• 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.9 no.2
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• pp.9-17
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• 2004

The performance characteristics of lean burn system in gasoline engine are mainly affected by the air-fuel mixture in cylinder, gas exchange process of manifold system, exhaust emission of engine, and the electronic engine control system. In order to obtain the effect of performance factors on the optimum conditions of lean burn engine, this study deal with the behavior of mixture formation, gas flow characteristics of air, flow and evaporation analysis of spray droplet in cylinder, vaporization and burning characteristics of lean mixture in the engine, and the control performance of electronic engine control system. The optimum flow conditions were investigated with the swirl and tumble flows in the combustion chamber with swirl control valve. The performance characteristics and optimum condition of flow field in intake system were analyzed by the investigation of inlet flow of air and combustion stabilization on cylinder.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.3
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• pp.221-228
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• 2013

An experimental study was carried out to investigate the effects of the injection timing on the spray and combustion characteristics in a spray-guided direct-injection spark-ignition (DISI) engine under lean stratified operation. An in-cylinder pressure analysis, exhaust emissions measurement, and visualization of the spray and combustion were employed in this study. The combustion in a stratified DISI engine was found to have both lean premixed and diffusion controlled flame combustion characteristics. The injection timing condition corresponding to the stratified mixture characteristics was verified to be a dominant factor for these flame characteristics. For the early injection timing, a non-luminous blue flame and low combustion efficiency were observed as a result of the lean homogeneous mixture formation. On the other hand, a luminous sooting flame was shown at the late injection timing because of an under-mixed mixture formation. In addition, the smoke emission and incomplete combustion products were increased at the late injection timing as a result of the increased locally rich area. On the other hand, the NOx emissions decreased and IMEP increased as the injection timing retarded. The combustion phasing produced by the injection timing was verified as the reason for this observation.

• Journal of ILASS-Korea
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• v.12 no.4
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• pp.211-219
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• 2007

The liquid film thickness inside a pressure-swirl nozzle was measured, and then the measured liquid film thickness was compared with the results from previous empirical equations. The liquid film inside the nozzle was visualized using extended transparent nozzles and a microscopic imaging system, and then the measurement error was evaluated using optical geometry analysis. The high injection pressures up to 7MPa were adopted to simulate the injection conditions of the direct-injection spark-ignition engines. The totally different two injectors with different fuels, nozzle lengths, nozzle diameters and swirlers were utilized to obtain the comprehensive equations. The results showed that the liquid film thickness very slightly decreased at high injection pressures and the empirical equations overestimated the effect of injection pressure. Most of empirical equations did not include the effect of nozzle length and swirler angle, although it caused significant change in liquid film thickness. A new empirical equation was suggested based on the experimental results with the effects of fuel properties, injection pressure, nozzle diameter, nozzle length and swirler angle.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.3
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• pp.362-374
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• 2002

For the purpose of development of a GDI engine, the in-cylinder phenomena, such as the spray behaviors, fuel distributions, unburned fuel, and flame characteristics were investigated in a single cylinder GDI engine. The GDI engine was equipped with a swirl type electronic injector and SCV(Swirl Control Valve). PLIF(Planar Laser Induced Fluorescence) system with KrF Excimer laser was used far the measurements of fuel distributions. The effects of the injector specifications, such as the spray cone angle and the offset angle on the in-cylinder phenomena were investigated. As a result, it was found that the injected fuel collided with the bottom of the bowl and moved upward along the exhaust side wall of piston bowl. This fuel vapor played an important role in the instance of spark ignition. The unburned fuel and flame characteristics were greatly influenced by the injector specifications.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.05a
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• pp.75-90
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• 2001

