• 한국연소학회지
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• 제7권3호
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• pp.16-22
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• 2002

Combustion performance of an internally cycloned circulating fluidized bed for paper sludge was discussed through a series of batch type experiments. Operation parameters such as water content, feeding mass of sludge and secondary air injection rate were varied to find out the effect on the combustion performance, which was examined with carbon conversion rate and pollutant emission such as CO and NOx. A conventional solid fuel reaction was observed in the experiments of varying water content and feeding mass of the sludge, which is characterized with kinetic limited reaction zone, diffusion limited reaction zone and transition zone. Secondary air injection with swirl enhances the mixing of the gas phase as well as the solid phase, and improves combustion efficiency accompanied with higher carbon conversion rate and lower pollutant emission rate.

• Journal of Microbiology and Biotechnology
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• 제21권9호
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• pp.988-994
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• 2011

A significant amount of nitrous oxide ($N_2O$), which is one of the serious greenhouse gases, is emitted from nitrification and denitrification of wastewater. Batch wastewater nitrifications with enriched nitrifiers were carried out under oxygen-limited condition with synthetic (without organic carbon) and real wastewater (with organic carbon) in order to find out the effect of ammonium concentration on $N_2O$ emission. Cumulated $N_2O$-N emission reached 3.0, 5.7, 6.2, and 13.5 mg from 0.4 l of the synthetic wastewater with 50, 100, 200, and 500 mg/l ${NH_4}^+$-N, respectively, and 1.0 mg from the real wastewater with 125 mg/l ${NH_4}^+$-N. The results indicate that $N_2O$ emission increased with ammonium concentration and the load. The ammonium removal rate and nitrite concentration also increased $N_2O$ emission. Comparative analysis of $N_2O$ emission from synthetic and real wastewaters revealed that wastewater nitrification under oxygen-limited condition emitted more $N_2O$ than that of heterotrophic denitrification. Summarizing the results, it can be concluded that denitrification by autotrophic nitrifiers contributes significantly to the $N_2O$ emission from wastewater nitrification.

• 한국자동차공학회논문집
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• 제18권4호
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• pp.31-39
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• 2010

Although driving patterns strongly influence greenhouse gas and air pollutant emission rate from light duty vehicles, emission measurements have been mainly based on chassis dynamometer testing with one standard driving pattern. And there has been limited work on quantifying the independent effect of driving parameters on emission rate because of multidimensional nature of real-world driving pattern. The objective of this study is to obtain the quantitative effect of relative positive acceleration (RPA) on vehicle emission rate. RPA has been used to define the occurrence of acceleration demanding large amounts of power in certain driving distance and shown to be a significant affecting parameter for real-world emission rate. 40 driving patterns have been developed with fixed driving parameters to investigate independent effect of RPA. For the same values of average vehicle speed and power, the trend in carbon dioxide emission rate and fuel consumption with respect to RPA is very clear. Emission rate of nitrogen oxide and particulate matter also increase with respect to RPA, but the trend is less clear. Carbon dioxide emission from diesel vehicle appear to be more affected by high accelerations compared to that from gasoline vehicle because of high intake air restriction during acceleration caused by turbocharger and intercooler. The results have implications for the possible reduction of environmental effects through better traffic planning and management, driver education and car design.

• 한국자동차공학회논문집
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• 제14권4호
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• pp.84-91
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• 2006

In this study, the effect of EGR and fuel injection pressure on the characteristics of combustion and emission performance of the common-rail diesel engine is investigated using DME fuel as a smoke-free alternative fuel. Because the heating value and density of DME fuel are lower than those of diesel fuel, the injection duration of the DME engine is relatively longer than the injection duration of the diesel engine with the same injection pressure. However, the higher injection pressure can shorten the injection duration for the DME engine. Although the smoke level of the DME engine is much lower than that of the diesel engine, the NOx is at a level similar to that of the diesel engine. As a proposed solution for this, the EGR technique is empirically applied to the DME engine. In the experiments, the injection pressure was changed from 200bar to 400bar, and the EGR rate was limited under 40%. With the same injection timing and fuel amount, the experiment results indicated that the increase of injection pressure led to the increase of IMEP while decreasing HC and CO emissions. However, the NOx emission tends to increase as the injection pressure becomes higher. On the other hand, as the EGR rate was increased, NOx emission and A/F were reduced while the HC and CO emissions were increased. Because HC and CO emissions have the critical A/F point where the emissions of HC and CO are rapidly increased, it is proposed that the EGR rate must be limited under the critical EGR rate.

• 한국연소학회:학술대회논문집
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• 한국연소학회 1998년도 제17회 KOSCI SYMPOSIUM 논문집
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• pp.1-8
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• 1998

Waste combustion above a grate is the core process of incineration systems, stability of which should be guaranteed for emission minimization. However, complicated reactions and heat and mass transfer phenomena make understanding the process difficult. One dimensional bed combustor with a numerical combustion model is utilized to investigate the combustion process of the bed, using cubic wood particles as a simulated fuel. Bed combustion behavior is characterized with apparent flame propagation speed, which has close relationship with air supply rate and chemical and physical characteristics of the fuel. Base on the availability of oxygen, two distinct reaction zone is identified; the oxygen-limited and the reaction-limited zone leading to the extinction by excessive convection cooling. The numerical modeling shows good agreement with the experimental results. The transient bed combustion behavior of local temperature and oxygen consumption rate is adequately reproduced. The numerical model is extended to model the waste bed combustion of a commercial incineration plant, which shows meaningful results as well.

