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( Keiya Nishida ),( Seok Su Moon ),( Wu Zhang ),( Yuhei Matsumoto ) 한국액체미립화학회 2010 한국액체미립화학회 학술강연회 논문집 Vol.2010 No.-
This paper focuses on the effects of wall-impinging conditions on penetration and evaporation of diesel spray injected by a group-hole nozzle (a group of closely spaced two-orifices) under high-load condition of direct-injection (DI) diesel engines. The spray characteristics of the group-hole nozzle are then compared to those of the single-hole nozzle which has the same total nozzle hole area with the group-hole nozzle. Experiments were performed inside a constant-volume vessel under simulated high-load condition of DI diesel engines. The wall-impinging spray characteristics of the test nozzles were investigated using a flat impingement wall under various wall-impingement angles. Spray geometry and vapor concentration of the evaporating diesel sprays were analyzed using a laser absorption scattering (LAS) technique. In the case of vertical wall-impingement (impingement angle of 90o), the group-hole nozzle spray showed simultaneous improvement in spray tip penetration and fuel evaporation resulted from momentum interaction of two adjacent wall-impinging jets. This improvement from the group-hole nozzle, however, disappeared at an inclined wall-impingement (impingement angle of 45o). The momentum interaction of two adjacent wall-impinging jets appeared later and weakened in the case of inclined wall-impingement. Consequently, both spray tip penetration and fuel evaporation of the group-hole nozzle spray were deteriorated compared to those of the single-hole nozzle spray in this inclined wall-impingement.
DEVELOPMENT OF AN LIF IMAGE PROCESSING TECHNIQUE FOR MEASURING DROP SIZES IN A PRE-SWIRL SPRAY
이지근,Keiya Nishida 한국자동차공학회 2008 International journal of automotive technology Vol.9 No.4
Depth of field effects in laser sheet imaging were considered for droplet sizing of a pre-swirl spray. A pre-swirl spray is formed before the hollow-cone type main-swirl spray from a D.I. gasoline injector, and shows transient characteristics with high axial velocity. A microscopic imaging technique was applied to obtain high spatial resolution LIF tomograms of the pre-swirl spray. A 1 mm thick Nd:YAG laser sheet was used as a light source to make the LIF tomograms that were imaged using a high-resolution CCD camera. The droplet sizing of the pre-swirl spray was carried out using an image processing technique. In the image processing procedure, the laser sheet-straddling large-sized droplets were carefully taken into account to remove the errors caused by the depth of field effects from the limited thickness and the energy distribution of the laser sheet. The mean intensity of the individual droplets and the line profile of the LIF signal around the droplet edge were inspected to screen the laser sheet-straddling large-sized droplets. In order to consider the effects of the size-dependent LIF signal intensity, the size classified or ensemble-averaged mean intensity of the individual droplets was introduced. The mean droplet sizes such as AMD and SMD were calculated using only screened droplets, and they slightly increase before considering the depth of field effects.
LAS (Laser absorption scattering) 기법을 통해 다단 분사 전략이 디젤 분무 혼합기 형성 및 연소에 미치는 영향 분석
김재헌(Jaeheun Kim),Keiya Nishida 한국연소학회 2019 KOSCOSYMPOSIUM논문집 Vol.2019 No.5
The split injection strategy was investigated in a constant volume chamber under evaporating, but non-reacting condition. Laser absorption scattering (LAS) technique was used to acquire the mixture concentration measurement, using a diesel surrogate fuel consists of n-tridecane and 1-methylnaphthalene. The effects of split ratio and dwell time between two injection events were investigated. Three split ratios, namely 3:7, 5:5, and 7:3 were selected. The split ratio of 7:3 was the best among three conditions in terms of mixture formation process. The spray from the second injection of the split ratio of 7:3 showed adequate vapor penetration, so that the fuel could be positioned within the fuel lean region formed from the first injection. The intensity of the diffusion flame was also lower with the split ratio of 7:3, due to the greater portion of the premixed combustion occurred during the first injection.
( Zhanbo Si ),( Nagisa Shimasaki ),( Keiya Nishida ),( Youichi Ogata ),( Chenglong Tang ),( Zuohua Huang ) 한국액체미립화학회 2017 한국액체미립화학회 학술강연회 논문집 Vol.2017 No.-
The fuel spray injected into a direct injection (DI) engine is strongly affected by both the in-cylinder air flow and the piston cavity wall impingement. The combined effect of the air flow and the wall impingement plays an important role on the spray development, mixture formation and subsequent combustion. In this study, the effects of the parallel cross-flow and the flat wall impingement were investigated on the spray development and dispersion. The spray was injected by a valve covered orifice (VCO) nozzle under various cross-flow velocities and ambient pressures. Tomographic images of the spray in a vertical and several horizontal planes were taken by a high-speed video camera and a continuous wave laser sheet. Moreover, the experiment results were compared with simulation which was calculated by the validated spray models based on the CONVERGE software. The results show that with increasing the cross-flow velocity, the spray tip penetration is decreased slightly before the impingement while the spray tip penetrates further in the cross-flow downstream direction after the impingement. The high ambient pressure tend to compress the spray profiles. Additionally, under the condition of the similar fuel injection and cross-flow momentum flux ratio, the distortion curves of the sprays in the cross flow upstream side agree well with each other whereas the spray dispersion in the downstream side is affected by the cross flow velocity. In the vertical plane along the flat wall, the head vortex is generated at the spray tip. With the head vortex growing, the surrounding air is significantly entrained into the spray. In the horizontal plane, an empty belt is observed near the head vortex core region. The quantitative analysis shows that the high velocity of the cross-flow favors the spray breakup and dispersion, leading to a larger head vortex and a wider spray angle.
