International Journal of Spray and Combustion Dynamics最新文献_第10页

Modelling the generation of temperature inhomogeneities by a premixed flame 预混火焰产生温度不均匀性的建模

IF 1.6 4区工程技术

International Journal of Spray and Combustion Dynamics Pub Date : 2018-06-01 DOI: 10.1177/1756827717738139

T. Steinbacher, M. Meindl, W. Polifke

{"title":"Modelling the generation of temperature inhomogeneities by a premixed flame","authors":"T. Steinbacher, M. Meindl, W. Polifke","doi":"10.1177/1756827717738139","DOIUrl":"https://doi.org/10.1177/1756827717738139","url":null,"abstract":"The response of a laminar, premixed flame to perturbations of upstream equivalence ratio is investigated and modelled, with emphasis on the generation of ‘entropy waves’, i.e. entropic inhomogeneities of downstream temperature. Transient computational fluid dynamics simulations of two adiabatic lean methane-air flames of different Péclet numbers provide guidance and validation data for subsequent modelling. The respective entropy transfer functions, which describe the production of temperature inhomogeneities, as well as transfer functions for the variation of the heat release, are determined from the computational fluid dynamics time series data by means of system identification. The processes governing the dynamics of the entropy transfer functions are segregated into two sub-problems: (1) heat release due to chemical reaction at the flame front and (2) advective and diffusive transport. By adopting a formulation in terms of a mixture fraction variable, these two sub-problems can be treated independently from each other. Models for both phenomena are derived and analysed using simple 0- and 1-dimensional configurations. The heat release process (1) is represented by a fast-reaction-zone model, which takes into account variations of the specific heat capacity with equivalence ratio in order to evaluate the magnitude of downstream temperature fluctuations with quantitative accuracy. For the transport processes (2), two types of models based on mean field data from the computational fluid dynamics simulation are proposed: A semi-analytical, low-order formulation based on stream lines, and a state-space formulation, which is constructed by Finite Elements discretisation of the transport equation for mixture fraction. Model predictions for the entropy transfer functions are found to agree well with the computational fluid dynamics reference data at very low computational costs.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":"10 1","pages":"111 - 130"},"PeriodicalIF":1.6,"publicationDate":"2018-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1177/1756827717738139","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47746946","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 11

The effect of an axial mean temperature gradient on communication between one-dimensional acoustic and entropy waves 轴向平均温度梯度对一维声波和熵波通信的影响

IF 1.6 4区工程技术

International Journal of Spray and Combustion Dynamics Pub Date : 2018-06-01 DOI: 10.1177/1756827717743910

Jingxuan Li, Dong Yang, A. Morgans

{"title":"The effect of an axial mean temperature gradient on communication between one-dimensional acoustic and entropy waves","authors":"Jingxuan Li, Dong Yang, A. Morgans","doi":"10.1177/1756827717743910","DOIUrl":"https://doi.org/10.1177/1756827717743910","url":null,"abstract":"This work performs a theoretical and numerical analysis of the communication between one-dimensional acoustic and entropy waves in a duct with a mean temperature gradient. Such a situation is highly relevant to combustor flows where the mean temperature drops axially due to heat losses. A duct containing a compact heating element followed by an axial temperature gradient and choked end is considered. The proposed jump conditions linking acoustic and entropy waves on either side of the flame show that the generated entropy wave is generally proportional to the mean temperature ratio across the flame and the ratio ( F - 1 ) , where F is the flame transfer function. It is inversely proportional to the Mach number immediately downstream of the flame M2. The acoustic and entropy fields in the region of axial mean temperature gradient are calculated using four approaches: (1) using the full three linearised Euler equations as the reference; (2) using two linearised Euler equations in which the acoustic and entropy waves are assumed independent (thus allowing the extent of communication between the acoustic and entropy wave to be evaluated); (3) using a Helmholtz solver which neglects mean flow effects and (4) using a recently developed analytical solution. It is found that the communication between the acoustic and entropy waves is small at low Mach numbers; it rises with increasing Mach number and cannot be neglected when the mean Mach number downstream of the heating element exceeds 0.1. Predictions from the analytical method generally match those from the full three linearised Euler equations, and the Helmholtz solver accurately determines the acoustic field when M 2 ≤ 0 . 1 .","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":"10 1","pages":"131 - 153"},"PeriodicalIF":1.6,"publicationDate":"2018-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1177/1756827717743910","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47022234","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 8