For the purpose of helping development of a GDI(Gasoline Direct Injection) engine, the in-cylinder phenomena, such as the spray behaviors and fuel distributions, unburned fuel, and flame characteristics were investigated in a single cylinder GDI engine. The GDI engine was equipped with a swirl type electronic injector and SCV(Swirl Control Valve). PLIF(Planar Laser Induced Fluorescence) system with KrF Excimer laser was used for the measurements of the fuel distributions. The effects of the injector specifications, such as the spray cone angle and the offset angle on the fuel distributions and combustion characteristics were investigated. As a result, it was found that the injected fuel spray collided with the bottom of the bowl and moved upward along the exhaust side wall of the piston bowl. This fuel vapor played a important role in the instance of spark ignition. The injector specifications has a great influence on the flame characteristics.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.5
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• pp.20-27
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• 2000

Characteristics of two favorite injection tools for gasoline direct injection application were compared. An air-assisted fuel injector (AAFI) and a high-pressure swirl injector (HPSI) were designed and fabricated for prototype development, and the characterization strategies and processes for both injection tool have been arranged in parallel. Characterization works were carried out mainly through measurements, and in some cases, computational fluid dynamic analysis was utilized. In this paper, overall characteristics defined as flow rate, spray pattern, penetration, internal spray structure and drop size distribution, was discussed. The AAFI was found to be advantageous in flexibility of fuel flow rate, and the HPSI in stability and precision. Spray shape factor was introduced to describe the development of intermittent sprays from both injectors. Axial penetration appeared to be almost linear in the case of the AAFI while its speed continuously decreased with time in the HPSI.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.5
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• pp.28-35
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• 2000

As a second part of the comparison study, microscopic features of an air-assisted fuel injector(AAFI) and a high-pressure swirl injector (HPSI) were characterized. They consist of the internal spray structure in terms of fuel mass and drop diameter, the overall atomization performance with respect to operating parameters and the drop size distribution. Large droplets are concentrated in around the head part of a spray field of the HPSI, while in the case of the AAFI, they were distributed in the tail part. Although the AAFI showed the better atomization performance, the feasible ranges of operating parameters such as injection and ambient pressure were found to be wider in the HPSI. Drop size distribution of the AAFI sprays was more dispersed than that of the HPSI. Drop size distribution of the AAFI sprays was more dispersed than that of the HPSI. However, at the well-atomized condition, it appeared to be very uniform.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.2
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• pp.44-51
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• 2005

According to the increasing concern on the global environment, the $CO_2$ regulation has been discussed including automobile emission regulation. In order to cope with this rapid changing circumstances, the development of an ultra low emission and super fuel economy automobile is essential. Direct injection LPG engine is the one of the possible future engine to maximize the engine efficiency. This experimental study for the development of direct injection LPG engine technology is promoted with two parts; spray characteristics of high pressure swirl injector, and performance characteristics of direct injection LPG engine. Engine characteristics according to the fuel was analyzed in order to establish stratified combustion technology for LPG engine by using the DISI engine. In the engine experiment, control system was manufactured for gasoline and LPG fuel. The engine was modified 2,000 cc GDI engine (fuel supply device, fuel injection device). Through this experiment, engine operating condition, engine speed and spark timing (MBT), fuel injection position, and fuel rate were investigated.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.3
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• pp.103-111
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• 2006

The spray behavior of direct-injection spark-ignition(DISI) engines is crucial for obtaining the required mixture distribution for optimal engine combustion. The spray characteristics of DISI engines are affected by many factors such as piston bowl shape, air flow, ambient temperature, injection pressure and fuel temperature. In this study, the effect of fuel temperature on the spray and combustion characteristics was partially investigated for the wall-guided system. The effect of fuel temperature on the fan spray characteristics was investigated in a steady flow rig embodied in a wind tunnel. The shadowgraphy and direct imaging methods were employed to visualize the spray development at different fuel temperatures. The microscopic characteristics of spray were investigated by the particle size measurements using a phase Doppler anemometry(PDA). The effect of injector temperature on the engine combustion characteristics during cold start and warming-up operating conditions was also investigated. Optical single cylinder DISI engine was used for the test, and the successive flame images captured by high speed camera, engine-out emissions and performance data have been analyzed. This could give the way of forming the stable mixture near the spark plug to achieve the stable combustion of DISI engine.