Proceedings of the Combustion Institute最新文献

{"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}

{"title":"Effect of a shear flow on the Darrieus–Landau instability in a Hele-Shaw channel","authors":"Prabakaran Rajamanickam, Joel Daou","doi":"10.1016/j.proci.2024.105671","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105671","url":null,"abstract":"The Darrieus–Landau instability of premixed flames propagating in a narrow Hele-Shaw channel in the presence of a strong shear flow is investigated, incorporating also the Rayleigh–Taylor and diffusive-thermal instabilities. The flow induces shear-enhanced diffusion (Taylor dispersion) in the two-dimensional depth averaged equations. Since the diffusion enhancement is in the streamwise direction, but not in the spanwise direction, this leads to anisotropic diffusion and flame propagation. To understand how such anisotropies affect flame stability, two important cases are considered. These correspond to initial unperturbed conditions pertaining to a planar flame propagating in the streamwise or spanwise directions. The analysis is based on a two-dimensional model derived by asymptotic methods and solved numerically. Its numerical solutions comprise the computation of eigenvalues of a linear stability problem as well as time-dependent simulations. These address the influence of the shear-flow strength (or Peclet number ), preferential diffusion (or Lewis number ) and gravity (or Rayleigh number ). Dispersion curves characterising the perturbation growth rate are computed for selected values of , and . Taylor dispersion induced by strong shear flows is found to suppress the Darrieus–Landau instability and to weaken the flame wrinkling when the flame propagates in the streamwise direction. In contrast, when the flame propagates in the spanwise direction, the flame is stabilised in mixtures, but destabilised in mixtures. In the latter case, Taylor dispersion coupled with gas expansion facilitates flame wrinkling in an unusual manner. Specifically, stagnation points and counter-rotating vortices are encountered in the flame close to the unburnt gas side. More generally, an original finding is the demonstration that vorticity can be produced by a curved flame in a Hele-Shaw channel even in the absence of gravity, whenever , and that the vorticity remains confined to the flame preheat and reaction zones.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"39 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946243","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":"Analysis of potential soot breakthrough during oxidation at aero-engine relevant conditions","authors":"Philipp Koob, Hendrik Nicolai, Robert Schmitz, Christian Hasse","doi":"10.1016/j.proci.2024.105672","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105672","url":null,"abstract":"Reducing emissions from aero-engines, vital for aviation climate goals, requires accurate prediction of pollutants like soot. In modern rich-quench-lean aero-engine combustion chambers, fresh air is introduced after the primary combustion zone to dilute the rich exhaust gases and to cool the combustor liner walls, which will consequently also lead to the oxidation of soot with O. In this study, a simplified configuration is derived from the actual aero-engine configuration that enables an in-depth analysis of these soot oxidation processes. Detailed chemistry, together with the split-based extended quadrature method of moments soot model, is used for a comprehensive analysis of soot oxidation, focusing on the influence of varying scalar dissipation rates, mixing times, and particle size distributions derived from the real combustor. It is shown that soot oxidation linearly connects to the oxidation time scale represented by the OH residence time, meaning more soot breakthrough with shorter oxidation times. Furthermore, the influence of the soot particle size distribution is investigated. By connecting the oxidation time and the soot particle size, a metric to quantify soot breaking through the mixing zone into the lean regions of the combustion chamber is proposed.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"51 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946239","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":"The role of thermodiffusion and dimensionality in the formation of cellular instabilities in hydrogen flames","authors":"Thorsten Zirwes, Feichi Zhang, Thomas L. Kaiser, Kilian Oberleithner, Oliver T. Stein, Henning Bockhorn, Andreas Kronenburg","doi":"10.1016/j.proci.2024.105665","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105665","url":null,"abstract":"Hydrogen is quickly becoming one of the most important fuels for combustion applications. However, compared to conventional hydro-carbon flames, the high diffusivity of hydrogen makes lean hydrogen flames prone to form cellular instabilities. In this work, the formation of cellular structures on a lean hydrogen–air flame is studied numerically in a laminar flow with prescribed initial perturbation. The flame is fully resolved and a detailed reaction mechanism as well as detailed diffusion models are utilized. In the literature, most numerical works directly studying cell formation are limited to two-dimensional setups. However, the additional principal curvature direction in three dimensions can have a strong impact on the cell formation and flame propagation. Because of this, simulations are performed both in 2D and 3D to directly quantify the effect of dimensionality on flame propagation. In the 3D simulations, higher local curvatures yield local heat release rates that exceed the ones from 2D simulations by 80%. In addition, simulations with and without thermo or Soret diffusion are carried out. While Soret diffusion leads to a decrease in flame speed for freely propagating flames, it accelerates the formation of thermodiffusively unstable cells as well as increases local heat release rates. This can be explained by an increase of local equivalence ratios in the reaction and post-oxidation zone due to the altered focusing of diffusive fluxes, leading to locally increased heat release rates for positively curved flame segments. The efficiency factor is evaluated to model the effect of the cellular structures on the local burning rate. increases during the formation of primary cells and reaches a quasi-steady value once the secondary structures are formed, which can present an approach for modeling the effect of cellular structures on hydrogen flame dynamics.