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The need to reduce global carbon dioxide (CO2) emissions is driving the conversion of coal-fired power plants to use methane, which can reduce CO2 emissions by >40%. However, conducting gas firing in coal boilers changes the heat transfer profile; therefore, preliminary evaluations using computational fluid dynamics are required prior to conversion. Here, methane was used as a heat input source in the simulation of an existing coal boiler, and combustion, nitrogen oxides (NOx) emission characteristics, and heat transfer profile changes inside the boiler were analyzed. Furthermore, changes in the burner zone stoichiometric ratio (BZSR) were simulated to restore the decreased heat absorption of the furnace waterwall, revealing that air distribution could change the heat absorption of the waterwall and tube bundles. However, this change was smaller than that caused by conversion from coal to methane. Therefore, to implement gas firing in coal boilers, alternatives such as output derating, using an attemperator, or modifying heat transfer surfaces are necessary. Despite these limitations, a 70% reduction in NOx emissions was achieved at a BZSR of 0.76, compared with coal. As the BZSR contributes significantly to NOx emissions, conducting gas firing in existing coal boilers could significantly reduce NOx and CO2 emissions.

In this work, subair injection was proposed to improve the combustibility and NOx emission in a 500 MW tangentially fired coal boiler. The location of injection ports was determined based on the coal particle trajectory and its effect was investigated numerically. The flow rate of subair was set to 0, 5, and 10% of the total combustion air. The secondary air flow rate was decreased appropriately to ensure that the total quantity of combustion air remained constant. The over-fire air was not adjusted to retain the effect of an air-staged combustion. The simulation results showed that the subair improved the combustibility of coal particles originating from burners A and B in the lower part of the furnace. Particles from other burners were not affected significantly. In addition, this method achieved reduction of NOx by 6.3 and 13.2% when the subair accounted for 5 and 10% of the combustion air, respectively. This reduction was attributed to the decrease in the peak temperature as a result of a wider combustion region. The proposed subair technique improved the coal combustibility and reduced the NOx emissions successfully in the furnace.

Ash problems, such as slagging and fouling, are important because of their negative effect of reducing the heat transfer on the furnace wall and tube in pulverized coal boilers and decreasing the boiler safety. However, slagging has positive effect on gasifier. Slagging is protecting furnace wall and reducing heat loss in gasifier. Slagging and fouling are related to ash deposition, which is determined by the coal-ash fusion temperature, chemical composition of coal ash, and boiler operating conditions et al. The coal-ash fusion temperature is a particularly important factor in slagging and fouling. To measure the ash fusion temperature, the ASTM D1857 test is used, not only by thermal power plants and steelmaking companies in South Korea but all over the world. In this study, the fluid temperature (FT) of ASTM D1857 was predicted by Thermo-Mechanical Analysis (TMA). Three bituminous coals (Glencore, Trafigura, Moolarben) and four sub-bituminous coals (KPU, Berau, Jembayan, PRB) were selected for the TMA tests, wherein T25, T50, T75, and T90 were measured. These four temperatures corresponded to shrinkage levels of 25%, 50%, 75%, and 90%, respectively. The T90 of the bituminous coals and T50 of the sub-bituminous coals were similar to the initial deformation temperature (IDT) of ASTM. The T90 of the bituminous coals was greater than 1300 °C, and the T90 of the sub-bituminous coals was ∼1250 °C. Two FT-prediction equations—for bituminous coal and sub-bituminous coal—were established according to the T25, T50, T75, and T90 relationships of each coal. The FT-prediction equations indicated an average gap of 71 °C in the sub-bituminous coals. For the sub-bituminous coals, the average difference was quite low: ∼23 °C. The FT-prediction equations matched the FT of ASTM and are useful for determining the ash fusion temperature in a short time.

Combustion of carbonaceous solid fuels was modeled using a number of methods, and the employed models were further improved by thoroughly studying the physical and chemical interactions between carbonaceous solid fuels and oxidizers. Simulation accuracy was improved by using special techniques to reduce the fitting errors of earlier models; e.g., errors in the isothermal coal char combustion rate model were reduced by modifying the well-established random pore model, with increased model flexibility generally considered vital for improvement. Thermogravimetric analyses were performed for four categories of carbonaceous fuels: semi-anthracite coals, bituminous coals, sub-bituminous coals, and biomass. Scanning electron microscopy imaging was employed to understand correlations between the fuel structure and model parameters. The obtained results were used to confirm the hypotheses of the used models, and a general model of carbonaceous solid fuel combustion, termed “flexibility-enhanced random pore model”,...

