Proceedings of the Combustion Institute最新文献

{"title":"Investigation of the near-field structure and stability of non-premixed NH[formula omitted]/H[formula omitted]/N[formula omitted] jet flames at various pressure and co-flow conditions","authors":"Alfaisal M. Albalawi, Ayman M. Elbaz, Mahmoud M.A. Ahmed, Zubayr O. Hassan, William L. Roberts","doi":"10.1016/j.proci.2024.105700","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105700","url":null,"abstract":"Inspired by the attractiveness of ammonia as an energy carrier coupled with the relative lack of experimental data at industrially-relevant conditions for ammonia/ammonia-blended flames, the current work was undertaken to help fill gaps in our understanding. This study reports the structure and stability of non-premixed, simulated cracked ammonia jet flames at three different cracking ratios (CR) (40%, 50%, and 60%) and pressures (1, 2, and 3 bar), and two different co-flow temperatures (295 and 573 K) using a newly commissioned high-pressure and temperature combustion duct. Measurements of qualitative OH and NO via PLIF were conducted to study the near-field flame structure. The results revealed that the detachment velocity increases monotonically with CR, however for a given CR, the detachment velocity decreases with pressure. For CR 55%, the jet flame exhibits a stable lifted flame behavior whereas blowout occurs directly after detachment for CR 55%. The visible flame length/size tends to slightly increase with pressure for the unheated co-flow cases, while the opposite trend was observed for the heated co-flow cases. As CR increases, the flame length/size slightly decreases regardless the pressure and co-flow temperature. It was observed that increasing CR increases the intensity of OH radicals while the NO intensity is reduced. It is suggested that the mismatch between peak NO and OH locations, which increases with CR, promotes the thermal-NO pathway rather than the fuel-NO pathway. Overall, increasing the pressure and co-flow temperature leads to a significant decrease in the peak NO and OH mismatch. Furthermore, as the pressure increases, both OH and NO intensities decrease when the co-flow is at room temperature. Nevertheless, increasing the pressure in the heated co-flow flames results in decreasing OH intensity while increasing that of the NO. This discrepancy between co-flow temperatures with pressure indicates the need for further investigation.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"21 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180208","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":"Influence of substrate, precursor, flow field, and hydrogen etching on the flame synthesis of monolayer graphene films","authors":"Hua Hong, Stephen D. Tse","doi":"10.1016/j.proci.2024.105594","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105594","url":null,"abstract":"Graphene films are grown in an open atmosphere on metal substrates using a modified multiple inverse-diffusion flame (m-IDF) burner with hydrogen as fuel and hydrocarbon as precursor (delivered by multiple distinct tubes staged above the m-IDF burner surface). The flame synthesis procedure uses three stages consisting of () pretreatment, () growth, and () hydrogen etching and produces monolayer graphene (MLG) films with methane as a precursor on copper substrates at 1000 °C. Substrate material (e.g., copper, nickel, silicon), purity, and smoothness (i.e., unpolished, electropolished); precursor composition (i.e., CH, CH, CH); substrate orientation (i.e., parallel, perpendicular, tilted 45˚) with respect to the post-flame flow field; and post-growth in-situ hydrogen etching are investigated for their impact on the quality (i.e., defect level, graphitic structure), uniformity, and number of layers of the as-synthesized graphene films. On low-purity Cu Substrates, defects are observed because of the impurity content. Interestingly, on smooth electropolished Cu substrates, high defect levels are produced presumably because of the high nucleation rates and density from the higher flow rates used in flame synthesis. When using CH and CH as precursors versus CH, growth rates are slower although the graphene film characteristics are similar. The small substrate sizes used are not in the boundary-layer regime, so the substrate orientation does not affect the characteristics of the film. The initial quality of graphene films and the substrate materials are the two key factors controlling the hydrogen etching effect and the healing effect because of thermal recrystallization. Hydrogen annealing can remove adlayers and improve the quality of graphene on Cu but has minimal or detrimental effects on films on other substrate materials.