• 한국자동차공학회논문집
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• 제17권4호
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• pp.93-100
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• 2009

Intake/exhaust valve timing and exhaust cam lift were changed to control the internal exhaust gas recirculation (IEGR) and combustion phase of homogeneous charge compression ignition (HCCI) engine. To measure the IEGR rate, in-cylinder gas was sampled during from intake valve close to before ignition start. The lower exhaust cam made shorter valve event than higher exhaust cam and made IEGR increase because of trapping the exhaust gas. IEGR rate was more affected by exhaust valve timing than intake valve timing and increased as exhaust valve timing advanced. In-cylinder pressure was increased near top dead center due to early close of exhaust valve. Ignition timing was more affected by intake valve timing than exhaust valve timing in case of exhaust valve lift 8.4 mm, while ignition timing was affected by both intake and exhaust valve timing in case of exhaust valve 2.5 mm. Burn duration with exhaust valve lift 2.5 mm was longer than other case due to higher IEGR rate. The fuel conversion efficiency with higher exhaust valve lift was higher than that with lower exhaust valve lift. The late exhaust and intake maximum open point (MOP) made the fuel conversion efficiency improve.

• 한국분무공학회지
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• 제17권2호
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• pp.71-76
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• 2012

The aim of this work was to investigate the combustion and nanoparticle emission characteristics of premixed charge compression ignition (PCCI) combustion at various test conditions using a single cylinder common-rail diesel engine. In order to create the homogeneity of fuel-air mixture, the premixed fuel (gasoline) was injected into premixing chamber during the intake process and then the diesel fuel was directly injected into the combustion chamber as an ignition source for the gasoline premixture. From these results, it revealed that the ignition delays and combustion durations were gradually prolonged and the peak combustion pressure were increased because diesel fuel was injected early injection timing with the increase of premixed ratio. In addition, as the increase of premixed ratio, total particle number is generally decreased and particle volume also indicated low levels at the direct injection timing from BTDC $20^{\circ}$ to TDC. At further advanced injection timing, total particle number and volume were generally increased

• 대한기계학회논문집B
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• 제31권6호
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• pp.514-521
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• 2007

This study focused on the effects of the $CO_2$ gas concentration in fresh charge and induction air temperature on the combustion characteristics of homogeneous charge compression ignition with dimethyl ether (DME) fuel, which was injected at the intake port. Because of adding $CO_2$ in fresh charge, start of auto-ignition was retarded and bum duration became longer. Indicated combustion efficiency and exhaust gas emission were found to be worse due to the incomplete combustion. Partial burn was observed at the high concentration of $CO_2$ in fresh charge with low temperature of induction air. However, indicated thermal efficiency was improved due to increased expansion work by late ignition and prolonged bum duration. Start of auto-ignition timing was advanced with negligible change of burn duration, as induction air temperature increased. Burn duration was mainly affected by oxygen mole concentration in induction mixture. Bum duration was increased, as oxygen mole concentration was decreased.

• 한국자동차공학회논문집
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• 제16권5호
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• pp.171-178
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• 2008

The combustion and exhaust emission characteristics were investigated in an DME fueled HCCI engine. Carbon dioxide, nitrogen and mixed gas, which was composed of carbon dioxide and nitrogen, were used as control parameters of combustion and exhaust emission. As the oxygen concentration in induction air, which was occurred by carbon dioxide, nitrogen and mixed gas, was reduced, the start of auto-ignition was retarded and the burn duration was extended due to obstruction of combustion and reduction of combustion temperature. Due to these fact, indicated mean effective pressure was increased and indicated combustion efficiency was decreased by carbon dioxide, nitrogen and mixed gas. In case of exhaust emission, hydrocarbon and carbon monoxide was increased by reduction of oxygen concentration in induction air. Especially, partial burning was appeared at lower than about 18% of oxygen concentration by supplying carbon dioxide. However it was overcome by intake air heating.

