Symposium (International) on Combustion最新文献

{"title":"The influence of evaporation on the autoignition-delay of n-heptane air mixtures under gas turbine conditions","authors":"M. Cano Wolff,&nbsp;J. Meisl,&nbsp;R. Koch,&nbsp;S. Wittig","doi":"10.1016/S0082-0784(98)80048-9","DOIUrl":"10.1016/S0082-0784(98)80048-9","url":null,"abstract":"<div><p>In this work, autoignition-delay times of liquid fuel sprays for flow situations similar to those in premixing ducts are calculated. An intensive parameter study was conducted to identify the influence of the evaporating spray on autoignition delay. The parameter variation covers duct conditions relevant to gas turbines. Three monodisperse sprays with droplet sizes of 10,50, and 100 <em>μ</em>m and two sprays with Rossin-Rammler droplet size distribution are investigated. A full 3-D Navier-Stokes code is used for the prediction of the turbulent flow. It is coupled to a code based on a Lagrangian formulation for the prediction of the motion and evaporation of the droplets. The evolution of the chemical kinetics is predicted with the CHEMKIN package for <em>n</em>-heptane, which is selected as fuel. A detailed <em>n</em>-heptane low-temperature mechanism including 168 species and 904 reactions describes the chemical kinetics.</p><p>For initial temperatures inside the negative temperature coefficient region (NTC), the only spray parameter influencing autoignition delay is the spray evaporation time. If the initial temperature is on the lower boundary of the NTC region, the strong temperature dependence of autoignition in this region leads to a substantially longer autoignition delay due to the cooling of the gas phase caused by evaporation. A delaying effect of evaporation time is only present if the evaporation time is higher than the first induction time. Generally, the safety margin between autoignition and the end of evaporation is enhanced by utilization of a spray with small droplets and a narrow droplet size distribution. Also, a minimum autoignition delay for lean conditions at <em>Φ</em>=0.5 is identified.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 2025-2031"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0082-0784(98)80048-9","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"98460158","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"HCO concentration in flames via quantitative laser-induced fluorescence","authors":"Eric W.-G. Diau ,&nbsp;Gregory P. Smith,&nbsp;Jay B. Jeffries,&nbsp;David R. Crosley","doi":"10.1016/S0082-0784(98)80434-7","DOIUrl":"10.1016/S0082-0784(98)80434-7","url":null,"abstract":"<div><p>Quantitative laser-induced fluorescence (LIF) measurements of the concentration of HCO are made in three 25-torr methane-oxygen-nitrogen flames: fuel lean (<em>φ</em>=0.81), near stoichiometric (<em>φ</em>=1.07), and fuel rich (<em>φ</em>=1.28). LIF is excited in the (000)-(000) band of the B-X system near 258 nm. The LIF signal from the flame is calibrated against nonflame measurements of a known HCO concentration produced by laser photolysis of acetaldehyde. The LIF signal is adjusted for the variation in the fraction of the population of the laser-excited level as the measured temperature changew with position in the flame and for the measured variation in quenching. The resulting concentration measurements agree well with model predictions for the fuel-lean and near-stoichiometric flame. The measurements in the fuel-rich flame are significantly larger than the model predictions: however, these measurements are subject to increased uncertainty due to the large, broadband background in the rich flame.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 453-460"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0082-0784(98)80434-7","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"100405203","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Thermodynamic and kinetic analysis using AB initio calculations on dimethyl-ether radical+O2 reaction system","authors":"Takahiro Yamada,&nbsp;Joseph W. Bozzelli,&nbsp;Tsan Lay","doi":"10.1016/S0082-0784(98)80406-2","DOIUrl":"10.1016/S0082-0784(98)80406-2","url":null,"abstract":"&lt;div&gt;&lt;p&gt;Reaction pathways and kinetics are analyzed on CH&lt;sub&gt;3&lt;/sub&gt;OC·H&lt;sub&gt;2&lt;/sub&gt;+O&lt;sub&gt;2&lt;/sub&gt; reaction system using &lt;em&gt;ab initio&lt;/em&gt; calculations to determine tehrmodynamic properties of reactants, intermediate radicals, and transitionstate (TS) compounds. Enthalpies of formation (&lt;em&gt;ΔH&lt;sub&gt;f298&lt;/sub&gt;&lt;sup&gt;o&lt;/sup&gt;&lt;/em&gt;) are determined