• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.3
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• pp.78-86
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• 2016

In this paper we propose a new frame transfer function model describing the variations of a heat release rate in response to an external flow oscillation in gas turbine systems. A critical difference of our model compared to the so-called $n-{\tau}$ model which has been widely used for a prediction of combustion instability (CI), is that our model is able to describe a nonlinear relation between phase and frequency. In contrast, the phase part of the $n-{\tau}$ model is a pure time delay and thus the phase should be a linear function of frequency, which is inconsistent with many experimental results of real combustion systems. For an illustration, our new model is applied to experimental data and the effect of phase nonlinearity is investigated in the context of combustion instability.

• Journal of the Korean Applied Science and Technology
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• v.33 no.2
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• pp.239-246
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• 2016

In this study, recycling sludge water of Ready-mixed concrete, and was carried out to optimize the system for recycling of the $CO_2$. The most important process in the liquid phase using a carbonation reaction can be recovered ready-mixed concrete is a process for the $Ca^{2+}$ release. $Ca^{2+}$ concentration of the experiment relative to the pH being lowered by the acidic substance during elution was performed. $CO_2$ was trapped in the MEA solution using a generator flue gas. In ready-mixed concrete can be synthesized $CaCO_3$ up to 11kg/1ton. The resulting $CaCO_3$ analysis results show that it is possible to use paper industry.

• The Journal of Korean Academy of Prosthodontics
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• v.42 no.2
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• pp.210-225
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• 2004

Statement of problem: Implant screw loosening has been remained problem in restorative practices. Surface treatment of screw plays a role of preventing screw from loosening in implant screw mechanism. Purpose : The purpose of this study was to investigate surface characteristics of TiN and ZrN film ion plated screw with titanium and gold alloy screw and to evaluate wear resistance, surface roughness, and film adhesion on screw surface using various instruments. Material and methods : GoldTite screws and titanium screws provided by 3i (Implant Innovation, USA) and TorqTite screws or titanium screws by Steri-Oss (Nobel Biocare, USA) and gold screws and titanium screws by AVANA (Osstem Implant, korea) were selected. Ion plating which is much superior to other surface modification techniques was carried out for gold screws and titanium screws using Ti and Zr coating materials with nitrogen gas. Ion nitrided surface of each abutment screw was observed with field emission scanning electron microscopy (FE-SEM, micro-diamond scratch tester, vickers hardness tester, and surface roughness tester. Results : 1) The surface of gold screw and GoldTite is more smooth than ones of other kinds of non coated screw. 2) The ZrN and TiN coated surface is the more smooth than ones of other kinds of screw. 3) The hardness of TiN and ZrN coated surface showed higher than that of non coated surface. 4) The TiN coated titanium screw and ZrN coated gold screw have a good wear resistance and adhesion on the surface. 5) The surface of ZrN coated screw showed low surface roughness compared with the surface of TiN coated screw. Conclusion : It is considered that the TiN and ZrN coated screw which would prevent a screw from loosening can be applicable to implant system and confirmed that TiN and ZrN film act as lubricant on surface of screw due to decrease of friction for recycled tightening and loosening.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.4
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• pp.130-136
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• 2011

This study describes the effect of EGR rate on the combustion and emissions characteristics of a four cylinder CRDI diesel engine using biodiesel (soybean oil) blended diesel fuel. The test fuel is composed of 30% biodiesel and 70% ULSD (ultra low sulfur diesel) by volumetric ratio. The experiment of engine emissions and performance characteristics were performed under the various EGR rates. The experimental results showed that ignition delay was extended, the maximum combustion pressure and heat release gradually were decreased with increasing EGR rate. Comparing biodiesel blended fuel to ULSD, the injection quantity of biodiesel blended fuel was further increased than ULSD. The emission results showed that $NO_x$ emission of biodiesel blended fuel becomes higher according to the increase of EGR rate. However, in the case of biodiesel blended fuel, HC, CO and soot emissions were decreased compared to ULSD.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.3
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• pp.178-185
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• 2006

This paper investigates the steady-state combustion characteristics of the Homogeneous charge compression ignition(HCCI) engine with variable valve timing(VVT) and dimethyl ether(DME) direct injection, to find out its benefits in exhaust gas emissions. HCCI combustion is an attractive way to lower carbon dioxide($CO_2$), nitrogen oxides(NOx) emission and to allow higher fuel conversion efficiency. However, HCCI engine has inherent problem of narrow operating range at high load due to high in-cylinder peak pressure and consequent noise. To overcome this problem, the control of combustion start and heat release rate is required. It is difficult to control the start of combustion because HCCI combustion phase is closely linked to chemical reaction during a compression stroke. The combination of VVT and DME direct injection was chosen as the most promising strategy to control the HCCI combustion phase in this study. Regular gasoline was injected at intake port as main fuel, while small amount of DME was also injected directly into the cylinder as an ignition promoter for the control of ignition timing. Different intake valve timings were tested for combustion phase control. Regular gasoline was tested for HCCI operation and emission characteristics with various engine conditions. With HCCI operation, ignition delay and rapid burning angle were successfully controlled by the amount of internal EGR that was determined with VVT. For best IMEP and low HC emission, DME should be injected during early compression stroke. IMEP was mainly affected by the DME injection timing, and quantities of fuel DME and gasoline. HC emission was mainly affected by both the amount of gasoline and the DME injection timing. NOx emission was lower than conventional SI engine at gasoline lean region. However, NOx emission was similar to that in the conventional SI engine at gasoline rich region. CO emission was affected by the amount of gasoline and DME.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.4
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• pp.518-525
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• 2016

