Ocktaeck Lim

The role of black carbon as a catalyst for environmental redox transformation

Black carbon (BC) is an important class of geosorbents that control the fate and transport of organic pollutants in soil and sediment. We previously demonstrated a new role of BC as an electron transfer mediator in the abiotic reduction of nitroaromatic and nitramine compounds by Oh and Chiu (Environ Sci Technol 43:6983–6988, 2009). We proposed that BC can catalyze the reduction of nitro compounds because it contains microscopic graphitic (graphene) domains, which facilitate both sorption and electron transfer. In this study, we assessed the ability of different types of BC—graphite, activated carbon, and diesel soot—to mediate the reduction of 2,4-dinitrotoluene (DNT) and 2,4-dibromophenol (DBP) by H2S. All three types of BC enhanced DNT and DBP reduction. H2S supported BC-mediated reduction, as was observed previously with a thiol reductant. The results suggest that BC may influence the fate of organic pollutants in reducing subsurface environments through redox transformation in addition to sorption.

A study for generating power on operating parameters of powerpack utilizing linear engine

2 Korea institute of Energy Research, 152 Gajeong street, Yuseong-gu, daejun, 305-343, Korea Abstract >> The research shows the experiment results according to the combustion characteristics and configuration of the linear generator of powerpack for the generating power applying the 2-stroke compact linear engine. The powerpack used in this paper consists of 2-stroke linear engine, linear generator and air compressor parts. For identifying the combustion characteristics and generating power of linear engine, some parameters were varied sucha as electric load, fuel input calorie, spark timing delay and equivalence ratio. Also generating power was confirmed at each operation conditions, when the air gap length of linear generator part was changed as each 1.0 mm and 2.0 mm. During the all operations, intake air was inputted under the wide open throttle. Mass flow rate of air and fuel was changed using mass flow controller, after these were premixed by premixture device, and then premixed gas was supplied directly into each cylinder. As a result, piston frequency and combustion characteristics were different at each conditions according to parameters affecting the combustion such as fuel input calorie, resistive load, spark timing delay and equivalence ratio. Consequently, these had an effect on generating power.

Effect of the Boost Pressure on Thermal Stratification on HCCI Engine Using Multi-Zone Modeling

The HCCI engine is a next generation engine, with high efficiency and low emissions. The engine may be an alternative to SI and DI engines; however, a pressure rise rate is a major limitation for high load range and power reduction. Recently, we were able to reduce the pressure rise rate using thermal stratification. Nevertheless, this was insufficient to produce high power. In this study, the reduction of the pressure rise rate using thermal stratification was confirmed and the HCCI engine power was increased using the boost pressure. The rate and engine power were produced by CHEMKIN and modified SENKIN. As a result of increasing the boost pressure, a higher IMEP was attained while the pressure rise rate increased only slightly in the HCCI with thermal stratification.

A Study on the Autoignition Characteristics of DME–LPG Dual Fuel in the HCCI Engine

This study investigated the potential increase of engine power through the mixture of dimethyl ether (DME) and liquefied petroleum gas (LPG) with homogeneous charge compression ignition combustion. The effects of mixing ratio of DME/LPG at a constant intake temperature were confirmed experimentally in a single-cylinder diesel engine. A numerical analysis was conducted through the detailed chemical kinetics by using CHEMKIN-PRO for the mixing model of DME and n-butane to clarify the underlying mechanism of autoignition, while considering the gas mixture heat loss to the cylinder wall to compare with the experiment. The results show that the increased amount of LPG reduces the low-temperature heat release and activates the high-temperature heat release, which increases in-cylinder pressure. Therefore, it has potential to raise the indicated mean effective pressure when mixing ratio was adjusted appropriately. Also, thermal efficiency was increased to 51.2% at the mixing ratio of 0.6. Finally, engine out emissions including total hydrocarbon increased a small amount and carbon monoxide was decreased to almost zero when the mixing ratio of DME decreased until the combustible zone. Numerical results agreed with the experiment, indicating weakened low-temperature oxidation from the increase of the n-butane amount.

The effects of Gasoline-Biodiesel Blended Fuels on Spray Characteristics

The current study has investigated the effects of biodiesel blended with gasoline on the spray characteristics in a Constant Volume Combustion Chamber (CVCC). With the concentration of 5, 10, 15 and 20% by volume, biodiesel was blended with commercial gasoline and performed on the macroscopic visualization test. Pure gasoline and biodiesel were also tested as the reference. The shadowgraph technique was conducted in the constant volume chamber. The spray images were recorded by a high speed video camera with frame speed 10,000 frame per second. Fuel injection was set at 800, 1000 and 1,350 bar with the simulated speed 1,500 and 2,000 rpm. The back pressure was controlled at 20 bar. The spray angle and penetration tip were measured and analyzed by using the image processing. At the high injection pressure, the spray penetration length with the simulated speed 1,500 rpm showed that B100 was lower than GB00-20 whereas the spray penetration length with the simulated speed 2,000 rpm exhibited that GB blends and B100 were insignificantly different. Due to biodiesel concentration, its effects on spray angles were observed throughout injection periods (T1, T2 and T3). At the simulated speed 1,500 rpm, the spray angle of GB blends and B100 presented the same pattern following injection timing. In addition, when the simulated speed increased to 2,000 rpm the different spray angle of all blends disappeared at main injection (T3).

