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Huh, Kang Y.
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Improved Lagrangian CMC for Simulation of Combustion Under Diesel-like Condition

Pohang Univ. of Science and Technology-Karam Han, Jaeyeob Seo, Kang Y. Huh
Published 2013-10-14 by SAE International in United States
The conditional moment closure (CMC) model has successfully been employed for simulation of turbulent nonpremixed combustion in diverse engineering problems. The solution procedure was developed for Lagrangian CMC with a single or multiple fuel or flame groups for a diesel engine in our previous work. Multiple flame groups may consider different histories and residence times through the sequence of evaporation, ignition and mixing controlled combustion. The Lagrangian CMC model has an advantage of less computational burden than Eulerian CMC with fixed spatially resolved grids. However, it cannot allow interaction among different flame groups through premixed combustion, while such interaction occurs through spatial transport terms in Eulerian CMC. In this work an improved version of the Lagrangian CMC model is proposed to consider interaction by premixed flame propagation along a constant mixture fraction contour between neighboring flame groups. The new Lagrangian CMC model is implemented in OpenFOAM and validated for turbulent spray jet flames in diesel-like conditions in the Engine Combustion Network (ECN). Simulations are performed with diverse arrangement of flame groups for a quasi-steady injection…
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Simulation of a Heavy Duty Diesel Engine Fueled with Soybean Biodiesel Blends in Low Temperature Combustion

KIMM-Seungmook Oh
Pohang Univ. of Science and Technology-Youngjae Lee, Kwonwoo Jang, Karam Han, Kang Y. Huh
Published 2013-04-08 by SAE International in United States
Low temperature combustion (LTC) may allow simultaneous reduction of nitrogen oxides (NOx) and soot with acceptable compromise in the efficiency of a diesel engine. Recently oxygenate biodiesel fuels were tested to resolve the problem of CO emission at higher exhaust gas recirculation (EGR) rates in LTC operation. In this paper 3-D simulation is performed by KIVA with soybean biodiesel blends of D100 and BD20 for a heavy duty test engine. The oxygen fraction in intake gas is controlled between 7% and 19% to simulate EGR in LTC operation. A surrogate mechanism is constructed by combining the skeletal mechanisms of methyl butanoate (MB) and n-heptane for low and high temperature chemistry. It consists of 76 species and 243 reaction steps with detailed NOx chemistry. The conditional moment closure (CMC) model is employed to address coupling between turbulence and chemistry. Results show acceptable agreement with measured pressure traces, heat release rates and CO, NOx and particulate matter (PM) emissions. There is no significant difference between D100 and BD20 for ignition delays in the test conditions. CO is…
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Prediction of Number Density, Volume Fraction and Size Distribution of Soot Particles in a Diesel Engine under Various Operating Conditions

Pohang Univ of Science and Technology-Jaeseo Lee, Kang Y. Huh
Published 2012-04-16 by SAE International in United States
Computation is performed to predict number density, volume fraction and size distribution of soot particles in typical operating conditions of a diesel engine. KIVA has been integrated with the CMC routine to consider turbulence/chemistry coupling and gas phase kinetics for heat release and soot precursors. The compositions of soot precursors are estimated by tracking Lagrangian particles to consider spatial inhomogeneity and differential diffusion in KIVA. The soot simulator SWEEP is employed as a postprocessing step to calculate conditional and integral quantities of soot particles. There are larger particles produced at a higher load or a lower rpm, but no consistent trend for injection timing in the conditional size distribution at the mixture fraction of 0.12. The integral results are obtained for number density, total mass and size distribution by summing up the histories of all tracked particles in the cylinder. They show similar overall trends as the conditional results, while the size distribution shows an opposite trend with respect to rpm due to the competing effects of time for particle growth and the degree of…
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Zero-Dimensional Simulation of Diesel Engine Combustion and Emissions Based on CMC Model and Skeletal Reaction Mechanism