Pulverized coal-fired boilers have been used for power generation in Korea for decades. Recently, an 870-MW wall-fired boiler with De-NO x TM burners and an air staging system was constructed for use with low-rank coal. The results of a full-scale simulation of its combustion characteristics agreed well with measurements obtained under normal operating conditions for temperature, unburned carbon, and nitric oxide. Contrasting trends in unburned carbon and NOx emissions were observed, depending on the particle size and the location of the standby burner within the boiler. Combustion was also found to shift forward with small particle sizes and backward with large particle sizes. The results of a Thermo-mechanical analysis (TMA) indicated that the actual sticking temperature was lower than that suggested by the initial deformation temperature (ASTM) criteria. A logistic function was used to describe TMA shrinkage. Locations subject to high deposition potential were predicted with reference to soot-blowing phenomena.

Pulverized Coal Injection (PCI) is one of the most effective technologies for reducing coke consumption in blast furnaces. Its main role is as the heating source and for the generation of CO gas. Generally, PCI coal is a high-rank coal, but steel mill companies are attempting to use low-rank coal as an energy source in PCI combustion blast furnaces because of the increasing cost of high-rank coal and decreasing reserves. The purpose of this investigation was to determine how the coal rank is correlated to the pulverized coal particle temperature and CO emission. This study was performed using a Laminar Flow Reactor (LFR), which represents the combustion environment of pulverized coal inside a blast furnace. Since the PCI system was developed for iron making, the combustion characteristics of pulverized coal are important in the iron and steel industries. According to the different types of coals, the coal flame structure, coal particle temperature, and exhaust gases (CO and CO 2 ) were investigated. This study demonstrated that the combustion characteristics of coal were influenced by several properties of individual coals. Primarily, the coal particle temperature and CO emission were found to have the strongest influence on the combustion characteristics of these coals. Moreover, the fragmentation phenomenon occurring in some coals was also an important factor influencing the PCI combustion characteristics. Therefore, this study significantly considered the coal properties, focusing on images of the burning coal particle flames, the particle temperature, and the CO/CO 2 emissions.

A temperature dependence of a width of Δ H = Δ B region has been studied for 5 wt.% (Fe, Ti) particle-doped MgB 2 superconductor, which is the region that increased applied magnetic field is the same as increasing magnetic induction in a superconductor. The result revealed that widths of the region are linear along temperature. In this paper, we present meanings of the result and details of the calculation. In previous report, we represented a theory that a width of Δ H = Δ B region is related with upper critical field of the superconductor, which is that pinned fluxes at volume defect are pick-out depinned and move in Δ H = Δ B region when the shortest distance between them is the same as that of upper critical field of the superconductor. Thus, we inspected the relationship between a width of the region and upper critical field along temperature theoretically and experimentally. The results show that the two are not only linear along temperature, but also are linear each other. The results support the theory because temperature dependence of a width of Δ H = Δ B region is linear to that of upper critical field of the superconductor.

Recently, much research has been put into finding the causes and solutions of slagging/fouling problems that occur at the end of the boiler. This slagging/fouling, caused by low-rank coal`s ash, disturbs the thermal power and greatly reduces efficiency. In environmental aspects, such as NOx pollution, governments have been implementing restrictions on the quantity of emission gases that can be released into the atmosphere. To solve these problems, research on Ash Free Coal (AFC), which eliminates ash from low-rank coal, is in progress. AFC has advantages over similar high-rank coals because it increases the heating value of the low grade coal, reduces the contaminants that are emitted, and decreases slagging/fouling problems. In this study, using a DTF, the changes of NOx emissions, unburned carbon, and the characteristics of ash deposition were identified. KCH raw coal, AFC extracted from KCH, residue coal, Glencore, and Mixed Coal (Glencore 85wt% and residue coal 15wt%) were studied. Results showed that AFC had a significantly lower emission of NOx compared to that of the raw coal and residue coal. Also, the residue coal showed a higher reactivity compared to raw coal. And finally, In the case of the residue coal and mixed coal, they showed a lower ash deposition than that of low-rank coal.

After a reheating furnace installation, the modification of the size and the heat capacity is very difficult. Therefore, the development of design package tool is required for the computation on the correct specifications before the design and the installation. Prior to development of the design tool, a module that calculates the amount of heat loss of each part according to the specifications for determining the thermal efficiency of a continuous heating furnace was developed and applied to the oxy-fuel industrial furnace. Through this, the effects of fuel type, oxygen fraction and recirculation on the efficiency of the furnace of which the output is 110Ton/hour were analyzed. In oxy-fuel combustion condition, the efficiency was 15% higher than air combustion conditions. With the using COG(Coke Oven Gas) instead of LNG, the efficiency was slightly increased. In the air combustion condition, the efficiency was increased about 33% with the preheated air. But, in oxy-fuel condition, the amount of exhaust gas was reduced, so the efficiency was increased about 7%.

