• Journal of ILASS-Korea
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• v.9 no.4
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• pp.38-45
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• 2004

This study describes the analysis results of unsteady cavitating flows behavior inside nozzle of the prototype piezo-driven injector. This piezo-driven injector has been recognised as one of the next generation diesel injector due to a higher driven efficiency than the conventional solenoid-driven injector. The three dimensional geometry model along the central cross-section regarding of one injection hole has been used to simulate the cavitating flows for injection time by at fully transient simulation with cavitation model. The cavitation model incorporates many of the fundamental physical processes assumed to take place in cavitating flows. The simulations performed were both fully transient and 'pseudo' steady state, even if under steady state boundary conditions. We could analyze the effect the pressure drop to the sudden acceleration of fuel, which is due to the fastest response of needle, on the degree of cavitation existed in piezo-driven injector nozzle

• Journal of ILASS-Korea
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• v.9 no.4
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• pp.53-66
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• 2004

An experimental study was carried out in order to investigate the influence of flow conditions on a boundary layer in the near-wake of a flat plate. The flow conditions in the vicinity of the trailing edge that is influenced by upstream condition history are an essential factor that determines the physical characteristics of a near-wake. Tripping wires attached at various positions were selected to change flow conditions of a boundary layer. The flows such as laminar, transitional, and turbulent boundary layer at 0.98C from the leading edge are imposed in order to investigate the evolution of symmetric and asymmetric wake. An x-type hot-wire probe(55P61) is employed to measure at 8 stations in the near-wake. Test results show that the near-wake for the case of a turbulent boundary layer is relatively insensitive to instability after separating at the trailing edge, and Reynolds shear stress in the near-wake for the case of a turbulent boundary layer collapses due to turbulent kinetic energy.

• Journal of ILASS-Korea
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• v.13 no.1
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• pp.1-8
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• 2008

It was investigated how fuel injection timing - early injection and later injection - in conjunction with throttle open rate effect the fuel-air mixing characteristics, Engine power, combustion stability and emission characteristics on a DI CNG spark Engine and control system that had been modified and designed according to the author's original idea. It was verified that the combustion characteristics were changed according to fuel injection timings and Engine conditions determined by different throttle open rates and rpm. It was found that the combustion characteristics greatly improved at the complete open throttle rate with an early injection timing and at the part throttle rate with a late injection timing. Combustion duration was governed by flame propagation duration in a late injection timing and by an early flame development duration in an early injection timing. As the result, we discovered that combustion duration is shortened, lean limit is improved, air-fuel mixing conditions controlled, and emissions reduced through control of fuel injection timing according to change of the throttle open rate.

• Journal of ILASS-Korea
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• v.16 no.3
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• pp.134-139
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• 2011

Recent research has focused on engine combustion technology as well as application of after-treatment in order to comply with emission regulation. However, it is much more efficient way to control emissions from engine itself and furthermore research on engine control will provide the direction of after-treatment technology in future. Furthermore, emission standard regulation for passenger diesel vehicles has been stringent compared to others and nano-particles will be included in EURO6 regulation in Europe and similar emission standard will be introduced in Korea. A 3.0 liter high speed diesel engine equipped with by CRDI system of 160MPa injection pressure, and an intake/exhaust system of V type 6 cylinder turbo-intercooler was applied. The injection duration and injection quantity, pilot injection types which are related to CRDI and air/fuel ratio control applied by EVGT were changed simultaneously. Standard experiment procedure constituted dilution apparatus and CPC system to collect nano-particles and these test results were compared with regulated materials of CO, HC, NOx and investigated their relations and characteristics of nano-particles.

• Journal of ILASS-Korea
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• v.16 no.3
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• pp.126-133
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• 2011

In HCCI Engine, combustion is affected by change of compression speed corresponding to engine speed. The purpose of this study is to investigate the mechanism of influence of engine speed on HCCI combustion characteristics by using numerical analysis. At first, the influence of engine speed was shown. And then, in order to clarify the mechanism of influence of engine speed, results of kinetics computations were analyzed to investigate the elementary reaction path for heat release at transient temperatures by using contribution matrix. In results, as engine speed increased, in-cylinder gas temperature and pressure at ignition start increased. And ignition start timing was retarded and combustion duration was lengthened on crank angle basis. On time basis, ignition start timing was advanced and combustion duration was shortened. High engine speed showed higher robustness to change of initial temperature than low engine speed. Because of its high robustness, selecting high engine speed was efficient for keeping stable operation in real engine which include variation of initial temperature by various factors. The variation of engine speed did not change the reaction path. But, as engine speed increased, the temperature that each elementary reaction would be active became high and reaction speed quicken. Rising the in-cylinder gas temperature of combustion start was caused by these gaps of temperature.