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"35 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180231","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":"Droplet combustion in a turbulent, elevated-pressure environment","authors":"Cameron Verwey, Arash Arabkhalaj, Madjid Birouk","doi":"10.1016/j.proci.2024.105693","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105693","url":null,"abstract":"Despite the enduring popularity of single-droplet vaporization studies, few researchers have systematically examined the influence of turbulence on droplet burning dynamics. Existing investigations have looked exclusively at large droplets or porous spheres while utilizing thermally conductive suspension schemes. To further understand how turbulence affects normal-gravity droplet burning, single droplets of heptane were suspended at the center of a fan-stirred chamber on a horizontal microfiber, rapidly ignited, and burned to completion. The experimental conditions were parametrically varied across 112 unique combinations of initial diameter, ambient pressure, turbulence intensity, and background oxygen content. The primary quantity of interest is the burning rate, and how individual and average burning rates are affected by the various parameters. To help interpret the results, the radiant soot emission was recorded alongside the temporal evolution of the droplet diameter. The burning rates of droplets in the super-millimeter range are up to 32% lower than those collected in otherwise identical conditions but with large fiber suspenders. Turbulence has little effect on the droplet burning rate until the ambient pressure is elevated. In these cases, turbulence initially augments the burning rate until a critical turbulence level is reached, after which the burning rate quickly falls. The reduction in the burning rate corresponds to the reoccurring appearance of temporary luminous extinction (TLE), where the hot incandescent region that normally surrounds the droplet disappears for a short period, thus tempering the overall burning rate. The cause of, and behavior during, TLE is contrasted with similar phenomena from the literature. Smaller, sub-millimeter droplets behave in largely the same manner, but with lower peak burning rates and greater run-to-run variation. Modest increases to the background oxygen content, from the baseline 21% up to 25% and 30%, delay the onset of TLE to higher turbulence levels. At the highest pressures, turbulent droplet burning rates of the oxygen-enriched cases can double their counterparts in ambient oxygen levels—a synergistic effect with turbulence playing a critical role.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"31 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180226","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":"Machine learning-driven screening of fuel additives for increased spark-ignition engine efficiency","authors":"Shashank S. Nagaraja, S. Mani Sarathy, Balaji Mohan, Junseok Chang","doi":"10.1016/j.proci.2024.105658","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105658","url":null,"abstract":"Fuel design aims to develop and optimize fuels to meet specific performance, environmental, and economic objectives. It encompasses a range of considerations, including selecting appropriate feedstocks, adjusting molecular structures, and incorporating additives to achieve desired characteristics. One critical aspect of fuel design is its relevance to addressing environmental concerns, such as reducing greenhouse gas emissions and air pollutants. In a spark-ignition engine, increasing engine efficiency leads to a reduction in CO2 emissions. The composition of the fuel plays a vital role in enhancing engine efficiency. Anti-knock properties, latent heat of vaporization (HoV), and laminar flame speed (LFS) are some of the fuel properties that can influence engine operating regimes. In the current study, we explore additives that can improve the efficiency of spark-ignition engines. Machine learning-based quantitative structure-property relationship (QSPR) models are developed to predict research and motor octane numbers, HoV, and LFS of 379,500 hydrocarbons containing only carbon, hydrogen, and oxygen atoms. The molecules are ranked based on an established merit function, and the top five candidates are selected. Methanol is the most promising additive candidate, allowing for the highest degree of efficiency enhancement among the screened candidates. Other potential candidates are substituted furans and tetrahydrofuran.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"111 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180228","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":"Design a novel Ca-Mn perovskite oxygen carrier with balanced performance in chemical looping combustion","authors":"Xin Wu, Xianyu Liu, Guangsheng Zou, Jinchen Ma, Cao Kuang, Haibo Zhao","doi":"10.1016/j.proci.2024.105645","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105645","url":null,"abstract":"The cornerstone of chemical looping combustion (CLC) is oxygen carriers (OCs), and most OCs have one or more ever-present problems with performance, cost, stability, and service life. It is vital to develop OCs with balanced performance. A novel CMTF-Mg OC is proposed in this study via B-site elemental substitution of CaMnO perovskite. Systematic experiments using a thermogravimetric analyzer (TGA), a batch fluidized bed reactor, a fixed bed reactor, and an air jet attrition apparatus are performed to evaluate various aspects of the performance of the OC manufactured by the hydraulic molding method. First, in isothermal TGA redox cycles, CMTF-Mg OC exhibits a high oxygen donation ratio (∼5.0 wt.%) and excellent cyclic stability. Mg substitution eliminates the activation effect and promotes lattice oxygen release. Then, the CH-fueled CLC experiments on a batch fluidized bed demonstrate that Mg B-site substitution promotes oxygen uncoupling (0.2 wt.