Circulating Fluidized Bed(CFB) combustion has the several advantages which are the fuel flexibility, the economy, the efficiency and the environment. It is necessary to apply a renewable energy to produce electricity due to the Renewable Portfolio Standard(RPS) mandates recently. So, in this study, co-combustion with a coal and a wood pellet was investigated to evaluate the combustibility and the environment as function of blending ratio of them in a Lab-scale CFB reactor. To investigate the characteristics of the co-combustion, the blending ratio which is the weight of wood pellet by the total calorific value of the supplied, was considered. Bed material was a river sand(No. 7). As increasing the blending ratio, the exhausted gas emissions such as CO, NOx, HC and SOx were decreased. But in case of wood pellet over 30%, CO, HC and SOx emission were increased. And the gas temperatures at the downstream were decreased.

This study examined the flux jump behaviors of Fe-doped MgB 2 according to content of FeTi particles at 5 K, at which flux jump has been shown to be more frequent. The samples were synthesized in a stainless steel tube with Mg, B and FeTi particles. The motives of flux jump in MgB 2 superconductors are over-moving fluxes around the defects and the low heat capacity of MgB 2 . MgB 2 was doped with FeTi particles to overcome these vulnerable points of MgB 2 . The flux jump of MgB 2 decreased with increasing content of doped FeTi particles. On the other hand, excessive doping of FeTi resulted in a decrease of diamagnetic properties and the flux pinning effects together. It is concluded that FeTi particles in MgB 2 do not block the flux jump itself, but the propagation of flux jump of MgB 2 .

The NOx correlation for fuel staged combustion on CH4/air flames was investigated as a function of operating conditions such as pressure, flame temperature, fuel-to-air ratio, and fuel staging ratio. Firstly, the flow characteristics for fuel staged combustion were investigated using particle image velocimetry (PIV) under atmospheric conditions, through which fuel and air mixing was correlated with the turbulence intensity. The turbulent intensity near the burner outlet was strong when the fuel staging ratio (α) was 3%, which provided better fuel and air mixing. NOx correlation for fuel staged combustion was investigated using a lab-scale gas turbine combustor at high pressure. In particular, NOx emissions scale with pressure (NOx = Pn) with n = 0.5 under premix combustion and n = 1.1 for fuel staged combustion. A new NOx correlation for fuel staged combustion is suggested in the form of NO x = a · e ( b · T fl + d · α ) · P n · far c under the operating conditions of real gas turbines.

This study was performed using a laminar flow reactor that could replicate the combustion environment of pulverized coal in a blast furnace. Since a pulverized coal injection system was developed for iron making, the combustion characteristics of pulverized coal have been important in the iron and steel industry. The flame structure, particle temperature, and exhaust gas were investigated for different types of coal. The results of this study demonstrated that the combustion characteristics of coal are influenced by several properties of individual coals. In particular, the CO emission and volatile matter content of individual coals were found to have a strong influence on their combustion characteristics. Thus, this study found the properties of the coals to be significant and focused on the particle temperature and CO and CO2 emissions.

Numerical study was investigated to obtain the database for developing a fast pyrolysis power boiler by waste fuel. The studies with various conditions were performed using ANSYS FLUENT. Also, the fuel properties was experimentally analyzed to utilize the input parameters for numerical analysis, that were proximate and ultimate analysis, reaction kinetics included pyrolysis and combustion. The results showed that temperature, combustion and exhausted gases was changed with heating value of fuel and feeding rate. Finally, the stable operating condition by analyzing results was proposed.

For thermal power generation companies, the use of refined ash (defined as having a loss on ignition (LOI) of less than 6%) has not only made it suitable to produce lightweight aggregate, but has also introduced significant cost benefits through recycling. However, the ash having a high unburned carbon content (greater than 6%) cannot be recycled and still must be disposed of underground and by landfill. In this paper, an ash recycling and reburning technology was examined to improve ash usage in 500 MW pulverized coal (PC) boiler and simulation was performed to find the optimal conditions of ash supplying position and its amount that would not affect the boiler condition. Kinetic parameters for the reaction rate of ash were derived from a drop tube furnace (DTF) and adopted to accurately describe the characteristics of high LOI ash. In addition, the simulation results were then validated through real scale tests. Based on the simulation results, this paper suggest that the optimal supply condition for ash reburning is D burner sight window and 4 ton/h (with 0.01% of total air) in terms of combustion stability and burnout because the upper burner location has more sufficient oxidizer in the particle pathway as well as maximized mixing effect between coal and oxidizer. The real scale tests evidently represent that ash reburning can be method to make low LOI ash.

