Improvement of Spray Characteristics for Direct Injection Diesel Engine by Cavitation in Nozzle Holes

Transcription

1 ILASS Americas 27th Annual Conference on Liquid Atomization and Spray Systems, Raleigh, NC, May 2015 Improvement of Spray Characteristics for Direct Injection Diesel Engine by Cavitation in Nozzle Holes N. Tamaki *, S. Minami and K. Nishikawa * Department of Mechanical Engineering, Kindai University 1 Takaya Umenobe, Higashihiroshima-shi, Hiroshima , Japan Graduate School, Kobe University 1-1, 5 Hukaeminami, Higashinada-ku, Kobe, Hyogo , Japan Graduate School, Kindai University 1 Takaya Umenobe, Higashihiroshima-shi, Hiroshima , Japan Abstract Diesel engine is lifted in terms of high thermal efficiency, reduction of carbon dioxide. The purpose of this study is to develop of a direct injection Diesel nozzle, which is obtained high-dispersion spray inside a cylinder by strong disturbance of liquid flow due to cavitation phenomena and swirling flow inside the nozzle hole. Authors have high expectation of this developed injection nozzle with suitable for lean burn combustion. In this study, it was mainly researched that effects of inclination of nozzle holes of the atomization enhancement nozzle, which was designed and invented at previous in this study, on spray characteristics. As a result, it was clarified that spread of spray of the nozzle, which is dressed with round inlet cutting at inlet of the multi-hole nozzle, becomes large about 60 p.c. and Sauter mean diameter of 20 μm order are obtained compared with one of sharp inlet shape nozzle. Moreover, volumetric flow rate of Nozzle-R di is obtained about 20 p.c. larger than sharp inlet sharp nozzle at all injection pressure regions. In general, although volumetric flow rate increases and improved by using the nozzle with round inlet cutting at inlet of the nozzle hole, spray characteristics becomes wrong rapidly. However, the atomization enhancement nozzle, which was designed and invented in this study, both spray characteristics and flow characteristics were improved. Furthermore, when the each nozzle holes of the multi-hole nozzle were inclined at 45 deg., spray angle becomes dramatically large about over 100 deg., spray characteristics were improved considerably. Nozzle Hole Bypass Upstream from Gap Gap Nozzle Holes Downstream from Gap Appendix Figure 1. Configuration of atomization enhancement nozzle (3D image). Nozzle Types S, S S, I Hole Number: N=4 Hole Diameter: D 1 =0.6 mm, D 2 =0.3 mm (N=4) Pitch Circle Diameter of Nozzle Hole: D p =3.0 mm Inclination Angle of Nozzle Hole: 45 deg. Injection Pressure: P i max. =8.0 MPa Nozzle-S, I Appendix Figure 2. One of developed nozzles. * Corresponding author: tamaki@hiro.kindai.ac.jp Appendix Figure 3. Effects of existence of inclination angle of nozzle hole on disintegration behavior of spray and dispersion of spray.