This paper presents the characteristics of non-fundamental multi-mode combustion instability and the effects of high-harmonic components on the Rayleigh criterion. Phenomenological observations of multi-harmonic-mode dynamic pressure waves regarding the intensity of harmonic components and the source of wave distortion have been explained by introducing examples of second- and third-order harmonics at various amplitudes. The amplitude and order of the harmonic components distorted the wave shapes, including the peak and the amplitude, of the dynamic pressure and heat release, and consequently the temporal Rayleigh index and its integrals. A cause-and-effect analysis was used to identify the root causes of the phase delay and the amplification of the Rayleigh index. From this analysis, the skewness of the dynamic pressure turned out to be a major source in determining whether multi-mode instability is driving or damping, as well as in optimizing the combustor design, such as the mixing length and the combustor length, to avoid unstable regions. The results can be used to minimize errors in predicting combustion instability in cases of high multi-mode combustion instability. In the future, the amount of research and the number of applications will increase because new fuels, such as fast-burning syngases, are prone to generating multi-mode instabilities.

• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.6
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• pp.64-71
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• 2013

In this study we designed a lean $NO_x$ trap (LNT) model with $GT-POWER^{TM}$ program and then the LNT model was compared to the bench flow reactor test results. This model consists of 9 kinetic reactions to represent the main steps of NO oxidation, $NO_x$ adsorption, $NO_x$ release and then its reduction. The comparison was performed on the operating conditions at the space velocity of 50,000 1/hr and 80,000 1/hr with the temperature range of $200^{\circ}C{\sim}500^{\circ}C$ with the even spaced temperature step of $50^{\circ}C$. The experimental results show that the $NO_x$ conversion efficiency was enhanced by the temperature up to $350^{\circ}C$ and then decayed at higher temperatures. The LNT model predicts the similar trend of the $NO_x$ conversion efficiency to the experimental results below $350^{\circ}C$, but overestimates above $350^{\circ}C$. This overestimation comes from the higher reduction efficiency which was obtained by the different reduction gas composition such as $C_3H_6$ in the model to replace $CH_4$, $C_2H_4$ in the bench test.

• Journal of Microbiology and Biotechnology
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• v.13 no.3
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• pp.437-443
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• 2003

Bioremediation technologies were applied to experimental microcosms, simulating an oil spill in a lower intertidal area. Three treatments (oil only, oil plus nutrients, and oil plus nutrients and microbial inocula) were applied, and each microcosm was repeatedly filled and eluted with seawater every 12 h to simulate tidal cycles. To minimize washing-out of the inoculum by the tidal cycles, microbial cells were primarily immobilized on diatomaceous earth before they were applied to the oiled sand. Oil degradation was monitored by gravimetric measurements, thin layer chromatography/flame ionization detector (TLC/FID) analysis, and gas chromatography (GC) analysis, and the loss of oil content was normalized to sand mass or nor-hopane. When the data were normalized to sand mass, no consistent differences were detected between nutrient-amended and nutrient/inoculum-amended microcosms, although both differed from the oil-only microcosm in respect of oil removal rate by a factor of 4 to 14. However, the data relative to nor-hopane showed a significant treatment difference between the nutrient-amended and nutrient/inoculum-treated microcosms, especially in the early phase of the treatment. The accelerating effect of inoculum treatment has hardly been reported in studies of oil bioremediation in the Tower intertidal area. The inoculum immobilized on diatomaceous earth seemed to be a very effective formulation for retaining microbial cells in association with the sand. Results of this study also suggest that interpretation of the effectiveness of bioremediation could be dependent on the selection of monitoring methods, and consequently the application of various analytical methods in combination could be a solution to overcome the limitations of oil bioremediation monitoring.

• Asian Journal of Atmospheric Environment
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• v.10 no.3
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• pp.125-136
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• 2016

In this study, the effects of the mesh barrier on the free dispersion of ammonia were numerically investigated under different atmospheric conditions. This study presents the detail and flow feature of the dispersion of ammonia through the mesh barrier on various free stream conditions to decline and limit the toxic danger of the ammonia. It is assumed that the dispersion of the ammonia occurred through the leakage in the pipeline. Parametric studies were conducted on the performance of the mesh barrier by using the Reynolds-averaged Navier-Stokes equations with realizable k-${\varepsilon}$ turbulence model. Numerical simulations of ammonia dispersion in the presence of mesh barrier revealed significant results in a fully turbulent free stream condition. The results clearly show that the flow behavior was found to be a direct result of mesh size and ammonia dispersion is highly influenced by these changes in flow patterns in downstream. In fact, the flow regime becomes laminar as flow passes through mesh barrier. According to the results, the mesh barrier decreased the maximum concentration of the ammonia gas and limited the risk zone (more than 500 ppm) lower than 2 m height. Furthermore, a significant reduction occurs in the slope of the upper boundary of $NH_3$ risk zone distribution at downstream when a mesh barrier is presented. Thus, this device highly restricts the leak distribution of ammonia in the industrial plan.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.5
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• pp.46-53
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• 2017

This paper deals with an acoustic model for a lean premixed gas turbine combustor composed of three stages: premixing chamber, nozzle and flame tube. Our model is given as an acoustic transfer function whose input is a heat release rate perturbation and output is a velocity perturbation at a flame location. We have shown that the resonance frequencies are functions of three round-trip frequencies of acoustic wave in each stage, and area ratios between stages. By analyzing poles of the acoustic transfer function, we could characterize resonant frequencies and their dependency on various system parameters of a combustor. It was found that our analytic findings match with existing numerical and experimental results in literature.