The critical current density and flux pinning properties of the Ba0.55K0.45Fe2As2 high-T c superconductor with T c = 37 K are studied using the field and the time dependences of the magnetization. The temperature dependence of the critical current density J c (T) has been found to follow the form J c ∝ (1−T/T c ) n and is consistent with δT c -type pinning due to randomly-distributed defects that are larger than the coherence length ξ. The temperature dependence of the magnetic relaxation rate S exhibits a peak at a much lower temperature, which corresponds to a smaller pinning energy in the Ba0.55K0.45Fe2As2 superconductor. Moreover, the effective pinning potential U o increases with increasing temperature and this behavior is in agreement with those of high-T c cuprate superconductors.

Background The whistle deformity is one of the common sequelae of secondary cleft lip deformities. Santos reported using a crossed-denuded flap for primary cleft lip repair to prevent a vermilion notching. The authors modified this technique to correct the whistle deformity, calling their version the cross-muscle flap. Methods From May 2005 to January 2011, 14 secondary unilateral cleft lip patients were treated. All suffered from a whistle deformity, which is characterized by the deficiency of the central tubercle, notching in the upper lip, and bulging on the lateral segment. The mean age of the patients was 13.8 years and the mean follow-up period was 21.8 weeks. After elevation from the lateral vermilion and medial tubercle, two muscle flaps were crossed and turned over. The authors measured the three vertical heights and compared the two height ratios before and after surgery for evaluation of the postoperative results. Results None of the patients had any notable complications and the whistle deformity was corrected in all cases. The vertical height ratios at the midline on the upper lip and the affected Cupid's bow point were increased (P Conclusions A cross muscle flap is simple and it leaves a minimal scar on the lip. We were able to reconstruct the whistle deformity in secondary unilateral cleft lip patients with a single state procedure using a cross-muscle flap.

This work presents an experimental investigation of NOx emissions according to inlet air temperature (550-660 K), stoichiometric air ratio (, 1.4-2.1), and elevated pressure (2-5 bar) in a High Press Combustor (HPC) equipped with a double cone burner, which was designed by Pusan Clean Coal Center (PC3). The exhaust-gas temperature and NOx emissions were measured at the end of the combustion chamber. The NOx emissions generally decreased as a function of increasing . On the other hand, NOx emissions were influenced by , inlet air temperature and pressure of the combustion chamber. In particular, when the inlet air temperature increased, the flammability limit was extended to leaner conditions. As a result, a higher adiabatic temperature and lower NOx emissions could be achieved under these operation conditions. The NOx emissions that were governed by thermal NOx were greatly increased under elevated pressures, and slightly increased at sufficiently low fuel concentrations ( >1.8).

The magnetic properties of the newly discovered iron-oxypnictide SmFeAsO 0.85 high-Tc superconductor with a Tc of around 55 K were investigated. Bulk SmFeAsO 0.85 was prepared by a method for high-pressure synthesis. The lower critical field H c1 was estimated from the magnetization at low fields; H c1 (0) was measured to be 212 Oe. A linear temperature dependence instead of saturation at low temperatures in H c1 (T) revealed unconventional superconductivity with a nodal gap structure in our SmFeAsO 0.85 superconductor. The results showed that the well-known secondary peak in the temperature dependence of the critical current density Jc is absent in the SmFeAsO 0.85 high-Tc superconductor. The irreversibility line B irr was fitted well by the power law dependence (1 - T/Tc)n with n ~ 1.5. This is indicative of the flux creep phenomena in the SmFeAsO 0.85 high-Tc superconductor. In addition, within the range of measurement temperatures in this study, no crossover was observed in the temperature dependence of the irreversibility line B irr which may be due to low anisotropy in our SmFeAsO 0.85 superconductor.