An analytical model based on the G-equation for the response of technically premixed flames to perturbations of equivalence ratio 基于g方程的技术预混火焰对等效比扰动响应解析模型

IF 1.6 4区工程技术

International Journal of Spray and Combustion Dynamics Pub Date : 2018-06-01 DOI: 10.1177/1756827717740776

Alp Albayrak, W. Polifke

{"title":"An analytical model based on the G-equation for the response of technically premixed flames to perturbations of equivalence ratio","authors":"Alp Albayrak, W. Polifke","doi":"10.1177/1756827717740776","DOIUrl":"https://doi.org/10.1177/1756827717740776","url":null,"abstract":"A model for the response of technically premixed flames to equivalence ratio perturbations is proposed. The formulation, which is an extension of an analytical flame tracking model based on the linearized G-equation, considers the flame impulse response to a local, impulsive, infinitesimal perturbation that is transported by convection from the flame base towards the flame surface. It is shown that the contributions of laminar flame speed and heat of reaction to the impulse response exhibit a local behavior, i.e. the flame responds at the moment when and at the location where the equivalence ratio perturbation reaches the flame surface. The time lag of this process is related to a convective time scale, which corresponds to the convective transport of fuel from the base of the flame to the flame surface. On the contrary, the flame surface area contribution exhibits a non-local behavior: albeit fluctuations of the flame shape are generated locally due to a distortion of the kinematic balance between flame speed and the flow velocity, the resulting wrinkles in flame shape are then transported by convection towards the flame tip with the restorative time scale. The impact of radial non-uniformity in equivalence ratio perturbations on the flame impulse response is demonstrated by comparing the impulse responses for uniform and parabolic radial profiles. Considerable deviation in the phase of the flame transfer function, which is important for thermo-acoustic stability, is observed.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":"10 1","pages":"103 - 110"},"PeriodicalIF":1.6,"publicationDate":"2018-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1177/1756827717740776","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42007471","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 6

Advective disturbances in combustor thermoacoustics 燃烧室热声学中的对流扰动

IF 1.6 4区工程技术

International Journal of Spray and Combustion Dynamics Pub Date : 2018-05-22 DOI: 10.1177/1756827718773164

A. Morgans

引用次数: 0

Measurements in swirling spray flames at blow-off 吹出时旋涡喷射火焰的测量

IF 1.6 4区工程技术

International Journal of Spray and Combustion Dynamics Pub Date : 2018-03-23 DOI: 10.1177/1756827718763559

R. Yuan, J. Kariuki, E. Mastorakos

{"title":"Measurements in swirling spray flames at blow-off","authors":"R. Yuan, J. Kariuki, E. Mastorakos","doi":"10.1177/1756827718763559","DOIUrl":"https://doi.org/10.1177/1756827718763559","url":null,"abstract":"Various characteristics of swirling spray flames of ethanol, n-heptane, n-decane, and n-dodecane have been measured at conditions far from and close to blow-off using phase Doppler anemometry and OH* chemiluminescence, OH-planar laser-induced fluorescence, and Mie scattering at 5 kHz. The blow-off transient has also been examined. The OH* showed that the two main heat release regions lie around the spray jet at the inner recirculation zone and along the outer shear layer between the inner recirculation zone and the annular air jet. The heat release region is shortened and more attached as the flame approached blow-off. Mie images and phase Doppler anemometry data showed a wider dispersion of the ethanol spray compared to the other fuels. Similar spatial distributions of the Sauter mean diameter were observed for the four fuels for identical flow conditions, with the Sauter mean diameter value increasing with decreasing fuel volatility, but with the exception of significant presence of droplets in the nominally hollow cone for the ethanol spray. The OH-planar laser-induced fluorescence measurements showed an intermittent lift-off from the corner of the bluff body and the average lift-off height decreased with increasing air velocity, with less extinction along the inner flame branch especially for the heavier fuels. At the blow-off conditions, local extinctions appeared at both flame branches. The blow-off process followed a gradual reduction of the size of the flame, with the less volatile fuels showing a more severe flame area reduction compared to the condition far from blow-off. The average blow-off duration, τ ext , calculated from the evolution of the area-integrated OH* signal, was a few tens of milliseconds and for all conditions investigated the ratio τ ext /(D/UB) was around 11, but with large scatter. The measurements provide useful information for validation of combustion models focusing on local and global extinction.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":"10 1","pages":"185 - 210"},"PeriodicalIF":1.6,"publicationDate":"2018-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1177/1756827718763559","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"65532786","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 27

