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Ryoichi Kurose - One of the best experts on this subject based on the ideXlab platform.

  • Displacement speed statistics in an open turbulent jet Spray Flame
    Fuel, 2021
    Co-Authors: Sean P. Malkeson, Umair Ahmed, C. Turquand D’auzay, Abhishek L. Pillai, Nilanjan Chakraborty, Ryoichi Kurose
    Abstract:

    Abstract In this study, a three-dimensional Direct Numerical Simulation of an open turbulent jet Spray Flame has been used to investigate the statistical behaviour of displacement speed S d and its components to provide physical explanations for the observed behaviours at different axial locations downstream of the jet exit. The open turbulent jet Spray Flame exhibits fuel-lean conditions close to the jet exit but fuel-rich conditions have been observed further downstream due to the evaporation of fuel droplets. For the axial locations considered, combustion takes place under low Damkohler number conditions. The displacement speed of reaction progress variable isosurfaces shows qualitatively similar behaviour for all axial locations considered – predominantly positive across the major part of the Flame but with small, potentially negative, values towards the burned-gas-side. The components of displacement speed arising from chemical reaction rate and Flame normal molecular diffusion remain leading order contributors and the competition between these determines the mean behaviour of displacement speed. These observations are consistent with studies of turbulent Spray Flames in canonical configurations and low Damkohler number turbulent premixed and stratified Flames. This suggests that flow geometry in the absence of mean curvature might not be important in determining the mean behaviour of displacement speed and its components. Therefore, the modelling methodologies employed for turbulent stratified Flames can potentially be extended for turbulent Spray Flames. However, the modelling methodologies, which implicitly assume equality between the surface-weighted values of density-weighted displacement speed and local laminar burning velocity, might be rendered invalid for turbulent Spray Flames.

  • two dimensional direct numerical simulation of Spray Flames part 1 effects of equivalence ratio fuel droplet size and radiation and validity of Flamelet model
    Fuel, 2013
    Co-Authors: Akitoshi Fujita, Hiroaki Watanabe, Ryoichi Kurose, Satoru Komori
    Abstract:

    The effects of equivalence ratio, fuel droplet size, and radiation on jet Spray Flame are investigated by means of two-dimensional direct numerical simulation (DNS). In addition, the validity of an extended Flamelet/progress-variable approach (EFPV), in which heat transfer between droplets and ambient fluid including radiation is exactly taken into account, is examined. n-decane (C10H22) is used as liquid Spray fuel, and the evaporating droplets’ motions are tracked by the Lagrangian method. The radiative heat transfer is calculated using the discrete ordinate method with S8 quadrature approximation. The results show that the behavior of jet Spray Flame is strongly affected by equivalence ratio and fuel droplet size. The general behavior of the jet Spray Flames including the heat transfer between droplets and ambient fluid with radiation effect can be captured by EFPV.

  • analysis and Flamelet modelling for Spray combustion
    Journal of Fluid Mechanics, 2008
    Co-Authors: Yuya Baba, Ryoichi Kurose
    Abstract:

    The validity of a steady-Flamelet model and a Flamelet/progress-variable approach for gaseous and Spray combustion is investigated by a two-dimensional direct numerical simulation (DNS) of gaseous and Spray jet Flames, and the combustion characteristics are analysed. A modified Flamelet/progress-variable approach, in which total enthalpy rather than product mass fraction is chosen as a progress variable, is also examined. DNS with an Arrhenius formation, in which the chemical reaction is directly solved in the physical flow field, is performed as a reference to validate the combustion models. The results show that the diffusion Flame is dominant in the gaseous diffusion jet Flame, whereas diffusion and premixed Flames coexist in the Spray jet Flame. The characteristics of the Spray Flame change from premixed-diffusion coexistent to diffusion-dominant downstream. Comparisons among the results from DNS with various combustion models show the modified Flamelet/progress-variable approach to be superior to the other combustion models, particularly for the Spray Flame. Where the behaviour of the gaseous total enthalpy is strongly affected by the energy transfer (i.e. heat transfer and mass transfer) from the dispersed droplet, and this effect can be accounted for only by solving the conservation equation of the total enthalpy. However, even the DNS with the modified Flamelet/progress-variable approach tends to underestimate the gaseous temperature in the central region of the Spray jet Flame. To increase the prediction accuracy, a combustion model for the partially premixed Flame for the Spray Flame is necessary.

