• 한국자동차공학회논문집
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• 제14권2호
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• pp.121-126
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• 2006

A gasoline-fueled stratified charge compression ignition (SCCI) engine with both direct fuel injection and intake temperature and compression ratio was examined. The fuel was injected directly by using the high temperature resulting from heating intake port. With this injection strategy, the SCCI combustion region was expanded dramatically without any increase in NOx emissions which were seen in the case of compression stroke injection. Injection timing during the intake temperature was found to be an important parameter that affects the SCCI region width. The effect of mixture stratification and the effect of fuel reformation can be utilized to reduce the required intake temperature for suitable SCCI combustion under each set of engine speed and compression ratio conditions.

• 한국분무공학회지
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• 제14권4호
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• pp.171-177
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• 2009

This study proposes a new stratified charge system for low emission and ultra lean burn. In order to examine combustion characteristics of the new system, sparkplug with a hole at positive pole and a common CNG injector for injecting fuel were used in this study as injector-type spark plug. The new stratified charge system injects fuel of extremely small quantities and ignites mixture around sparkplug gap. Also, the system was fitted in a visualized constant volume chamber. Then, for analysis of the combustion characteristics, we examined combustion pressure, lean inflammable limit, and visualized combustion flame according to equivalence ratio by comparison with homogeneous charge (HC) method and the new stratified charge (SC) method. As results of this study, in the case of using this system, the propagation speed of initial flame was increased and total combustion period was reduced in the ultra lean burn in the same equivalence ratio. These phenomena occurred clearly under the conditions of lean equivalence ratio. Furthermore, the lean inflammable limit of mixture was extended by using the injector-type spark plug.

• 한국자동차공학회논문집
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• 제17권3호
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• pp.8-14
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• 2009

Effect of heterogeneity of combustion chamber has been thought as one of the way to avoid dramatically generating heat in HCCI Combustion. The purpose of this research is to investigate the effect of heterogeneity, especially thermal stratification and fuel strength stratification on HCCI Combustion fueled with DME and n-Butane. Thermal stratification is formed in Combustion Chamber of Rapid Compression Machine with 3 Kinds of pre-mixture has different properties. The stratified charge mixture is adiabatic compressed and on that process, in cylinder gas pressure and two-dimensional chemiluminescence images are measured and analyzed.

• International Journal of Automotive Technology
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• 제8권2호
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• pp.127-135
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• 2007

The objective of this study is to analyze the effect of velocity and vorticity on stratified mixture formation in the visualization engine. In order to investigate spray behavior, the pray velocity is obtained through the cross-correlation PIV method, a useful optical diagnostics technology and the vorticity calculated from the spray velocity component. These results elucidated the relationship between vorticity and entropy, which play an important role in the diffusion process for the early injection case and the stratification process for the late injection case. In addition, we quantified the homogeneous diffusion ate of spray using entropy analysis based on Boltzmann's statistical thermodynamics. Using these methods, we discovered that the homogeneous mixture distribution is more effective as a momentum dissipation of surrounding air than that of the spray concentration with a change in the injection timing. We found that the homogenous diffusion rate increased as the injection timing moved to the early intake stroke process, and BTDC $60^{\circ}$ was the most efficient injection timing for the stratified mixture formation during the compression stroke.

• 한국자동차공학회논문집
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• 제13권2호
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• pp.178-185
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• 2005

The synergistic effect of ethylene/propane mixture on soot formation is studied experimentally using a concentric co-flow diffusion burner, which provides the stratified fuel mixture. The soot volume fraction, soot particle diameter, number density and PAH concentrations are measured with various fuel supply configurations and compared to the homogeneously mixed case. When propane is supplied through the inner nozzle, an increase of soot formation is observed. However, when propane is supplied through the outer nozzle, a decrease is observed. The reaction path of PAH's formed from the pyrolysis process of propane is likely to be responsible to the observed differences. When propane is supplied through the outer nozzle, PAH's are formed in the relatively near oxidation region and exposed to the oxidization environment; on the other hand, when propane is supplied through the inner nozzle, PAH's are not likely to be oxidized and thus get involved in soot formation process. The synergistic effect in ethylene/propane diffusion flames is found to be affected not only by the com position of the mixture but also by the way of mixing.

