Analysis of the transient atomization characteristics of diesel spray using time-resolved PDPA data

International Journal of Automotive Technology, Vol. 9, No. 3, pp. 297�305 (2008)DOI 10.1007/s12239�008�0036�3

Copyright © 2008 KSAE1229�9138/2008/040�06

297

ANALYSIS OF THE TRANSIENT ATOMIZATION CHARACTERISTICS OF DIESEL SPRAY USING TIME-RESOLVED PDPA DATA

D. J. KIM1) and J. K. LEE2)*

1)Korea Automotive Technology Institute, 74 Yongjeong-ri, Pungse-myeon, Cheonan-si, Chungnam 330-912, Korea2)Division of Mechanical and Aerospace System Engineering, Chonbuk National University, RCIT, Jeonju-si,

Cheonbuk 561-756, Korea

(Received 29 August 2007; Revised 23 March 2008)

ABSTRACT�The transient atomization characteristics of a single-hole diesel spray were investigated to clarify the time-dependent droplet formation process of the spray through time-resolved analysis of the droplet size data acquired by using a2-D PDPA (phase Doppler particle analyzer). Comparisons among the three single-hole diesel nozzles on the atomizationcharacteristics were made to confirm the effects of the hole-diameter. The hole diameter of the single-hole diesel nozzlesvaried with dn=0.22, 0.32 and 0.42 mm. The time-resolved diameter, SMD (Sauter mean diameter) and AMD (arithmeticmean diameter) of droplets in diesel spray injected into still ambient air were measured. The SMD and AMD decreased withdecreasing nozzle hole diameter. The SMD distribution along the spray centerline steeply decreased with increasing axialdistance before reaching a constant value. In the time-dependent analysis of the SMD of the whole flow field, the SMDgradually increased with time after the initiation of injection, reached a maximum value, and then decreased.

KEY WORDS : Transient atomization characteristics, Diesel spray, SMD (Sauter Mean Diameter), PDPA (Phase DopplerParticle Analyzer)

1. INTRODUCTION

The distribution of fuel droplets in the combustion chamberof direct injection (D.I.) diesel engines is a dominant factorin governing the fuel-air mixture formation process.Research on producing more efficient and less pollutingcombustion of the fuel-air mixture in the combustionchamber requires a better knowledge of the droplet size andvelocity distribution of fuel sprays. There have been manyexperimental (Doudou and Maslouhi, 2007; Park et al.,2005; Lee et al., 2005; Arcoumanis et al., 1990) andtheoretical studies (Lee and Ryu, 2006; Reitz and Diwakar,1987) of fuel sprays. However, most of these experimentalstudies have been carried out under steady state. Accord-ingly, there is little fundamental understanding regardingthe behavior of transient fuel sprays.

Diesel fuel sprays are transient and intermittent in naturebecause of variations in injection pressure, so the dropletsize distributions change with time and space. Therefore,observation of the injected fuel droplets’ behavior �throughout the whole flow field of the spray and over theduration of the spray after the start of injection (SOI) � isnecessary to clarify the time-dependent droplet formationprocess. Moreover, important physical behavior arisingfrom the transient nature of diesel sprays might be omittedin the studies of steady-state sprays (Lee et al., 2005; Park

et al., 2005; Hosoya and Obokata, 1993). These insuffi-cient results suggest the need for an in-depth study toobtain detailed information on the droplet formation pro-cess for transient diesel sprays.

For twenty years, laser diagnostic techniques, such asLDV (laser Doppler anemometry) and PDPA (phase Dopplerparticle analyzer), have been applied for measuring thespray flow field. In particular, PDPA (Pitcher and Wigley,1992; Safman et al., 1988) works based on simultaneousdetection of the frequencies and phases of the Dopplersignals provided by the scattered light from a dropletmoving through the measurement volume. The obtainedDoppler frequency indicates the droplet velocity, while thedroplet size is determined from phase differences betweenthe signals detected at different locations in the detectingplane. Moreover, this technique makes it possible to collecttiming information of the measured droplet, along witheach droplet diameter and velocity. This dominant featureleads us to choose PDPA for characterizing transient dieselsprays.

