• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.4
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• pp.50-55
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• 2001

To simulate the combustion process under stratified charged conditions, like GDI engines, the new combustion model is proposed, which is based on Welter's FAE model and Peters' PDF model for considering primary reactions. In addition to these models, the new laminar burning velocity correlation and diffusion flame model are also included in the proposed model. The former can be applicable to much wider range of equivalence ratio, pressure and temperature than the others, such as Keck's and Guilder's models, and the latter has been derived from water-gas shift reaction and hydrogen oxidation, by which the secondary reactions can be considered after primary reactions. 3-D computation has been performed by using STAR-CD v3.05 in the simple cylindrical geometry under stratified charged condition. Judging from the calculated results, the present model proves to be reasonable to simulate the characteristics of flame propagation and concentrations of products in burned regions.

• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.97-100
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• 2014

The combustion and emission characteristics of propane and n-butane which are the main components of LPG were compared with gasoline. The experiment was performed in a stratified DISI engine under lean combustion conditions. Mixtures of propane and n-butane wre more homogeneous because propane and n-butane have better evaporation characteristics. As a result, combustion speeds of n-butane and propane were slower, and emission levels of NOx and PM were lower. However, in spite of better evaporation, PM from propane was higher.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.5
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• pp.54-66
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• 2000

A gasoline direct injection single cylinder engine has been developed to study operational characteristics for highly stratified conditions. Parameters related to design and experiment were also studied to understand the characteristics of combustion and emissions at some part load conditions. It was found that optimal timings between the end of fuel injection and spark ignition were existed for stable combustion under the stratified modes, In a low engine speed, fuel spray behavior around piston bowl was important for stable combustion. The in-cylinder air motion affecting fuel spray behavior was found to be a dominant factor at higher engine speed as fuel injection timing had to be advanced to secure enough time for fuel evaporation and mixing with surrounding air. As swirl ratio increased, spark timing could be advanced for stable combustion and a higher compression ratio could be used for improved fuel consumption and stable combustion at the stratified mode. It was also observed that electrode geometry and piston bowl shape played an important role for combustion and emission characteristics and some results were shown for comparison.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.2
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• pp.48-55
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• 2003

The effects of pressure charge on combustion stability and emissions have been analyzed using a GDI single cylinder engine. A late injection mode of stratified condition at the air-fuel ratio of 40:1 for 1200∼2400 rpm was tested while the boosted pressure ratio was increased up to 1.5:1. In-cylinder CFD analysis was also performed for better understanding of in-cylinder flow and fuel spray behavior. With a higher boosted pressure ratio the IMEP was increased greatly due to the increased engine load, and the ISFC was improved by more than 10% at all engine speeds. The regime of stable stratified combustion was extended to a higher engine speed, but the spark ignition angle had to be more advanced for stable combustion. The emissions of ISHC and ISNOx did not show a particular trend for the increased engine speed but a general trend of lower ISHC and higher ISNOx for a gasoline engine.

• Journal of ILASS-Korea
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• v.14 no.4
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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.

• International Journal of Automotive Technology
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• v.5 no.3
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• pp.181-188
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• 2004

A cylindrical constant-volume combustion chamber was used to investigate the flow characteristics at the spark electrode gap and the combustion characteristics of an inhomogeneous charge methane-air mixture under several parameters such as stratified pattern, initial charge pressure, ignition time and the excess air ratio of the initial charge mixture. Flow characteristics including mean velocity and turbulence intensity were analyzed by a hot-wire anemometer. The combustion pressure development, measured by a piezo-electric pressure transducer, was used to investigate the effect of initial charge pressure, excess air ratio and ignition times on combustion pressure and combustion duration. It was found that the mean velocity and turbulence intensity had the maximum value around 200-300 ms and then decreased gradually to near-zero value at 3000 ms. For the stratified patterns, the combustion rate under the rich injection (RI) condition was the fastest. Under the initial charge conditions, the second mixture was accompanied by an increase in the combustion rate, and that the higher the mass which is added in the second stage injection, the faster the combustion rate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.9
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• pp.1317-1324
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• 1998