Liquid jet breakup unsteadiness in a coaxial air-blast atomizer 同轴空气射流雾化器中液体射流破裂的不稳定性

IF 1.6 4区工程技术

International Journal of Spray and Combustion Dynamics Pub Date : 2018-03-22 DOI: 10.1177/1756827718760905

Abhijeet Kumar, S. Sahu

{"title":"Liquid jet breakup unsteadiness in a coaxial air-blast atomizer","authors":"Abhijeet Kumar, S. Sahu","doi":"10.1177/1756827718760905","DOIUrl":"https://doi.org/10.1177/1756827718760905","url":null,"abstract":"The aim of this paper is to experimentally characterize the liquid jet breakup unsteadiness in a coaxial air-blast atomizer. The current research focuses on the measurement of the fluctuations of the jet breakup length and the flapping instability of the liquid jet, which contribute to the downstream fluctuations of the spray characteristics. The optical connectivity technique was used to measure the instantaneous breakup length of the water jet. Also, time resolved shadowgraph images of the primary jet breakup process were captured by high-speed imaging to characterize the jet instabilities at different axial locations from the atomizer exit. Experiments were performed for a wide range of air-to-liquid momentum flux ratio (M) and aerodynamic Weber number (Weg) corresponding to membrane- and/or fiber breakup mode of the jet disintegration process. The mean jet breakup length was found to vary inversely with M through a power law relation in agreement with the literature, while the breakup length fluctuations were found to first decrease and then increase with M. In order to capture the unsteady dynamics of the jet breakup process, the proper orthogonal decomposition analysis of the optical connectivity images was performed. The jet flapping and the fluctuations of the jet breakup length were identified as the second and the third spatial proper orthogonal decomposition modes, respectively, for all operating conditions of the atomizer. The amplitude and the frequency of the instabilities were measured by temporal tracking of the liquid–air interface on the shadowgraph images. The disturbance close to the injector exit corresponds to the Kelvin–Helmholtz instability, while close to the jet breakup point the jet exhibits the flapping instability, which is characterized by lateral oscillation of the jet about the atomizer axis. The influence of the liquid jet Reynolds number and momentum flux ratio on the KH and the flapping instabilities are examined.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":"10 1","pages":"211 - 230"},"PeriodicalIF":1.6,"publicationDate":"2018-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1177/1756827718760905","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44403251","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 29

Cycle-by-cycle variations in autonomous and spark assisted homogeneous charge compression ignition combustion of stoichiometric air–fuel mixture 化学计量空气-燃料混合物的自主和火花辅助均匀充气压缩点火燃烧中的逐循环变化

IF 1.6 4区工程技术

International Journal of Spray and Combustion Dynamics Pub Date : 2018-03-16 DOI: 10.1177/1756827718763564

J. Hunicz

{"title":"Cycle-by-cycle variations in autonomous and spark assisted homogeneous charge compression ignition combustion of stoichiometric air–fuel mixture","authors":"J. Hunicz","doi":"10.1177/1756827718763564","DOIUrl":"https://doi.org/10.1177/1756827718763564","url":null,"abstract":"This study investigates cycle-by-cycle variations in a gasoline fuelled, homogeneous charge compression ignition (HCCI) engine with internal exhaust gas recirculation. In order to study the effects of exhaust-fuel reactions occurring prior to the main combustion event fuel was injected directly into the cylinder at two selected timings during the negative valve overlap period. The engine was operated as both autonomous HCCI and spark assisted HCCI (SA-HCCI). The primary interest in this work was the operating region where the engine is switched between HCCI and spark ignition modes, thus operation with stoichiometric air–fuel mixture, which is typical for this region, was considered. Cycle-by-cycle variations in both combustion timing and indicated mean effective pressure (IMEP) were investigated. It was found that long-period oscillations of the IMEP occur when fuel injection is started at early stages of the negative valve overlap period, and that these can be suppressed by delaying the start of injection. This behaviour remained even when fuel injection was split into early and late-negative valve overlap injections. Spark assisted operation allowed eliminating late combustion cycles, thus improving thermal efficiency. However, characteristic patterns of IMEP variations were found to be the same for both HCCI and SA-HCCI operations, irrespective of the adopted negative valve overlap fuel injection strategy, as evidenced by using symbol-sequence statistics.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":"10 1","pages":"231 - 243"},"PeriodicalIF":1.6,"publicationDate":"2018-03-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1177/1756827718763564","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46275269","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 10

