Sunyoup Lee

Effect of Boron Contents on Weldability in High Strength Steel

Three experimental flux cored wires(basic type) designed to produce systematic variations in the concentrations of boron of 32 ppm, 60 ppm and 103 ppm in the weld metal were prepared. A previous study of crack properties, morphology and microstructure in accordance with welding conditions was published in Welding Journal(Lee, 2006). Microstructure, strength and absorbed energy were studied for EH32 TMCP (Thermo-Mechanical Controlled Process) 40 mm thick plate welded with a gas-shielded flux cored arc welding.The volume fraction of acicular ferrite decreased with increasing boron contents 32 to 103 ppm. The upper bainite instead of acicular ferrite was formed in the 103 ppm boron weld metal. The hardness values welded with 32 ppm and 60 ppm boron wire welds were in the range of Hv 190–210, while those welded with 103 ppm boron wire weld were in the range of Hv 230–235.The absorbed energy slightly decreased with increasing boron contents from 32 ppm to 60 ppm, but significantly decreased with increasing boron contents from 60 ppm to 103 ppm. In the weld joint welded with 32 ppm and 60 ppm boron content electrode, no cracks were detected. However, cracks were detected the specimen welded with 103 ppm boron content electrode.

Chamfered-bowl piston for ultra-low particulate combustion with diesel and soybean biodiesel in a single-cylinder compression-ignition engine

Piston bowl geometries are critical to the combustion and emission characteristics of diesel engines. The present study investigated chamfered-bowl designs and biodiesel blending under a low-temperature combustion regime in order to achieve ultra-low particulate combustion (ULPC). The target soot level for ULPC was set at a filter smoke number value of 0.1 and engine experiments were conducted at the medium load condition. The injection visualization experiment provided the start of injection difference between the diesel and biodiesel fuels, while a three-dimensional computational simulation was conducted to examine the spray and combustion phenomena inside the engine cylinder. The experimental engine was a 1 l single-cylinder diesel engine equipped with a common-rail direct-injection system. The engine was operated at a speed of 1400 rev/min and the intake pressure was set at 200 kPa for a 50 per cent load condition. Two chamfered-bowl pistons were prepared for comparison with the conventional re-entrant bowl piston, and the experimental results showed that the chamfered-bowl pistons achieved significant soot reduction. In addition, computational analysis using a KIVA model showed that the chamfered bowls achieved wider fuel distribution and enhanced combustion. Biodiesel blending further reduced soot emission, and an increase in nitric oxides with biodiesel blends was also observed.

Enhancing Low Temperature Combustion With Biodiesel Blending in a Diesel Engine at a Medium Load Condition

The present study investigated the effects of biodiesel blending under a wide range of intake oxygen concentration levels in a diesel engine. This study attempted to identify the lowest biodiesel blending rate that achieves acceptable levels of nitric oxides (NOx), soot, and coefficient of variation in the indicated mean effective pressure (COVIMEP). Biodiesel blending was to be minimized in order to reduce the fuel penalty associated with the biodiesels lower caloric value. Engine experiments were performed in a 1-liter single-cylinder diesel engine at an engine speed of 1400 rev/min under a medium load condition. The blend rate and intake oxygen concentration were varied independently of each other at a constant intake pressure of 200 kPa. The biodiesel blend rate varied from 0% (B000) to 100% biodiesel (B100) at a 20% increment. The intake oxygen level was adjusted from 8 to 19% by volume (vol %) in order to embrace both conventional and low-temperature combustion (LTC) operations. A fixed injection duration of 788 μs at a fuel rail pressure of 160 MPa exhibited a gross indicated mean effective pressure (IMEP) between 750 kPa and 910 kPa, depending on the intake oxygen concentration.The experimental results indicated that the intake oxygen level had to be below 10 vol% to achieve the indicated specific NOx (ISNOx) below 0.2g/kWhr with the B000 fuel. However, a substantial soot increase was exhibited at such a low intake oxygen level. Biodiesel blending reduced NOx until the blending rate reached 60% with reduced in-cylinder temperature due to lower total energy release. As a result, 60%-biodiesel blended diesel (B060) achieved NOx, soot, and COVIMEP of 0.2 g/kWhr, 0.37 filter smoke number (FSN), and 0.5, respectively, at an intake oxygen concentration of 14 vol%. The corresponding indicated thermal efficiency was 43.2%.Copyright

Characterization of Coarse, Fine, and Ultrafine Particles Generated from the Interaction between the Tire and the Road Pavement

