed method is competent in reconstructing three-dimensional models of agglomerates with varying diameters over time, allowing for visualizing the evolution of the oxide cap distribution and drift on the droplet surface. Quantitative measurements of the oxide cap and droplet areas are obtained, with the oxide cap area ratio ranging from 10% to 40%. This method provides technical support for deeper insights into the analysis of oxide cap dynamics.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"276 ","pages":"Article 114108"},"PeriodicalIF":5.8,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143697464","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Boundary layer flashback of H2/Air premixed flames in a swirling flow around a central body","authors":"Justin Bertsch ,&nbsp;Thierry Poinsot ,&nbsp;Nicolas Bertier","doi":"10.1016/j.combustflame.2025.114123","DOIUrl":"10.1016/j.combustflame.2025.114123","url":null,"abstract":"<div><div>Fast and thin premixed hydrogen flames can lead to flashback scenarios which are unusual, especially for swirled configurations. Flashback can occur far from all walls, in the bulk flow, if the flow speed is less than the flame speed: this is a scenario which is usually avoided by increasing flow rates. However, flashback can also occur near walls where the flow speed goes to zero. Injector walls boundary layers always contain a zone where the local flow speed is less than the flame speed, even if the bulk flow velocity is large. The size of this zone is controlled by the velocity gradient at the wall which is the classical parameter used to predict flashbacks in boundary layers.</div><div>In this study, flashback of lean hydrogen–air flames is computed using DNS (Direct Numerical Simulation)(flame resolved). Without swirl, results are compared and validated against experimental measurements and usual flashback criteria based on wall velocity gradient. DNS are also performed with swirl in a sector of an annular chamber, providing maps of flashback occurrence as function of swirl number and wall velocity gradient. Results show that swirl enhances flashback propensity and that thermodiffusive effects must be accounted to build a flashback criteria, indeed very lean H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> flames flashback for flow speeds higher than expected.</div><div><strong>Novelty and significance</strong></div><div>Almost all injection systems designed for hydrogen face a new, key issue in terms of operability: flashback. This study presents for the first time an analysis of the combined effects on flashback of the velocity gradients at the wall and of swirl. DNS of a swirling flow around a central body are performed and flashback maps are produced in a (swirl-velocity gradient) diagram of direct use for systems injecting lean premixed hydrogen–air mixtures.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"276 ","pages":"Article 114123"},"PeriodicalIF":5.8,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143697762","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A comparative study on the effects of NO2 addition on the auto-ignition behavior of n-heptane, iso-octane and toluene at engine relevant conditions","authors":"Shijun Dong ,&nbsp;Da Yao ,&nbsp;A. Abd El-Sabor Mohamed ,&nbsp;Jinhua Li ,&nbsp;Wenxue Gao ,&nbsp;Yang Cao ,&nbsp;Zhaowen Wang ,&nbsp;Jinhu Liang ,&nbsp;Henry J. Curran ,&nbsp;Xiaobei Cheng","doi":"10.1016/j.combustflame.2025.114118","DOIUrl":"10.1016/j.combustflame.2025.114118","url":null,"abstract":"<div><div>It is necessary for gasoline surrogate models to simulate the effect of NOx addition on fuel auto-ignition behavior, as NOx can affect engine combustion via exhaust gas recirculation (EGR). Toluene is often used as a representative aromatic component in gasoline surrogate models, and hence it is important to investigate the effect of NOx addition on its auto-ignition behavior and to fully understand the interaction chemistry between toluene and NOx. In this paper, high-pressure shock tubes and a rapid compression machine are used to measure the ignition delay times (IDTs) of toluene in ‘air’ mixtures with and without the addition of nitrogen dioxide (NO₂), at a pressure of 20 atm and at temperatures in the range 600–1400 K. The IDTs of <em>n</em>-heptane, <em>iso-</em>octane and a mixture of toluene/<em>n</em>-heptane/<em>iso-</em>octane are measured at the same conditions for comparison. The experimental results show that the auto-ignition behavior of toluene exhibits significantly different sensitivity to NO₂ addition compared to <em>n</em>-heptane and <em>iso-</em>octane. NO₂ significantly promotes the reactivity of toluene at low temperatures (600–1000 K), in which the IDTs decreased by two orders of magnitude when 1000 ppm of NO₂ is added, whereas there is an order of magnitude decrease with the addition of 200 ppm NO₂. The promoting effect of NO₂ on toluene oxidation reduces significantly at temperatures above 1000 K. The experimental results also show that NO₂ addition exhibits a slight promoting effect on the reactivity of <em>n</em>-heptane and <em>iso-</em>octane at temperatures above 750 K at the conditions studied. A kinetic model is proposed based on C3MechV3.3 in which the interaction chemistry between these gasoline surrogates and NOx is updated. The proposed kinetic model can simulate well the effect of NO₂ addition on the auto-ignition behavior of these surrogates. Flux and sensitivity analyses are performed to highlight the important interaction reaction pathways.</div></div>","PeriodicalId":280,"journal":{"name":"Combustion and Flame","volume":"276 ","pages":"Article 114118"},"PeriodicalIF":5.8,"publicationDate":"2025-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143684403","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}