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Numerical study on the interaction between methane–air and syngas–air premixed flames is conducted according to equivalence ratio and global strain rate in detailed chemistry. This study targets at understanding of an interacting combustion system as an alternative retrofit concept where one can modify the existing facilities minimally in industrial and power plant burners in order to reduce the emission of carbon dioxide. It is seen that methane premixed flame interacting with syngas premixed flame can be sustained even over the rich flammable limit of single methane premixed flame. The inspection of detailed flame structure such as the distributions of major species and chain carrier radicals, flame separation distance, spatial flow velocity, and spatial distribution of the rate of production and consumption of CH4, H2, and CO is also conducted to depict the flame interactions. The importance of global strain rate and thus the flame separation distance in the enhanced burning of methane premixed flame is also stressed through the inspection of the consumption rates of H2, CO, and CH4. Anomalous phenomena such as the migration of premixed flame cross the stagnation plane and the nearly constant flame separation distance are also discussed.

： A numerical analysis of reactive flow in a liftoff flame is acc omplished to elucidate the characteristics of flame propagation velocity and volume integral of reaction rate with the variation of fuel injection velocity at the fuel rich region, fuel lean region and diffusion flame region. The increase of fuel in jection velocity enhances flame propagation velocity, but its effect on the flame propaga tion velocity is not much greater under 4%. The increase of fuel injection velocity affec ts directly and linearly on the flame surface area in the fuel rich region and so enhances volume integral of reaction rate to accommodate the increment of fuel. Key words ：liftoff flame(부상높이), flame propagation velocity( 화염전파속도), volume integral of reaction rate( 체적연소반응속도), flame surface area(화염표면적) †교신저자(계명대학교 에너지환경과학과, E-mail:jisooha@kmu.ac.kr, Tel: 053-580-5919) * 계명대학교 기계자동차공학부** 부경대학교 기계공학부 1. 서 론 일반적으로 연료노즐에서 분출된 연료는 공기와 만나서 제트확산화염을 형성한다. 연료분출속도가 증가되어 연료노즐에 부착된 화염이 노즐에서 분리되어 부상화염이 형성되면 연료노즐 분출 중심선 부근은 연료가 과농한 연소가 일어나고 중심선에서 떨어진 영역인 공기측은 연료가 희박한 연소가 일어난다. 연료가 과농한 영역에서 연소가 일어나고 난 뒤 남은 연료는 다시 공기와 확산 화염을 형성하게 된다. 이렇게 하여 부상화염은 과농연소영역, 희박연소 영역, 확산화염 영역의 세 부분으로 이루어지고 이 세 부분이 만나는 곳을 삼지점(triple point)이라고 하고 이러한 화염을 삼지화염(triple flame)이라고 한다. 삼지화염은 화염의 점화 및 소화에 관계한 화염안정화를 위해 많은 연구자들에 의해 연구되어져 왔다. Mungal

An infrared thickness measuring technique for thin film coated on the metal mold was developed and applied to thickness measuring of the artificial breast implant pack. The infrared light emitted from a metal mold itself was partly absorbed to the silicon film, and the remainder of the infrared light was transmitted through the film. The relationship between the thermal image captured by an infrared camera and the film thickness was analyzed. The thicker the film, the bigger the amount absorbed. The new infrared thickness measuring technique agreed well with the results directly measured by a microscope when applied to the artificial breast implant pack.

Numerical study is conducted to understand the impact of fuel composition and flame radiation in flame structure and their oxidation process in H2/CO synthetic gas diffusion flame with and without CO2 dilution. The models of Sun et al. and David et al., which have been well known to be best-fitted for H2/CO synthetic mixture flames, are evaluated for H2/CO synthetic mixture flames diluted with CO2. Effects of radiative heat loss to flame characteristics are also examined in terms of syngas mixture composition. Importantly contributing reaction steps to heat release rate are compared for the synthetic gas mixture flames of high contents of H2 and CO, individually, with and without CO2 dilution. The modification of the oxidation pathways is also addressed.

Numerical study is conducted to grasp preferential diffusion effects on flame characteristics in syn-gas diffusion flames diluted with . The models of Sun et al. and David et al., which have been well known to be best-fitted for synthetic mixture flames. are evaluated for synthetic mixture flames diluted with . Comparison of flame structures with mixture-averaged species diffusion and suppression of the diffusivities of and H was made. The behaviors of maximum flame temperatures with those species diffusion models are not explained by scalar dissipation rate but by the nature of chemical kinetics. Importantly-contributing reaction steps to heat release rate are also compared for the three species diffusion models in flames with and without dilution.