  • effects of radiation on Spray Flame characteristics and soot formation
    Combustion and Flame, 2008
    Co-Authors: Hiroaki Watanabe, Ryoichi Kurose, Satoru Komori, Heinz Pitsch
    Abstract:

    Two-dimensional numerical simulations are applied to Spray Flames formed in a laminar counterflow and the effects of radiation on Spray Flame characteristics and soot formation are studied. N-Decane (C10H22) is used as the liquid fuel, and the droplet motion is calculated by the Lagrangian method. A single-step global reaction is employed for the combustion reaction model. A kinetically based soot model with a Flamelet model is used to predict soot formation. Radiation is taken into account using the discrete ordinate method. The results show that radiation strongly affects the Spray Flame behavior and soot formation. Without the radiation model, Flame temperature and soot volume fraction are greatly overestimated. The soot is formed in the diffusion Flame regime, and its radiation emission increases with the increase in the equivalence ratio of the droplet fuel. This trend is in good agreement with that of the luminous Flame behavior observed in the experiments.

  • characteristics of Flamelets in Spray Flames formed in a laminar counterflow
    Combustion and Flame, 2007
    Co-Authors: Hiroaki Watanabe, Ryoichi Kurose, Seungmin Hwang, Fumiteru Akamatsu
    Abstract:

    Abstract A two-dimensional numerical simulation of a Spray Flame formed in a laminar counterflow is presented, and the Flamelet characteristics are studied in detail. The effects of strain rate, equivalence ratio, and droplet size are examined in terms of mixture fraction and scalar dissipation rate. n-Decane (C10H22) is used as a liquid Spray fuel, and the droplet motion is calculated by the Lagrangian method without the parcel model. A one-step global reaction is employed for the combustion reaction model. The results show that there appear large differences in the trends of gaseous temperature and mass fractions of chemical species in the mixture fraction space between the Spray Flame and the gaseous diffusion Flame. The gas temperature in the Spray Flame is much higher than that in the gaseous diffusion Flame. This is due to the much lower scalar dissipation rate and the coexistence of premixed and diffusion-limited combustion in the Spray Flame. For the Spray Flames, gas temperature and mass fractions of chemical species are not unique functions of the mixture fraction scalar dissipation rate. This is because the production rate of the mixture fraction, namely evaporation rate of the droplets, in the upstream region is not in proportion to its transport-diffusion rate in the downstream region. The behavior shows marked differences as the strain rate decreases, the equivalence ratio increases, or the droplet size decreases.

Keiya Nishida - One of the best experts on this subject based on the ideXlab platform.

  • experimental study on flat wall impinging Spray Flame and its heat flux on wall under diesel engine like condition first report effect of impingement distance
    Proceedings of the Institution of Mechanical Engineers Part D: Journal of Automobile Engineering, 2019
    Co-Authors: Rizal Mahmud, Keiya Nishida, Toru Kurisu, Yoichi Ogata, Jun Kanzaki, Tadashi Tadokoro
    Abstract:

    Reducing heat loss is one of the most important development concerns for improving the thermal efficiency of the diesel engine. In order to know heat transfer through the combustion chamber wall mo...

  • effects of micro hole nozzle and ultra high injection pressure on air entrainment liquid penetration Flame lift off and soot formation of diesel Spray Flame
    International Journal of Engine Research, 2017
    Co-Authors: Keiya Nishida, Xianyin Leng, Zhixia He
    Abstract:

    Increasing the injection pressure and downsizing the nozzle orifice diameter have been major measures for diesel engines to facilitate fuel–ambient gas mixture formation and combustion processes. The objective of this investigation is to carry out a quantitative analysis on the effects of micro-hole nozzle and ultra-high injection pressure on the mixing and combustion characteristics of diesel Spray Flame. Hence, laser-induced fluorescence and particle image velocimetry technique was employed to quantitatively access the gas entrainment of diesel Spray emerging from nozzle with orifice diameter down to 80 µm under injection pressure up to 300 MPa, together with OH* chemiluminescence imaging and two-color pyrometry techniques to resolve the combustion and soot formation processes. Additionally, numerical simulation on the multi-phase flow inside injector nozzle was conducted to obtain information on internal flow dynamics. Experimental results show that over 80% of the ambient gas entrained into a Spray pl...