The non-exhaust coarse, fine, and ultrafine particles were characterized by on-road driving measurements using a mobile sampling system. The on-road driving measurements under constant speed driving revealed that mass concentrations of roadway particles (RWPs) were distributed mainly in a size range of 2~3 and slightly increased with increasing vehicle speed. Under braking conditions, the mode diameters of the particles were generally similar with those obtained under constant speed conditions. However, the PM concentrations emitted during braking condition were significantly higher than those produced under normal driving conditions. Higher number concentrations of ultrafine particles smaller than 70 nm were observed during braking conditions, and the number concentration of particles sampled 90 mm above the pavement was 6 times higher than that obtained 40 mm above the pavement. Under cornering conditions, the number concentrations of RWPs sampled 40 mm above the pavement surface were higher than those sampled 90 mm above the pavement. This might be explained that a nucleation burst of a lot of vapor evaporated from the interaction between the tire and the road pavement under braking conditions continuously occurred by cooling during the transport to the sampling height 90 mm, while, for the case of cornering situations, the ultrafine particle formation was completed before the transport to the sampling height of 40 mm.

Effect of Intake Pressure on Emissions and Performance in Low Temperature Combustion Operation of a Diesel Engine

One of the effective ways to reduce both NOx and PM at the same time in a diesel CI engine is to operate the engine in low temperature combustion (LTC) regimes. In general, two strategies are used to realize the LTC operation-dilution controlled LTC and late injection LTC - and in this study, the former approach was used. In the dilution controlled regime, LTC is achieved by supplying a large amount of EGR to the cylinder. The significant EGR gas increases the heat capacity of in-cylinder charge mixture while decreasing oxygen concentration of the charge, activating low temperature oxidation reaction and lowering PM and NO x emissions. However, use of high EGR levels also deteriorates combustion efficiency and engine power output. Therefore, it is widely considered to use increased intake pressure as a way to resolve this issue. In this study, the effects of intake pressure variations on performance and emission characteristics of a single cylinder diesel engine operated in LTC regimes were examined. LTC operation was achieved in less than 8% O 2 concentration and thus a simultaneous reduction of both PM and NOx emission was confirmed. As intake pressure increased, combustion efficiency was improved so that THC and CO emissions were decreased. A shift of the peak Soot location was also observed to lower O2 concentration while NOx levels were kept nearly zero. In addition, an elevation of intake pressure enhanced engine power output as well as indicated thermal efficiency in LTC regimes. All these results suggested that LTC operation range can be extended and emissions can be further reduced by adjusting intake pressure.

A Study on the Combustion Characteristics of a Generator Engine Running on a Mixture of Syngas and Hydrogen

Key Words: Syngas(합성가스), Hydrogen(수소), LHV(저위발열량), Generator(발전기), Combustion stability(연소안정성)초록: 바이오매스나기타유기성폐기물로부터가스화공정을거쳐얻을수있는합성가스는환경보호와화석연료고갈방지측면에서유망한대체연료중하나로여겨지고있다. 그러나가스화로부터얻어지는합성가스는일반적인천연가스와같은가스연료에비해발열량이낮고연료조성이불균일하여내연기관에적용시안정적이고지속적인운전이어렵다는단점이있다. 따라서본연구에서는이러한저발열량과불균일한가스조성의특징을가진합성가스가연소에미치는영향을파악하여고효율의엔진을개발하고자연구를수행하였다. 저발열량의합성가스를모사하기위하여천연가스에질소를희석한연료를사용하였다. 또한체적당발열량을유지하면서동일유량조건으로합성가스에수소혼합비율을10 ~30%로변화시키면서연소특성변화를살펴보았다.Abstract: Internal combustion engines running on syngas, which can be obtained from biomass or organicwastes, are expected to be one of the suitable alternatives for power generation, because they areenvironment-friendly and do not contribute to the depletion of fossil fuels. However, syngas has variablecompositions and a lower heating value than pure natural gas, owing to which the combustion conditions needto be adjusted in order to achieve stable combustion. In this study, a gas that has the same characteristics assyngas, such as low heating value (LHV), was produced by mixing N