% gaseous oxygen) and significantly improves its reactivity with CH. Following that, an agglomeration resistance test on a packed bed reveals that CMTF-Mg OC particles expand slightly yet exhibit remarkable agglomeration resistance. Further characterization results from SEM, EDS, and XRD analysis show that the perovskite phase is formed in fresh CMTF-Mg OC via solid-phase synthesis at 1350 °C, and OC has high thermal and chemical stability during the multiple redox cycles. According to the attrition test results, CMTF-Mg OC has an 8333-hour service life. Last, CMTF-Mg OC has a material cost of $0.892/kg and a use cost of 0.00217 ($/kg[O]/h). In summary, this CMTF-Mg OC has excellent and balanced performance in reactivity, stability, agglomeration resistance, attrition resistance, and cost, which is of great value for industrial demonstration of CLC in the later stage.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"2012 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180229","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":"Flame transfer function analysis of hydrogen diffusion swirl flames","authors":"Guoqing Wang, Abel Faure-Beaulieu, Bruno Schuermans, Nicolas Noiray","doi":"10.1016/j.proci.2024.105727","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105727","url":null,"abstract":"This paper investigates the first Flame Transfer Functions (FTFs) of hydrogen diffusion swirl flames, which are crucial for predicting and mitigating thermoacoustic instabilities. Given the need to develop new combustion technologies for hydrogen, it is therefore essential to accurately measure and analyze these FTFs. Employing acoustic and optical methods, we obtained the FTFs over a wide frequency range from 50 to 1000 Hz. Using the acoustic method, the FTFs are deduced from the flame transfer matrices. The FTFs exhibit a low-pass filter behavior with gains decreasing significantly above 150 Hz. Strouhal number normalization effectively collapses the FTFs across various thermal powers, bulk mass flow rates and global equivalence ratios. This result suggests that a generic flame response to acoustic perturbations exists and that the FTF can be interpolated over a range of operating conditions. This study identifies two dominant combustion modes in these hydrogen diffusion swirl flames: a diffusion-mode thin reaction layer near the nozzle and a partially premixed thicker reaction layer downstream. Phase-averaged OH* and OH-PLIF imaging revealed non-uniform transversal oscillations of the reaction zone, offering key insights into the complex swirling flow and the convective wavelength of the coherent heat release rate oscillations along these turbulent hydrogen diffusion swirl flames.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"64 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180230","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":"Effects of air-staging and heat losses on NO emissions of NH3/CH4/air swirling flames","authors":"Shixing Wang, Ayman M. Elbaz, Zhihua Wang, William L. Roberts","doi":"10.1016/j.proci.2024.105724","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105724","url":null,"abstract":"Ammonia (NH) is considered a promising carbon-free fuel in the context of carbon neutrality. However, the emission characteristics of NH swirling flames respond strongly to the influence of heat loss and fuel staging. This study investigated the NO emissions of NH/CH/air mixtures in an air-staging swirling combustor. The ammonia mole fractions range from = 0.3, 0.6, to 1.0, with the primary and overall equivalence ratios ranging from = 0.7 to 1.7 and = 0.5 to 0.7, respectively. Four different secondary air injection strategies and three heat losses rates were adopted to differentiate the thermal and chemical effects on NO emissions. O, NO, and CO emissions were measured using a flue gas analyzer. In-flame temperature was measured by fine-wire thermocouples, and chemiluminescence (OH*, NH*) was captured by an intensified CCD camera. The chemical reactor network approach was used to simulate the two-stage combustion. Secondary gas injection initially has a thermal effect by cooling the downstream flame temperature on the lean side. After = 1.3, the chemical effect dominated while the flame was challenged by lift-off instability. = 1.3 showed the minimum NO emission, while = 1.1, = 0.7 with cooling exhibited low NO levels and high flame stability. Flame at > 1.3 tended to lift-off and merge with secondary air, diminishing the air-staging effect. NH* and OH* indicate the flame lift-off and secondary flame formation. Simulation results show that NO removal is favored at cooling conditions in the primary stage and NO production is suppressed at thermal-insulation conditions in the secondary stage. To ensure low NO emissions, complete ammonia oxidation, and flame stability, stabilizing the primary flame zone close to = 1.0 and overall equivalence ratio close to = 0.7 in combination with the cooling strategy is effective.