2 Introduction Diesel engine; direct injection Diesel engine has the highest thermal efficiency, excels in fuel consumption rate and it leads to reduce carbon dioxide caused by global warming. In order to improve combustion efficiency, exhaust gas characteristics and progress of fuel consumption rate the authors have aimed at improvement of spray characteristics of fuel spray. It is a matter of great urgency to reduce carbon dioxide, which is caused by global warming. The final objects of this study are improvement of combustion characteristics of a direct injection Diesel engine, reduction of soot emission and progress of thermal efficiency and fuel consumption rate by improvement over the injection nozzle and spray characteristics. In the previous studies included of this study, it was clarified that cavitation phenomena in the nozzle hole is considerably affected to atomization of spray, and it is effective to make aggressively use of cavitation in the nozzle hole, that is, disturbance of liquid flow due to collapse of cavitation bubbles [1]-[5]. Moreover, it was developed the atomization enhancement nozzle, which excellent spray characteristics with large spread angle, short breakup length, that is, short liquid core length for a direct injection Diesel engine, almost uniformly droplets and small droplet diameters, are obtained at a standstill injection pressure or relatively lowinjection pressure. At the previous the author s studies, design of the atomization enhancement nozzle, which highdispersion and high-efficiency spray are obtained at engine combustion, and improvement of spray and flow characteristics have been done by using the multi-hole nozzle separated one nozzle hole to four nozzle holes [6], [7]. The purpose of this study is to improve spray and flow characteristics of a direct injection Diesel injector from the point of view of only changing the part of the nozzle hole. This is because reduction of unit price of a Diesel injector. The hole nozzle for the direct injection Diesel engine is dressed with round inlet cutting at inlet of the nozzle hole in order to improve flow characteristics. This leads to become large of discharge coefficient. Generally, it is well known that although discharge coefficient becomes large by using the nozzle with round inlet cutting at the inlet of the nozzle hole, spray characteristics becomes wrong and considerably highinjection pressure is needed to obtain excellent spray characteristics. In this study, on the basis of the previous the author s studies and results concerning design of the highdispersion atomization nozzle, it was designed that the gathered multi-hole spray, which the same spray like that the actual Diesel injection nozzle as the sprays injected from the actual multi-hole nozzle, is obtained by dividing one nozzle hole in the four small nozzle holes. In this paper, it was described that effects of geometric shapes of inlet and outlet of four nozzle holes, which was divided one nozzle hole, on improvement of spray characteristics, and effect of the nozzle, which was inclined angle of 45 deg. at nozzle holes to injection direction, on spread of spray and improvement of spray characteristics. Where, schematic of structure of a Diesel injector for direct injection Diesel engine in common use and the atomization enhancement nozzle are shown in Figs. 1and 2, respectively Injector Body Sac Nozzle Holes Chamber (a) Diesel injector for direct injection Diesel engine in common use. (b) Single hole nozzle Figure 1. Schematic of structure of a Diesel injector for direct injection Diesel engine in common use. Correspond to Sac Chamber Detail of Injector Tip Bypass Nozzle Hole Upstream from Gap Gap Nozzle Holes Downstream from Gap Figure 2. Schematic of structure of atomization enhancement nozzle.

3 As shown in Fig.1, each of nozzle holes of a multiholes Diesel injector for direct injection is arranged on vertically, sideways and diagonally with arbitrary angle, and nozzle holes get a straight hole. As shown in Fig.2, the atomization enhancement nozzle, which was invented in previous in this study, consists of the gap, the bypass, the nozzle hole upstream from the gap and four nozzle holes downstream from the gap. The gap is space which is larger than nozzle holes, it is dressed at the middle of the nozzle hole. The bypass is holes, which is connected between upstream chamber correspond to sac chamber in actual Diesel injector and the gap. Roles of the bypass are to increase pressure in the gap from upstream chamber with high-pressure condition, and to give swirling flow to liquid flow in the gap. Roles of the gap are that pressure in the gap is increased by incoming from the bypass, and after collapse of cavitation bubbles at the nozzle hole upstream from the gap, generation of cavitation bubble nuclei. Where, nozzle internal flow at single hole nozzle is shown in Fig. 3. In general, in case a nozzle, which sharp inlet shape nozzle, was used, since with increases in injection pressure decreases in static pressure at inlet of the nozzle hole, and cavitation bubbles are generated. It has been researched that static pressure at there decreases near vapor pressure of the test liquid. When injection pressure increases more larger, cavitation bubbles collapse at vicinity of outlet of the nozzle hole, where static pressure in the nozzle hole improves from near vapor pressure, it is well known that considerably large disturbance occurs at there, issuing spray from the nozzle expands widely. Where, behavior of liquid flow and occurrence of cavitation in the nozzle of the atomization enhancement Inception of Cavitation Bubbles Collapse of Cavitation Bubbles P i MPa Hole Diameter : D=2.0 mm, L/D=4 Increasing of Injection Pressure Figure 3. Nozzle internal flow at single hole nozzle. nozzle and disintegration behavior of spray, and static pressure in the gap and the nozzle hole downstream from the gap as a function of injection pressure are shown in Figs. 4 and 5, respectively. It has been reported that the same phenomena take place on the atomization enhancement nozzle with the bypass and the gap at nozzle holes. As shown in Fig. 4, with increases in injection pressure, cavitation, that is, inception of cavitation bubbles, collapse of them take place at vicinity of the gap and inlet and outlet of nozzle holes upstream and downstream from the gap, spread of sprays becomes widely. As shown in Fig. 5, in case when injection pressure at measurement point B keeps constant of about atmospheric pressure, and one of A begins to increase Pressure in Nozzle Hole P n MPa P i MPa Nozzle-S, L 1 =3.0 mm, L 2 =3.0 mm, D=3.0 mm Figure 4. Photographs of liquid flow and occurrence of cavitation in nozzle of atomization enhancement nozzle and disintegration behavior of spray Nozzle-S L 1 =3.0 mm L 2 =3.0 mm D=φ3.0 mm P a =0.1 MPa With Bypass : Measurement Point A : Measurement Point B Atmospheric Pressure (0.1MPa) Vapor Pressure of Water at 293 K (2.3 kpa) A B Differential Injection Pressure Pressure of Injection P P i MPa i MPa Figure 5. Variations of static pressure in gap and nozzle hole downstream from gap as a function of injection pressure. 2