Flue Gas Waste Heat and Water Recovery Organic Rankine Cycle

Extended Abstract Fossil fuel-based power plants consume significant amount of water. Therefore, the power plants can cause an environmental impact and its locations are very limited by the availability of water. Water recovery from flue gas in the power plants could contribute to reduce water requirement. For example, a 600MW coal power plant releases 45 ton/min of flue gas including 7.2 ton/min of moisture [1]. Several technologies including water condensation by cooling water [1], liquid desiccant dehumidification system (LDDS) [2], and transport membrane condenser (TMC) [3] have been developed. In this study, in order to condense the moisture in flue gas, the flue gas is firstly cooled down by a waste heat recovery (WHR) organic Rankine cycle (ORC) system and is further cooled down below dew point (55°C) by a pumped heat pipe cooling loop combined with the ORC system. Two-phase cooling by the organic working fluid instead of cooling water can reduce the large surface area [4] of condensing heat exchanger for low-temperature flue gas. Furthermore, an ejector cooling system or vapor compression refrigeration system driven by the waste heat of flue gas [5], combined with the ORC system, can be used to further cool down the flue gas because it is very difficult to condense the moisture in the flue gas with a high ambient temperature. In the case of the 600MW coal power plant releasing 150°C of flue gas, the WHR ORC system can produce about 6.7MW of additional power and recover 50% of water in flue gas by cooling the flue gas to 40°C at the evaporation temperature of 30°C for R134a. Furthermore, with the help of the vapor compression cooling system driven by the heated high pressure working fluid, it can recover 70% of water in flue gas by cooling the flue gas to 30°C at the evaporation temperature of 20°C for R134a. Along with the water recovery in the condensing heat exchanger, condensable particulate matter (CPM) can be separated from the flue gas for environmental friendliness [6,7].

PM Reduction Characteristics of Gasoline Direct Injection Engines with Different Types of GPFs

In the recent times, the use of gasoline direct injection (GDI) engines has been regarded as a means of enhancing conformance to emission regulations and improving fuel efficiency. GDI engines have been widely adopted in the recent years for their better engine performance and fuel economy compared to those of conventional MPI gasoline engines. However, they present some disadvantages related to the mass and quantity of particulate matter generated during their use. This study investigated the nanoparticle characteristics of the particulate matter exhausted from a GDI engine vehicle installed with different types of gasoline particulate filters, after subjecting it to ultra-lean burn driving conditions. Three metal foam and metal fiber filters were used for each experimental condition. The number concentrations of particles were analyzed for understanding their behavior, and the reduction characteristics were obtained for each type of filter.

Enhancing Low-Temperature Combustion With Biodiesel Blending in a Diesel Engine at a Medium Load Condition

The present study investigated the effects of biodiesel blending under a wide range of intake oxygen concentration levels in a diesel engine. This study attempted to identify the lowest biodiesel blending rate that achieves acceptable levels of nitric oxides (NOx), soot, and coefficient of variation in the indicated mean effective pressure (COVIMEP). Biodiesel blending was to be minimized in order to reduce the fuel penalty associated with the biodiesels lower caloric value. Engine experiments were performed in a 1-liter single-cylinder diesel engine at an engine speed of 1400 rev/min under a medium load condition. The blend rate and intake oxygen concentration were varied independently of each other at a constant intake pressure of 200 kPa. The biodiesel blend rate varied from 0% (B000) to 100% biodiesel (B100) at a 20% increment. The intake oxygen level was adjusted from 8 to 19% by volume (vol %) in order to embrace both conventional and low-temperature combustion (LTC) operations. A fixed injection duration of 788 μs at a fuel rail pressure of 160 MPa exhibited a gross indicated mean effective pressure (IMEP) between 750 kPa and 910 kPa, depending on the intake oxygen concentration.The experimental results indicated that the intake oxygen level had to be below 10 vol% to achieve the indicated specific NOx (ISNOx) below 0.2g/kWhr with the B000 fuel. However, a substantial soot increase was exhibited at such a low intake oxygen level. Biodiesel blending reduced NOx until the blending rate reached 60% with reduced in-cylinder temperature due to lower total energy release. As a result, 60%-biodiesel blended diesel (B060) achieved NOx, soot, and COVIMEP of 0.2 g/kWhr, 0.37 filter smoke number (FSN), and 0.5, respectively, at an intake oxygen concentration of 14 vol%. The corresponding indicated thermal efficiency was 43.2%.Copyright

Effect of Injection Pressure on Low Temperature Combustion in CI Engines

Diesel low temperature combustion (LTC) is the concept where fuel is burned at a low temperature oxidation regime so that NOx and particulate matters (PM) can simultaneously be reduced. There are two ways to realize low temperature combustion in compression ignition engines. One is to supply a large amount of EGR gas combined with advanced fuel injection timing. The other is to use a moderate level of EGR with fuel injection at near TDC which is generally called Modulated kinetics (MK) method. In this study, the effects of fuel injection pressure on performance and emissions of a single cylinder engine were evaluated using the latter approach. The engine test results show that MK operations were successfully achieved over a range of with 950 to 1050 bar in injection pressure with 16% O2 concentration, and NOx and PM were significantly suppressed at the same time. In addition, with an increase in fuel injection pressure, the levels of smoke, THC and CO were decreased while NOx emissions were increased. Moreover, as fuel injection timing retarded to TDC, more THC and CO emissions were generated, but smoke and NOx were decreased.