Safman et al. (1988) measured the droplet size andvelocity distribution of a single-hole diesel spray by using aLDV and PDA system. Koo and Martin (1990) simultane-ously obtained the droplet size and velocity distributionsfor a transient diesel spray at atmospheric pressure by usingPDPA. In their studies, the size distributions showed a verystrong dependence on time and spatial position of thespray, especially in the radial direction. Ikeda et al. (1997)*Corresponding author. e-mail: [email protected]

298 D. J. KIM and J. K. LEE

investigated fuel droplet dispersion and mixture formation,including the droplet size and velocity distribution of thespray, in a practical twin-fluid atomizer by using a PDPA.They showed that the size-classified technique is suitablefor understanding the droplet dispersion and momentumtransfer of the spray. Ismailov et al. (1999) utilized a PDPAto obtain the mean velocity and SMD of high-pressureswirl-type sprays. In their studies, it was revealed that thetime-series of dynamic values allows detailed analysis ofthe spray flow transitions, and the PDA is an effectivetechnique to evaluate transient fuel sprays.

In this paper, the transient atomization characteristics ofa single-hole diesel spray were investigated to clarify thetime-dependent droplet formation process of the spraythrough the time-resolved analysis of the droplet size dataacquired by using a 2-D PDPA. Comparisons among thethree single-hole diesel nozzles on the atomization charac-teristics were made to confirm the effects of the hole-diameter, resulting in better understanding of the fuel-airmixture formation process of diesel nozzles.

2. EXPERIMENTAL APPARATUS

2.1. Fuel Injection SystemIn order to investigate the transient atomization characteri-stics of the spray formed by a single-hole diesel nozzle atroom temperature and atmospheric pressure, an experi-mental apparatus composed of the fuel injection systemand PDPA was used. The fuel injection system was com-posed of the fuel injection pump, DC motor, droplet collec-tion device and fixed frame, as shown in Figure 1. The fuelinjection pump was an in-line PE type with 8 barrels. It wasdriven by a 15 kW DC motor that was able to rotate atmaximum speed of 3600 rpm. The fuel used in this test wasKS #2 diesel oil with specific gravity of 0.8315, kinematicviscosity of 3.71 cSt, and refraction rate of 1.468 at 24oC.

2.2. Single-Hole Diesel NozzleThe fuel injection nozzle was a mini-sac type single-hole

diesel nozzle with a 2-spring nozzle holder. There is atested hole in the vertex of the nozzle tip. The prelift andthe total lift of the nozzle needle were set to 0.06±0.02 and0.39 mm, respectively. The first and the second needleopening pressures were set to 150 and 220 bar, respec-tively.

The effects of the hole diameter on the atomizationcharacteristics were examined while changing the hole dia-meter of the nozzle to 0.22, 0.32 and 0.42 mm with aconstant hole length of 0.9 mm. The hole length to dia-meter ratio (ln/dn) of each nozzle was also changed to 4.09,2.81 and 2.14, respectively. Table 1 shows the specifi-cations for the three single-hole diesel nozzles tested. Therotation speed of the pump was set up to 500 rpm. Theinjection quantity was set to 7.31 mm3/st, regardless of thehole diameter. The injection durations (ID) were 0.85, 0.80and 0.79 ms for hole diameters of 0.22, 0.32 and 0.42 mm,respectively.

2.3. PDPA System for Droplet SizingThe simultaneous measurement of the droplet size andvelocity was carried out by using a 2-D PDPA (DantecCo.). The PDPA consists of transmitter optics with a 750mW air-cooled Ar-ion laser as a light source, receiver opticsfor collecting the scattered light, signal processing electronics(Dantec Co., 58N50), a three-dimensional traverse, and adata acquisition system including a computer. Two laserbeams, with wavelengths of 514.5 (green) and 488 (blue)nm, emerge from the transmitting optics and cross at onepoint to form a measurement volume. Receiving opticsdetect the scattered light produced when droplets passthrough the measurement volume, and then transmit to thesignal processor. The droplet size and velocity of the fuelspray is measured by the frequency and phase difference ofthe Doppler signal.

The measurements of the droplet size and velocity wereconducted in two dimensions because the diesel spraycould be considered as an axi-symmetric structure in theflow field. Figure 2 shows the schematic diagram of thetypical structure of transient diesel sprays and the coordi-nate system adopted. The direction of the nozzle axis wasdefined as Z, and the radial direction was defined as R. Theorigin was located at the nozzle tip.

The measurement was performed at the axial distancesFigure 1. Experimental apparatus and PDPA setup.

Table 1. Specifications of single-hole diesel nozzles.

