An experimental study on combustion processes and nox emission characteristics of the air-staged burner

The combustion processes and emission characteristics in air-staged burner have been experimentally studied. The light fuel oil doped with pyridine(C₅H₅N) is used to investigate the fuel NO_X emission characteristics. Experiments are carried out for a wide range of operating conditions of single-staged and multi-staged burner. The detailed discussions are made for the flame structure of the air-staged burner as well as effects of excess air ratios, staged air flow percentage, and spray conditions on flame pattern and NO_X emission characteristics.     

Experimental investigation on the turbulence augmentation of a gun-type gas burner by slits and swirl vanes

The purpose of this paper is to investigate the effects of slits and swirl vanes on the turbulence augmentation in the flow fields of a gun-type gas burner using an X-type hot-wire probe. The gun-type gas burner adopted in this study is composed of eight slits and swirl vanes located on the surface of an inclined baffle plate. Experiment was carried out at a flow rate of 450 //min in burner model installed in the test section of subsonic wind tunnel. Swirl vanes play a role diffusing main flow more remarkably toward the radial direction than axial one, but slits show a reverse feature. Consequently, both slits and swirl vanes remarkably increase turbulence intensity in the whole range of a gun-type gas burner with a cone-type baffle plate.     

Effects of a swirling and recirculating flow on the combustion characteristics in non-premixed flat flames

The effects of swirl intensity on non-reacting and reacting flow characteristics in a flat flame burner (FFB) with four types of swirlers were investigated. Experiments using the PIV method were conducted for several flow conditions with four swirl numbers of 0, 0.26, 0.6 and 1.24 in non-reacting flow. The results show that the strong swirling flow causes a recirculation, which has the toroidal structures, and spreads above the burner exit plane. Reacting flow characteristics such as temperature and the NO concentrations were also investigated in comparison with non-reacting flow characteristics. The mean flame temperature was measured as the function of radial distance, and the results show that the strong swirl intensity causes the mean temperature distributions to be uniform. However the mean temperature distributions at the swirl number of 0 show the typical distribution of long flames. NO concentration measurements show that the central toroidal recirculation zone caused by the strong swirl intensity results in much greater reduction in NO emissions, compared to the non-swirl condition. For classification into the flame structure interiorly, the turbulence Reynolds number and the Damkohler number have been examined at each condition. The interrelation between reacting and non-reacting flows shows that flame structures with swirl intensity belong to a wrinkled laminar-flame regime.     

An experimental study on heat transfer characteristics with turbulent swirling flow using uniform heat flux in a cylindrical annuli

An experimental study was performed to investigate heat transfer characteristics of turbulent swirling flow in an axisymmetric annuli. The static pressure, the local flow temperature, and the wall temperature with decaying swirl were measured by using tangential inlet conditions and the friction factor and the local Nusselt number were calculated for Re=30000-70000. The local Nusselt number was compared with that obtained from the Dittus-Boelter equation with swirl and without swirl. The results showed that the swirl enhances the heat transfer at the inlet and the outlet of the test tube.     

基于无线技术的医用血氧监测系统的设计与应用

针对传统血氧饱和度仪的不足,对其进行改造,主要包括了血氧探头的无线连接、血氧信号的过滤与计算、血氧信号的存储及血氧指数的分析与显示等多个方面,设计出适合现代化医院使用的血氧监测系统。将无线技术应用于血氧监测系统,使测试数据实现网络化共享,同时利用傅里叶算法对测试数据进行精确处理。实验测试和临床应用表明,系统精度完全达到使用要求,不仅可以有效提高临床的诊疗质量,而且有利于医护人员的急救工作,并且大量的血氧数据还可以为临床医学研究提供有力的支持。     

An experimental study on the performance optimization of a radiant burner with a surface flame structure

An experimental study was carried out on a newly developed, gas-fired radiant burner to optimize its performance for three different conditions of firing rate (80.5, 107.4, and 134.2 kW/m²). The operational equivalence ratios ranged from 0.6 to 1.3. Gas temperatures along the mat and upstream/downstream of the ceramic mat were obtained to investigate the effects of firing rate and equivalence ratio. The temperature of the unburned mixture in the burner port decreased as the firing rate increased. The opposite trend appeared in response to change in the equivalence ratio. This was mainly due to mixture velocity and residence time. The mechanism of temperature variations in the mat with the equivalence ratio and firing rate was described in detail. Results on flue gas emissions, such as the concentrations of EINO and CO, were also presented. It was confirmed that in lean-mixture conditions, the concentration of CO remains below 100 ppm for all firing rates. Lastly, radiation and water-boiling efficiencies were measured as functions of the equivalence ratio, firing rate, cookware diameter (D_p), and height of the burner housing (H). It was observed that conduction heat transport dominated the radiation effect less as the firing rate increased. From these observations, the effective heat input in the present radiant burner was determined to optimize its performance.     