Common features in the thermoacoustics of flames and engines 火焰和发动机热声学的共同特征

IF 1.6 4区工程技术

International Journal of Spray and Combustion Dynamics Pub Date : 2018-03-01 DOI: 10.1177/1756827717743911

C. Lawn, G. Penelet

引用次数: 20

Dynamic responses of anchored ducted flames to harmonic velocity forcing 锚定导管火焰对谐波速度强迫的动力响应

IF 1.6 4区工程技术

International Journal of Spray and Combustion Dynamics Pub Date : 2018-03-01 DOI: 10.1177/1756827717735301

Ze-tian Ren, Suhui Li, Min Zhu

{"title":"Dynamic responses of anchored ducted flames to harmonic velocity forcing","authors":"Ze-tian Ren, Suhui Li, Min Zhu","doi":"10.1177/1756827717735301","DOIUrl":"https://doi.org/10.1177/1756827717735301","url":null,"abstract":"This paper aims at developing a computationally inexpensive method to investigate the premixed flame instabilities. The kinematic G-equation is combined with a two-dimensional discrete vortex method, and the conformal mapping is applied to make calculations for complicated geometries more efficiently. The vortex dynamics and flame response to harmonic velocity forcing of an anchored ducted V-flame are investigated, and the effects of harmonic forcing, Reynolds number, and bluff body geometry are examined. Results show that the vortex structures, flow instability, and flame response are closely coupled with each other. The unsteady vortex structures generate instabilities at the flame base, and the convection of the flame wrinkles then influences the flame dynamics downstream. The flame heat release fluctuates with larger amplitude under low-frequency forcings, while the phase of the flame transfer function is quasi-linear with increasing forcing frequency. Both higher inflow velocity and sharper bluff body corners can result in more unsteady large-scale vortex structures and hence influence the flame responses.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":"10 1","pages":"72 - 85"},"PeriodicalIF":1.6,"publicationDate":"2018-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1177/1756827717735301","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42872745","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Light sheet fluorescence microscopic imaging for high-resolution visualization of spray dynamics 用于喷雾动力学高分辨率可视化的光片荧光显微成像

IF 1.6 4区工程技术

International Journal of Spray and Combustion Dynamics Pub Date : 2018-03-01 DOI: 10.1177/1756827717734078

E. Berrocal, E. Kristensson, L. Zigan

{"title":"Light sheet fluorescence microscopic imaging for high-resolution visualization of spray dynamics","authors":"E. Berrocal, E. Kristensson, L. Zigan","doi":"10.1177/1756827717734078","DOIUrl":"https://doi.org/10.1177/1756827717734078","url":null,"abstract":"In this study, the use of light sheet fluorescence microscopic imaging is demonstrated for viewing the dynamic of atomizing sprays with high contrast and resolution. The technique presents several advantages. First, liquid fluorescence gives a more faithful representation of the structure of liquid bodies, droplets, and ligaments than Mie scattering does. The reason for this is that the signal is emitted by the fluorescing dye molecules inside the liquid itself and not generated at the air–liquid interfaces. Second, despite the short depth of field (∼200 µm) obtained when using the long range microscope, the contribution of out-of-focus light is much smaller on a light sheet configuration than for line-of-sight detection, thus providing more clearly sectioned images. Finally, by positioning the light sheet on the spray periphery, toward the camera objective, the effects due to multiple light scattering phenomena can be reduced to some extent. All these features provide, for many spray situations, good fidelity images of the liquid fluid, allowing the extraction of the velocity vectors at the liquid boundaries. Here, double frame images were recorded with a sCMOS camera with a time delay of 5 µs between exposures. A typical pressure-swirl atomizer is used producing a water hollow-cone spray, which was imaged in the near-nozzle region and further downstream for injection pressures between 20 bar and 100 bar. Furthermore, near-nozzle spray shape visualization of a direct-injection spark ignition injector was conducted, describing the disintegration of the liquid fuel and droplet formation. Such data are important for the validation of computational fluid dynamics models simulating liquid breakups in the near-field spray region.","PeriodicalId":49046,"journal":{"name":"International Journal of Spray and Combustion Dynamics","volume":"10 1","pages":"86 - 98"},"PeriodicalIF":1.6,"publicationDate":"2018-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1177/1756827717734078","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49352169","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 12