Items Nozzle typesNozzle hole diameter

(mm) �0.22�1 �0.32�1 �0.42�1

Nozzle hole length (mm) 0.9 0.9 0.9

Length/Diameter 4.09 2.81 2.14Nozzle hole area

(mm2) 0.038 0.080 0.139

ANALYSIS OF THE TRANSIENT ATOMIZATION CHARACTERISTICS OF DIESEL SPRAY 299

of Z=10, 20, 30, 50, 70, 90, 120, 150 and 180 mm from thenozzle tip. The measurement positions at the radial direc-tion were densely set near the axis because the velocity ofthe spray varies sharply, but their intervals became largernear the outer region of the spray. The number of points atthe radial distance was 15. The number of measured data ateach measurement position was 20,000, and the measure-ment mode was set not to exceed 300 sec.

3. RESULTS AND DISCUSSION

3.1. Spray Images of Single-Hole Diesel SprayFigure 3 shows the spray images of the nozzle (dn=0.32mm) with time after SOI. The sprays were illuminated by atungsten lamp and imaged by a CCD camera (TOSHIBAIK-536) using Mie scattering light.

The spray structure shows time-dependent developmentprocesses, unlike continuous sprays. The sprays are formedand developed in the early injection periods. They aremixed with and finally diffused into the ambient air. In

particular, the structural behavior of the spray is differentwith each spray region: the leading edge, the mixing flowregion, the central part and the trailing edge, as shown inFigure 2. Moreover, the development process of the fourspray regions changes with time after SOI. As a result,time-resolved analysis is needed to clarify the time-dependent development process of the spray.

3.2. Time-Resolved Axial and Radial Velocity ProfilesFigure 4 shows the time-resolved axial velocity distributionof the spray with time after SOI at the two axial positionsof Z=30 and 90 mm and at the spray centerline. From thesetime-resolved axial velocity distributions, the internal struc-ture of the spray can be divided into regions “I”, “II” and“III”. These regions show different flow regimes from eachother.

At Z=30 mm, as shown in Figure 4(a), the axial velocityreaches a maximum value a little while after the droplets ofthe leading edge arrive at the measurement point. Then, theaxial velocity decreases gradually and finally reaches theequilibrium state. The reason for the smaller velocity in theleading edge, displayed as region “I”, than that in thecentral part, displayed as region “II”, is that the droplets inthe leading edge are greatly affected by the drag force

Figure 2. Typical structure of transient diesel spray andcoordinate system adopted.

Figure 3. Spray images of single-hole diesel nozzle (dn=0.32 mm) with time after SOI.

Figure 4. Time-resolved evolution of axial velocity withtime after SOI to 3.0 ms at axial positions of Z=30 and 90mm at spray centerline.


induced by the velocity difference with the ambient air. Asa result, the velocity of droplets in the central part becomeshigher, which means that the following droplets catch upwith the first injected droplets. However, this phenomenondisappears with increasing axial distance, as shown inFigure 4(b). At Z=90 mm, far from the nozzle tip, it isdifficult to discriminate the boundary between the leadingedge and the central part of the spray.

The radial velocity distribution was considered to investi-gate the diffusion process of the spray. Figure 5 shows thetime-resolved radial velocity distributions of the spray,with time after SOI at the two axial positions of Z=30 and90 mm and at the spray centerline.

The radial velocity distribution of the spray is symmetri-cal, based on the radial velocity of zero. The fluctuatingwidth of the radial velocity becomes larger around the endof injection, and the duration with increased fluctuatingwidth becomes longer with the increase in the axial di-stance of the spray, as shown in Figure 5(b). It indicatesthat the expansion of the spray and the diffusion to theambient air actively take place at the downstream region ofthe spray. This process promotes turbulent mixing.

3.3. Time-Resolved Droplet Size Distributions

The time-dependent development process of the spray wasexamined through time-resolved analysis of the dataacquired during the many injection events. In the case of Ninjection events, the Sauter mean diameter (SMD, D32)with respect to the time window, is defined by

(1)D32 t ,�t� �=

i 1=

Nc

� j 1=

Nd

� Dij3 t �t

2-----+

� �

i 1=

Nc

� j 1=

Nd

� Dij2 t �t

2-----+

� �----------------------------------------------

Figure 5. Time-resolved evolution of radial velocity withtime after SOI to 3.0 ms at axial positions of Z=30 and 90mm at spray centerline.

Figure 6. Time-resolved evolution of droplet diameter,AMD and SMD at axial distance of 30 mm at spraycenterline for three single-hole diesel nozzles.


and the arithmetic mean diameter (AMD, D10), is given by

(2)

(Koo and Martin, 1990), where Nc is the number of injec-tion cycle averaged, and Nd is the number of data during theith cycle. In this study, the time windows of 0.15 ms wereselected after considering data rates and effective datavalidations.