An examination of the condition of the flow leaving the impeller exit kinetic energy often accounts for 30-50% of the shaft work input to the compressor stage, and for energy efficiency it is important to recover as much of this as possible. This is the function of the diffuser which follows the impeller. The purpose of this study is to investigate the sensitivity of how compressor performances changes as vaned diffuser geometry is varied. Three kinds of vaned diffusers were studied and its results were compared. First vaned diffuser type is based on NACA airfoil and second is channel diffuser and third is conformal transformation of NACA65(4A10)06 airfoil. Mean-line prediction method was applied to investigate the performance and stability for three kinds of diffusers. And CFD analyses have been done for comparison and detailed interior flow pattern study. NACA65(4A10)06 airfoil showed the widest operating range and higher pressure characteristics than the others.

An aerodynamic design for centrifugal compressor which was applied to medium speed diesel engine has been done. First of all, exact compressor specifications must be defined by accurate engine system matching. This matching program has been developed. Using the meanline prediction method, geometric design and performance curves for compressor were established and verified by comparing three dimensional viscous CFD results. The deviation at the design point was about 2.3%. Combustor has been designed and manufactured for the performance test of medium speed diesel engine turbocharger. Fuel nozzle of combustor was designed and its characteristics was analyzed by PIV and PDPA test equipment. Through these results, spray characteristics were studied and flow coefficient equation was deduced.

The ventilation performance for the various venting duct arrays has been experimentally compared in the scaled model of the container hold. Most container ships have the ventilation duct system to remove effectively the condensing heat released from container refrigerator. The existing duct system is vertically installed and basically has the number of duct as many as the columns of reefer container stack. In this study, to make up for the weak points having stagnantly hot legions in the centered area of container hold for the present system, the horizontal upward jotting duct system was proposed and proved by temperature rising tests on the scaled model. In this paper, the expected flow regimes and the thermal and hydrodynamic analogies as well as the measured temperature distributions in a hold for various duct types and heat released rates are deeply discussed.

A thermal vapor compressor in which the subsonic/supersonic flow appears simultaneously, has been accurately designed through the CFD analysis for the various shape parameters such as the primary nozzle shape, converging duct shape, mixing tube diameter, and so on. The performance of the developed thermal vapor compressor has been experimentally verified to be installed in a Multi Effect Desalination(MED) plant as an important element. In this paper, the effects of each parameter are discussed on the basis of CFD results and the experimental results for various boundary conditions(motive pressure, suction pressure, and discharge pressure) are presented in compared with CFD results. The two results show a good agreement with each other within 2 % accuracy with regard to the entrainment ratio.

A thermal vapor compressor (TVC) in which the subsonic/supersonic flow appears simultaneously, has been accurately designed through the CFD analysis for the various shape parameters such as the primary nozzle shape, converging duct shape, mixing tube diameter, and so on. The performance of the developed TVD has been experimentally verified to be installed in a multi-effect desalination (MED) pilot plant. In this paper, the experimental results for various boundary conditions (motive pressure, suction pressure, and discharge pressure) are presented in comparing with CFD results. The two results show a good agreement with each other within 3.5% accuracy with regard to the entrainment ratio.

This paper presents a lightweight prefix-based routing (LPR) for content-centric networking. In CCN, every communication with the named data is based on hierarchical naming convention and forwarding decision using the longest-prefix matching mechanism. However, there are no comprehensive researches on designing a general routing protocol over such a naming hierarchy. Our LPR scheme provides a lightweight management of routing table and Forwarding Information Base (FIB) table that manage a lower number of routes enough to perform the longest-prefix matching. Also, a method is proposed to cope with connections between CCN routers in different hierarchies. We evaluate the proposed LPR against the existing routing approaches and show that it leads to less control overhead and FIB size.