• 한국전기전자재료학회논문지
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• 제19권1호
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• pp.13-17
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• 2006

The one-dimensional ZnO nanostructures prepared through thermal evaporation under various cooling down procedures by changing the flow rates of the carrier gas and the reactive gas were investigated. The nanorod structures were changed into the nanonail types with a broad head through the reduction of the flow rate of the carrier gas. The decrease of the reactive gas reduced the length of the nail heads due to the limited mass transport of reactive gas. The intensity ratio of the ultraviolet emission/green emission of photoluminescence was proportional to the length of the broad head showing a larger surface area. The vertically aligned nanostructures were grown along the [0001] direction of ZnO regardless of the aligned directions. The crystal direction of the nanostructures was determined by that of the initial ZnO crystal.

• 한국수소및신에너지학회논문집
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• 제9권1호
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• pp.1-7
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• 1998

Most of today's energy supply is obtained from fossil fuels. Despite of high energy density, higher store efficiency and long mileage, fossil fuels cause environmental pollution and their reserves are limited. In this study pure hydrogen gas and oxygen gas are burned without the emission of pollution. A gas turbine is used to obtain power. Water is injected into a combustor, which prevents overheating and recovers cooling heat. Excessively supplied water is recirculated. With variation of mass flow rate and equivalence ratio, the affection of water injection rate and the temperature of injected water on efficiency and power are experimented. Injected water gets cooling heat, is expanded from liquid to vapor and raises the thermal efficiency. It is enable to determine the rate of water injection, which makes the maximum power. The increase of temperature of water injection raises the efficiency of the system.

• 한국재난정보학회 논문집
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• 제11권4호
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• pp.581-588
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• 2015

본 연구는 구획된 소공간유형의 EPS실에서 케이블 등의 가연성물질에 대한 화재특성을 시뮬레이션(FDS6)을 활용하여 진행하였다. 구획된 공간인 EPS실에서는 산소의 공급이 원활하지 않아 표준화재곡선에서와 같은 우상향의 연소곡선이 나타나지 않았다. 환기가 제한되는 상황에서 열방출율과 연기 방출량에 대한 시뮬레이션 결과는 상승과 하락을 반복하며 불안정한 형태의 복잡한 화재특성을 보였다. 화재시간은 화재하중에 비하여 길게 나타났다. 열방출율에 비하여 연기 방출량의 변화는 느리게 진행되었으나 전체적인 면에서 변화양상은 유사성을 보이는 것으로 확인되었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.184-184
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• 2012

Recently, InGaN/GaN multi-quantum well grown on GaN pyramid structures have attracted much attention due to their hybrid characteristics of quantum well, quantum wire, and quantum dot. This gives us broad band emission which will be useful for phosphor-free white light emitting diode. On the other hand, by using quantum dot emission on top of the pyramid, site selective single photon source could be realized. However, these structures still have several limitations for the single photon source. For instance, the quantum efficiency of quantum dot emission should be improved further. As detection systems have limited numerical aperture, collection efficiency is also important issue. It has been known that micro-cavities can be utilized to modify the radiative decay rate and to control the radiation pattern of quantum dot. Researchers have also been interested in nano-cavities using localized surface plasmon. Although the plasmonic cavities have small quality factor due to high loss of metal, it could have small mode volume because plasmonic wavelength is much smaller than the wavelength in the dielectric cavities. In this work, we used localized surface plasmon to improve efficiency of InGaN qunatum dot as a single photon emitter. We could easily get the localized surface plasmon mode after deposit the metal thin film because lnGaN/GaN multi quantum well has the pyramidal geometry. With numerical simulation (i.e., Finite Difference Time Domain method), we observed highly enhanced decay rate and modified radiation pattern. To confirm these localized surface plasmon effect experimentally, we deposited metal thin films on InGaN/GaN pyramid structures using e-beam deposition. Then, photoluminescence and time-resolved photoluminescence were carried out to measure the improvement of radiative decay rate (Purcell factor). By carrying out cathodoluminescence (CL) experiments, spatial-resolved CL images could also be obtained. As we mentioned before, collection efficiency is also important issue to make an efficient single photon emitter. To confirm the radiation pattern of quantum dot, Fourier optics system was used to capture the angular property of emission. We believe that highly focused localized surface plasmon around site-selective InGaN quantum dot could be a feasible single photon emitter.

• Structural Engineering and Mechanics
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• 제72권3호
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• pp.313-327
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• 2019

Damage evolution in the form of void nucleation, propagation and coalescence is the primary cause that is responsible for the ductile failure of microalloyed steels. The Gurson-Tvergaard-Needleman (GTN) damage model has proven to be extremely robust for characterizing the microscopic damage behavior of ductile metals. Nonetheless, successful applications of the model on a given metal type are limited by the correct identification of damage parameters as well as the validation of the calculated void growth rate. The purpose of this study is two-fold. First, we aim to identify the damage parameters of the GTN model for Q345 steel (Chinese code), due to its extensive application in mechanical and civil industries in China. The identification of damage parameters is facilitated by the well-suited response surface methodology, followed by a complete analysis of variance for evaluating the statistical significance of the identified model. Second, taking notched Q345 cylinders as an example, finite element simulations implemented with the identified GTN model are performed in order to analyze their microscopic damage behavior. In particular, the void growth rate predicted from the simulations is successfully correlated with experimentally measured acoustic emissions. The quantitative correlation suggests that during the yielding stage the void growth rate increases linearly with the acoustic emissions, while in the strain-hardening and softening period the dependence becomes an exponential function. The combined experimental and finite element approach provides a means for validating simulated void growth rate against experimental measurements of acoustic emissions in microalloyed steels.