Figure 6 shows the time-resolved evolution of the drop-let diameter, AMD and SMD at the axial distance of 30 mmand at the spray centerline for the three single-hole dieselnozzles.

Time window (�t), which is a time interval for calcu-lating the mean droplet sizes such as AMD and SMD, wasset to 0.15 ms. It was carefully selected to represent thetime-dependent transient characteristics, as well as themean characteristics of the droplet sizes. Several studieshave been carried out on the selection of the time window.Pitcher and Wigley (1992) set the time window at 0.04 ms.Arcoumains et al. (1993) set the time window at 0.1 ms tocalculate the mean velocity and mea droplet sizes of thediesel spray.

Using the time-resolved evolution of the droplet sizemeasured at the spray centerline, the internal structure ofthe transient spray could be investigated. There is a certainperiod, known as the spray tip arrival time, in which theleading edge of the spray reaches the measurement posi-tion. Just after the leading edge of the spray arrives at themeasurement point, comparatively small-sized droplets aredetected. These arriving droplets can be distinguished fromthe floating droplets around the measurement point. Afterthe leading edge of the spray passes, the detecting frequ-ency of the droplets is remarkably reduced in a certainperiod. This duration is a period in which the central partenclosing the leading edge and mixing flow region of thespray, as shown in Figure 2, passes through the measure-ment point. The low detection frequency indicates that theshape of the droplets passing through the measurementpoint during this period are not spherical. In connectionwith this phenomenon, Safman et al. (1988) concluded thatthe reduction of the number density of droplets during thisperiod is due to the large-sized ligaments undergoing dis-integration. The PDPA calculated the droplet size based onthe phase difference of the scattered light produced whenthe spherical droplets pass through the measurement volume.In this study, when the droplets were the same sizes, ortheir differences were within 10%, we regarded them asspherical droplets. Therefore, there would be ligaments,non-spherical droplets or large-sized droplets exceedingthe measurement range of the PDPA near the central part ofthe spray.

Meanwhile, after the central part of the spray passesthrough the measurement point, the detection frequency ofthe droplets increases prominently. From this time-resolvedevolution of the droplet size, the structure of the dieselspray can be divided into three main parts, as depicted inFigure 2: (a) the leading edge affected by the ambient air;(b) the central part surrounded by the leading edge andmixing flow region, and scarcely affected by the ambientair; and (c) the trailing edge formed after the central partpassed.

Figure 6(a) shows the results for a hole diameter of 0.22

D10 t ,�t� �=

i 1=

Nc

� j 1=

Nd

� Dij t �t2-----+

� �

i 1=

Nc

� j 1=

Nd

�----------------------------------------------

Figure 7. Time-resolved evolution of droplet diameter,AMD, and SMD at axial distance of 30 mm at radialdistance of 2.2 mm for three single-hole diesel nozzles.


mm. The large droplets above 50 m are detected near thestarting point of the trailing edge. At 1.6 ms after SOI, thesize of most droplets is below 25 m, but large-sized drop-lets are detected irregularly. In particular, the large-sizeddroplets due to the 2nd injection appear around 2.75 msafter SOI. The AMD is approximately 25 m during theinjection period, and it maintains the value of about 10 mafter 1.6 ms after SOI. Figure 6(b) shows the results for thehole diameter of 0.32 mm. Many large-sized droplets over100 m are detected after the central part passes throughthe measurement point. The AMD is approximately 30 mduring injection period, but it maintains the value of about15 m after 1.6 ms after SOI. The SMD for this case tendsto change more irregularly than that for the hole diameterof 0.22 mm. The difference between the AMD and theSMD is large within 2 ms.

This observation indicates that the droplet distribution isnot uniform because the SMD, which is defined as the ratioof volume (d3) to surface area (d2), is biased to the large-sized droplets, so that the difference between the AMD andthe SMD increases when the droplet size shows a widelydispersed distribution.

Figure 6(c) shows the results for the hole diameter of0.42 mm. Many large-sized droplets over 150 m aredetected until 2.0 ms after the central part passes throughthe measurement point. The SMD is higher than that for theother two nozzles. From these time-resolved droplet sizedata, it can be concluded that both the SMD and the AMDincrease with an increase in the hole diameter. In particular,the difference between them also increases, which impliesthe increase in the dispersion degree of the droplets.