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"111 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142180232","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":"An extension of the artificially thickened flame approach for premixed hydrogen flames with intrinsic instabilities","authors":"Vinzenz Schuh, Christian Hasse, Hendrik Nicolai","doi":"10.1016/j.proci.2024.105673","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105673","url":null,"abstract":"Despite the growing interest in hydrogen as a fuel, current combustion models are still incapable of considering the effects of intrinsic flame instabilities, such as increased flame surface area and local stratification. A significant challenge arises due to the substantial impact on the laminar flame consumption speed, complicating the transfer of established combustion models. This study proposes an extension of the artificially thickened flame (ATF) approach to encompass laminar self-wrinkling flames subject to intrinsic instabilities, serving as a foundation for advancing turbulent combustion models. Several 2D numerical simulations were conducted to analyze the interaction of ATF and thermodiffusive instabilities in unstable lean hydrogen flames. The assessment of characteristic length scales revealed a linear scaling relationship with the thickening factor , causing the domain size at which instabilities manifest to expand and modify the consumption speed of the thickened flame. To compensate for these deviations, a novel efficiency function is derived from the fractal characteristics of the flame front. Using the critical wavelength and a geometric length scale as inner and outer cut-offs, respectively, the improved ATF model was evaluated successfully in fully coupled simulations of the 2D planar flames. To facilitate the use of the new model, a practical on-the-fly procedure for estimating a characteristic geometric length scale required for the efficiency function is proposed and successfully employed.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"39 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946255","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":"Speed-up drivers for [formula omitted]-enriched flames in Porous Media Burners","authors":"Enrique Flores-Montoya, Pierre-Alexandre Masset, Thierry Schuller, Laurent Selle","doi":"10.1016/j.proci.2024.105666","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105666","url":null,"abstract":"An experimental study on the influence of porosity and hydrogen enrichment on the stabilization of premixed -Air flames in Porous Media Burners (PMBs) is presented. Flame stabilization is analyzed via direct flame front tracking, which is made possible by a novel experimental apparatus. The use of additive manufacturing for computer-generated topologies allows making optically-accessible PMBs featuring see-through directions. This methodology also enables topology tailoring which is here exploited to study the influence of porosity on the performance of the burner. Flame front tracking reveals a different stabilization trend in highly -enriched flames. A comparison with a theoretical model is used to remove the effect of preheating and focus on other fuel properties. This suggests a flame-speed enhancement mechanism driven by Lewis number effects in mixtures. Together with recent 3D Direct Numerical Simulations, these results provide evidence that preferential diffusion effects are key in the stabilization of flames in PMBs. These phenomena, not considered in state-of-the art 1D-Volume Averaged Models, remain crucial for the design of efficient PMB using hydrogen as a fuel.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"51 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946247","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":"3D flame surface curvature analysis from reconstructed scanning across spherical expanding flames","authors":"Yutao Zheng, Pervez Ahmed, Simone Hochgreb","doi":"10.1016/j.proci.2024.105688","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105688","url":null,"abstract":"We analyze 3D reconstructed surfaces based on previously reported high frequency measurements of flame edge location across expanding flames using Mie scatter. For the first time, principal curvatures of flame surfaces are estimated from eigenvalues of the second fundamental forms of the reconstructed surfaces, allowing the determination of the statistics of mean and Gaussian curvatures as a function of time and thus flame mean radius. Measurements and analysis were made for both lean methane and hydrogen mixtures as a function of time and turbulence levels. The mean 3D flame curvature was found to be inversely proportional to flame radius, and relatively insensitive to turbulence intensity, even in the case of larger, more planar flames. Mean 3D curvatures across the flame brush were determined to be positive (convex) towards the reactant mixture at the leading edge, and negative (concave) towards the trailing edge, as predicted from DNS measurements. The mean and probability distributions of 3D mean curvatures were found to be significantly different than 2D curvatures extracted from the central planes, with the 3D measurements showing much narrower distributions and lower values. Differences between 3D and 2D measurements were different by an order of magnitude in the case of hydrogen flames, possibly owing to the onset of thermodiffusive instabilities which affect the local fine structure of the flame.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"138 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946256","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}