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"47 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946241","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":"Interactions between liquid sprays and shock waves in underexpanded flows","authors":"Christopher B. Reuter, Steven G. Tuttle","doi":"10.1016/j.proci.2024.105244","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105244","url":null,"abstract":"The interactions between droplets and shock waves have many applications, but few studies have investigated how the distributions of droplet diameters and droplet velocities in a spray are modified after passing through a shock. This study examines the droplet statistics upstream and downstream of shock waves in an underexpanded jet by performing phase Doppler interferometry in combination with Schlieren imaging. A mixture of water and propylene glycol is employed as the liquid. It is observed that, when the spray passes through an oblique shock, the droplet diameters decrease and then increase but the droplet velocities remain steady. When the droplets pass through a weak normal shock, on the other hand, the most probable droplet diameter decreases, some very large droplets appear, and the velocity distribution splits into three distinct regions. However, a strong normal shock causes the mean droplet diameters and the mean droplet velocities to decrease consistently. Reasons for these different behaviors are given, and secondary breakup regimes are estimated in terms of the Weber number. Additionally, droplet probability distribution fits are compared to the measured values for each of the different cases. The droplet statistics presented here can be used to improve computational modeling of spray-shock interactions.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"44 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946096","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":"Insight into premixed diethoxymethane flames: Laminar burning velocities, temperatures, and emissions behaviour","authors":"Sven Eckart, Krishna P. Shrestha, Binod R. Giri, Qilong Fang, Wei Li, Fabian Mauss, Hartmut Krause, Yuyang Li","doi":"10.1016/j.proci.2024.105579","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105579","url":null,"abstract":"Diethoxymethane ((CHCHO)CH, DEM) is a promising carbon-neutral fuel. DEM is a diether or acetal with a molecular structure similar to oxymethylene ethers (CHO–(CHO)–CH, OME). Thus, DEM can be expected to have a similar combustion behavior to OMEs, reducing harmful emissions such as NO and particulate matter (PM) in internal combustion engines. From both experimental and kinetic modeling, fundamental studies on DEM are scarce in the literature. More studies are required to gain a detailed insight into the oxidation kinetics of DEM. Laminar burning velocity (LBV) is a critical property that allows a detailed assessment of the potential application of DEM in combustion devices. Unfortunately, the literature on the LBV of DEM is limited. Therefore, in this study we have investigated the LBV of DEM using two reactors for the first time, namely a heat flux burner and a combustion chamber. The experimental data is reported for equivalence ratio between 0.7 and 1.7, initial temperatures of 368–423 K, and initial pressure of 1–5 bar. In addition, we developed a detailed kinetic model extending our recent work of Shrestha et al. () to characterize the combustion behavior of DEM utilizing the new experimental data from this work and the literature data. Our model performs remarkably well in capturing the newly measured LBV experimental data over various experimental conditions. We found that DEM and dimethoxy methane (DMM) have similar values of LBVs (within ±1.5 cm/s) for a given condition, which indicates that intermediate chemistry governs the flame chemistry. Despite DEM being a larger molecule that is expected to have slightly lower LBVs than DMM, its effect on the measured values of LBVs is negligible. Finally, we experimentally measured NO formation in DEM flame for the first time. The stochiometric flame has the highest NO formation. The proposed model predicted the equivalence ratio dependence of NO nicely. However, it overestimates the NO formation for stoichiometric DEM/air mixtures by ∼30 %. The model suggests that the thermal NO formation route is favored at lean and stochiometric conditions. In contrast, the prompt NO formation route is enhanced for rich mixtures.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"21 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946244","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":"Effect of ferric chloride addition on soot formation during ethylene pyrolysis in a laminar flow reactor","authors":"Qingyan He, Yuxin Zhou, Xiaoqing You","doi":"10.1016/j.proci.2024.105677","DOIUrl":"https://doi.org/10.1016/j.proci.2024.105677","url":null,"abstract":"In this work, we investigated the effect of ferric chloride (FeCl) addition on soot formation during ethylene pyrolysis in a laminar flow reactor by characterizing particles sampled at the reactor outlet. To avoid the interference of oxygen atoms on soot formation, we selected FeCl as an iron-based additive and used a diffusion dryer to absorb water in the FeCl solution. By studying particle size distribution, morphology, and chemical composition, we found that iron-containing particles evolved from iron nuclei to core-shell particles and finally to aggregates. These iron-containing particles, which had an overall higher charge fraction, hindered the agglomeration of iron nuclei but promoted the formation of core-shell particles. In addition, ReaxFF molecular dynamics simulations were performed to study the interaction between FeCl and pyrene molecules in the early stages of soot formation. Simulation results show that FeCl would undergo thermal decomposition to form Fe-C sosoloid as the core of the core-shell particles.","PeriodicalId":408,"journal":{"name":"Proceedings of the Combustion Institute","volume":"48 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141946236","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}