KeyWords: Ash(회), Boiler(보일러), CFD(전산유체역학), LOI(점화감소량), TGA(열중량분석), DTF(수직형전기로)초록: 석탄은고정탄소분, 휘발분, 수분, 회로구성되며, 연소시회성분과소량의고정탄소분이남게된다. 석탄화력발전소에서는석탄연소후나오는잔여물(고정탄소분, 회)를통칭하여석탄회라고부르고있다. 현재발전소에서는정제회(LOI함량6%미만)는경량골재의원료로재활용해수익을창출하고있으나, LOI함량이높은회는재활용이불가능해땅에매립하고있다. 이에따라환경적인부담금을줄이고정제회판매의수익을올리기위해회성분의LIO감량은필수적이다. 본연구에서는TGA(Thermo-gravime- tric analysis)와DTF(Drop tube furnce)실험을통해석탄과석탄회연소를위한실험적인상수값을결정하였다. 500MW급표준화력발전보일러를모델링하고, 전산해석을위해격자를형성시키고적절한해석모델을선정하였으며, 석탄회재연소시뮬레이션을수행하여석탄회투입시보일러내부의온도및유동을모사하였다. 보일러내부석탄입자와회입자의이동궤적을통해가능한높은버너위치에서석탄회를투입하는것이적절함을나타내었다. 또한실제설치가능한D버너에서6ton/h로공급시에기존의보일러에큰영향을주지않으며재연소가능함을알수있다.Abstract: In thermal power generation companies, the recycling of refined ash (LOI 6%) in a PC-firing furnace can be an alternative. In this study, a numerical analysis was performed todemonstrate the effects of ash re-burning. An experimental constant value was decided by TGA (thermo-gravimetricanalysis), and a DTF (drop-tube furnace) was used in the experiment for calculating the combustion of ash. On thebasis of the trajectory of the moving particles of coal and ash, it was concluded that supplying ash near the burner,which is located high above the ground, is appropriate. On the basis of numerical results, it was concluded that an ashsupply rate of 6 ton/h is suitable for combustion, without affecting the PC-firing boiler.

The main objective of this study is to investigate the variation in the ignition characteristics of coals as a function of moisture content in a laminar flow reactor (LFR) equipped with a fuel moisture micro-supplier designed by the Pusan Clean Coal Center. The volatile ignition position and time were observed experimentally when a pulverized coal with moisture was fed into the LFR under burning conditions similar to those at the exit of the pulverizer and real boiler. The reaction-zone temperature along the centerline of the reactor was measured with a , R-type thermocouple. For different moisture contents, the volatile ignition position was determined based on an average of 15 to 20 images captured by a CCD camera using a proprietary image-processing technique. The reaction zone decreased proportionally as a function of the moisture content. As the moisture content increased, the volatile ignition positions were 2.92, 3.36, 3.96, and 4.65 mm corresponding to ignition times of 1.46, 1.68, 2.00, and 2.33 ms, respectively. These results indicate that the ignition position and time increased exponentially. We also calculated the ignition-delay time derived from the adiabatic thermal explosion. It showed a trend that was similar to that of the experimental data.

A one-dimensional model that describes diffusion and advection process has been developed. The approximate solution to the nonlinear equations has been obtained analytically with an iterative method. A two-dimensional numerical solution with computational fluid dynamics (CFD) software is also derived for a two-dimensional crucible around which the convective and diffusive flows are more precisely presented. The results showed that as long as both heat and oxygen diffusion processes are considered at a time, the one-dimensional solution could provide as accurate a result as that obtained by using the two-dimensional solution evaluated in terms of temperature, but not in terms of the oxygen content. The weight and the geometry of the soot bed significantly affect the distribution of temperature and oxygen content that warrants the use of two-dimensional model because a two-dimensional character such as a buoyant upward flow from the relatively hot bed is predominant.

Because there has been a recent increase in the use of low calorific coal compared to standard coal, it is crucial to control the char flame length governing the burning life-time of coal in a coal-fired utility boiler. The main objective of this study is to develop a simplified model that can theoretically predict the flame length for burning coal in a laboratory-scale entrained laminar flow reactor (LFR) system. The char burning behavior was experimentally observed when sub-bituminous pulverized coal was fed into the LFR under burning conditions similar to those in a real boiler: a heating rate of 1000 K/s, an oxygen molar fraction of 7.7 %, and reacting flue gas temperatures ranging from 1500 to 2000 K. By using the theoretical model developed in this study, the effect of particle size on the coal flame length was exclusively addressed. In this model, the effect of particle mass was eliminated to compare with the experimental result performed under a constant mass feeding of coal. Overall, the computed results for the coal flame length were in good agreement with the experimental data, particularly when the external oxygen diffusion effect was considered in the model.

