The Experts below are selected from a list of 14631 Experts worldwide ranked by ideXlab platform
C. K. Chan - One of the best experts on this subject based on the ideXlab platform.
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Large-Eddy Simulation of Ethanol Spray Combustion Using a Finite-Rate Combustion Model
Cleaner Combustion and Sustainable World, 2012Co-Authors: L.x. Zhou, C. K. ChanAbstract:Large-eddy simulation of Spray Combustion is under its rapid development, but the Combustion models are less validated by detailed experimental data. In this paper, large-eddy simulation of ethanol-air Spray Combustion was made using an Eulerian-Lagrangian approach, a subgrid-scale kinetic energy stress model, and a finite-rate Combustion model. The simulation results are validated in detail by experiments. The LES obtained statistically averaged temperature is in agreement with the experimental results in most regions. The instantaneous LES results show the coherent structures of the shear region near the high-temperature flame zone and the fuel vapor concentration map, indicating the droplets are concentrated in this shear region. The droplet sizes are found to be in the range of 20–100μm. The instantaneous temperature map shows the close interaction between the coherent structures and the Combustion reaction.
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A pure Eulerian model for simulating dilute Spray Combustion
Fuel, 2002Co-Authors: C. K. ChanAbstract:A pure Eulerian model is developed to simulate steady-state dilute Spray Combustion. This model is based on a fundamental description of various interacting processes which occur during Spray Combustion including gas-phase and Spray droplet-phase turbulent flow, gas-phase turbulent Combustion, radiation heat transfer and Spray droplet evaporation. Both gas-phase and Spray droplet-phase conservation equations are described using Eulerian coordinates. A comprehensive mathematical model is used to simulate isothermal flow, combusting flow and kerosene Spray combusting flow in an axisymmetric sudden-expansion combustor. Validity of the model and the simulation scheme are established from the good agreement of the prediction with experimental data in gas-phase isothermal flow and propane combusting flow. Simulation of kerosene Spray Combustion shows that small droplets evaporate rapidly and do not enter the recirculation zone. For larger droplets, the length of recirculation zone is almost the same as that of the gas-phase. Simulated velocity, temperature and oxygen concentration for kerosene Combustion also agrees well with experimental results.
Tiegang Fang - One of the best experts on this subject based on the ideXlab platform.
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high speed imaging of oh chemiluminescence and natural luminosity of low temperature diesel Spray Combustion
Fuel, 2012Co-Authors: Ji Zhang, Wei Jing, Tiegang FangAbstract:Abstract This study focused on Spray Combustion of ultra low sulfur diesel (ULSD) fuel under low oxygen conditions with low temperature Combustion (LTC) mode in an optically accessible constant volume Combustion chamber. The ambient oxygen concentration was configured as 10% and 15% to achieve low flame temperature. The ambient gas temperature varied from 800 K to 1200 K. High speed imaging of OH* chemiluminescence and natural luminosity (NL) was used to visualize the instantaneous Spray Combustion process. The heat release rate was analyzed using the transient Combustion pressure and the flame structure was studied based on the Combustion images. Results show that a higher oxygen concentration case features a shorter ignition delay and higher heat release rate. The LTC mode can be realized by decreasing the oxygen concentration and ambient temperature simultaneously and it features a longer ignition delay, a slower reaction rate, and apparently lower soot radiation heat loss. The visualization results of NL and OH* show that the high temperature reaction occurs mainly in the mid-stream and downstream of the Spray Combustion, but not in the region very close to the chamber wall. This study validates the LTC process by showing very weak OH* chemiluminescence signal. The results also indicate that in order to realize LTC mode, it is important to control the ambient oxygen and ambient temperature at the same time. By only reducing the ambient oxygen concentration it may not be effective to suppress soot generation.
