• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.1
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• pp.8-19
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• 2001

A number of atomization and droplet breakup models have been developed and used to predict the diesel spray characteristic. Most of these models could not provide reasonable computational result of the diesel spray characteristic because they have only considered the primary breakup. A hybrid model is, therefore, required to develop by considering the primary and secondary breakup of liquid jet. according to this approach, wave breakup(WB) model was used compute the primary breakup of the liquid jet and droplet deformation and breakup(DDB) model was used for the secondary breakup of droplet. Development of hybrid model by using KIVA-II code was performed by comparing with the experimental data of spray tip penetration and SMD from the literature. A hybrid model developed in this study could provide the good agreement with the experimental data of spray tip penetration. The prediction results of SMD were in good agreement between 0.5 and 1.0 ms after the start of injection. Numerical results obtained by the present hybrid model have the good agreement with the experimental data with the breakup time constant in WB model of 30, and DDB model constant Ck of 1.0 when the droplet becomes less than 95% of maximum droplet diameter injected.

• Journal of ILASS-Korea
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• v.5 no.2
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• pp.35-42
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• 2000

A number of atomization and droplet breakup models have been developed and used to predict the diesel spray characteristics. Of the many atomization and droplet breakup models based on the breakup mechanism due to aerodynamic liquid and gas interaction, four models classified as mathematical models, such as TAB, modified TAB, DDB, WB and one of the hybrid model based on WB and TAB models were selected for the assessment of prediction ability of diesel spray dynamics. The assessment of these models by using KIVA-II code was performed by comparing with the experimental data of spray tip penetration and sauter mean diameter(SMD) from the literature. It is found that the prediction of spray tip penetration and SMD by the hybrid model was only influenced by the initial parcel number. All the atomization and droplet breakup models considered here was strongly dependent on the grid resolution. Therefore it is important to check the grid resolution to get an acceptable results in selecting the models. At low injection pressure, modified TAB model could only give the good agreement with experimental data of spray tip penetration and both of modified TAB and DDB models were recommendable for the prediction of SMD. At high injection pressure, hybrid model could only give the good agreement with the experimental data of spray tip penetration and the prediction of all of the selected models did not match the experimental data. Spray tip penetration was increased with the increase the $B_1$ and the increase of $B_1$ did not affected the prediction of SMD.

• International Journal of Automotive Technology
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• v.4 no.4
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• pp.157-164
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• 2003

An experimental and numerical study was performed to investigate the macroscopic and microscopic atomization characteristics of high-speed diesel spray issued from the common-rail injection system. For the experiments, spray visualization system and a phase Doppler particle analyzer system were utilized to obtain the spray atomization characteristics such as the process of spray development, spray tip penetration, and SMD distribution. In order to analyze the process of spray atomization with KIVA-3 code, the TAB breakup model is changed to the KH-DDB competition model, which assumes the competition between the wave instability and droplet deformation causes the droplet breakup above the breakup length. The calculated results were also compared with the experiments in terms of spray tip penetration and SMD distribution. The results provide the process of spray development, axial and radial distribution of SMD, and calculated overall SMD as a function of time after start of injection.

• Journal of ILASS-Korea
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• v.5 no.2
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• pp.53-60
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• 2000

An aerodynamically progressed model, which is called APTAB model. has been proposed for more accurate prediction of the deformation and breakup of a spray. Especially, the effects of the droplet deformation on the droplet aerodynamic external force are considered in this model, which was neglected in TAB model. It is found that the predicted droplet deformation using APTAB model shows better agreement with experimental data than those of other models for the droplets in both bag-type and shear-type breakup regimes. A new breakup criterion has been proposed to predict more reasonable breakup quantities, such as breakup deformation length, time and so on; i.e., it is defined that the breakup occurs when the internal liquid phase pressure of the deformed droplet at the equator is greater than that of the pole. The proposed breakup criterion shows more physical relationship between the degree of droplet deformation at breakup and the corresponding breakup Weber number as compared with the results with TAB and DDB models. Therefore, it provides better predictions of the experimental data than TAB and DDB models for the droplet deformation and time in both bag-type and shear-type breakup regimes.

• Journal of Mechanical Science and Technology
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• v.17 no.11
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• pp.1812-1819
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• 2003

This paper presents the effect of injection pressure on the atomization characteristics of high-pressure injector in a direct injection gasoline engine both experimentally and numerically. The atomization characteristics such as mean droplet size, mean velocity, and velocity distribution were measured by phase Doppler particle analyzer. The spray development, spray penetration, and global spray structure were visualized using a laser sheet method. In order to investigate the atomization process in more detail, the calculations with the LISA-DDB hybrid model were performed. The results provide the effect of injection pressure on the macroscopic and microscopic behaviors such as spray development, spray penetration, mean droplet size, and mean velocity distribution. It is revealed that the accuracy of prediction is promoted by using the LISA-DDB hybrid breakup model, comparing to the original LISA model or TAB model alone. And the characteristics of the primary and secondary breakups have been investigated by numerical approach.

• Journal of ILASS-Korea
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• v.10 no.4
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• pp.47-53
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• 2005

This paper presents the effects of ambient pressure on atomization characteristics of high-Pressure injector in a direct injection gasoline engine both experimentally and numerically. The atomization characteristics such as mean droplet size, mean velocity, and velocity distribution were measured by phase Doppler particle analyzer. The spray development, spray penetration, and global spray structure were visualized using a shadowgraph technique. In order to investigate the atomization process numerically, the LISA-DDB hybrid model was utilized. This breakup model assumes that the primary breakup occurs when the amplitude of the unstable waves is equal to the radius of the ligament of liquid sheet near the nozzle and the droplet deformation induces the secondary breakup. The results provide the effect of ambient pressure on the macroscopic and microscopic behaviors such as spray development, spray penetration, mean droplet size, and mean velocity distribution. It is also revealed that the accuracy of prediction of LISA-DDB hybrid model is pretty good in terms of spray developing process, spray tip penetration, and SMD distribution.

• Journal of ILASS-Korea
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• v.4 no.1
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• pp.1-12
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• 1999

• Journal of ILASS-Korea
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• v.4 no.2
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• pp.1-9
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• 1999

• Journal of ILASS-Korea
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• v.4 no.3
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• pp.1-7
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• 1999

• Journal of Mechanical Science and Technology
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• v.18 no.7
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• pp.1177-1186
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• 2004

In this paper, the spray atomization characteristics of a gasoline direct-injection injector were investigated experimentally and numerically. To visualize the developing spray process, a laser sheet method with a Nd :YAG laser was utilized. The microscopic atomization characteristics such as the droplet size and velocity distribution were also obtained by using a phase Doppler particle analyzer system at the 5 ㎫ of injection pressure. With the experiments, the calculations of spray atomization were conducted by using the KIVA code with the LISA-DDB breakup model. Based on the agreement with the experimental results, the prediction accuracy of LISA-DDB breakup model was investigated in terms of the spray shapes, spray tip penetration, SMD distribution, and axial mean velocity. The results of this study provides the macroscopic and microscopic characteristics of the spray atomization, and prediction accuracy of the LISA-DDB model.