The recent resurgence of knitting is an ambiguous social phenomenon because it has pre-industrial connotations in late modern society. Knitting is inherently an ambiguous practice which blurs the boundary between production and consumption, the material and the mental and subject and object. This paper explores Korean knitting practice from the angle of social practice. An examination of knitting practice in Korea revealed that the inherent heterogeneity is intricately intertwined with the complex landscape of knitting practice, which is dispersed in a range of different forms of subgroups. Also, the multifaceted aspect of these subgroups which combines consumption, production, education and socialization, refers to the complicated and contrasting aspects of contemporary consumption and consumers. This paper particularly pays attention to the role of practical understanding as a form of skill, know-how and knowledge in the formulation and transformation of knitting practice. It also examines the emotional landscape of knitting practice, which is constructed and mediated in close interconnection with the material dimensions of the practice.

The experimental and numerical studies of the boundary layer diffusion flame over a porous plate have been conducted for two different flows in the presence and absence of flow separation. The present study investigates the local acceleration induced by flame and the interaction between separation of flow and diffusion flame. The main conclusions are summarized as follows: In the flow without flow separation, positive local acceleration makes the distortion and the overshoot of velocity in the boundary layer with diffusion flame. In the flow affected by flow separation, the effect of chemical reaction suppresses the tendency for flow separation. In the case of a lower fuel mass flux, a less active chemical reaction does not overcome the influence of flow separation, therefore separation bubble still exists and velocity overshoot could not be observed. On the other hand, a more active chemical reaction in the case of a higher fuel mass flux changes the pressure distribution as the favorable gradient so tha...

The centrifugal compressor of marine engine turbocharger is composed of impeller, 1st vaneless diffuser, vaned diffuser, 2nd vaneless diffuser and volute casing. An examination of the condition of the flow leaving the impeller exit kinetic energy often accounts for 30–50% of the shaft work input to the compressor stage, and for energy efficiency it is important to recover as much of this as possible. This is the function of the diffuser which follows the impeller. Effective pressure recovery downstream of an impeller is very important to realize a centrifugal compressor with high efficiency and high pressure ratio, and an appropriate selection of a diffuser for a specific impeller is a critical step to develop the compressor accordingly. The purpose of this study is to investigate the sensitivity of how compressor performances changes as vaned diffuser geometry is varied. Three kinds of vaned diffusers were studied and its results were compared. First vaned diffuser type is based on NACA airfoil and second is channel diffuser and third is conformal transformation of NACA 65 airfoil. Mean-line prediction method was applied to investigate the performance and stability for three kinds of diffusers. And CFD analyses have been done for comparison and detailed interior flow pattern study. In this study, the off design behavior of three different type of diffuser, given by mean-line prediction, was investigated using CFD results and selected best diffuser geometry which satisfy wider operating range and higher pressure recovery than the others. The numerical results were compared with experimental data for validation.Copyright © 2006 by ASME

Accurate heat release analysis based on the cylinder pressure trace is important for evaluating combustion process of diesel engines. However, traditional single-zone heat release models (SZM) have significant limitations due mainly to their simplified assumptions of uniform charge and homogeneity while neglecting local temperature distribution inside cylinder during combustion process. In this study, a heat release analysis based on single-zone model has been evaluated by comparison with computational analysis result using Fire-code, which is based on multi-dimensional model (MDM). The limitations of the single-zone assumption have been estimated. To overcome these limitations, an improved model that includes the effects of spatial non-uniformity has been applied. From this improved single-zone heat release model (Improved-SZM), two effective values of specific heats ratios, denoted by γV and γH in this study, have been introduced. These values are formulated as the function of charge temperature changing rate and overall equivalence ratio by matching the results of the single-zone analysis to those of computational analysis using Fire-code about medium speed marine diesel engine. Also, it is applied that each equation of γV and γH has respectively different slopes according to several meaningful regions such as the start of injection, the end of injection, the maximum cylinder temperature, and the exhaust valve open. This calculation method based on improved single-zone model gives a good agreement with Fire-code results over the whole range of operating conditions.Copyright © 2005 by ASME

A fuel injection with high pressure in a medium speed diesel engine would increase the possibility of cavitation damage in the fuel injection system or secondary injection to the combustion chamber. The purpose of this study is to prevent cavitation and secondary injection in a medium speed diesel engine by modifying the design of the delivery valve and the constant pressure valve in a fuel injection system. Three-dimensional flow analyses for the fuel injection nozzle, delivery valve, constant pressure valve and spill port were performed using FLUENT S/W to calculate loss coefficients of them. Simulation of fuel injection system with loss coefficients from results of three-dimensional flow analyses were performed using FLOWMASTER2 S/W and the simulation results were compared with the experimental data. The delivery valve and constant pressure valve were modified to prevent cavitation and secondary injection and proved in the field test.

