• Title/Summary/Keyword: Turbulence Combustion Interaction

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Numerical Study on the Characteristics of Spray Combustion Processes in the DME and n-heptane Fueled Diesel-like Engine Conditions (DME 및 n-Heptane 연료의 디젤엔진 조건에서 분무연소특성 해석)

  • Yu, Yong-Wook;Suk, Jun-Ho;Lee, Sang-Kil;Kim, Yong-Mo
    • Journal of ILASS-Korea
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    • v.13 no.2
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    • pp.91-98
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    • 2008
  • In the present study, in order to understand the overall spray combustion characteristics of DME fuel as well as to identify the distinctive differences of DME combustion processes against the conventional hydrocarbon liquid fuels, the sequence of the comparative analysis have been systematically made for DME and n-heptane liquid fuels. To realistically represent the physical processes involved in the spray combustion, this studyemploys the hybrid breakup model, the stochastic droplet tracking model, collision model, high-pressure evaporation model, and transient flamelet model with detailed chemistry. Based on numerical results, the detailed discussions are made in terms of the autoignition, spray combustion processes, flame structure, and turbulence-chemistry interaction in the n-heptane and DME fueled spray combustion processes.

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Supersonic Combustion Modeling and Simulation for Scramjets

  • Ladeinde, Foluso
    • 한국연소학회:학술대회논문집
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    • 2015.12a
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    • pp.23-24
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    • 2015
  • In this talk, we will present what we believe is the state-of-the-art of the numerical modeling and simulation of the combustion processes as they relate to typical scramjet engines. The free-stream Mach number is hypersonic, but the speed is not sufficiently decelerated at the inlet/isolator, as in ramjets, so that combustion takes place under supersonic conditions. This creates some difficulties for most turbulence-combustion models. We delve into the details of these problems, by discussing the software programs that have a long track record for scramjet combustion simulation; with a focus on the accuracy of the baseline numerical methods used, the turbulence modeling/simulation approach, the comparative fidelity of the turbulence-combustion interaction models, ability to simulate premixed/non-premixed/partially-premixed, quenching/re-ignition capabilities, the numerical spark-plug method, Damkholer number regimes supported, and the effects of variable Prandtl, Schmidt, and Lewis numbers. Validation results from high-speed and low-speed combustion applications will also be presented.

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Numerical Analysis of a Highly Unstable Detonation Considering Viscosity and Turbulence Effects (점성 및 난류 효과를 고려한 강한 불안정 데토네이션 파의 수치 해석)

  • Kang, Ki-Ha;Shin, Jae-Ryul;Cho, Deok-Rae;Choi, Jeong-Yeol
    • Journal of the Korean Society of Propulsion Engineers
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    • v.15 no.4
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    • pp.57-64
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    • 2011
  • It has been suggested that turbulent effect should be considered for the study of highly unstable detonation of hydrocarbon fuels, as in the case of pulse detonation engine (PDE). A series of numerical study are carried out to understand the characteristics of the highly unstable detonation by considering viscosity, turbulence model and turbulence-combustion interaction model. Through studies of the different levels of modeling, it is understood that the viscosity and turbulence have negligible effects on low frequency characteristics, but tend to enhance the high frequency characteristics. It is also considered that the turbulence-chemistry interaction model should be taken the influence of the activation energy into account for detonation studies.

Numerical Study on Turbulent Nonpremixed Pilot Stabilized Flame using the Transported Probability Density Function Model (수송확률밀도함수 모델을 이용한 난류비예혼합 파일럿 안정화 화염장 해석)

  • Lee, Jeong-Won;Kim, Yong-Mo
    • Journal of the Korean Society of Combustion
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    • v.15 no.4
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    • pp.15-21
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    • 2010
  • The transported probability density function(PDF) model has been applied to simulate the turbulent nonpremixed piloted jet flame. To realistically account for the mixture fraction PDF informations on the turbulent non-premixed jet flame, the present Lagrangian PDF transport approach is based on the joint velocity-composition-turbulence frequency PDF formulation. The fluctuating velocity of stochastic fields is modeled by simplified Langevin model(SLM), turbulence frequency of stochastic fields is modeled by Jayesh-Pope model and effects of molecular diffusion are represented by the interaction by exchange with the mean (IEM) mixing model. To validate the present approach, the numerical results obtained by the joint velocity-composition-turbulence frequency PDF model are compared with experimental data in terms of the unconditional and conditional means of mixture fraction, temperature and species and PDFs.

Transported PDF Model for Turbulent Nonpremixed Flames (수송 확률밀도함수모델을 이용한 비예혼합 난류화염장 해석)

  • Lee, Jeong-Won;Seok, Joon-Ho;Kim, Yong-Mo
    • Journal of the Korean Society of Combustion
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    • v.14 no.2
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    • pp.32-41
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    • 2009
  • The transported probability density function model combined with the consistent finite volume (FV) method has been applied to simulate the turbulent bluff-body reacting flows. To realistically account for the non-isotropic turbulence effects on the turbulent bluff-body reacting flows, the present PDF transport approach is based on the joint velocity- turbulent frequency-composition PDF formulation. The evolution of the fluctuating velocity of a particle is modeled by a simplified Langevin equation and the particle turbulence frequency is represented by the modified Jayesh - Pope model. Effects of molecular diffusion are represented by the interaction by exchange with the mean (IEM) mixing model. To validate this hybrid FV/PDF transport model, the numerical results are compared with experimental data for the turbulent bluff-body reacting flows.