using the CBS-q//MP2(full)/6-31G(d,p) method with isodesmic reactions. Entropies (&lt;em&gt;S&lt;/em&gt;&lt;sub&gt;298&lt;/sub&gt;&lt;sup&gt;o&lt;/sup&gt;) and heat capacities (&lt;em&gt;C&lt;sub&gt;p&lt;/sub&gt;(T)&lt;/em&gt; 300≤&lt;em&gt;T/K&lt;/em&gt;≤1500) are determined using geometric parameters and vibrational frequencies obtained at the MP2(full)/6-31G(d,p) level of theory. Quantum Rice-Ramsperger-Kassel (QRRK) analysis is used to calculated energy-dependent rate constants, &lt;em&gt;k(E)&lt;/em&gt;, and the master equations is used to account for collisional stabilization. The dimethyl-ether radical CH&lt;sub&gt;3&lt;/sub&gt;OC·H&lt;sub&gt;2&lt;/sub&gt; (&lt;em&gt;ΔH&lt;sub&gt;f298&lt;/sub&gt;&lt;sup&gt;o&lt;/sup&gt;&lt;/em&gt;=0.1 kcal/mol) adds to O&lt;sub&gt;2&lt;/sub&gt; to form a peroxy radical CH&lt;sub&gt;3&lt;/sub&gt;OCH&lt;sub&gt;2&lt;/sub&gt;OO·(&lt;em&gt;ΔH&lt;sub&gt;f298&lt;/sub&gt;&lt;sup&gt;o&lt;/sup&gt;&lt;/em&gt;=−33.9 kcal/mol). The peroxy radical can undergo dissociation back to reactants or isomerize via hydrogen shift (&lt;em&gt;E&lt;sub&gt;a,rxn&lt;/sub&gt;&lt;/em&gt;=17.7 kcal/mol) to form a hydroperoxy alkyl radical C·H&lt;sub&gt;2&lt;/sub&gt;OCH&lt;sub&gt;2&lt;/sub&gt;OOH, (&lt;em&gt;ΔH&lt;sub&gt;f298&lt;/sub&gt;&lt;sup&gt;o&lt;/sup&gt;&lt;/em&gt;=−26.5 kcal/mol). This alkyl radical can undergo β-scission reaction to formaldehyde (CH&lt;sub&gt;2&lt;/sub&gt;O)+hydroperoxy methyl radical (C·H&lt;sub&gt;2&lt;/sub&gt;OOH), (&lt;em&gt;E&lt;sub&gt;a, rxn&lt;/sub&gt;&lt;/em&gt;=24.7 kcal/mol). The hydroperoxy methyl radical rapidly decomposes to a second CH&lt;sub&gt;2&lt;/sub&gt;O plus OH. The reaction barriers for CH&lt;sub&gt;3&lt;/sub&gt;OCH&lt;sub&gt;2&lt;/sub&gt; +O&lt;sub&gt;2&lt;/sub&gt; to 2 CH&lt;sub&gt;2&lt;/sub&gt;O+OH are lower than the energy needed for reaction back to CH&lt;sub&gt;3&lt;/sub&gt;OC·H&lt;sub&gt;2&lt;/sub&gt;+O&lt;sub&gt;2&lt;/sub&gt;, and provide a low-energy chain propagation path for dimethyl-ether oxidation.&lt;span&gt;&lt;span&gt;&lt;span&gt;&lt;math&gt;&lt;mtable&gt;&lt;mtr&gt;&lt;mtd&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;mo&gt;C&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mo&gt;C&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;→&lt;/mo&gt;&lt;mo&gt;C&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mo&gt;C&lt;/mo&gt;&lt;mo&gt;⋅&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mtd&gt;&lt;/mtr&gt;&lt;mtr&gt;&lt;mtd&gt;&lt;munder&gt;&lt;mrow&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;mo&gt;C&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mo&gt;C&lt;/mo&gt;&lt;mo&gt;⋅&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;→&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;mo&gt;C&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;/mrow&gt;&lt;mo&gt;¯&lt;/mo&gt;&lt;/munder&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mtd&gt;&lt;/mtr&gt;&lt;mtr&gt;&lt;mtd&gt;&lt;mo&gt;C&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mo&gt;C&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;→&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;mo&gt;C&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;msub&gt;&lt;mo&gt;H&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;O&lt;/mo&gt;&lt;/mtd&gt;&lt;/mtr&gt;&lt;/mtable&gt;&lt;/math&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;Comparison of calculated fallof","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 201-209"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0082-0784(98)80406-2","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"104412710","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Nonlinear instabilities leading to rapid mixing and combustion in confined supersonic double-shear-layer flow","authors":"Akira Umemura,&nbsp;Yoichi Takihana","doi":"10.1016/S0082-0784(98)80061-1","DOIUrl":"10.1016/S0082-0784(98)80061-1","url":null,"abstract":"<div><p>Direct numerical simulations conducted in the present study show that a slow fuel gas stream issued between supersonic high-temperature air streams confined in a constant-area channel can mix with air quickly to cause explosive combustion along the following processes: (1) linear flaw instability excitation, (2) eddy formation without shocks, fuel flow acceleration to supersonic speed and enhanced mixing with air, associated with fuel layer meandering, (3) explosive combustion, and (4) thermally choked burnt gas flow. The underlying physics of the supersonic instabilities involved are revealed by interpreting the simulation results in an attempt to find an effective mixing enhancement technique.