The irreversible properties of a rare-earth high-Tc superconductor are investigated using grain-aligned Sm1-xEuxBa2Cu3O7−δ (x = 0.0, 0.3, 0.5, 0.7, and 0.9) samples. The samples were synthesized using the usual solid–state reaction method. It is found that the transition temperature Tc and the critical current density Jc calculated by the Bean model are significantly improved in the optimally doped samples (x = 0.5 and 0.7). Furthermore, the double logarithmic graph of the irreversibility line Birr in the grain-aligned series samples obeys approximately a power law dependence ( 1 − T / T c ) n . Results show that in the case of optimally doped samples with x = 0.5 and 0.7 the graph of Birr is fitted well with the relation ( 1 − T / T c ) n with the model-dependent parameter n ∼1.5 without any crossover in the entire temperature range, while in samples with x = 0.0, 0.3, and 0.9 Birr does show a prominent crossover and can be characterized with n ∼1.5 only near Tc, above which Birr varies more rapidly. Finally, it is suggested that Birr is strongly dependent on the extrinsic properties of our grain-aligned samples.

Air-staged combustion is known to be one of the techniques of NOx reduction. The objective of this study is to determine the optimal ratio of air flow distributed for CCOFA and SOFA; at this optimal ratio, the combustion and exhaust emission characteristics of a pulverized coal-fired boiler are maintained at a satisfactory level. A numerical investigation was performed at various airflow ratios of 16.7/83.3%, 25/75%, 50/50%, 75/25%, and 83.3/16.7%. An inert gas was considered as a substitute for air to isolate the effects of the cooling process and chemical reaction on NOx reduction; during NOx reduction in air-staged combustion, both the effects typically occur simultaneously. The results of our study show that the optimum condition, under which the maximum NOx reduction and highest boiler efficiency can be obtained, corresponds to the equal splitting of the over-fire air between CCOFA and SOFA.

In this study, the effect of particle size on the combustion characteristics of pulverized sub-bituminous coal was experimentally investigated. A laminar-flow-entrained reactor was designed and implemented to realize the desired heating ratio and temperature corresponding to the combustion atmosphere of a pulverized-coal-fueled furnace. The flame length and structure of burning particles according to different sizes were investigated. Coal combustion processes were clearly distinguished by direct visual observation of the flame structure. The onset point of volatile ignition is greatly affected by changes in the particle size, and the burning time of the volatiles is least affected by changes in the particle size. The length and instability of char flame also increase with the increase of the particle size. However, the char consumption rate within the residential time remains nearly constant.

The experimental study was performed to investigate the effects of partial premixing, varying the equivalence ratio, mixing degree, swirl intensity, mixing length on the characteristics of flame structure and NOx emission. Experiments were conducted in a dump combustor at 1 bar using methane as fuel. Inlet air temperature was 570K. OH chemiluminescence images were acquired with an ICCD camera. As a result of the experimental investigation of characteristics of flame and NOx emission in partial premixed combustor, we can conclude the results as below. With the increase of swirl number, The flame length decreases and the flame width increases and it helps flame stabilization. It means that lean flammability limit is extended. With the increase of mixing of fuel-air length ratio, Flame goes to be stabilized and NOx emission and OH* intensity decrease. Through the comparison of preceding results, It is possible that the exhausted NOx emission from a gas turbine combustor will be able to predict through the OH* intensity. 책임저자 회원 부산대학교 기계공학부

Lean premixed combustors are used for significant NOx reduction which one of issues in current gas turbine combustor. This study was investigated to estimate the effects of the unmixedness of fuel-air, equivalence ratio on the instability mechanism, NOx emission and combustion oscillation in a lean premixed combustor. The experiments were conducted in a dump combustor at atmospheric pressure conditions using methane as fuel. The swirler angle was 45°, the degrees of fuel-air mixing were 0, 50 and 100 and inlet temperature was 650K. The equivalence ratio was ranging from 0.5 to 0.8. This paper shows that NOx emission was increased when the degree of fuel-air mixing is increased in same equivalence ratio and when equivalence ratio is increased. And the range of the combustion instability was enlarged as a function of increasing of the degree of fuel-air mixing.

Many researches have been carried out to reduce the emission levels and lower the fuel consumption in SI engines. Recently electronically controlled injection system is widely adapted to a passenger car to achieve these goals. Throttle body is also an important factor which influences on the emissions and engine power. In this study we redesigned a throttle body and conducted an experimental study to see the effects on engine performance and emission characteristics. We could find that idle speed control(ISC) showed stable operation characteristics as the cooling water temperature varied. And CO and HC emissions also satisfied the regulation limit.