SAE International Journal of Engines

Pohang Univ. of Science and Technology-Jaesung Kwon, Jaeyeob Seo, Dongkyu Lee, Kang Y. Huh
  • Journal Article
  • 2011-01-0845
Published 2011-04-12 by SAE International in United States
A zero-dimensional code is developed to simulate turbulent spray combustion and NOx and soot emission in direct injection diesel engines. The code consists of two major parts; mixing calculation for the probability density function (PDF) based on the multi-zone model by Hiroyasu et al., (1983) and the flame structure by the conditional moment closure (CMC) model (Klimenko & Bilger, 1999). The skeletal mechanism of n-heptane is employed with the elementary reaction steps for heat release and the NOx chemistry in GRI 3.0. The spray model accounts for evaporation and mixing based on momentum balance of the spray zones, while the CMC model incorporates the conditional flame structures with one fuel group or flame structure for each injection. The spatially integrated density-weighted PDF, F(η), is defined to represent inhomogeneous mixture distribution in the cylinder. The one-equation soot model is employed for prediction of the soot emission. The program has been validated over a wide range of load and rpm with different injection schedules and EGR levels. Comparison shows reasonable agreement with measurements for the pressure trace…
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Parametric Evaluation of Design and Operating Conditions of a Low Temperature Combustion Diesel Engine through 3-D Simulation

Korea Institute of Machinery & Materials-Seung M. Oh, Sunyoup Lee
Pohang Univ. of Science and Technology-Young J. Lee, Kang Y. Huh
Published 2011-04-12 by SAE International in United States
A low temperature combustion (LTC) diesel engine has been under investigation for reduction of NOx and soot with acceptable compromise in the efficiency through modification of the combustion process. In this paper computational simulation is performed as a preliminary step for development of an LTC diesel engine for off-highway construction vehicles. Validation is performed for major physical models against measurements in LTC conditions. The conditional moment closure (CMC) is employed to address coupling between chemistry and turbulence in KIVA-CMC. The Kelvin-Helmholtz/Rayleigh-Taylor (KH-RT) model is employed for spray breakup and a skeletal n-heptane mechanism for both low and high temperature chemistry. Parametric evaluation is performed for design and operating conditions including EGR rate and injection timing. Results are obtained for efficiency, IMEP, CO, NOx and PM emissions at intake boost pressures of 1, 2 and 3 bar. A possible range of the LTC operation is identified with understanding of the relevant physical phenomena in the given engine conditions. It was possible to reduce both NOx and PM with a high EGR rate for the selected baseline…
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Extended CMC Model for Turbulent Spray Combustion in a Diesel Engine

Pohang University of Science and Technology-Jaeyeob Seo, Yongun Lee, Insuk Han, Kang Y. Huh
Ssangyong Moters Co-Hyunok Kim
Published 2008-10-06 by SAE International in United States
This study presents an extended Conditional Moment Closure (CMC) model [1] for turbulent spray combustion of a diesel engine. A spatially integrated CMC equation involves multiple flame structures, evaporation source terms for mixture fraction variance and scaled conditional scalar dissipation rates (CSDR) and probability density functions (PDF). An independent transport equation is solved for each flame group with equal mass of sequentially injected and evaporated fuel group. The implementation strategy in KIVA is to determine mean scalar variables instead of mean reaction rates in terms of conditional flame structures and local PDF's. Simulation is performed to test the suggested CMC model for a heavy duty diesel engine with early injection timings. NOx chemistry [2] is combined with skeletal chemistry of n-heptane [3] while soot is modeled by both one equation model [4] and two equation model [5]. Parametric investigation is performed with respect to EGR (Exhaust Gas Recirculation) and injection timing. Results show that pressure traces, NOx and soot emissions are in reasonable agreement with measurements in a wide range of EGR levels and injection…
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A New Combustion Model Based on Transport of Mean Reaction Progress Variable in a Spark Ignition Engine

