• Journal of Power System Engineering
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• 제10권3호
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• pp.5-10
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• 2006

In a conventional and lean operating engine, the state of mixture is very important in the combustion and emission characteristics. Lean operation is known to decrease the formation while maintaining a good fuel economy, but the unstable operation due to misfire and erratic combustion prevents engines from being operated at very lean mixtures, so both combustion rates and exhaust emission formation need to be satisfied comparably. In this study, it is designed and experimented the modified engine, and analyzed the combustion and exhaust emission according to the change of engine speed and with adding ozone. The conclusions were drawn out and enumerated as follows. 1. At the experimental result of automobile diesel engine, it has been verified that the formation of particulate matter(PM) gas is able to be lower with the addition of optimum quantities of ozone. 2. Carbon monoxide(CO) was formed by the lack of oxygen and the thermal dissociation in the combustion process. Therefore, with the change of swirl valve's position and addition of oxygen and ozone, CO formation was decreased by the increasing of excessive O2, but it was increased by the temperature of combustion gas growing higher. As a result of the two effects, CO formation was decreased in this study. 3. Hydrocarbon(HC) was formed by the lack of O2, and the flow of mixture in cylinder. According to opening of the swirl valve and adding the oxygen and ozone, hydrocarbon gas was decreased by 20%, 9%, and 27.5%, respectively. 4. Nitric oxides($NO_x$) was strongly affected by the combustion gas temperature. As a result of respectively experimental conditions, $NO_x$ formation was increased about 20% due to (be the) high(er) combustion gas temperature.

• Journal of Hydrogen and New Energy
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• 제26권2호
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• pp.164-169
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• 2015

Recent research has focused on alternative fuel to improve engine performance and to comply with emission regulation. Finding an alternative fuel and reducing environment pollution are the main goals for future internal combustion engines. The purpose of this study is to obtain low-emission and high-efficiency by hydrogen enriched CNG fuel in SI engine and is to clarify the effects of hydrogen enrichment in CNG fuelled engine on exhaust emission and performance. An experimental study was carried out to obtain fundamental data for performance and emission characteristics of hydrogen enrichment in SI engine. The experiment was conducted at 2500 rpm, bmep 2 bar, 4 bar conditions while CNG fuel was mixed with 10, 20 and 30% hydrogen blends. From the experimental results, combustion duration was shortened due to rapid flame propagation velocity of hydrogen and these were attributed to the burning velocity increasing exponentially with increasing hydrogen blending ratio. Hydrogen has much wider flammable limit than methane, gasoline and the minimum ignition energy is about an order of magnitude lower than for other combustion. By adding hydrogen, $CO_2$ and HC were reduced. However, $NO_X$ was increased dut to high rate of heat release for hydrogen substitutions.

• Transactions of the Korean Society of Automotive Engineers
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• 제18권2호
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• pp.7-13
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• 2010

To satisfy the needs on fuel economy and engine performance, continuous variable valve lift systems are applying to engines. In the CVVL system, fuel economy can be improved by reducing pumping loss during the induction process, and engine performance can be also improved by controlling volumetric efficiency and the residual gas fraction. Because the residual gas fraction directly affects volumetric efficiency, engine performance, combustion efficiency and emissions in SI engines, controlling residual gas fraction is one of the important things in engine development process. This analysis investigates the residual gas fraction and volumetric efficiency with changes of intake valve lifts and intake valve timings. In this study, unsteady state solutions were solved during exhaust and induction processes. Results show variation of the residual gas fraction and volumetric efficiency by changing intake valve timing and lift. Decreasing intake valve lift leads to increase the residual gas fraction and to decrease volumetric efficiency.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 한국추진공학회 2009년도 제33회 추계학술대회논문집
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• pp.433-438
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• 2009

The main objective of this research effort is to develop the performance of C/SiC composites manufactured by LSI (Liquid Silicon Infiltration) method for solid and liquid rocket propulsion system and ensure the performance analysis technique. The high performance and reliability of C/SiC composite are proved for solid and liquid rocket propulsion system. And the performance analysis technique related to mathematical ablation model is originated.