An experimental study on the effects of spring stiffness on the combustion and dynamic characteristics of a linear engine

We investigated the effects of the stiffness of springs applied to linear compressor chambers experimentally. The applied springs could prevent conflict between the engine piston head and engine head cover as well as be available to save the regenerative energy. The linear engine bore size was 30 mm, the maximum stroke was 31 mm and effective stroke volume of a cylinder was 25.45 cc. The spring stiffness was varied: 0, 0.5, 1.00, 2.9 and 14.7 N/mm. The linear engine was fueled with a pre-mixture combined with LPG (propane 99%) and air. As an experimental result, higher spring stiffness affected growth in regenerative energy and stroke. Also, IMEP was increased by rising stroke. Finally, increased IMEP and regenerative energy made more electricity than no spring.     

An experimental study on the effects of impingement-walls on the spray and combustion characteristics of SIDI CNG

Compressed natural gas (CNG) is regarded as one of the most promising alternative fuels, and maybe the cleanest fuel for the sparkignition (SI) engine. In the SI engine, direct injection (DI) technology can significantly increase the engine volumetric efficiency and decrease the need of throttle valve. During low load and speed conditions, DI allows engine operation with the stratified charge, and the use of extremely lean fuel-air mixture enables relatively higher combustion efficiency. In this study, a combustion chamber with a visualization system is designed. The spray development and combustion propagation processes SIDI CNG were digital recorded. It was found that high injection pressure reduced the ignition probability significantly because of quenching of flame kernel. To improve the ignition probability, three kinds of impingement-walls were designed to help the mixture preparation. It was found that the CNG-air mixture can be easily formed after spray-wall impingement and the ignition probability was also improved. The results of this study can contribute important data for the design and optimization of spark-ignition direct injection (SIDI) CNG engine.     

A study on friction and wear characteristics of nanometer Al2O3 /PEEK composites under the dry sliding condition

The friction and wear properties of the polyetheretherketone (PEEK) based composites filled with 5 mass% nanometer or micron Al₂O₃ with or without 10 mass% polytetrafluroethylene (PTFE) against the medium carbon steel (AISI 1045 steel) ring under the dry sliding condition at Amsler wear tester were examined. A constant sliding velocity of 0.42 m s⁻¹ and a load of 196 N were used in all experiments. The average diameter 250 μm PEEK powders, the 15 or 90 nm Al₂O₃ nano-particles or 500 nm Al₂O₃ particles and/or the PTFE fine powders of diameter 50 μm were mechanically mixed in alcohol, and then the block composite specimens were prepared by the heat compression moulding. The homogeneously dispersion of the Al₂O₃ nano-particles in PEEK matrix of the prepared composites was analyzed by the atomic force microscopy (AFM). The wear testing results showed that nanometer and micron Al₂O₃ reduced the wear coefficient of PEEK composites without PTFE effectively, but not reduced the friction coefficient. The filling of 10 mass% PTFE into pure PEEK resulted in a decrease of the friction coefficient and the wear coefficient of the filled composite simultaneously. However, when 10 mass% PTFE was filled into Al₂O₃/ PEEK composites, the friction coefficient was decreased and the wear coefficient increased. The worn scars on the tested composite specimen surfaces and steel ring surfaces were observed by scanning electron microscopy (SEM). A thin, uniform, and tenacious transferred film on the surface of the steel rings against the PEEK composites filled with 5 mass% 15 nm Al₂O₃ particles but without PTFE was formed. The components of the transferred films were detected by energy dispersive spectrometry (EDS). The results indicated that the nanometer Al₂O₃ as the filler, together with PEEK matrix, transferred to the counterpart ring surface during the sliding friction and wear. Therefore, the ability of Al₂O₃ to improve the wear resistant behaviors is closely related to the ability to improve the characteristics of the transfer film.     