</p><p>The basic flow configuration consists of a confined, plane, double shear/mixing layer flow with forcing fluctuations at the inlet. The difference in velocities between inlet air and fuel streams is supersonic. The reflection condition imposed at the walls serves to disturb acoustically the double shear layer flow in such a way that the walls reflect Mach waves radiated from the inlet disturbance. The most unstable wave excited downstream is skew-symmetric with respect to the centerline, thus leading to the meandering of fuel layer accompanied by Karman-vortex-like eddies. A series of instability excitations couples with the fuel layer meandering in a confined flow region, enhances the exchange of momentum and species between the fuel and air streams, thus accelerating the mixture to a supersonic speed within a short distance prior to explosive combustion. The behavior of the flame front resembles that of lifted turbulent-jet flames. Flame flashback, stationary flame front and flame blowout take place, depending on the inlet condition. Their criteria are provided in terms of the Chapman-Jouguet detonation wave speed.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 2135-2142"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0082-0784(98)80061-1","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"113187041","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Extinction of stretched spray flames with nonunity Lewis numbers in a stagnation-point flow","authors":"Shuhn-Shyurng Hou ,&nbsp;Ta-Hui Lin","doi":"10.1016/S0082-0784(98)80046-5","DOIUrl":"10.1016/S0082-0784(98)80046-5","url":null,"abstract":"<div><p>The extinction of stretched premixed flames under the influence of dilute fuel sprays is studied using activation energy asymptotics. A completely prevaporized mode and a partially prevaporized mode of flame propagation are identified. Three parameters for flame extinction in the analysis consist of the mass fraction of liquid fuel and the initial droplet size of the spray, indicating the internal heat loss and heat gain for rich and lean sprays, respectively, and the flow stretch coupled with Lewis number (Le) that intensifies and weakens the burning strength of the Le&lt;1 and Le&gt;1 flame, respectively. The study presents sample calculations on lean ethanol-spray flames (Le&gt;1), rich ethanol-spray flames (Le&gt;1), and rich methanol-spray flames (Le&lt;1). Results show that the burning intensity of a spray flame with Le&gt;1 is weakened by the flow stretch: however, it is enhanced (further reduced) when the lean (rich) spray has a larger amount of liquid fuel loading or a smaller initial droplet size. It is generally found that the external heat loss associated with the flow stretch dominates the trend for flame extinction. The coupling effects of flow stretch and internal heat gain result in that there exists flame flashback instead of flame extinction for rich methanol-spray flames (Le&lt;1).</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 2009-2015"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0082-0784(98)80046-5","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"100793353","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Detection of extremely fine carbonaceous particles in the exhausts of diesel and spark-ignited internal combustion engines, by means of broad-band extinction and scattering spectroscopy in the ultraviolet band 190-400 NM","authors":"Antonio Borghese,&nbsp;simona S. Merola","doi":"10.1016/S0082-0784(98)80057-X","DOIUrl":"https://doi.org/10.1016/S0082-0784(98)80057-X","url":null,"abstract":"<div><p>Recent studies have shown that organic matter found in fine aerosol or sampled in flames can be only partially speciated, the major part being unidentified. Instrumental limitations of chemical analysis at very high molecular masses and of particle detectors at very low sizes leave unexplored the nanometric size range, where organic molecular clusters might accumulate.</p><p>This work reports on the detection of organic extremely fine particles in the exhausts of both diesel <em>and</em> spark-ignited engines, by means of broad-band extinction and scattering spectroscopy in the ultraviolet 190–400 nm band.</p><p>The detection techniques rely on a light source, resulting from the laser-induced optical breakdown of air, which features “blackbody” ultraviolet-visible emission, duration of few tens of nanoseconds and tighly confined spot volume.