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High speed imaging of OH* chemiluminescence and natural luminosity of low temperature diesel Spray Combustion
Fuel, 2012Co-Authors: Ji Zhang, Wei Jing, Tiegang FangAbstract:Abstract This study focused on Spray Combustion of ultra low sulfur diesel (ULSD) fuel under low oxygen conditions with low temperature Combustion (LTC) mode in an optically accessible constant volume Combustion chamber. The ambient oxygen concentration was configured as 10% and 15% to achieve low flame temperature. The ambient gas temperature varied from 800 K to 1200 K. High speed imaging of OH* chemiluminescence and natural luminosity (NL) was used to visualize the instantaneous Spray Combustion process. The heat release rate was analyzed using the transient Combustion pressure and the flame structure was studied based on the Combustion images. Results show that a higher oxygen concentration case features a shorter ignition delay and higher heat release rate. The LTC mode can be realized by decreasing the oxygen concentration and ambient temperature simultaneously and it features a longer ignition delay, a slower reaction rate, and apparently lower soot radiation heat loss. The visualization results of NL and OH* show that the high temperature reaction occurs mainly in the mid-stream and downstream of the Spray Combustion, but not in the region very close to the chamber wall. This study validates the LTC process by showing very weak OH* chemiluminescence signal. The results also indicate that in order to realize LTC mode, it is important to control the ambient oxygen and ambient temperature at the same time. By only reducing the ambient oxygen concentration it may not be effective to suppress soot generation.
Luc Vervisch - One of the best experts on this subject based on the ideXlab platform.
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Analysis of weakly turbulent dilute-Spray flames and Spray Combustion regimes
Journal of Fluid Mechanics, 2005Co-Authors: Julien Reveillon, Luc VervischAbstract:Spray Combustion is analysed using a full simulation of the continuous gaseous carrier phase, while dilute-Spray modelling is adopted for the discrete phase. The direct numerical simulation of the flow is performed in an Eulerian context and a Lagrangian description is used for the Spray. The numerous physical parameters controlling Spray flames are first studied to construct two synthetic model problems of Spray Combustion: a laminar Spray flame that propagates freely over a train of droplets and a weakly turbulent Spray-jet with coflowing preheated air. It is observed that the flame structures can be classified with respect to three dimensionless quantities, which characterize the fuel/air equivalence ratio within the core of the Spray-jet, the ratio between the mean distance between the droplets and the flame thickness, and the ratio between an evaporation time and a flame time. A large variety of reaction zone topologies is found when varying those parameters, and they are scrutinized by distinguishing between premixed and diffusion Combustion regimes. Partially premixed Combustion is observed in most of the Spray-jet flames and the Spray parameters that make the flame transition from non-premixed to premixed Combustion are determined. A Combustion diagram for dilute-Spray Combustion is then proposed from the identification of those various regimes.
Ji Zhang - One of the best experts on this subject based on the ideXlab platform.
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high speed imaging of oh chemiluminescence and natural luminosity of low temperature diesel Spray Combustion
Fuel, 2012Co-Authors: Ji Zhang, Wei Jing, Tiegang FangAbstract:Abstract This study focused on Spray Combustion of ultra low sulfur diesel (ULSD) fuel under low oxygen conditions with low temperature Combustion (LTC) mode in an optically accessible constant volume Combustion chamber. The ambient oxygen concentration was configured as 10% and 15% to achieve low flame temperature. The ambient gas temperature varied from 800 K to 1200 K. High speed imaging of OH* chemiluminescence and natural luminosity (NL) was used to visualize the instantaneous Spray Combustion process. The heat release rate was analyzed using the transient Combustion pressure and the flame structure was studied based on the Combustion images. Results show that a higher oxygen concentration case features a shorter ignition delay and higher heat release rate. The LTC mode can be realized by decreasing the oxygen concentration and ambient temperature simultaneously and it features a longer ignition delay, a slower reaction rate, and apparently lower soot radiation heat loss. The visualization results of NL and OH* show that the high temperature reaction occurs mainly in the mid-stream and downstream of the Spray Combustion, but not in the region very close to the chamber wall. This study validates the LTC process by showing very weak OH* chemiluminescence signal. The results also indicate that in order to realize LTC mode, it is important to control the ambient oxygen and ambient temperature at the same time. By only reducing the ambient oxygen concentration it may not be effective to suppress soot generation.