• 한국자동차공학회논문집
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• 제14권5호
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• pp.58-64
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• 2006

Homogeneous charge compression ignition(HCCI) combustion is an advanced technique for reducing the hazardous nitrogen oxide(NOx) and particulate matter(PM) in a diesel engine. NOx could be reduced by achieving lean homogeneous mixture resulting in combustion temperature. PM could be also reduced by eliminating fuel-rich zones which exist in conventional diesel combustion. However previous researches have reported that power-output of HCCI engine is limited by the high intensive knock and misfiring. In an attempt to extend the upper load limit for HCCI operation, supercharging in combination with Exhaust Gas Recirculation(EGR) has been applied: supercharging to increase the power density and EGR to control the combustion phase. The test was performed in a single cylinder engine operated at 1200 rpm. Boost pressures of 1.1 and 1.2 bar were applied. High EGR rates up to 45% were supplied. Most of fuel was injected at early timing to make homogeneous mixture. Small amount of fuel injection was followed near TDC to assist ignition. Results showed increasing boost pressure resulted in much higher power-output. Optimal EGR rate influenced by longer ignition delay and charge dilution simultaneously was observed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1401-1406
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• 2004

In this paper, we present the theoretical and numerical results of scavenge characteristics in a small prechamber of an HCCI(Homogeneous Charge Compression Ignition) engine. Two theoretical models are proposed in prediction of the scavenge time and the efficiency ; one is the non-mixing models in which it is assumed that the input gas($CH_{4}$) and the existing gas(air) do not mix with each other, and the other is the fully-mixed model in which the two gases are assumed to mix completely before ejecting to the ambient air. Focus is also given to the effect on the scavenge performance of the size of the chamber oulet.

• 대한기계학회논문집B
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• 제29권9호
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• pp.1006-1012
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• 2005

The effects of premixed fuels(diesel or n-heptane) and exhaust gas recirculation on combustion and exhaust emission characteristics in a DI diesel engine were experimentally investigated. To improve homogeneity of fuel-air mixture in the conventional diesel engine, the premixed fuel is injected by high pressure(5.5 MPa) into the premixing chamber prior to engine cylinder, And several additional systems such as an EGR system, air heating system and back pressure control system were equipped in the DI diesel engine. The results showed that premixed fuel-air mixture undergoes typical HCCI combustion prior to the combustion of DI diesel fuel. The ignition timing of HCCI combustion is delayed by application of EGR, and it also shows that HCCI combustion can be controlled by an EGR.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2013년도 제46회 KOSCO SYMPOSIUM 초록집
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• pp.37-40
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• 2013

Hydrogen-dimethy ether (DME) and hydrogen-diesel compression ignition engine combustion were investigated and compared each other in a single cylinder compression ignition engine. Hydrogen and DME were used as low carbon alternative fuels to reduce green house gases and pollutant. Hydrogen was injected at the intake manifold with an injection pressure of 0.5 MPa at fixed injection timing, $-210^{\circ}CA$ aTDC. DME and diesel were injected directly into the cylinder through the common-rail injection system at injection pressure of 30 MPa. DME and diesel inejction timing was varied to find the optimum CI combustion to reduce CO, HC and NOx emissions. When DME was injected early, CO and HC emissions were high while NOx emission was low. Fuel consumption, heat release rate, and exhaust emissions were measured to analyze each combustion characteristics of each ignition promoter. Fuel consumption was decreased when diesel was used as an ignition promoter. This is due to the lower volatility of diesel which created more stratified charge than DME.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2012년도 제45회 KOSCO SYMPOSIUM 초록집
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• pp.311-312
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• 2012

Homogeneous charge compression ignition combustion with multiple-injection strategy using dimethyl-ether was investigated in a single cylinder direct-injection compression-ignition engine. The combustion performance and exhaust emissions were tested by varying the post injection conditions. The experiments were carried out under low load and low speed conditions. By the late post injection near the top dead center, the combustion phase was retarded and lengthened, and the fuel conversion efficiencies improved without the drawbacks of exhaust emissions increment.

• 대한기계학회논문집B
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• 제35권1호
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• pp.75-82
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• 2011

디젤의 대체연료인 디메틸 에테르의 반응기구 축소에 관한 수치해석을 수행하였다. 상세반응기구(79 개의 화학종과 351 개의 반응단계)를 기초로, 최대몰농도 해석과 민감도 해석을 균질 반응기 모델에 적용하였다. 축소반응기구는 상세반응기구의 착화지연기간과 비교하여 구축하였는데, 기준값으로 $7.5{\times}10^{-5}$을 적용했을 때 44 개의 화학종과 166 개의 반응단계로 구성된다. 축소반응기구의 계산 정확도를 검증하기 위하여 두 반응기구를 단일영역 균일예혼합 압축착화 엔진모델에 적용하였고, 축소반응기구의 계산결과는 상세반응기구의 결과와 일치하였다. 따라서 본 연구의 축소반응기구는 계산의 정확도의 손실 없이 DME 를 연료로 사용하는 압축착화엔진의 착화 및 연소 과정을 모사하는데 이용될 수 있다.