• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.422-427
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• 2000

Propagation characteristics of tribrachial flames have been investigated experimentally in both two-dimensional and axisymmetric counterflows. Mixture fraction gradient at stoichiometric location is controlled by varying equivalence ratios at the two nozzles, one of which maintains rich while the other lean premixture. Tribrachial flames propagating through these mixtures are investigated. The propagation speed of tribrachial flames in two-dimensional counterflow decreases with fuel concentration gradient and has much higher speed than the maximum speed predicted previously in two-dimensional mixing layers. From an analogy with premixed flame propagation, this excessively large propagation speed can be attributed to the tribrachial flame propagating with respect to burnt gas. Corresponding maximum speed in the limit of small mixture fraction gradient is estimated and extrapolated experimental results substantiate this limiting speed. As mixture fraction gradient approaches zero, a transition in propagation characteristics occurs, such that the propagation speed of tribrachial flame approaches stoichiometric laminar burning velocity with respect to burnt gas. Similar behavior has been obtained for tribrachial flames propagating in axisymmetric counterflow.

• 대한기계학회논문집
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• 제19권10호
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• pp.2690-2698
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• 1995

Fuel atomization and mixture formation in an gasoline engine has influence on the engine performance and pollutant emission. The throttle valve installed in an intake system plays a greater role in control of mixture quantity in accordance with engine drive condition. In this study, the characteristics of secondary atomization developed at the downstream of the valves were observed using an image processing method. Two major kinds of valves, solid and perforated ones, are chosen in order to compare the valve performance with the experimental parameters of air flow rate, valve opening angle, and valve shapes. For the perforated valve, we can obtain the relatively small sized droplets, and nearly uniformed and dense distributed sprays with low loss coefficient than for the solid valve.

• 한국자동차공학회논문집
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• 제23권2호
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• pp.214-220
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• 2015

Since resources of fossil fuels are limited, development of alternative energies is emphasized and research on new-regenerative energy is actively in progress worldwide. In present research, physical and chemical characteristics of mixed fuel are analyzed in detail for the different mixture rate of conventional and bio-diesel and ultrasonic irradiation time. Experimental setup consists of ultrasonic generator, vibrator, horn, and reflector. Various physical and chemical characteristics of fuel are investigated for volumetric mixture rate of bio-diesel from 0 to 100%. As results, viscosity and surface tension is increased as mixture rate of bio-diesel is increased. Also, molecular splits and reunions are increased and decreased repeatedly after some period of time as ultrasonic energy irradiation time is increased. As conclusion of experiments, Olefin rate, Branch index, and Aromatic rate are influenced by ultrasonic irradiation time.

• International Journal of Automotive Technology
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• 제2권1호
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• pp.25-31
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• 2001

It is necessary to understand the combustion process and cycle-by-cycle variation in combustion to improve the engine stability and consequently to improve the fuel economy and exhaust emissions. The pressure related parameters instead of mass fraction burned were compared for the effect of initial combustion pressures on the following combustion and the analysis of cycle-by-cycle variation in combustion for two pen injected SI engines. The correlation between IMEP and pressures at referenced crank angles showed almost the same trends for equivalence ratios, but the different mixture preparations indicated different tendency. The dependency of IMEP on pressure at the referenced crank angles increases as the mixture becomes leaner for both engines. The mixture distribution in the combustion chamber was varied with the coolant temperature and intake valve deactivation due to the evaporation of fuel and air motion. The correlation between pressure related parameters were also compared for the coolant temperatures and air motion.

• 한국연소학회지
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• 제16권2호
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• pp.9-15
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• 2011

Homogeneous charge compression ignition(HCCI) is the best concept able to provide low NOx and PM in diesel engine emissions. This new alternative combustion process is mainly controlled by chemical kinetics in comparison with the conventional combustion in internal combustion engine. In this paper, combustion characteristics of HCCI engine with suggested diesel surrogate(heptane/toluene mixture fuel) reaction mechanism were numerically investigated by heptane/toluene mixture ratio and EGR ratio. As results, the ignition timing became faster with increasing of heptane, and an initial oxidation and the ignition timing of the mixture fuel were affected by heptane and toluene, respectively.