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MIXING CONDITIONS WITH SPRAY-JET INTERACTION FOR EFFECTIVE SOOT REDUCTION IN DIESEL COMBUSTION

  • Chikahisa, Takemi;Hishinuma, Yukio;Ushida, Hirohisa
    • International Journal of Automotive Technology
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    • v.3 no.1
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    • pp.17-26
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    • 2002
  • The authors have reported significant reductions in particulate emissions of diesel engines by generating strong turbulence during the combustion process. This study aims to identify optimum conditions of turbulent mixing for effective soot reduction during combustion. The experiments were conducted with a constant volume combustion vessel equipped with abet-generating cell, in which a small amount of fuel is injected during the combustion of the main spray. The jet of burned gas from the cell impinges the main flame, causing changes In the mixing of fuel and air. Observation was made for a variety combinations of distances between spray nozzle and Jet orifice at different directions of impingement. It Is shown that compared with the case without Jet flame soot decreases when the jet impinges. When the jet is very close to the flame, it penetrates the soot cloud and causes little mixing. There were no apparent differences in the combustion duration when the direction of impingement was varied, although the mechanisms of soot reduction seemed different. An analysis of local turbulent flews with PIV (Particle image Velocimetry) showed the relationship between the scale of the turbulence and the size of the soot cloud.

An Experimental Study on Turbulent Counter Jet Flame near Stagnation Point (대향 제트 정체점 주변의 난류 화염에 관한 연구)

  • Ko, Il-Min;Seo, Jeong-Il;Hong, Jung-Goo;Shin, Hyun-Dong
    • 한국연소학회:학술대회논문집
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    • 2006.04a
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    • pp.128-134
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    • 2006
  • A characterization of turbulent reacting flows has proved difficult owing to the complex interaction between turbulence, mixing, and combustion chemistry. There are many types of time scales in turbulent flame which can determine flame structure. This counter jet type premixed burner produces high intensity turbulence. The goal is to gain better insights into the flame structures at high turbulence. 6 propane/air flames gave been studied with high velocity fluctuation in bundle type nozzle and in one hole type nozzle. By measuring velocity fluctuation, turbulent intensity and integral length scale are obtained. And sets of OH LIF images were processed to see flame structure of the mean flame curvatures and flame lengths for comparison with turbulence intensity and turbulent length scales. The results show that the decrease in nozzle size generates smaller flow eddy and mean curvatures of the flame fronts, and a decrease in Damkohler number estimated from flow time scale measurement.

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Effects of Swirl number and Pressure on Flame Structure of Supercritical Kerosene Propellant Subscale Injector (선회수와 압력이 초임계상태 케로신 추진제 축소형 다중분사기의 화염구조에 미치는 영향 해석)

  • Park, Sangwoon;Kim, Taehoon;Kim, Yongmo
    • 한국연소학회:학술대회논문집
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    • 2013.06a
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    • pp.81-82
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    • 2013
  • This study has been mainly motivated to numerically model the supercritical mixing and combustion processes encountered in the liquid propellant rocket engines. In the present approach, turbulence is represented by the standard k-e model. To account for the real fluid effects, the propellant mixture properties are calculated by using generalized cubic equation of state. In order to realistically represent the turbulence-chemistry interaction in the turbulent nonpremixed flames, the flamelet approach based on the real fluid flamelet library has been adopted. Based on numerical results, the detailed discussions are made for the effects of swirl on flame structure of supercritical kerosene liquid propellant combustion.

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Numerical Prediction of NOx in the Nonpremixed Hydrogen-Air Flame using the Quasi-Laminar Reaction Modelling (준충류 근사를 이용한 수소-공기 비예혼합화염의 질소산화물 생성예측)

  • Kim, Seong-Lyong;Jeung, In-Seuck;Yoon, Young-Bin
    • Journal of the Korean Society of Combustion
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    • v.4 no.1
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    • pp.131-139
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    • 1999
  • A Numerical Analysis of NOx production in Hydrogen-Air flame is performed using the quasi-laminar reaction modelling. As results, in low global strain rate region, $U_F/D_F\;{\leq}\;50,000$, the quasi-laminar reaction modelling reproduces the experimentally observed EINOx half power scaling that the ratio of EINOx and flame residence time, $L_f^3(D_F^2U_F)$, is proportional to the square root of global strain rate. Thus, it suggests that turbulence-chemistry interaction has a minor impact on the trend of NOx production in low global strain rate region. However, the quasi-laminar reaction modelling predicts the higher temperature and NOx than experimentally observed. This overprediction may be due to the lack of radiation and quasi-laminar reaction modelling.

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Numerical Modeling for Vaporization, Auto-Ignition and Combustion Processes of Dimethyl Ether (DME) Fuel Sprays (DME 연료의 증발, 점화 및 분무연소특성 해석)

  • Yu, Yong-Wook;Lee, Jeong-Won;Kim, Yong-Mo
    • Journal of the Korean Society of Combustion
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    • v.12 no.3
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    • pp.33-39
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    • 2007
  • The present study is mainly motivated to investigate the vaporization, auto-ignition and combustion processes in high-pressure engine conditions. In order to realistically simulate the dimethyl ether (DME) spray dynamics and vaporization characteristics in high-pressure and high-temperature environment, the high-pressure vaporization model is utilized. The interaction between chemistry and turbulence is treated by employing the Representative Interaction Flamelet (RIF) model. The detailed chemistry of 336 elementary steps and 78 chemical species is used for the DME/air reaction. Numerical results indicate that the RIF approach, together with the high-pressure vaporization model, successfully predicts the essential feature of ignition and spray combustion processes.

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