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High speed imaging of OH* chemiluminescence and natural luminosity of low temperature diesel Spray Combustion
Fuel, 2012Co-Authors: Ji Zhang, Wei Jing, Tiegang FangAbstract:Abstract This study focused on Spray Combustion of ultra low sulfur diesel (ULSD) fuel under low oxygen conditions with low temperature Combustion (LTC) mode in an optically accessible constant volume Combustion chamber. The ambient oxygen concentration was configured as 10% and 15% to achieve low flame temperature. The ambient gas temperature varied from 800 K to 1200 K. High speed imaging of OH* chemiluminescence and natural luminosity (NL) was used to visualize the instantaneous Spray Combustion process. The heat release rate was analyzed using the transient Combustion pressure and the flame structure was studied based on the Combustion images. Results show that a higher oxygen concentration case features a shorter ignition delay and higher heat release rate. The LTC mode can be realized by decreasing the oxygen concentration and ambient temperature simultaneously and it features a longer ignition delay, a slower reaction rate, and apparently lower soot radiation heat loss. The visualization results of NL and OH* show that the high temperature reaction occurs mainly in the mid-stream and downstream of the Spray Combustion, but not in the region very close to the chamber wall. This study validates the LTC process by showing very weak OH* chemiluminescence signal. The results also indicate that in order to realize LTC mode, it is important to control the ambient oxygen and ambient temperature at the same time. By only reducing the ambient oxygen concentration it may not be effective to suppress soot generation.
Nijso Beishuizen - One of the best experts on this subject based on the ideXlab platform.
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modeling of turbulent dilute Spray Combustion
Progress in Energy and Combustion Science, 2012Co-Authors: Patrick Jenny, Dirk Roekaerts, Nijso BeishuizenAbstract:Abstract In a real turbulent Spray flame, dispersion, continuous phase turbulence modification, dispersed phase inter-particle collisions, evaporation, mixing and Combustion occur simultaneously. Dealing with all these complexities and their interactions poses a tremendous modeling task. Therefore, in order to advance current modeling capabilities, it seems reasonable to aim for progress in individual sub-areas like breakup, dispersion, mixing and Combustion, which however cannot be viewed in complete isolation. Further, one has to consider advantages and disadvantages of the general modeling approaches, which are direct numerical simulation (DNS), large eddy simulation (LES), simulations based on Reynolds averaged equations and probability density function (PDF) methods. Not least one also has to distinguish between Eulerian and Lagrangian dispersed phase descriptions. The goal of this paper is to provide a review of computational model developments relevant for turbulent dilute Spray Combustion, i.e. the dense regime, including collisions as well as primary and secondary atomization, is not covered. Also not considered is breakup in dilute Sprays, which can occur in the presence of sufficiently high local turbulence. It is intended to guide readers interested in theory, in the development and validation of predictive models, and in planning new experiments. In terms of physical phenomena, the current understanding regarding turbulence modification due to droplets, preferential droplet concentration, impact on evaporation and micro-mixing, and different Spray Combustion regimes is summarized. In terms of modeling, different sets of equations are discussed, i.e. the governing conservation laws without and with point droplet approximation as employed by DNS, the filtered equations considered in LES, the Reynolds averaged equations, and Lagrangian evolution equations. Further, small scale models required in the context of point droplet approximations are covered. In terms of computational studies and method developments, progress is categorized by the employed approaches, i.e. DNS, LES, simulations based on Reynolds averaged equations, and PDF methods. In terms of experiments, various canonical Spray flame configurations are discussed. Moreover, some of the most important experiments in this field are presented in a structured way with the intention to provide a database for model validation and a guideline for future investigations.