Figure 7 shows the time-resolved evolution of the drop-let diameter, AMD and SMD at a radial distance of R=2.2mm and at a fixed axial distance of Z=30 mm. This radialposition, which was selected after investigating the axialvelocity distribution, corresponds to the mixing flow region,as shown in Figure 2.

At the moment when the spray reaches the measurementpoint, many droplets are detected. Moreover, the drop sizedistribution is more uniform than that at the central part, asshown in Figure 6. For all three single-hole diesel nozzles,the detection frequency of the droplets is significantlyincreased, to the extent that it is difficult to discriminate theboundary between the leading edge and the central part ofthe spray. The SMD becomes more uniform with a de-crease in the hole diameter from 0.42 to 0.22 mm. Inaddition, the difference between the SMD and the AMD isrelatively small.

3.4. Mean Droplet Size ProfilesFigure 8 shows the SMD distributions with radial distanceat the four axial positions of Z=10, 20, 30 and 40 mm forthe three single-hole diesel nozzles. The time windowapplied for calculating the SMD is 20 ms after SOI. Thistime window is of relatively longer duration than the injec-tion periods of 0.85, 0.80 and 0.79 ms for dn=0.22, 0.32 and

0.42 mm, respectively. Thus, the SMD distributions repre-sent the whole spray characteristics during the single injec-tion event.

In the case of the nozzle of dn=0.22 mm, as shown inFigure 8(a), the SMD decreases with an increase in theaxial distance. At Z=40 mm, it reaches approximately 40 m near the spray axis. In addition, the SMD has a highervalue around the spray center, which is a typical charac-teristic of the solid cone spray, such as hole-type dieselsprays, and it decreases rapidly towards the outer region ofthe spray. It has a constant value in the range of 20-30 m

Figure 8. SMD distributions with radial distance at fouraxial positions of Z=10, 20, 30 and 40 mm for the threesingle-hole diesel nozzles.


at R > 2 mm. In the case of the nozzle with dn=0.32 mm, asshown in Figure 8(b), the SMD decreases with an increasein the axial distance, but it has a higher value near the sprayaxis than that for the nozzle with dn=0.22 mm. The SMDdecreases gradually with an increase in the radial distance,and a constant value is reached at R > 2 mm. In the case ofthe nozzle with dn=0.42 mm, as shown in Figure 8(c), asimilar trend in the SMD is observed in the redial distribu-tions. However, the SMD near the spray axis is higher thanfor the other two nozzles.

For all three single-hole diesel sprays, the larger SMDdistributions near the spray axis indicate the location of thecentral part of the spray. This region can be discriminatedfrom the outer region of the spray that has a low and uni-form SMD distribution. In addition, this result illustratesthat the outer region of the spray is formed through thedisintegration processes of the central part of the spray.According to these SMD distributions with radial distance,the spray structure of the spray can be classified into thethree regions: (a) the inner region showing a high SMDdistribution; (b) the mixing flow region where the shearflow structure would be constructed; (c) the outer regionformed through the disintegration processes of the spray’sinner region and composed of fine droplets.

Figure 9 shows the SMD along the spray centerline forthe three single-hole diesel nozzles. After reaching a maxi-mum value in the vicinity of the nozzle tip, the SMD pro-files show a rapid decrease, and then reach constant valuesnear Z=50 mm, regardless of the hole diameter. This resultindicates that the internal structure of the single-hole dieselspray is dramatically changed within the near field of thenozzle tip, and the disintegration processes of these spraysactively take place within the region where the atomizationprocesses are most critical. As expected, the nozzle withdn=0.22 mm shows the lowest SMD distribution along thespray centerline, and the SMD increases with an increase inthe hole diameter.

3.5. Time-Dependent SMD ProfilesFigure 10 shows the SMD distribution, which was calcu-

lated with a time window of 0.15 ms for all the measure-ment points (144 points) of the spray flow field, from Z/dn=31 to 562, with time after SOI. That is, the SMD for thewhole flow field indicates the overall mean value of theSMD. This quantity can help to illustrate the developmentand atomization processes of the transient diesel spray.