An experimental study on the spray characteristics of a dual-orifice type swirl injector at low fuel temperatures

The objective of this study is to investigate the effects of fuel temperature on the spray characteristics of a dual-orifice type swirl injector used in a gas turbine. The major parameters affecting spray characteristics are fuel temperature and injection pressure entering into the injector. In this study, the spray characteristics of a dual-orifice type swirl injector are investigated by varying fuel temperature from — 30°C to 120°C and injection pressure from 0.29 to 0.69 MPa. Two kinds of fuel having different surface tension and viscosity are chosen as atomizing fluids. As a result, injection instability occurs in the low fuel temperature range due to icing phenomenon and fuel property change with a decrease of fuel temperature. As the injection pressure increases, the range of kinematic viscosity for stable atomization becomes wider. The properties controlling the SMD of spray is substantially different according to the fuel temperature range.     

Experimental study on the characteristics of longitudinal fin air-heating vaporizers in different seasons

Air-heating vaporizers are usually used to regasify LNG at satellite areas because of the small demand for natural gas there. The common type of air heating vaporizer which exists in the market is the longitudinally finned type with 8 fins, 50mm fin length and 2mm fin thickness. To contribute in developing an efficient air-heating vaporizer, experiment on finned type air-heating vaporizer using 8 fins, 50mm fin length with 2mm fin thickness (8fin50le)-which exist in the market-and 4 fins, 75mm fin length with 2mm fin thickness (4fin75le), which is proposed, were conducted. Then, both types of vaporizers are compared. The experiments were conducted in one hour by varying the ambient condition and the length of the vaporizer. The ambient air was controlled so that it has the same condition (same temperature, humidity and air velocity) with air condition in every season available and the length was varied 4000mm, 6000mm and 8000mm for each type of vaporizer. Additional experiment with longer duration, i.e., 4 hours and in a single room condition was conducted to validate the previous result. In this experiment, the main aspects in analyzing the characteristics of the air heating vaporizer are the inlet-outlet enthalpy difference and the outlet temperature of the working fluid. LN₂ is used to substitute LNG for safety reasons. The results show that the characteristics of the finned type 4fin75le vaporizer are comparable to the finned type 8fin50le vaporizer.     

Effect of nitrogen atoms desorption on the friction of the CNx coating against Si3N4 ball in nitrogen gas

Phase transition of CNx coatings by sliding against a Si₃N₄ ball has been studied by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) to understand this super-low friction phenomena in N₂. A pin-on-disk type tribometer was constructed to determine the tribological properties of this coating when sliding against a Si₃N₄ ball in N₂. The analytical results by AES and XPS showed that the nitrogen atoms desorbed from the top layers of the coating, and that the layers changed to a graphite-like structure without nitrogen during a friction coefficient decrease to lower than 0.01. The structural transition of CNx is discussed in this paper.     

Effects of friction on topography and vice versa

Experimental results of friction and topography measurements are presented which demonstrate the mutual modification of friction and contact topography. The effect of topographical ‘landmarks’ on friction was tested by Al₂O₃-balls sliding over Ti-ridges on Ti-surface and by Si₃N₄-balls sliding over grooves in SiO₂-surfaces. However, experiments of 100Cr6-balls sliding against 100Cr6-substrates in ultrahigh vacuum, Al₂O₃-balls sliding on DLC coated 100Cr6 and Si₃N₄-balls sliding on SiO₂-surfaces reveal that the formation of triboreaction layers and moreover the creation of wear particles can screen the effect of the topographical ‘landmarks’ completely. Wear particles and their exact behaviour in the contact area can affect friction in a stochastical and hence unpredictable way. Most modern friction theories have difficulties in coping with this problem.     

A study on the characteristics of in-cylinder intake flow in spark ignition engine using the PIV

In this study, to investigate m-cyhnder tumble or swirl intake flow of a gasoline engine, the flow characteristics were examined with opening control valve (OCV) and several swirl control valves (SCV) which intensify intake flow through steady flow experiment, and also turbulent characteristics of m-cyhnder flow field were investigated by 2-frame cross-correlation particle image velocimetry (PIV) method In the investigation of intake turbulent characteristics using PIV method, the different flow characteristics were showed according to OCV or SCV figures The OCV or SCV installed engine had higher vorticity and turbulent kinetic energy than a baseline engine, especially around the wall and lower part of the cylinder Above all, SCV B type was superior to the others About energy dissipation and reynolds shear stress distribution, a baseline engine had larger loss than OCV or SCV installed one because flow impinged on the cylinder wall It should be concluded, from what has been said above, as swirl component was added to existing tumble flow adequately, it was confirmed that turbulent intenstty was enlarged, flow energy was conserved effectively through the experiment In other words, there is a suggestion that flow characteristics as these affected to m-cyhnder combustion positively     