The characteristics of combustion and flow for a lean premixed flame in lab-scale gas turbine combustor was studied through experiment and numerical analysis. From the experiment, flame structure and heat release rate were obtained from OH emission spectroscopy. Qualitative comparisons were made line-integrated OH chemiluminescence image and abel-transformed one. NOx analyzer was implemented to get the characteristic of NOx exhaust from the combustor. From the numerical analysis, the thermal distribution and characteristic of recirculation zone with the change of fuel-air mixing degree, the characteristic of methane distribution with equivalence ratio in the combustor respectively. Total heat release rate is increased with increasing equivalence ratio. Thermal Nox is reduced with increasing fuel-air mixing degree. Increasing equivalence ratio results in the decrease of the size of reaction zone and alteration of the position of the reaction zone into the entrance of the combustor.기호설명Φ : 당량비V:유동의 평균속도(㎧)θ : 위상 각 (deg)σ : 연료-공기 혼합정도(%)

With environmental concerns over emitted particulate matters(PM) from combustion systems, various researches have been conducted on reduction and measurement techniques of particulate matters. The LII analysis results from numerical models and experiments in an ethylene/air laminar diffusion flame at elevated pressure up to 2.0 MPa with laser fluence 0.07 J/cm2, detection wavelength 400 nm were compared to validate a modified LII numerical model. The lifetime of the LII signal decreased as the elevated pressure increased, so that LII decay time also decreased in both results. In the aspect of heat transfer mechanism, it becomes earlier that dominant conduction starts. This shows that the results matched well under the pressure conditions. It is concluded that the LII numerical model could be applied to decide particle size in TIRE-LII at the high-pressure condition.

The effect of superconductivity and inhomogeneity on the phase coherence between superconducting grains for Bi 2 Sr 2 CaCu 2 O 8+ δ (Bi-2212) is discussed. We find that in the UD regime, inhomogeneity plays a central role in establishing the phase coherence between superconducting grains. By decreasing hole concentration, p , the phase stiffness for the thermal fluctuations is suppressed, whereas the phase coherence between the superconducting grains is enhanced. In particular, the phase coherence between the superconducting grains is established almost immediately as the superconductivity for Bi-2212 with p ≃ 0.075 appears.

As increasing interest for soot emission. etc in combustion systems, various studies are being carried out for the reduction and measurement techniques of soot. Especially, laser induced incandescence is the useful measurement technique which has distinguished spatial and temporal resolution for primary particle size, volume fraction and aggregated particle size etc. Time resolved laser induced incandescence is the technique for measuring primary particle size that is decided to solve the signal decay rate which is related to the cooling behavior of heated particle by pulsed laser. The cooling behavior of heated particle is able to represent the heat and mass transfer model which are involved constants of soot property for surround gas temperature on the our previous work. In this study, it is applied to the time-dependence thermodynamic properties for soot temperature instead of constants of soot property for surround gas temperature and compared two different model results.

An experimental study was performed to investigate the characteristics of chemiluminescence in a radiant burner, varying the excess air ratio from 0.91 to 1.67 at firing rate 80.5 to 134.2 kW/m2 on in LNG-Air premixed flames. The signals from electronically excited states of were detected using a Intensified Couple Charged Detector (ICCD) camera. The measurements of exhausted emission were made to investigate the correlation between chemiluminescence and emissions. The chemiluminescence intensity was increased with increase of firing rate like characteristics of emission. also increased with increase of firing rate and excess air ratio. It is found that offset of firing rate is more dominant excess air ratio emission. The maximum chemiluminescence intensity occurs near the stoichiometric excess air ratio or lean conditions in case of high firing rate and the maximum intensity occurs rather than rich conditions in case of relatively low firing rate. Amount of emission is maximum at near stoichiometric excess air ratio, which is chemiluminescence intensity is maximum.

Recently there is an increasing interest in particulate matter emission because of new emission regulations, health awareness and environmental problems. It requires to improve particulate measurement techniques as well as to reduce soot emissions from combustion systems. As mentioned above, it is demanded that reduction techniques together with measurement techniques of exhausted particulate matters in combustion systems such as vehicles. However, measurement techniques of particulate matters should be prior to reduction techniques of that because it is able to know an increase and a decrease of exhausted particulate matters when measured particulate matters. Therefore, in this study, we report the measurement of soot primary-particle size using time-resolved laser induced incandescence (TIRE-LII) technique in laminar ethylene diffusion flame. As an optical method, laser induced incandescence is one of well known methods to get information for spatial and temporal soot volume fraction and soot primary particle size. Furthermore, TIRE-LII is able to measure soot primary particle size that is decided to solve the decay ate of signal S and S at two detection time. In laminar ethylene diffusion flame, visual flame height is 40 mm from burner tip and measurement points are height of 15, 20, 27.5, 30 mm above burner tip along radial direction. As increasing the height of the flame from burne. tip, primary particle size was increased to HAB(Height Above Burner tip)