The SMD for all three single-hole diesel nozzlesincreases gradually with time after SOI, and then tends todecreases after reaching a maximum value near 1.6 msafter SOI. The increased SMD distribution near 4.0 ms atthe nozzle of dn=0.22 mm is caused by the 2nd injection, asshown in Figure 6(a). The increasing trend within 1.6 msafter SOI, denoted as the region “I”, is a little different fromthe general tendency of the disintegration processes of thediesel spray. As the liquid columns or ligaments changeinto the droplets, the SMD decreases with time after SOI.The increasing trend within 1.6 ms could be related to thecharacteristics of the PDPA. As mentioned in Figure 6, thePDPA calculates the droplet size only in the case that thephase difference detected at different locations in thedetecting plane are the same, or their differences are within10%. Consequently, ligaments, non-spherical droplets, orlarge-sized droplets that exceed the measurement rangenear the central part of the spray were not considered inFigure 10. Conversely, it can be concluded that 1.6 ms afterSOI is the time needed for the ligaments or larger dropletsto change into spherical droplets. After 1.6 ms, denoted asthe region “II”, the SMD distributions show a decreasingtrend with time after SOI. This trend is attributed to thedisintegration of the ligaments or large droplets within theregion “I” into fine droplets through a second atomizationcaused by the resistance of the ambient air. With regard tothe time dependence of the SMD distribution, Doudou andMaslouhi (2007), who investigated high-pressure spraysinjected by a common rail system, obtained similar resultsshowing an increasing trend for SMD during a certainperiod after SOI.

Comparing the three single-hole diesel nozzles, the nozzleof dn=0.22 mm shows the smallest SMD distribution,excepting near 3.0-5.0 ms when that of the second spray is

Figure 9. SMD distributions along spray centerline forthree single-hole diesel nozzles.

Figure 10. SMD distribution with time after SOI to allmeasurement points of spray flow field.


smallest. The SMD decreases with a decrease in the holediameter for the single-hole diesel nozzle. The difference inSMD between the nozzles of dn=0.42 and 0.22 mm is about25.5% at 1.6 ms after SOI. In addition, the mean value ofthe SMD during t < 5 ms after SOI is 23.1, 25.0 and 30.9 m for dn=0.22, 0.32 and 0.42 mm, respectively. Thedifference in the SMD among the three nozzles is thegreatest at 1.6 ms, and it decreases gradually until theSMDs become similar at 4.7 ms. Consequently, the geo-metrical characteristics of the nozzle are most importantduring the initial period after starting the injection. As timepasses, the geometrical characteristics disappear, and thetransient characteristics are obscured by the coherence anddisintegration of droplets.

3.6. Effects of Hole Diameter on Atomization Characteri-sticsFigure 11 shows the effects of the hole diameter on theatomization characteristics of the single-hole diesel nozzle.The SMD was averaged for all 114 measurement points,with a time window of 20 ms. The SMD was calculated as39.4, 29.8 and 27.2 m for the hole diameter of 0.42, 0.32and 0.22 mm, respectively. The difference in the SMDbetween dn=0.42 and dn=0.22 mm is 31.0%. The decreasingtendency of SMD with a decrease in hole diameter is inagreement with results obtained by Hiroyasu et al. (1989).However, in the SMD measurements of the current work,injection pressure and hole length to diameter ratio (ln/dn)were simultaneously changed, because of the change of thenozzle hole diameter. As a result, the SMD variations,shown in Figure 11, incorporate the effects of two para-meters, including the hole diameter.

4. CONCLUSIONS

The transient atomization characteristics of the single-holediesel spray were investigated through time-resolved ana-lysis of the 2-D droplet size data acquired by using a 2-DPDPA (phase Doppler particle analyzer). Comparisons ofthe atomization characteristics among the three single-hole

diesel nozzles were made to confirm the effects of the hole-diameter. Concluding remarks are summarized below.(1) The SMD and AMD decreased with a decrease in the

nozzle hole diameter, as did the difference betweenthem, which is related to the degree of dispersion of thedroplets.

(2) The SMD distributions near the spray axis were veryhigh, to the extent that they were clearly discriminatedfrom the outer region of the spray. In addition, thespray at the outer region showed a relatively uniformSMD distribution in radial distance.

(3) The SMD distribution along the spray centerline steeplydecreased with an increase in the axial distance, beforereaching a constant value. In addition, the developmentprocess of the spray was dramatically changed near thenozzle tip.

(4) In the time-dependent analysis of the SMD for thewhole flow field, the SMD gradually increased withtime after SOI, and it decreased after reaching amaximum value.

ACKNOWLEDGEMENT�This work was supported by theresearch fund of Chonbuk National University (104187001).

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Documents

Analysis of the transient atomization characteristics of diesel spray using time-resolved PDPA data