• Journal of Korea Foundry Society
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• 제9권3호
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• pp.221-227
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• 1989

The effect of sulfur content and inoculant on solidification microstructure and mechanical properties of gray cast iron have been investigated. The main results obtained are as follows, 1. In the FeSi3Ca1Ba inoculated irons, with the variation of sulfur content, low sulfur levels (${\sim}0.03%$) yield low chill depth, high tensile strength, good wear resistance and type A graphite with a pearlite matrix. High sulfur levels( >0.08%) provide high chill depth, low mechanical proper ties and type D graphite with small amount ferrite. 2. In case of inoculant variation with normal FeSi, FeSi3Ca1Ba, 30CaSi and uninoculation at 0.03%S level, lower chill depth and higher tensile strength was obtained in the order ; 30CaSi, FeSi3Ca1Ba normal FeSi, uninoculation.

• Transactions of the Korean Society of Automotive Engineers
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• 제14권6호
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• pp.50-56
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• 2006

Residual gas fraction in a combustion process is very crucial to improve combustion and cyclic variations. Especially, the residual gas fraction is strongly affected by backflow of the residual gas during the valve overlap period in an idle operation. Therefore, it is one of the most interesting that valve timings can affect flow characteristics of gas exchange process, especially during idle operation. This analysis investigates residual gas fraction with respect to valve timing changes which is critical for combustion efficiency and engine performance. Flow characteristics of residual gas by changing intake and exhaust valve timing are calculated by CFD methodology during an idle operation in an SI engine. It is analyzed that retarded EVO and advanced IVO results in the increase of valve overlap period and consequently, residual gas fraction. Futhermore, changes in IVO have stronger effects on variation of residual gas fraction.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제10권12호
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• pp.3553-3558
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• 2009

This study has been conducted to improve coolant flow pattern in the gasoline engine. Flow field has been calculated for the coolant passage mainly around the exhaust ports and valves. For the original model, a flow stagnant region has existed between exhaust valves of the second cylinder. To improve coolant flow characteristics, coolant passage area has been re-modeled and optimized. Furthermore, for the improved coolant core model, coolant passage under the exhaust manifold has been added to reduce exhaust-gas temperature. It was found that the flow through a gasket plays a critical role for the flow in the cylinder head and around exhaust valves. Finally, coolant flow around exhaust valves and in the cylinder head has been improved in terms of flow rate distribution.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제32권11호
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• pp.884-890
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• 2008

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.

• Journal of the Korean Society for Precision Engineering
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• 제19권7호
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• pp.80-87
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• 2002

Liquefied petroleum gas (LPG) is used in spark ignition (SI) engines. Fuel injection rate of an injector is affected by fuel temperature and pressure in LPG liquid injection systems for either a multi-point-injection (MPI) or a direct injection (DI) engine. Even fuel injection conditions are varied, the air-fuel ratio should be accurately controlled to reduce exhaust emissions. In this study, a correction factor fur the fuel injection rate of an injector is derived from density ratio and pressure difference ratio. A compensation method of injected fuel amount is proposed for a fuel injection control system. The experimental results for the LPG liquid injection system in a SI engine show that this system works well fur a full range of engine speed and load condition, and the air-fuel ratio is accurately controlled by the proposed correction factor.

• Transactions of the Korean Society of Automotive Engineers
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• 제4권3호
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• pp.122-129
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• 1996

The spark timing is one of major parameters to the engine performance and emissions. The ECU controls the spark timing based on preset values, which are functions of load and speed, in most of today's automotive SI engine. In this system, the preset spark timing can be different from optimum value due to the deviations from mass production, aging effects and so on. In the present study, a control logic is investigated for real time adaptation of spark timing to optimal value. It has been found that crank angle of miximum cylinder pressure is one of the appropriate parameters to estimate the optimum spark timing throught experiment. It has also been observed for spark timing convergence by variation of engineering model factors. The simulation program including engineering model for cycle by cycle variation of combustion is developed for surveying spark timing control logic. It is also shown that simulation results reflect experiment outputs and reasonableness of spark timing control logic for crank angle of maximum cylinder pressure.