In general, DI gasoline engine has the advantages of higher power output, higher thermal efficiency, higher EGR tolerance and lower emissions due to the operation characteristics of increased volumetric efficiency, compression ratio and ultra-lean combustion scheme. In order to apply the concept of stratified charge into direct injection gasoline engine, some kinds of methodologies have been adapted in various papers. In this study, a reflector was adapted around the injector nozzle to apply the concept of stratified charge combustion which leads the air-fuel mixture to be rich near spark plug. Therefore, the mixture near the spark plug is locally rich to ignite while the lean mixture is wholly introduced into the combustion chamber. The characteristics of combustion is analyzed with the variations of fuel injection pressure and load in a stratified -charge direct injection single cylinder gasoline engine. The obtained results are summarized as follows ; 1. The MBT spark timing approached to TDC with the increase of load on account of the increase of evaporation energy, but has little relation with fuel injection pressure. 2. The stratification effects are apparent with the increase of injection pressure. It is considered by the development of secondary diffusive combustion and the increase of heat release of same region, but proceed rapidly than diesel engine. Especially, in the case of high pressure injection (l70bar) and high load (3.0kgf m), the diffusive combustion parts are developed excessively and results in the decrease of peak pressure than in the case of middle load. 3. The index of engine stability, COVimep value, is drastically decreased with the increase of load. 4. To get better performance of DI gasoline engine development, staged optimizaion must be needed such as injection pressure, reflector, intake swirl, injection timing, chamber shape, ignition system and so on. In this study, the I50bar injection pressure is appeared as the optimum.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.5
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• pp.58-65
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• 2004

A cylindrical constant volume combustion chamber was used to investigate the combustion characteristics of stratified methane-air mixture under several initial charge conditions in the author's previous reports. The results showed that the improvement of thermal efficiency and reduction of heat loss was realized simultaneously by using 2-stage injection method. This paper deals with the reason why the stratified combustion has showed better combustion rate through the measurement and analysis of chemiluminescence of C $H^{*}$ and $C_{2}$$^{*}$ radicals. An optic fiber bundle is used to measure the local emission of C $H^{*}$ and $C_{2}$$^{*}$ radicals to map the relationship between the excess air ratio and local radical intensity ratio in the combustion vessel at 5 mm apart form the geometric center. The results show that there exist a relationship between the intensity ratio and the air-fuel ratio. It is revealed that the improvement of combustion rate in a lean-stratified mixture is realized through the 2-stage injection method. method.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.704-709
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• 2000

Laminar burning velocities of propane- and iso-octane-air mixtures have been numerically modelled over a wide range of equivalence ratio, pressure and temperature. These correlations are applicable to the modelling of stratified charged combustion like that of lean bum and GDI engine combustion. The numerical models are based on the results calculated by PREMIX code with Sloane's detailed chemical reaction mechanism for propane and FlameMaster code with Peters' for iso-octane. Laminar burning velocity for two fuels showed a pressure and temperature dependence in the following form, in the range of $0.1{\sim}4MPa$, and $300{\sim}1000K$, respectively. $S_L={\alpha}\;{\exp}[-\xi({\phi}-{\phi}_m)^2-{\exp}\{-{\xi}({\phi}-{\phi}_m)\}-{\xi}({\phi}-{\phi}_m)]$ where ${\phi}_m=1.07$, and both of ${\alpha}$ and ${\xi}$ are functions of pressure and temperature. Compared with the results of the existing models, those of the present one showed the good agreement of the recent experiment data, especially in the range of lean and rich sides. Judging from the calculated results of the stratified charged combustion by using STAR-CD, the above modelling prove to be more suitable than the other ones.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.2
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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.