Time dependent magnetization was measured on two forms (polycrystal and aligned grains) of high- T c superconductor SmBa 2 Cu 3 O y . The flux-creep activation energy obtained in the aligned grains showed inverse dependence on current density as expected from collective flux-creep theory. However, that obtained from a polycrystal, which can be called intergranular flux-creep activation energy, showed linear dependence on current density as suggested by Kim-Anderson model. This proves that Kim’s critical state model is more suitable to the intergranular system, where flux lines should be in fixed positions and have fixed sizes, than the flux bundle system. In the critical state, where the pinning force is balanced with Lorentz force, the collective pinning theory is proved to be related to the generalized critical state model, which needs to be modified by surface-barrier effect when it is applied to M − H curve fitting of aligned grains.

The flux-creep crossover was observed from the magnetic relaxation measurement of an aligned Hg-1223 superconductor. Generally, the critical state in Type II superconductor is defined as the state that the Lorentz force is equal to the pinning force. According to our analysis, however, since near surface there is a attractive force between surface and vortex besides the Lorentz force, the near-surface region is under a critical state different from the inside of the sample, causing the crossover on the magnetic relaxation. As the temperature increased, the flux-creep crossover was shifted to a shorter time due to the reduced surface barrier effect and pinning force. In sufficiently high T and H , the two flux-creep crossover points were observed, the second crossover point meaning the end of the relaxation. By considering the surface barrier effect, we analyzed the magnetic relaxation and M – H hysteresis loop, which was different from what was expected in the critical state model.

The ac susceptibilities of polycrystalline HgBa 2 Ca 2 Cu 3 O 8+ δ with weak coupling, (Tl,Pb,Bi) 1 (Ba,Sr) 2 Ca 2 Cu 3 O y with intermediate coupling, and Bi 1.6 Pb 0.4 Sr 2 CaCu 2 O 8+ δ with strong coupling were measured as a function of temperature, magnetic field and frequency. We have found that the intergranular properties for Bi 1.6 Pb 0.4 Sr 2 CaCu 2 O 8+ δ are much better than those for other high temperature superconductors. Therefore, we propose Bi 1.6 Pb 0.4 Sr 2 CaCu 2 O 8+ δ as a promising material for a long scale application.

We fabricated polycrystalline high-Tc superconducting Tl0.8Pb0.4Sr1.8Ba0.2Ca2Cu3Ox with unconventional granular morphology. The morphology of the superconducting grains in the sample was revealed by scanning electron microscope and we found that the grains are connected tightly with each other though there are a number of holes surrounded by the grains. The ac susceptibility of the sample was measured as a function of temperature at different ac field and compared with a Tl-based polycrystalline sample with weak link between grains. Even in the weak field of 0.1 Oe, the out-of-phase component χ″(T) of the ac susceptibility showed double peaks just below Tc. As the ac field increased from 0.1 Oe, the temperature difference between the two peaks decreased, which is the opposite of what is commonly observed. The two peaks overlapped and look like one peak above 4 Oe. Above the ac field of 13 Oe, the peak divided into two peaks again. We propose possible flux pinning mechanism in the sample, and it is proved that the ac response is caused by the granular morphology of the sample.

The pinning mechanism of Bi 1.6 Pb 0.4 Sr 2 CaCu 2 O 8+ δ single crystal was investigated by analyzing the normalized pinning forces. We found that our single crystal showed a very strong secondary peak effect in a wide temperature range, from 20 to 80 K ( T c =92 K). We observed that the pinning mechanism was changed from δ l pinning to δ T c pinning at low fields and from the catastrophic instability to a combination of the catastrophic instability and the avalanche instability at high fields with temperature.

We are facing the serious environmental pollution difficulties such as acid rain, green house effects, etc. The gaseous matter NOx, SOx, VOCs which are regarded as main factors for these current pollutions are mainly emitted from power plants and vehicles. Therefore several leading countries are regulating the emissions strictly, especially the exhaust emissions from a Diesel engine without an aftertreatment device. The objective of this study is to find out soot and NO removal characteristics focused on the emissions of a Diesel engine by using nonthermal plasma for each engine speeds and loads. Electrostatic precipitator(wire-to-plate type reactor) is used for soot removal. Radicals generated from outer air and put into a mixing chamber in the end of exhaust line are used for NO removal. Concentration of exhaust emissions is analyzed from the gas analyzer(KaneMay) and FTIR to estimate by-products.