An Investigation on the Spray Characteristics of DME with Variation of Nozzle Holes Diameter using the Common Rail Fuel Injection System

DME spray characteristics were investigated about varied ambient pressure and fuel injection pressure using the DME common rail fuel injection system when the nozzle holes diameter is varied. The common rail fuel injection system with DME cooling system was used since DME has properties of compressibility and vaporization in atmospheric temperature. The fuel injection quantity and spray characteristics were measured. The spray analysis parameters were spray shape, penetration length, and spray angle at six nozzle holes. Three types of injector were used, the nozzle holes diameter were 0.166 mm (Injector 1), 0.250 mm (Injector 2), and 0.250 mm with enlargement of orifice hole from 0.6 mm to 1.0 mm (Injector 3). The fuel injection pressure was varied by 5MPa from 35 to 70MPa when the ambient pressure was varied 0, 2.5, and 5MPa. When using Injector 3 in comparison to the others, the DME injection quantity was increased 1.69 ~ 2.02 times. Through this, it had the similar low heat value with diesel which was injected Injector 1. Among three types of injector, Injector 3 had the fastest development velocity of penetration length. In case of spray angle, Injector 2 had the largest spray angle. Through these results, only the way enlargement the nozzle holes diameter is not the solution of DME low heat value problem.

A Numerical Simulation for the Spring Hardness of a Free Piston Linear Engine

This research numerically analyses the effects of the damping device on the operation characteristics of a free piston linear engine. In this paper, the free piston linear engine uses spring as a damping device. The investigated parameter is spring hardness which is varied at 0.5, 1, 2.9, and 14.7 N/mm. The effects of spring hardness on the dynamic characteristic, thermodynamic characteristic and electric power of the engine are investigated. Beside, the equivalent ratio is also changed to provide more information for this study. The simulation results show that, by increasing spring hardness from 0.5 to 14.7 N/mm, all of parameters related to dynamic characteristic such as piston velocity, acceleration, displacement, and frequency increase accordingly. Beside, the peak pressure in the cylinder and electric power are also increased when increasing spring hardness. The tendency is also observed at varied equivalent ratios.

The Experimental Research for the Combustion and Dynamic Characteristics of the Linear Engine on the Variable Spring Stiffness

This study was experimentally investigated on the effects of spring stiffness applied to linear compressor chambers. The springs prevented piston head from colliding with engine cover, stored the kinetic energy and regenerated the kinetic energy. The linear engine has two combustion chambers and four compressor chamber. The combustion chamber bore size was 30 mm, maximum stroke was 31 mm and effective stroke volume was 25.45 cc respectively. The spring stiffness was varied such as 0, 0.5, 1.00, 2.9 and 14.7 N/mm. The linear engine was fueled with premixed LPG (propane 99%) and air by pre-mixture device. As an experimental result, The stroke, piston velocity and the piston frequency were increased by high spring stiffness. Also, thermal efficiency was grown. because the increased stroke made the higher compression ratio. In conclusion, electric power and efficiency were improved.

An Investigation on the Spray Characteristics of Diesel-DME Blended Fuel with Variation of Ambient Pressure in the Constant Volume Combustion Chamber

The aim of this study was to compare the spray characteristics of a typical fuel (100% diesel, DME) and diesel-DME blended fuel in a constant volume combustion chamber (CVCC). The typical fuel (100% diesel, DME) and diesel-DME blended fuel spray characteristics were investigated at various ambient pressures (pressurized nitrogen) and fuel injection pressures using a common rail fuel injection system when the fuel mixture ratio was varied. The fuel injection quantity and spray characteristics were measured including spray shape, penetration length, and spray angle. Common types of injectors were used.

Characteristics of auto-ignition in gasoline–biodiesel blended fuel under engine-like conditions

The purpose of this study is to demonstrate the effects of biodiesel fraction on auto-ignition for gasoline–biodiesel blended fuel, which combines two fuels with widely different auto-ignition characteristics. First, gasoline was blended with biodiesel at 5%, 10%, 15%, and 20% by volume, and then tested in a rapid compression expansion machine at a compression ratio of 11 and a temperature range of 720–850 K to observe the auto-ignition delay phenomenon under engine-like conditions. The experimental conditions are focused on improving the auto-ignition characteristic of gasoline direct-injection compression ignition combustion strategies under low load and cold start. The heat release rate of the blended fuels was calculated from the pressure trace and displacement history of the piston in order to identify first-stage ignition and second-stage (auto-ignition) ignition delay. Second, a gasoline–biodiesel reaction mechanism was developed to predict the chemical ignition delay of the blended fuels. The reaction mechanism with 4285 species and 15,246 reactions was validated and implemented using the CHEMKIN PRO software. Finally, the chemical ignition delay was predicted by the simulation which was further compared to the experimental measured results. These results revealed that a higher biodiesel fraction helps to obtain shorter ignition delay, which reduces the requirement of intake temperature. The blended fuel with 20% biodiesel showed the lowest ambient temperature at the injection timing requirement and was 80 K lower than gasoline. Each blended fuel exhibited two-stage ignitions in the measured temperature range. The combustion duration and pressure peak of every blended fuel were similar to each other after increasing the biodiesel fraction.