Hyundai Motor Company-Je-Hyung Lee, Sung-Jun Kim
Korea Automotive Technology Institute-Woo Kang, Yongtae Kim
Published 2008-04-14 by SAE International in United States
In this study a new model is proposed for turbulent premixed combustion in a spark-ignition engine. An independent transport equation is solved for the mean reaction progress variable in a propagation form in KIVA-3V. An expression for turbulent burning velocity was previously given as a product of turbulent diffusivity in unburned gas, laminar flame speed and maximum flame surface density. The model has similarity with the G equation approach, but originates from zone conditionally averaged formulation for unburned gas. A spark kernel grows initially as a laminar flame and becomes a fully developed turbulent flame brush according to a transition criterion in terms of the kernel size and the integral length scale. Simulation of a homogeneous charge pancake chamber engine showed good agreement with measured flame propagation and pressure trace. The model was also applied against experimental data of Hyundai θ-2.0L SI engine. Intake flow is calculated by STAR-CD with the resulting flow field mapped as an initial condition in KIVA. Predicted pressure traces showed reasonable agreement with measurement with adjusted constants in the ignition…
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Simulation of Fuel/Air Mixture Formation for Heavy Duty Liquid Phase LPG Injection (LPLI) Engines

Korea Advanced Institute of Science and Technology-Jaejoon Choi, Choongsik Bae
Pohang University of Science and Technology-Eunju Lee, Jinwoo Park, Kang Y. Huh
Published 2003-03-03 by SAE International in United States
Submodels are developed for injection, evaporation and wall impingement of a liquid LPG spray. The injection model determines the quality of fuel as two-phase choke flow at the nozzle exit. Wind tunnel experiments show the spray penetration more sensitive to ambient flow velocity than to injection pressure. Most evaporation occurs during choking, while heat transfer from surrounding air has a negligible effect on downstream droplet sizes. Three dimensional simulation shows that the bathtub cavity is better than the dog-dish cavity for stable flame propagation in lean-burn conditions. The injection timing during the IVC period has a negligible effect, while injection during an intake stroke enhances fuel/air mixing to result in more homogeneous cylinder charge.
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Numerical Prediction and Validation of Fuel Spray Behavior in a Gasoline Direct-Injection Engine

Pohang University of Science and Technology-Miok Joh, Kang Y. Huh
Wayne State Univ.-Joon-Ho Yoo, Ming-Chia Lai
Published 2001-09-24 by SAE International in United States
Analysis of flow field and charge distribution in a gasoline direct-injection (GDI) engine is performed by a modified version of the KIVA code. A particle-based spray model is proposed to simulate a swirl-type hollow-cone spray in a GDI engine. Spray droplets are assumed to be fully atomized and introduced at the sheet breakup locations as determined by experimental correlations and energy conservation. The effects of the fuel injection parameters such as spray cone angle and ambient pressure are examined for different injectors and injection conditions. Results show reasonable agreement with the measurements for penetration, dispersion, global shape, droplet velocity and size distribution by Phase Doppler Particle Anemometry(PDPA) in a constant-volume chamber. The test engine is a 4-stroke 4-valve optically accessible single-cylinder engine with a pent-roof head and tumble ports. Parametric study is performed with respect to the fuel injection timing,spray cone angle and injector position. It is shown that the current numerical methods are capable of reproducing the proper qualitative trend of mixture distribution against visualization images by pulsed-laser Mie scattering.
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Experimental Study on the Combustion Characteristics of Emulsified Diesel in a RCEM

Jae W. Park, Kang Y. Huh, Kweon H. Park
  • Technical Paper
  • 2000-05-0077
Published 2000-06-12 by Society of Automotive Engineers of Korea in South Korea
Combustion characteristics of the emulsified diesel fuels are investigated in a Rapid Compression and Expansion Machine(RCEM). Among the test cases the 40 W/O fuel injected at BTDC 20° has shown the best performance with respect to the efficiency and NOx and soot emissions. The pressure trace of the 40 W/O fuel is characterized by a longer ignition delay and a lower rate of pressure rise in premixed combustion. High speed photographs show reduced flame luminosity and lower flame temperature with the increasing W/O ratio. Micro-explosions of emulsified fuel droplets which affect the local shape and brightness of the flame are identified in magnified flame images.