  • effects of ultra high injection pressure and micro hole nozzle on Flame structure and soot formation of impinging diesel Spray
    Applied Energy, 2011
    Co-Authors: Xiangang Wang, Olawole Abiola Kuti, Zuohua Huang, Wu Zhang, Keiya Nishida
    Abstract:

    The effects of ultra-high injection pressure (Pinj = 300 MPa) and micro-hole nozzle (d = 0.08 mm) on Flame structure and soot formation of impinging diesel Spray were studied with a high speed video camera in a constant volume combustion vessel. Two-color pyrometry was used to measure the line-of-sight soot temperature and concentration with two wavelengths of 650 and 800 nm. A flat wall vertical to the injector axis is located 30 mm away from the injector nozzle tip to generate impinging Spray Flame. Three injection pressures of 100, 200 and 300 MPa and two injector nozzles with diameters of 0.16 and 0.08 mm were used. With the conventional injector nozzle (0.16 mm), ultra-high injection pressure generates appreciably lower soot formation. With the micro-hole nozzle (0.08 mm), impinging Spray Flame shows much smaller size and lower soot formation at the injection pressure of 100 MPa. The soot formation is too weak to be detected with the micro-hole nozzle at injection pressures of 200 and 300 MPa. With eliminating the impact of injection rate on soot level, both ultra-high injection pressure and micro-hole nozzle have an obvious effect on soot reduction. Soot formation characteristics of impinging Spray Flame were compared with those of free Spray Flame using both the conventional and micro-hole nozzles. With the conventional nozzle, flat wall impingement deteriorates soot formation significantly. While soot formation characteristics of free Spray Flame with the micro-hole nozzle are not altered obviously by flat wall. Liquid length of the 0.16 mm nozzle is longer than the impingement distance and liquid length of the 0.08 mm nozzle is shorter than the impingement distance. Liquid impingement upon the wall is responsible for the deteriorated soot level of impinging Flame compared to that of free Flame with the conventional nozzle.

  • Effect of Injection Pressure on Flame and Soot Characteristics of the Biodiesel Fuel Spray
    Combustion Science and Technology, 2010
    Co-Authors: Xiangang Wang, Keiya Nishida, Olawole Abiola Kuti, Wu Zhang, Zuohua Huang
    Abstract:

    The authors studied the effect of injection pressure on nonevaporating Spray and Spray Flame characteristics of biodiesel fuel injected by a common rail injection system in a constant volume combustion vessel. Two biodiesels, biodiesel from palm oil (BDFp) and biodiesel from cooked oil (BDFc) were investigated, including JIS#2 Diesel. Mie scattering technique was employed to investigate nonevaporating Spray characteristics. High-speed direct photography and two-color pyrometry were applied for Spray Flame characteristics. Injection pressures of 100, 200, and 300 MPa and ambient environment typical of diesel engine were used. Nonevaporating Spray result showed that biodiesel fuels give longer Spray tip penetrations and narrower Spray angles especially for BDFp. Integrated Flame luminosity of BDFp and BDFc show lower values compared to that of diesel at injection pressure of 100 MPa, and integrated Flame luminosity of BDFp and BDFc is even lower than that of diesel at injection pressures of 200 and 300 MPa....

Matthias Ihme - One of the best experts on this subject based on the ideXlab platform.

  • analysis of low temperature chemistry in a turbulent swirling Spray Flame near lean blow out
    Proceedings of the Combustion Institute, 2020
    Co-Authors: Danyal Mohaddes, Wenwe Xie, Matthias Ihme
    Abstract:

    Abstract An n-dodecane swirling Spray Flame from the Cambridge Flame series is simulated using large-eddy simulation (LES) at conditions near the lean blow-out (LBO) limit. The focus of this study is to examine effects of low-temperature chemistry (LTC) and Spray evaporation in turbulent Spray combustion. To this end, a first simulation is performed using a finite rate chemistry model with a 55-species skeletal mechanism including LTC in a fully compressible Eulerian-Lagrangian formulation. A second simulation is performed using the same formulation, but with the LTC chemical sub-mechanism deactivated. The interactions of Spray and gas-phase mixing and combustion are investigated through the consideration of mean and instantaneous LES results. Chemical explosive mode analysis (CEMA) is extended to account for droplet evaporation in the context of Spray combustion, the results of which reveal that the Flame is dominated by non-premixed combustion without significant auto-ignitive behavior. CEMA results further show that the effect of Spray evaporation on the reaction is two-fold, namely to inhibit reaction near the injector through heat absorption, and to facilitate reaction further downstream by supplying fuel to the gas phase. Mixture fraction-conditioned analysis is then performed to evaluate the importance of LTC in the turbulent Spray Flame, showing its effect on heat release despite the Flame not exhibiting auto-ignitive behavior. A polar mapping is proposed for analyzing the complex interplay of low and high temperature chemistry heat release. The results have consequences for numerical modeling of Spray combustion systems where LTC effects are commonly neglected.

  • assessment of Spray combustion models in large eddy simulations of a polydispersed acetone Spray Flame
    Proceedings of the Combustion Institute, 2019
    Co-Authors: Qing Wang, Thomas Jaravel, Matthias Ihme
    Abstract:

    Abstract Spray combustion is of practical importance to various applications. To study Spray Flames, benchmark cases were investigated both experimentally and numerically. Previous numerical studies of these Flames have identified sensitivities to gas-phase combustion models and the description of the droplet evaporation. The objective of this work is to examine effects of combustion models on the structure of an acetone Spray Flame. To this end, three different combustion models are examined, namely a finite-rate chemistry model, a Flamelet/progress variable model, and a Flame prolongation of intrinsic low dimensional manifold model. In the two Flamelet approaches, effects of Spray evaporation are considered in the limit of small Stokes number. By examining radial profiles and employing a doubly-conditioned analysis on gaseous mixture fraction and liquid-to-gas mass ratio, it is shown that both Flamelet models show differences in the evaporation and subsequent gas phase combustion and temperature field. The use of a finite-rate combustion model in conjunction with a reduced chemical mechanism provide improved predictions of heat release and Spray-Flame structure.

  • analysis of segregation and bifurcation in turbulent Spray Flames a 3d counterflow configuration
    Proceedings of the Combustion Institute, 2015
    Co-Authors: Benedetta Franzelli, Matthias Ihme, Tianfeng Lu, Hai Wang
    Abstract:

    Abstract The understanding of Spray combustion processes is of primary importance, as it is encountered in a wide range of industrial applications. In the present work, mesoscale-resolved simulations of a 3D turbulent counterflow Spray configuration are conducted. Primary focus is on examining the effect of the coupling between turbulence, evaporation, mixing, and combustion. By considering different initial droplet diameters and through comparisons with turbulent and laminar configurations at the same operating condition, it is shown that preferential concentration can lead to conditions of locally high mixture-fraction composition. In addition, local variability in strain rate and droplet diameter introduces a bifurcation of the Spray Flame. This bifurcation consists of Spray Flame structures exhibiting single-reaction or double-reaction structures. It is shown that this bimodal behavior is linked to the existence of a hysteresis in the laminar Spray Flame structure for droplet diameter variations, as well as the occurrence of a bifurcation for strain rate variations. These results have direct implications for Flamelet-based tabulation methods, since identifying the appropriate Flamelet structure in turbulent Spray Flames would require informations about boundary conditions and the Flamelet history.

Uno Renou - One of the best experts on this subject based on the ideXlab platform.

  • simultaneous imaging of soot volume fraction pah and oh in a turbulent n heptane Spray Flame
    Combustion and Flame, 2019
    Co-Authors: Irfa A Mulla, Uno Renou
    Abstract:

    Abstract Soot formation and oxidation in a turbulent n-heptane jet Spray Flame are investigated through simultaneous imaging of quantitative soot volume fraction (fv), Flame-front (OH), and soot-precursor marked by smaller (2–4 ring) polycyclic aromatic hydrocarbons (PAH). Laser-induced incandescence (LII) and laser-induced fluorescence (LIF) techniques are used. The Spray Flame is composed of a dual branch axisymmetric structure. The inner composite branch (B1) consists of fuel-lean and non-premixed reaction zones, whereas combustion in the outer branch (B2) occurs in a non-premixed mode. Frequent local Flame extinctions occur along B1, while no extinctions are observed in B2. Consequently, the soot inception occurs near B2. In the onset of soot detection (fv ≥ 0.03 ppm) region, soot layers are thinner than those from downstream regions where soot occupies nearly the same area as of PAH. Soot generally oxidizes across the Flame-front as evidenced from the absence of soot-OH overlap. The soot structures are intermittent with peak soot probability of 60%. The most probable peak fv measures 1 ppm, while the conditional mean is 0.42 ppm which is 2.5 times that of time-averaged fv. Conditional mean fv shows monotonically increasing trend with height. The Flame lift-off height and local extinctions do not instantaneously influence the soot concentration, possibly due to larger convective and soot formation timescales. Soot-PAH correlations are explored. However, no strong instantaneous correlations are noted, most likely due to different chemical timescales of soot and the imaged smaller-PAH. Nevertheless, a few distinct trends are noted in soot-PAH correlations. fv weakly increases with the PAH-LIF intensity. The PAH intensity from soot onset to peak region decreases, while both soot and PAH are nearly consumed at a local Flame-tip (oxidation) region. The soot-PAH overlap decreases consistently from soot onset to oxidation region. The reported database and deduced insights can aid in the development and validation of soot models in two-phase reacting flows.

  • quantitative imaging of nitric oxide concentration in a turbulent n heptane Spray Flame
    Combustion and Flame, 2019
    Co-Authors: Irfa A Mulla, Gilles Cabo, Gilles Godard, Frederic Grisch, Uno Renou
    Abstract:

    Abstract The present work reports quantitative planar imaging of Nitric Oxide (NO) concentration in a dilute Spray Flame at atmospheric pressure, contributing to CORIA Rouen Spray Burner (CRSB) database. Mean NO mole fraction (χNO) is measured using planar laser-induced fluorescence (PLIF) technique, while the Flame front is located simultaneously using OH-PLIF. An optimum NO excitation scheme is selected to minimize temperature-quenching dependence based on LIF simulations. Furthermore, the temperature and collisional quenching effects on NO fluorescence are corrected by using the temperature and gas composition obtained from large eddy simulation performed in previous work [Proc. Combust. Inst., 36 (2017), 2567-2575]. Additionally, interference in NO-PLIF from polycyclic aromatic or unburned hydrocarbon fluorescence is corrected by detuned (NO off-transition) signal subtraction. The spatial distribution of χNO is discussed in the context of a Spray Flame topology, which exhibits two distinct branches. The results suggest the formation of prompt NO on the inner composite branch (fuel-lean and non-premixed) and thermal NO on the outer pure non-premixed branch. χNO at 60 mm height above burner measures 33 ppm near the inner branch, and 75 ppm around the outer branch.

  • experimental study of local Flame structures and fuel droplet properties of a Spray jet Flame
    Proceedings of the Combustion Institute, 2017
    Co-Authors: Antoine Verdie, Javier Marrero Santiago, Alexis Vandel, Sawitree Saengkaew, Gilles Cabo, Gerard Greha, Uno Renou
    Abstract:

    Abstract An n-heptane Spray jet Flame is characterised through quantitative measurements using laser-based techniques. The experimental set-up is composed of an annular non-swirled air co-flow that surrounds a central hollow-cone Spray injector, leading to a stable Flame with well- defined boundary conditions. Phase Doppler anemometry (PDA) measurements contribute to this investigation through the analysis of air and droplet aerodynamics and OH-PLIF images describe the two dimensional Flame structure. The polydisperse Spray distribution yields small droplets along the centreline axis while the majority of the mass is situated as big droplets along the Spray borders. The Flame structure presents a classical shape, with an inner wrinkled partially premixed Flame front and an outer diffusion Flame front. In addition Global Rainbow Refractometry Technique (GRT) has been used to measure droplet temperature in the different regions of the Spray jet Flame. This technique was first applied with a continuous laser (C-GRT) to get temporally averaged values of fuel droplet temperature according to the methodology developed initially by Letty et al. [1] . This technique has been extended to measure instantaneous and local fuel droplet temperature by using a pulsed laser. Therefore, conditional averaged measurements of fuel droplet temperature according to the distance of Flame front are reported for the first time by coupling instantaneous GRT (I-GRT) with OH-PLIF. New insights on the thermal droplet behaviour in a Spray Flame are discussed.