A turbocharger has been designed to fulfill the requirements of medium speed marine engines, 900 kW output power at nominal operation point. The main objective of the design was to meet the requirements of engine power and increased engine operating range. This must be achieved by improving the degree of aerodynamic efficiency and the pressure ratio. The design was performed by the two stages. First, quasi-two dimensional program code was used to determine the main geometry of the compressor. Second, the detailed geometries of compressor blade were completed by using a three dimensional fluid flow analysis. The analyzed performance results were compared with the experimental data for the verification of their validity. Also, the designed three different impeller exits allow for a substantial performance variation. Increased compression ratio and mass flow rate of new optimized impeller were 10.08 and 27.3 percent higher than those of origin impeller, respectively. This simple change of design parameter offers considerable advantages to customers when upgrading their engines.Copyright © 2005 by ASME

The spray-induced mixing characteristics and thermal decomposition of aqueous urea solution into ammonia have been studied to design optimum sizes and geometries of the mixing chamber in SCR (Selective Catalytic Reduction) system. The cold flow tests about the urea-injection nozzle were performed to clarify the parameters of spray mixing characteristics such as mean diameter and velocity of drops and spray width determined from the interactions between incoming air and injected drops. Discrete particle model in Fluent code was adopted to simulate spray-induced mixing process and the experimental results on the spray characteristics were used as input data of numerical calculations. The simulation results on the spray-induced mixing were verified by comparing the spray width extracted from the digital images with the simulated particle tracks of injected drops. The single kinetic model was adopted to predict thermal decomposition of urea solution into ammonia and solved simultaneously along with the verified spray model. The hot air generator was designed to match the flow rate and temperature of the exhaust gas of the real engines. The measured ammonia productions in the hot air generator were compared with the numerical predictions and the comparison results showed good agreements. Finally, we concluded that the design capabilities for sizing optimum mixing chamber were established.

The centrifugal compressor design of the high-speed marine engine (500–900 kW) turbocharger has been done. Increased Higher compressed air and power density help improvement of the engine performance and power. The centrifugal compressor of the marine engine turbocharger is composed of impeller, 1st vaneless diffuser, vaned diffuser, 2nd vaneless diffuser and volute casing. The design process is achieved by three following stages. First, quasi-two dimensional code is used to determine the main geometry of the compressor. Second, three-dimensional compressible Navier-Stokes equation is applied to analyze the flow pattern and structures of the compressor blade loading. Here, among compressor impeller geometry, blade height variables are mainly changed. Smooth flow guidance has to precede and flow separation symptoms must not appear within compressor impeller. When the loading distribution is inadequate from blade hub to shroud, new curved profile should be designed to minimize the pressure loss. By analyzing the internal flow fields for the compressor impeller geometry variations, three dimensional impeller design profile has been confirmed. Compressed air pressure and mass flow rates from new optimized design were 2.7%, 27.3% higher than that of old one each other. Third, analyzed results are compared with experimental data for the verification of the present design method.Copyright © 2004 by ASME

Prediction of the ROHR (rate of heat release) and NOx production in medium-speed marine diesel engines was investigated. The subject of this paper is qualitative and quantitative evaluation of the numerical results. FIRE code v8.1 was used to examine the behavior of spray and combustion phenomena in diesel engine. Wave breakup and Zeldovich models were adopted to describe the atomization characteristics and NOx formation. The spray visualization was performed experimentally in the constant-volume high-pressure chamber to clarify numerical results on the spray characteristics of the spray angle and penetration. Time-resolved spray behaviors were captured by high-speed digital camera. The simulation results were tested with the experimental data of the real engine. Finally, with adjustment of some model constants, reasonable agreements between experimental and simulated results on the ROHR and NOx were shown.

This paper describes velocity fields for fully developed periodic laminar flow in a rigid tube with a porous wall. We obtained an analytical solution of the flow by the linear approximation of the Navier-Stokes equation. Unlike the previous works with a constant seepage rate along the axis, we used a wall velocity which contained hydraulic permeation constant Lp. The axial velocity profile shows a local maximum velocity near the wall at a large Womersley number α. This suggests that concentration polarization in porous tubular membrane may be reduced at high frequencies if a membrane device is operated under pulsatile flow conditions. The magnitude of wall permeation velocity deceases linearly along the tube axis because the damping of the pressure difference between the inside and the outside of the tube is very small.