</p><p>Samples of internal combustion (IC) engines' emissions have been analyzed in two forms:(a) ordinarily air-diluted exhausts, for extinction measurements and (b) solution/suspension of condensed combustion water, which proved to increase the trapped species concentrations to levels suitable for spectral scattering measurements.</p><p>Extinction and scattering spectral data have led to characterize the scatters in terms of: (1) their complex index of refraction in the ultraviolet band 190–450 nm: (2) their average size, in the order of few nonometers and (3) their volume fraction <em>f</em>_v (hundreds of ppm) in the water-trapped exhausts.</p><p>The spectral shapes of the extinction coefficient α(λ) in the ultraviolet band have been interpreted in the framework of the solid-state physics, by relating the spatial structures of organic molecular clusters to the value <em>E</em>_g of the optical gap, derived experimentally by the Tauc relationship.</p><p>Resulting optical gaps are very low (<em>E</em>_g=0.2 eV) for air-diluted diesel exhausts, involving the presence of soot, as expected, whereas, in all the other cases explored, <em>E</em>_g spans over values greater than 3 eV, associated with carbon-containing nanoparticles.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 2101-2109"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0082-0784(98)80057-X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"137402257","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The role of equivalence ratio oscillations in driving combustion instabilities in low NOx gas turbines","authors":"Tim Lieuwen,&nbsp;Ben T. Zinn","doi":"10.1016/S0082-0784(98)80022-2","DOIUrl":"10.1016/S0082-0784(98)80022-2","url":null,"abstract":"<div><p>This paper presents a theoretical investigation of combustion instabilities in low NO_<em>X</em> gas turbines (LNGT) that burn fuel in a lean premixed mode. It is shown that these instabilities may be caused by interactions of combustor pressure oscillations with the reactants' supply rates, producing equivalence ratio perturbations in the inlet duct. These perturbations are convected by the mean flow to the combustor where they produce large-amplitude heat-release oscillations that drive combustor pressure oscillations. It is shown in this study that in contrast to earlier analyses, which assumed a uniform instantaneous heat release throughout the flame region, the heat release within the flame may exhibit strong spatial dependence that can significantly affect the combustor stability. The proposed instability mechanism is incorporated into a model that is used to predict LNGT stability limits. The model results show that LNGT are highly prone to combustion instabilities, especially under lean operating conditions, and that the regions of instability can be approximately described in terms of a ratio of the reactants' convective time from the fuel injector to the combustor and the period of the oscillations (with some modifications that account for the structure of the combustion region). Significantly, the developed model's predictions are in good agreement with available experimental data, strongly suggesting that the proposed mechanism and the developed model properly account for the essential physics of the problem.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 1809-1816"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0082-0784(98)80022-2","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"108415680","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Planar laser-induced fluorescence imaging of flame heat release rate","authors":"Phillip H. Paul,&nbsp;Habib N. Najm","doi":"10.1016/S0082-0784(98)80388-3","DOIUrl":"10.1016/S0082-0784(98)80388-3","url":null,"abstract":"<div><p>Local heat release rate represents one of the most interesting experimental observables in the study of unsteady reacting flows. The direct measure of burning or heat release rate as a field variable is not possible. Numerous experimental investigations have relied on inferring this type of information as well as flame-front topology from indirect measures that are presumed to be correlated. A recent study has brought into question many of the commonly used flame-front marker and burning-rate diagnostics. This same study found that the concentration of formyl radical offers the best possibility for measuring flame burning rate. However, primarily due to low concentrations, the fluorescence signal level from formyl is too weak to employ this diagnostic for single-pulse measurements of turbulent-reacting flows.