• 한국자동차공학회논문집
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• 제16권5호
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• pp.157-163
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• 2008

The HCCI combustion mode poses its own set of narrow engine operating by knocking. In order to solve this, inhomogeneity method of mixture and temperature is suggested. The purpose of this research is to get fundamental knowledge about the effect of thermal stratification on HCCI combustion of PRF -Air mixture. The temperature stratification is made by buoyancy effect in combustion chamber of RCM. The analysis items are pressure, temperature of in-cylinder gas and combustion duration. In addition, the structure of flames using the two dimensional chemiluminescence's images by a framing camera are analyzed. Under stratification, the LTR starting time and the HTR starting time are advanced than that of homogeneous. Further, the LTR period of homogeneous conditions became shorter than that of the stratified conditions. With the case of homogeneous condition, the luminosity duration becomes shorter than the case of stratified condition. Additionally, under stratified condition, the brightest luminosity intensity is delayed longer than at homogeneous condition.

• 한국자동차공학회논문집
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• 제5권5호
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• pp.114-122
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• 1997

Nowadays, gasoline direct injection engines are being commercialized by virtue of improvement in control technology of spray, flow, air fuel ratio. The stratified charge type has the advantage of improving lean limit. The homogeneous type has the advantage of reducing engine-out hydrocabon emissions in the first 30 seconds after a cold start, in addition, improving transient air fuel ratio control. The vaporization and mixing if injected fuel with air has to e completed in a short time and the fuel film in cylinder and on piston has to be minimized. So, the flow and injection should be well controlled. This paper surveyed the spray characteristics of gasoline direct injection by using laser equipment and the combustion characteristics of the single cylinder engine using homogeneousas-mixture type gasoline direct injection.

• Journal of Mechanical Science and Technology
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• 제16권4호
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• pp.557-563
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• 2002

In this paper, the characteristics of flow and spray motions affected by from piston head configurations were investigated numerically. Calculations were carried out from intake process to the end of compression. GTT (Generalized Tank and Tube method) code, which includes a third order upwind Chakravarthy-Osher TVD scheme and k-$\varepsilon$ turbulence model with fuel spray analysis was used for the calculations. As a results, piston heads with smaller radii of curvature were found to give stronger reverse tumble than those with larger radii of curvature. Similar results are shown in the convection and diffusion of fuel sprays.

• 대한기계학회논문집B
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• 제27권8호
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• pp.1033-1041
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• 2003

Two-phase flow pattern data during horizontal in-tube flow boiling are presented for pure and mixed refrigerants of R134a and Rl23, The flow pattern is observed through tubular sight glasses located at inlet and outlet of the test section, which is made of a stainless steel tube, 2m long with 10mm I.D., 1.5mm wall thickness. The obtained results are compared with the available various correlations for flow pattern. The flow pattern map of Hashizume was in good agreement with the present data except the region of low mass velocity. Weisman flow pattern map was also known to satisfactorily predict data for refrigerants in the region of annular flow. In this study, the flow pattern are simply classified into two groups; stratified(including intermittent, stratified and stratified-wavy) flow and annular flow. The transition quality from stratified to annular flow was obtained by modifying the liquid Froude number.

• 대한기계학회논문집B
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• 제37권3호
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• pp.221-228
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• 2013

분무유도식 DISI엔진의 성층연소운전조건에서 분무 및 화염특성에 대한 실험적 연구가 수행되었다. 연소가시화를 통하여 성층연소 DISI의 연소는 희박 예혼합 연소와 확산연소의 성격을 모두 가지고 있는 것으로 확인되었다. 분사시기에 따른 혼합기 형성특성이 연소의 특성을 결정하는 중요한 인자임을 관찰하였다. 분무와 혼합기 가시화를 통해 낮은 분위기압에서의 over-mixing, 높은 분위기압에서의 under-mixing이 발생하는 것을 확인하였으며 이러한 혼합기 형성과정의 결과에 따라 화염특성, 연소효율 등의 연소특성이 결정되는 것을 살펴볼 수 있었다. 또한, NOx, IMEP도 분사시기에 따른 경향성을 보였으며, 분사시기에 따른 연소상의 변화에 의한 영향임을 확인하였다.