• 한국자동차공학회논문집
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• 제15권2호
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• pp.1-7
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• 2007

The effect of injector geometries including the injection angle and number of nozzle holes on homogeneous charge compression ignition (HCCI) engine combustion has been investigated in an automotive-size single-cylinder diesel engine. The HCCI engine has advantages of simultaneous reduction of PM and NOx emissions by achieving the spatially homogenous distribution of diesel fuel and air mixture, which results in no fuel-rich zones and low combustion temperature. To make homogeneous mixture in a direct-injection diesel engine, the fuel is injected at early timing. The early injection guarantees long ignition delay period resulting in long mixing period to form a homogeneous mixture. The wall-impingement of the diesel spray is a serious problem in this type of application. The impingement occurs due to the low in-cylinder density and temperature as the spray penetrates too deep into the combustion chamber. A hole-type injector (5 holes) with smaller angle ($100^{\circ}$) than the conventional one ($150^{\circ}$) was applied to resolve this problem. The multi-hole injector (14 holes) was also tested to maximize the atomization of diesel fuel. The macroscopic spray structure was visualized in a spray chamber, and the spray penetration was analyzed. Moreover, the effect of injector geometries on the power output and exhaust gases was tested in a single-cylinder diesel engine. Results showed that the small injection angle minimizes the wall-impingement of diesel fuel that results in high power output and low PM emission. The multi-hole injector could not decrease the spray penetration at low in-cylinder pressure and temperature, but still showed the advantages in atomization and premixing.

• International Journal of Automotive Technology
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• 제7권5호
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• pp.585-593
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• 2006

The effect of the shape of the side wall on vaporization and fuel mixture were investigated for the impinging spray of a direct injection(DI) gasoline engine under a variety of conditions using the LIEF technique. The characteristics of the impinging spray were investigated under various configurations of piston cavities. To simulate the effect of piston cavity configurations and injection timing in an actual DI gasoline engine, the parameters were horizontal distance from the spray axis to side wall and vertical distance from nozzle tip to impingement plate. Prior to investigating the side wall effect, experiments on free and impinging sprays for flat plates were conducted and these results were compared with those of the side wall impinging spray. For each condition, the impingement plate was located at three different vertical distances(Z=46.7, 58.4, and 70 mm) below the injector tip and the rectangular side wall was installed at three different radial distances(R=15, 20, and 25 mm) from the spray axis. Radial propagation velocity from spray axis along impinging plate became higher with increasing ambient temperature. When the ambient pressure was increased, propagation speed reduced. High ambient pressures tended to prevent the impinging spray from the propagating radially and kept the fuel concentration higher near the spray axis. Regardless of ambient pressure and temperature fully developed vortices were generated near the side wall with nearly identical distributions, however there were discrepancies in the early development process. A relationship between the impingement distance(Z) and the distance from the side wall to the spray axis(R) was demonstrated in this study when R=20 and 25 mm and Z=46.7 and 58.4 mm. Fuel recirculation was achieved by adequate side wall distance. Fuel mixture stratification, an adequate piston cavity with a shorter impingement distance from the injector tip to the piston head should be required in the central direct injection system.

• 연구논문집
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• 통권29호
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• pp.29-38
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• 1999

In comparison with gasoline engine, LPG direct injection engine has some advantages not only in emission and fuel efficiency but also in prevention of power decrease and back fire etc. which are disadvantages of conventional LPG engine. In this study, comparision tests of the incylinder spray and combustion characteristics between of LPG and gasoline fuels were performed in the RCEM as a basic research for the development of future LPG engine with low emission and high fuel efficiency During the direct injection of LPG fuel and gasoline into the inside of RCEM, spray development characteristics according to the injection condition have been photographed by the high speed shadow graph methods. The conditions for the optimum mixture distribution of LPG and gasoline fuels are achievable at the selected ignition timing, respectively.

• Journal of Advanced Marine Engineering and Technology
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• 제33권3호
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• pp.378-386
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• 2009

The effect of fuel mixing on soot structure with methane, ethane, and propane to ethylene-base counterflow diffusion flames has been investigated by measuring the volume fraction, number density, and particle size of soot by adopting the light extinction/scattering techniques. The experimental result showed that the mixing of ethane and propane in ethylene diffusion flame increased soot volume fraction while the mixing of methane decreased. As compare to the ethylene-base flame, the diameters of soot particles for mixture flames are slightly smaller. While the soot number densities for the mixture flames are much higher. Thus, the increase in the soot volume fraction can be attributed to the appreciably increased soot number density by the fuel mixing.

• 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.