</p><p>In this paper, we describe and demonstrate a new fluorescence-based reaction-front imaging diagnostic suitable for single-shot applications. The measurement is based on taking the pixel-by-pixel product of OH and CH₂O planar laser-induced fluorescence (PLIF) images to yield an image closely related to a reaction rate. The spectroscopic and collisional processes affecting the measured signals are discussed, and the foundation of the diagnostic, as based on laminar and unsteady flame calculations, is presented. We report the results of applying this diagnostic to the study of a laminar premixed flame subject to an interaction with an isolated line-vortex pair.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 43-50"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0082-0784(98)80388-3","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"95217768","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Triple flames in mixing layers with nonunity lewis numbers","authors":"J. Daou,&nbsp;A. Linán","doi":"10.1016/S0082-0784(98)80459-1","DOIUrl":"10.1016/S0082-0784(98)80459-1","url":null,"abstract":"<div><p>The present paper is devoted to the study of the effects of nonunity Lewis numbers on triple-flame propagation in nonuniform mixtures. For definiteness, the case of a strained reactive mixing layer is considered. The fuel and oxidizer that are fed to the mixing layer are allowed to have different initial temperatures. Specifically, we examine how the triple flames encountered in this context are influenced by (a) the transverse gradients in the temperature and composition of the fresh reactive mixture and (b) by differential-diffusion effects.</p><p>The analysis is carried for a single irreversible reaction with a large activation energy and using the thermo-diffusive model. Analytical expressions describing the flame shape, the local burning speed, and the propagation velocity of the triple flame are obtained. In particular, it is found that the Lewis numbers affect the propagation of the triple flame in a way similar to that obtained in the studies of stretched premixed flames. For example, the flame curvature determined by the transverse gradients in the frozen mixing layer leads to flame-front velocities that grow with decreasing values of the Lewis numbers.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 1","pages":"Pages 667-674"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0082-0784(98)80459-1","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"106399244","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Kinetic modeling of the ignition delays in monomethylhydrazine/oxygen/argon mixtures","authors":"L. Catoire ,&nbsp;T. Ludwig ,&nbsp;X. Bassin ,&nbsp;G. Dupré ,&nbsp;C. Paillard","doi":"10.1016/S0082-0784(98)80087-8","DOIUrl":"10.1016/S0082-0784(98)80087-8","url":null,"abstract":"<div><p>Ignition delay times for monomethylhydrazine (MMH or CH₃NHNH₂)/O₂/Ar gaseous mixtures have been modeled by a reaction scheme containing 70 species and 373 equilibrated elementary reactions. For many reactions, the rate constants had to be estimated or adjusted because rate constants are available for only a few reactions. The basis for a comparison with reality is measurements of ignition delay times behind reflected shock waves performed over a range of temperatures pressures, and composition. Good agreement between measured and calculated ignition delay times was obtained for lean and less dilute mixtures. A least-squares analysis of the computed ignition delays provides power dependences of the concentrations and an activation energy very similar with those obtained experimentally. The relative importance of the different reactions has been clearly shown by performing different sensitivity analyses. The reaction begins with the scission of the N-N bond in MMH, but elimination reactions from MMH also have to be considered, especially at high initial temperature. The NH₂ radicals formed react with MMH to give CH₃NNH₂ radicals and products. These radicals react with O₂ to produce methyldiazene (CH₃N=NH) and HO₂ radicals. These two species appear to be very important for this specific chemistry. In particular, HO₂ radicals react with MMH to give CH₃NNH₂ radicals and H₂O₂, this last species playing a major role through its thermal decomposition that produces hydroxyl radicals.</p></div>","PeriodicalId":101203,"journal":{"name":"Symposium (International) on Combustion","volume":"27 2","pages":"Pages 2359-2365"},"PeriodicalIF":0.0,"publicationDate":"1998-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0082-0784(98)80087-8","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"92677388","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}