( Shintaro Uchitomi ),( Hongliang Luo ),( Keiya Nishida ),( Youichi Ogata ),( Wu Zhang ),( Tatsuya Fujikawa ) 한국액체미립화학회 2017 한국액체미립화학회 학술강연회 논문집 Vol.2017 No.-
The recent strict regulation of emission for internal combustion engines requires the reduction of pollutant emissions such as soot. The direct-injection spark-ignition (DISI) engine, which has been widely used for passenger cars, can improve thermal efficiency and reduce the emission of carbon dioxide. However, as fuel is injected directly into the cylinder, it is difficult to avoid the wall impingement of spray on the combustion chamber. And liquid films inevitably form on the piston and cylinder surfaces. These films are possible sources of unburnt hydrocarbons and soot emissions. In addition, liquid films have a significant influence on combustion efficiency. To improve the combustion performance of DISI engines, better understandings of the spray-wall interaction and liquid film formation processes are needed. This work investigated the wall impingement and liquid film formation by sprays injected from a mini-sac injector with a single-hole. The experiments were conducted in a constant-volume vessel under various ambient pressure and temperature. A quartz glass with rough surface was used as the flat wall. The refractive index matching (RIM) technique was applied to investigate the spatial distribution and formation process of liquid films. The results showed that the adhered liquid mass and spatial distribution of liquid films, liquid film formation process are affected by the ambient pressure and temperature. In particular, the effect of ambient temperature on liquid film formation is significant. The results of RIM method provided insights into the effects of ambient conditions on the wall impingement behavior and liquid film formation processes.
( Kang Yang ),( Shintaro Yasaki ),( Keiya Nishida ),( Yoichi Ogata ) 한국액체미립화학회 2017 한국액체미립화학회 학술강연회 논문집 Vol.2017 No.-
The objective of this study is to show the measurement of fuel vapor / liquid concentration distributions in diesel spray. In order to observe the spray mixture formation process, the tracer Laser Absorption Scattering (LAS) technique was adopted. The n-tridecane which does not absorb UV and visible lights was used to simulate the diesel fuel, and the 1- methylnaphthalene which strongly absorbs UV light was selected as a tracer to detect distribution of vapor phase. Tracer LAS fuel with 97.5 vol% of n-tridecane and 2.5 vol% of 1-methylnaphthalene (α-MN) was employed. The fuel was injected into a high pressure and high temperature constant volume vessel by a single-hole nozzle with a hole-diameter of 0.133 mm. Three kinds of injection pressures (100, 150, 170 MPa) were selected to analyze the effect of injection pressure on the diesel spray mixture formation process. The experimental results revealed that high injection pressure promotes fuel evaporation process. It was found that the vapor equivalence ratio becomes rich first and then becomes lean as time elapses. The vapor phase of high injection pressure becomes the much more homogenous at the post spray mixture process than that of low injection pressure. The axial distribution of the total fuel (vapor and droplets) of LAS results under evaporation conditions were compared with the calculated result by the momentum theory. The measured □ of high injection pressure agrees well with predicted model than that of low injection pressure. A comparison of the total fuel concentration along the spray axis obtained by LAS results and the momentum theory under two different ambient temperatures but same ambient gas density was also discussed. The measured □ of non-evaporation agrees much more well with predicted model than that of evaporation condition.
( Jee Keun Lee ),( Keiya Nishida ),( Byoung Joon Rho ) 한국액체미립화학회 2005 한국액체미립화학회 학술강연회 논문집 Vol.2005 No.-
The depth of field effects in the laser sheet imaging was considered for the droplet sizing of the pre-swirl spray, which is formed before the hollow-cone type main-swirl spray from a D.I. gasoline injector, and which shows the high transient characteristics and axial velocity. In addition, a microscopic imaging technique was applied to get the spatially high-resolution LIF tomograms of the pre-swirl spray. The Nd:YAG laser sheet with 1 mm thick was used as a light source to make the LIF tomograms that was imaged using a high-resolution CCD camera. The image processing technique was applied to determine the droplet size. In the image processing procedure, the laser sheet-straddling large-sized droplets were carefully taken into account to remove the errors caused by the depth of field effects coming from the limited thickness and the energy distribution of the laser sheet. The mean intensity of the individual droplets and the line profile of the LIF signal around the droplet edge were inspected for screening the laser sheet-straddling large-sized droplets. In order to consider the effects of the size-dependent LIF signal intensity, the size-classified or ensemble-averaged mean intensity of the individual droplets was introduced. The mean droplet sizes such as AMD and SMD were calculated using only screened droplets, and they increase a little before considering the depth of field effects.