• Journal of ILASS-Korea
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• v.17 no.1
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• pp.1-8
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• 2012

This study described the effect of the multiple injections and diesel-ethanol on the NVH, combustion and emission characteristics of 4 cylinder common rail diesel engine. In order to investigate the influence of diesel-ethanol blended fuel in a light-duty common rail diesel engine, the injection strategy was varied with pilot injection, double pilot injections, and one main injection at various operating conditions. The results showed that diesel-ethanol blended fuel had longer ignition delay than that of the ultra low diesel fuel(ULSD). Also, in the case of multiple injections, the combustion pressure is increased smoothly near the TDC and the NVH are decreased. In the emission characteristics, diesel-ethanol blended fuel produced lower indicated specific nitrogen oxides(IS-NOX) and indicated specific Soot(IS-soot) emissions, however, indicated specific unburned hydrocarbon(IS-HC) and indicated specific carbon monoxide(IS-CO) emissions are slightly increased.

• Journal of ILASS-Korea
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• v.17 no.1
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• pp.14-19
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• 2012

The present study conducts experimental investigation on spreading and deposition characteristics of a $4.3{\mu}l$ de-ionized (DI) water droplet impacting upon aluminum (Al 6061) flat and textured surfaces. The micro-textured surface consisted the micro-hole arrays (hole diameter: $125{\mu}m$, hole depth: $125{\mu}m$) fabricated by the conventional micro-computer numerical control (${\mu}$-CNC) milling machine process. We examined the surface effect of texture area fraction ${\varphi}_s$ ranging from 0 to 0.57 and impact velocity of droplet ranging from 0.40 m/s to 1.45 m/s on spreading and deposition characteristics from captured images. We used a high-speed camera to capture sequential images for investigate spreading characteristics and the image sensor to capture image of final equilibrium deposition droplet for analyze spreading diameter and contact angle. We found that the deposition droplet on textured surfaces have different wetting states. When the impact velocity is low, the non-wetting state partially exists, whereas over 0.64 m/s of impact velocity, totally wetting state is more prominent due to the increase kinetic energy of impinging droplet.

• Journal of ILASS-Korea
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• v.19 no.2
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• pp.55-63
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• 2014

Pyrolysis oil (PO), also known as Bio crude oil (BCO), has the potential to displace significant amounts of fuels that are currently derived from petroleum sources. PO has been regarded as an alternative fuel for petroleum fuels to be used in diesel engine. However, the use of PO in a diesel engine requires modifications due to low energy density, high water contents, low acidity, and high viscosity of the PO. One of the easiest way to adopt PO to diesel engine without modifications is emulsification of PO with the fuels that has higher cetane number. However, PO that has high amount of polar chemicals is immiscible with non polar hydrocarbons of diesel. Thus, to stabilize a homogeneous phase of diesel-PO blends, a proper surfactant should be used. In this study, a DI diesel engine operated with diesel and diesel-PO emulsions was experimentally investigated. Performance and gaseous & particle emission characteristics of a diesel engine fuelled by diesel-PO emulsions were examined. Results showed that stable engine operation was possible with the emulsions and engine output power was comparable to diesel operation.

• Journal of ILASS-Korea
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• v.19 no.2
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• pp.69-74
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• 2014

The comparison of the flow characteristics between circular and swirl jets which were controlled by the spinner attachment inside the airtube were conducted in this study. Swirl jet means a flow in whirls by mixing the flow of axial and tangential direction. Swirl flow has been used for the improvement of the combustion efficiency in the combustor. This flow is controlled by the spinner which has several vanes inclined by certain angles to the axial direction. In this study, angle of vane $30^{\circ}$ and diameter ratio of outlet to inlet of the airtube 0.73 were made. These spec. should find on the general gun type burner built in the domestic small size boiler. As the flow characteristics, axial and tangential velocities were measured by using the 2-D hot-wire velocimeter system and analyzed statistically. And also this research conducted a practical experiment considering to the attached belongings likes as ignitor, nozzle etc. on the airtube of the gun type burner. As a result, swirl occurred at the occasion of beingness and flow region extended considerably toward the radial direction. But effect of swirl did not transmit to the downstream. And the complicated flow was appeared regardless of the existence of spinner because of the effect of belongings.

• Journal of ILASS-Korea
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• v.19 no.2
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• pp.75-81
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• 2014

Swirl flow in the gun type burner has a decisive effect on the stabilization of the flame, improvement of the combustion efficiency, and also a reduction of NOx. This swirl flow is created by the spinner which is inside the airtube that guide the combustion air. Gun type burner has generally the inner devices composed nozzle adapter, spark gap ignitor, and spinner. These inner components change the air flow behavior passing through air tube. Meanwhile, turbulent characteristics of this air flow are important to understand the combustion phenomena in the gun type burner, because the mixture of fuel and air are depended on. However, nearly all of the studies have been analyzed the turbulent flow of simplified combustion formation without the inner devices. So, this study conducted the measurement using by hot-wire anemometer and analyzed turbulent flow characteristics of the swirl flow discharged from the air tube with inner devices. Turbulence characteristics come up in this study were turbulence intensity, kinetic energy and shear stress of the air flow with the change of the distance of axial direction from the exit of the air tube.