The Adhesion of Monomolecular Hydroxyl-terminated Perfluoropolyether Liquid Films on the Sputtered Silicon Nitride Surface as a Function of End Group Acidity and Mobility

The intermolecular interactions at the interface between monomolecular hydroxyl-terminated perfluoropolyether (PFPE) liquids (Zdol, Zdol-TX, Z-Tetraol, Zdiac) and a sputtered amorphous silicon nitride film (SiN_x) are investigated using contact angle goniometry, Fourier transform infrared spectroscopy, and ab initio computational chemistry. The results demonstrate that the adhesion between the PFPE liquids and the SiN_x surface occur via the polar interactions between the PFPE end groups (-OH, -COOH) and the polar sites on the SiN_x surface (e.g., SiOH). The attractive interactions lead to a lowering of the polar surface energy with increasing PFPE coverage up to a monolayer. The binding energy is computed to be approximately −4 to −9 kcal/mol, depending upon the polarity of the PFPE end group. Adsorbed water is shown to compete with PFPE for surface bonding sites on SiN_x (−4.4 kcal/mol) that can lead to a significantly reduced level of adhesion for some of the hydroxyl-terminated PFPEs. A higher level of adhesion between the PFPEs and SiN_x can be attained by increasing the strength of the hydrogen bond and/or increasing the configurational entropy of the PFPE end group to facilitate the hydrogen bonding reaction.     

Experimental study on micro EDM-drilling of Ti6Al4V using helical electrode

There is a growing interest in the machining of micro-holes with high aspect-ratio in difficult-to-machine alloys for the aerospace industry. Processes based on electro discharge machining (EDM) and developed for the manufacture of both micro-electrode and micro-hole are actually used, but most of them involve micro-EDM machines. In this work, the influence of EDM parameters on material removal rate, electrode wear, machining time and micro-hole quality when machining Ti6Al4V is studied. Due to an inefficient removal of debris when increasing hole depth, a new strategy based on the use of helical-shaped electrodes has been proposed. The influence of helix angle and flute depth with respect to process performance has been addressed. Main results include 37% reduction in machining times (hole diameter 800 μm) when using electrode helix angle of 45° and flute-depth of 50 μm, and an additional 19% with flute-depth of 150 μm. Holes of 661 μm diameter and as much as 6.81 mm depth, which yields in aspect ratio of 10:1, have successfully been machined in Ti6Al4V.     

Comparative study on tribology and microhardness of laser synthesized Ti-Al2O3/Zn coatings on Ti-6Al-4V alloy

ABSTRACT

The study of laser cladding of 90Ti-10Al₂O₃, 90Ti-8Al₂O₃-2Zn and 90Ti-4Al₂O₃-6Zn coatings onto Ti-6Al-4V alloy, with intention to produce defect-less, high microhardness and wear resistant coating was carried out. The coatings were deposited onto Ti-6Al-4V alloy at 900 W laser power and 0.6 m/min laser scan speed. Microstructures and phase constituents of the developed coatings were investigated by using a scanning electron microscope (SEM) and X-ray diffractometer correspondingly. Vickers microhardness tester and pin-on-disk tribometer were employed to characterize microhardness and wear behaviour of the Ti-Al₂O₃/Zn coatings respectively. SEM was also used to examine the worn track. It was observed that 90Ti-10Al₂O₃ coating yielded optimal microhardness along with maximal wear resistance in comparison to the other coatings and Ti-6Al-4V alloy. It has been established that laser cladding of Ti-Al₂O₃ coating with Zn contents on Ti-6Al-4V alloy alleviates the formation of cracks, however, microhardness and wear properties are negatively affected.     

First-principles study on incidence direction, individual site character, and atomic projection dependences of ELNES for perovskite compounds

The incidence direction dependence, the individual site character dependence, and the atomic projection dependence of O-K near edge fine structure of the EEL spectrum (ELNES) from YBa2Cu3O7 (YBCO) and SrTiO3 were theoretically simulated using the first-principles band structure calculation. In order to calculate ELNES, a core-hole was introduced at the oxygen 1s orbital, and sufficiently large supercells composed of more than 100 atoms were employed. We found that the intensity of the first peak of O-K ELNES from YBCO strongly depends on the atomic projection direction, and disappears when the spectrum is measured with the other projection directions. The large projection dependence was also predicted in the O-K ELNES of SrTiO3. It was found that those spectral changes according to the position of the projection are caused by the unidirectional Ti-O-Ti bond in SrTiO3.     