  • experimental and numerical analysis of a turbulent Spray Flame structure
    Proceedings of the Combustion Institute, 2017
    Co-Authors: F Shumkiva, Antoine Verdie, Gilles Cabo, Uno Renou, Marrero J Santiago, Eleonore Ribe, Enedicte Cueno
    Abstract:

    Abstract An experimental and numerical study of an academic n -heptane/air lab-scale jet Spray burner is presented. The objective is to provide new insight on turbulent Spray Flame complex structures similar to those encountered in industrial combustors by joint experimental and numerical diagnostics. Experimental measurements include PDA for air velocity and droplet size as well as velocity and OH-PLIF images for the Flame analysis. Numerical simulations consist in Large Eddy Simulation (LES) coupled to Discrete Particle Simulation for the dispersed phase. The comparison between experiment and simulation confirms the capability of LES to reproduce the gaseous and liquid flow structure in both non-reacting and reacting cases with good accuracy. The lifted stabilized Spray Flame exhibits a complex shape due to interactions between turbulence, chemistry and evaporation. A detailed analysis shows that both partially-premixed and diffusion Flames are present, depending on the capacity of droplets to evaporate. Furthermore, an attempt is made to identify the processes leading to two-phase Flame stabilization.

Aoxiang Peng - One of the best experts on this subject based on the ideXlab platform.

  • selective cyclohexene oxidation with o2 h2o2 and tert butyl hydroperoxide over Spray Flame synthesized laco1 xfexo3 nanoparticles
    Catalysis Science & Technology, 2020
    Co-Authors: Julia Uke, Christof Schulz, Aris Alka, Wei Xia, Jonas Schulwitz, Daniel Waffel, Tobias Falk, Hartmu Wiggers, Marti Muhle, Aoxiang Peng
    Abstract:

    The elimination of waste and by-product generation and reduced dependence on hazardous chemicals are the key steps towards environmentally sustainable chemical transformations. Heterogeneously catalysed oxidation of cyclohexene with environmentally friendly oxidizing agents such as O2, H2O2 and tert-butyl hydroperoxide (TBHP) has great potential to replace existing processes using stoichiometric oxidants. A series of Spray-Flame synthesised nanoparticulate LaCo1−xFexO3 catalysts was employed for cyclohexene oxidation, and the comparative results showed that TBHP led to the highest initial activity and allylic selectivity, but O2 resulted in higher conversion for longer reaction times. Furthermore, the influence of Fe substitution was studied, which did not show any beneficial synergistic effects. LaCoO3 was found to be the optimum catalyst for cyclohexene oxidation with O2, following first-order reaction kinetics with an apparent activation energy of 57 kJ mol−1. The catalyst showed good reusability due to its highly stable particle size, morphology and perovskite structure. 7-Oxabicyclo[4.1.0]heptan-2-one was identified to be formed by the oxidation of 2-cyclohexene-1-one with 2-cyclohexene-1-hydroperoxide.

  • towards mechanistic understanding of liquid phase cinnamyl alcohol oxidation with tert butyl hydroperoxide over noble metal free laco1 xfexo3 perovskites
    ChemPlusChem, 2019
    Co-Authors: Daniel Waffel, Christof Schulz, Aris Alka, Hartmu Wiggers, Marti Muhle, Aoxiang Peng, Yenting Che, Stefa Schmid
    Abstract:

    : Noble-metal-free perovskite oxides are promising and well-known catalysts for high-temperature gas-phase oxidation reactions, but their application in selective oxidation reactions in the liquid phase has rarely been studied. We report the liquid-phase oxidation of cinnamyl alcohol over Spray-Flame synthesized LaCo1-x Fex O3 perovskite nanoparticles with tert-butyl hydroperoxide (TBHP) as the oxidizing agent under mild reaction conditions. The catalysts were characterized by XRD, BET, EDS and elemental analysis. LaCo0.8 Fe0.2 O3 showed the best catalytic properties indicating a synergistic effect between cobalt and iron. The catalysts were found to be stable against metal leaching as proven by hot filtration, and the observed slight deactivation is presumably due to segregation as determined by EDS. Kinetic studies revealed an apparent activation energy of 63.6 kJ mol-1 . Combining kinetic findings with TBHP decomposition as well as control experiments revealed a complex reaction network.