• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.3
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• pp.662-669
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• 1994

In the combustion system, the optimum spray conditions reduce the pollutant emission of exhaust gas and enhance the fuel efficiency. The spray characteristics-the drop size, the drop velocity, the number density and the mass flux, become increasingly important in the design of combustor and in testifying numerical simulation of spray flow in the combustor. The purposes of this study are to clarify the spray characteristics of twin-fluid nozzle and to offer the data for combustor design and the numerical simulation of a spray flow. Spatial drop diameter was measured by immersion sampling method. The mean diameter, size distribution and uniformity of drop were analyzed with variations of air/liquid mass flow ratio. The results show that the SMD increases with the liquid supply flow rate and decreases with the air supply velocity. The radial distribution of SMD shows the larger drops can diffuse farther to the boundary of spray. And the drop size range is found to be wider close to the spray boundary where the maximum SMD locates.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.6
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• pp.454-460
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• 2009

To analyze the mixture formation process of evaporating diesel spray is important for emissions reduction in actual engines. Then the effects of change in density of ambient gas on spray structure in high temperature and pressure field have been investigated in this study. The ambient gas density was changed from ${\rho}_a=5.0kg/m^3$ to ${\rho}_a=12.3kg/m^3$ with CVC(Constant Volume Chamber). Also, simulation study by modified KIVA-II code was conducted and compared with experimental results. The ambient temperature and injection pressure are kept as 700K and 72MPa, respectively. The images of liquid and vapor phase in the evaporating free spray were simultaneously taken by exciplex fluorescence method. As experimental results, with increasing ambient gas density, the tip penetration of the evaporating free spray decreases due to the increase in the drag force from ambient gas. The spatial structure of a diesel spray can be verified as 2-regions consisted of liquid with momentum decrease and vapor with large-scale vortex. The calculated results obtained by modified KIVA-II code show good agreements with experimental results.

• Journal of ILASS-Korea
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• v.5 no.4
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• pp.40-46
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• 2000

To understand the basic the structure of the spray field and to obtain the initial conditions for computational models for shear coaxial twin-fluid injectors. the atomization characteristics under different flow and geometric conditions were examined. The spray characteristics such as SMD, mean axial and radial velocities, Dia. of droplets and volume flux with a P.D.P.A. Water and nitrogen gas under atmospheric conditions were used as a test fluids. The drops produced by shear coaxial injectors continue to disintegrate along the spray axis and decrease their sizes. SMD was the maximum at the spray center of spray and decreased with increasing radial distance. The results of this parametric study showed that SMD decreased with increasing gas injection velocity as well as with decreasing liquid injection mass flow rate, The relative velocity between gas and liquid flow played a significant role resulted in decreasing SMD and in spreading the spray. Recessing the liquid orifice resulted decreasing SMD and a spreading the spray. Recess of liquid orifice by 5.0mm showed best atomization characteristics in this experiment. Although drop diameter changes, shear coaxial injector sprays had constant velocity and exhibited a high degree of radial symmetry.

• Journal of ILASS-Korea
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• v.18 no.2
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• pp.73-80
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• 2013

The purpose of this study was compared the spray, combustion and emissions (NOx, CO, HC, smoke) characteristics of a typical fuel (100% Diesel, DME) and Diesel-DME blended fuel in a Constant Volume Chamber (CVC) and a single-cylinder DI diesel engine. Spray characteristics were investigated under various ambient and fuel injection pressures when the Diesel-DME blended ratio is varied. The parameters of spray sturdy were spray shape, penetration length, and spray angle. Common types of injectors having seven holes and made by Bosch were used. As of use, the typical fuel (100% Diesel, DME) and the blended fuel by mixture ratio 95:5, 90:10 (Diesel:DME) were used. The Injection pressure was fixed by 70.1MPa, when the ambient Pressure was varied 0.1, 2.6 and 5.1 MPa. The combustion experiments was conducted with single cylinder engine equipped with common rail injection system. injection pressure is 70 MPa. The amount of injected fuels is adjusted to obtain the fixed input calorie value as 972.2 J/cycle in order to compare with the fuel conditions.

• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.3
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• pp.30-37
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• 2003

Spray angle of dual swirl injector is established according to the velocity ratio at orifice exit. Due to the internal mixing at recess and lack of correlation for the combined two fluid injection, prediction of spray angle is very difficult. This study deal with experimental work and numerical simulation on spray angle with different recess length. Among the multiphase flow models, the VOF model was selected to simulate the spray angle. Feasibility of numerical analysis are confirmed by comparing the results with the experimental data, and the effect of recess on spray angle are analyzed for single and combined spray case.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.255-259
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• 2008

This paper presents the spray characteristics of the oxidizer rich preburner injector which can be used in the high-thrust rocket system. We designed the basic shape of the liquid-liquid coaxial swirl injector for the rocket oxidizer rich preburner injection system. To understand the spray angle variation with the high pressure environment, the spray visualization in the high pressure chamber was preformed. Also we measured the droplet velocity, the Sauter Mean Diameter(SMD), the volume flux and the number density with the PDPA system by using water in atmospheric pressure. The results show that the spray angle is reduced by increasing ambient pressure and maximum droplet velocity is shown from a nozzle tip and then the droplet velocity decreases as a spray moves to the downstream. The SMD decreases on the axial distance from 20 mm to 50 mm but it increases over 50 mm. That is due to the increasing number of collision with each droplet and interaction with ambient air on going downstream direction.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3062-3067
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• 2007

HVOF thermal spray guns are now being widely used to produce protective coatings, on the surfaces of engineering components. HVOF technology employs a combustion process to heat the gas flow and melt the coating materials which are particles of metals, alloys or cermets. Particle flow which is accelerated to high velocities and combustion gas stream are deposited on a substrate. In order to obtain good quality coatings, the analysis of torch design must be performed. The reason is that the design parameters of torch influence gas dynamic behaviors. In this study, numerical analysis is performed to predict the gas dynamic behaviors in a HVOF thermal spray gun with various torch shapes. The CFD model is used to deduce the effect of changes in nozzle geometry on gas dynamics. Using a commercial code, FLUENT which uses Finite Volume Method and SIMPLE algorithm, governing equations have been solved for the pressure, velocity and temperature distributions in the HVOF thermal spray torch.

• Journal of ILASS-Korea
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• v.7 no.4
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• pp.9-15
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• 2002

Convolution Fourier transformation tomographically reconstructs the spatially resolved spray injection rate from direct measuring cells. Asymmetric sprays generated from a twin-hole air shroud injector are tested with 12 equiangular projections of measurements. For each projection angle, line of sight integrated injection rate was measured at 35 positions with equal spacing measuring cells of 3 mm in width, 100 mm in length, 55 mm in depth and 0.5 mm thickness of separating wall. Interpolated data between the projection angles effectively increase the number of projections, which significantly enhances the signal-to-noise level in the reconstructed data. This modified convolution Fourier transformation scheme predicts well the structure of asymmetric sprays. Comparative study has been made between sprays with and without air shrouding. Tomograhpic reconstruction of injection rate from direct measuring cells obtained can be used to estimate the accuracy of volume fraction of spray from the LDPA tomographic reconstruction.

• Journal of ILASS-Korea
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• v.5 no.2
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• pp.43-52
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• 2000

Numerical simulation of steady, non-evaporating hollow-cone sprays interacting with concentric annular air jets is performed using the discrete stochastic particle method in KIVA. The spray characteristics such as SMD, mean droplet velocity, liquid volume flux, air/liquid mass ratio, and droplet number density arc obtained and compared with the measurements involving different air flow rates in large and small annuli. Overall satisfactory agreement is achieved between calculation and experiment except for the deviation in the downstream SMD arising from uncertainty in the size distribution function at injection, and inaccuracy in the averaged spray parameters due to the small volumes of axisymmetric 2-D sector meshes close to the axis.

• Journal of Power System Engineering
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• v.9 no.4
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• pp.214-219
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• 2005

The effects of change in injection pressure on spray structure in high temperature and pressure field have been investigated. The analysis of liquid and vapor phases of injected fuel is important for emissions control of diesel engines. Therefore, this work examines the evaporating spray structure using a constant volume vessel. The injection pressure is selected as the experimental parameter, is changed from 72MPa to 112MPa by using a common rail injection system(ECD-U2). The images of liquid and vapor phase in the evaporating free diesel spray are simultaneously taken by exciplex fluorescence method. As a result, it can be confirmed that the distribution of vapor concentration is more uniform in the case of the high injection than in that of the low injection pressure.