Experimental study on heat transfer characteristics of internal heat exchangers for CO2 system under cooling condition

This paper presents the heat transfer characteristics of the internal heat exchanger (IHX) for CO₂ heat pump system. The influence on the IHX length, the mass flow rate, the shape of IHX, the operating condition, and the oil concentration was investigated under a cooling condition. Four kinds of IHX with a coaxial type and a micro-channel type, a mass flow meter, a pump, and a measurement system. With increasing of the IHX length, the capacity, the effectiveness, and the pressure drop increased. For the mass flow rate, the capacity of micro-channel IHX are higher about 2 times than those of coaxial IHX. The pressure drop was larger at cold-side than at hot-side. In the transcritical CO₂ cycle, system performance is very sensitive to the IHX design. Design parameters are closely related with the capacity and the pressure drop of CO₂ heat pump system. Along the operating condition, the performance of CO₂ IHXs is different remarkably. For oil concentration 1, 3, 5%, the capacity decreases and the pressure drop increased, as compared with oil concentration 0%. This paper was recommended for publication in revised form by Associate Editor Yong Tae Kang Prof. Young-Chul Kwon received his B.S. degree in Precision Mechanical Engineering from Pusan National University, Korea, in 1989. He then received his M.S. and Ph.D. degrees from POSTECH, in 1991 and 1996, respectively. Dr. Kwon is currently a Professor at the Division of Mechanical Engineering at Sunmoon University in Chungnam, Korea. He serves as a chief of the Institute of Automation and Energy Technology. Dr. Kwon’s research interests include heat exchanger, CO₂ cycle, heat pump, and energy recovery ventilator for HVAC&R. Mr. Dae-Hoon Kim is currently Doctoral student at the Mechanical Engineering from Hanyang University in Seoul, Korea. His research topics include experimental and numerical of CO₂ heatpump system. He has conducted a study on the Analysis of Refrigerating & Air-Conditioning Equipment Industry and Its Forecasting Supervising and Testing for Performance of Refrigerator, Freezer and Air-Conditioner. Prof. Jae-Heon Lee received his B.S. degree in Mechanical Engineering from Seoul National University, Korea, in 1971. He then received his M.S. and Ph. D. degree from Seoul National University in 1977 and 1980, respectively. Dr. Lee is currently a Professor at the school of Mechanical Engineering at Hanyang University in Seoul, Korea. Dr. Lee is currently a president at the Korea Institute research interests include simulation of thermal fluid and Plant engineering and construction. Dr. Jun-Young Choi received his B.S. degree in Mechanical Engineering from Yonsei University, Republic of Korea, in 1989. He then received his M.S. and Ph. D. degrees from Yonsei University in 1991 and 1999, respectively. Dr. Choi is currently a chief researcher with the 18 years experience on the energy performance testing of HVAC/R product. He is now assigned to the Energy Technology Center at Basic Industry Division at Korea Testing Laboratory. He has been involved in the development of Design and Manufacturing Technology for Air-Conditioner E.E.R. and Performance Testing Equipment for Cooling and Heating System with Non-CFCs, and natural refrigerants. He has conducted a study on the Analysis of Refrigerating & Air-Conditioning Equipment Industry and Its Forecasting Supervising and Testing for Performance of Refrigerator, Freezer and Air-Conditioner. Dr. Sang Jae Lee received his Ph.D. degree in Mechanical Engineering from Hanyang University, KOREA, in 2008. Dr. Lee is currently a Researcher at the Korea Institute of Industrial Technology in Cheonan, Korea. Dr. Lee’s research interests CO₂ heatpump system, liquid desiccant air conditioning system and Micro heat exchanger.     

Synergistic effect on frictional characteristics under rolling-sliding conditions due to a combination of molybdenum dialkyldithiocarbamate and zinc dialkyldithiophosphate

The frictional characteristics of molybdenum dialkyldithiocarbamate (MoDTC) and/or zinc dialkyldithiophosphate (ZnDTP) in a paraffinic mineral oil were studied using a two-roller machine, in which the synergistic effect for reducing friction was found for the oil containing ZnDTP together with MoDTC. Variation in chemical composition of the surface film over time indicated preferential formation of the products through decomposition of ZnDTP. The reduction in friction was mainly due to MoS₂ derived from MoDTC, while ZnDTP had a role in enhancing the wear resistance and promoting the formation of MoS₂. More severe conditions such as an increase in sliding speed tended to more significantly decrease friction.