4 slightly. When injection pressure more increases up to occur cavitation in nozzle holes upstream and downstream from the gap (P i =0.32 MPa), with increases in injection pressure, increases in static pressure in the gap and decreases in static pressure in the nozzle hole downstream from the gap. On the basis of these backgrounds and results, the authors have contrived a new atomization enhancement nozzle, which spread of spray becomes wide significantly and Sauter mean diameter becomes small, which almost the same small droplet diameter as an actual Diesel spray under injection pressure of about 200 MPa. As a result, it was clarified that when the atomization enhancement nozzle with round inlet cutting was used, breakup length, that is, liquid core length becomes short about 20 p.c. and spray angle becomes large about two times, compared with the sharp inlet shapes of the nozzle hole. Moreover, when the nozzle, which inclined nozzle holes of the multi-hole nozzle from vicinity of center of the injection nozzle to outside of one, was used, breakup length becomes considerably short about 2 mm for hole number of four and hole diameter of 0.3 mm per one nozzle hole (correspond to one nozzle hole diameter of 0.6 mm), spread of spray becomes dramatically large and spray angle becomes considerably large about over 100 deg., Sauter mean diameter was obtained about 20 μm and spray characteristics was improved significantly compared with the previous actual multi-hole nozzle. Experimental Apparatus Schematic of experimental apparatus is shown in Fig. 6. Equipment consists of the high-pressure pump worked by the air compressor, two spark light sources for taking photographs of spray and apparatus for measurement of droplet size and its distributions LDSA particle analyzer. Estimation of measure of atomization of spray was used breakup length of liquid core, spray angle, Sauter mean diameter and droplet size distributions. Water at room temperature, which was pressurized by the high-pressure pump, was continuously injected under atmospheric pressure condition. Maximum injection pressure is P i =8 MPa for total sectional area of the multi-hole nozzle which is corresponded to sectional area of one nozzle hole by restriction of the continuous injection system, and experimental data is discussed at spray region that even though injection pressure is increased, breakup length and spray angle are almost constant. Disintegration behavior of spray was photographed by scattered light, using two stroboscopes. Breakup length of a liquid core, which is defined as distance from the nozzle exit to breakup point of liquid core, was measured by electrical resistance method [1] in which the screen detector was used. Breakup length was defined as liquid core length, which was injected from four nozzle holes. Measurement method and definition of breakup length of the multi-hole nozzle which spray was injected from vertical direction and from inclined angle of 45 deg. are shown in Fig. 7. Figure 7 (a) is in case direction of four nozzle holes are vertical injection direction, and (b) is in case direction of four Figure 6. Schematic of experimental apparatus. (a) In case direction of four nozzle holes are vertical injection direction. (b) In case direction of four nozzle holes are inclined 45 deg. toward vertical injection direction. Figure 7. Measurement method and definition of breakup length of multi-hole nozzle.

5 nozzle holes are inclined 45 deg. toward vertical injection direction. As shown in Fig. 7 (a), in case of the multi-hole nozzle, which sprays are injected vertically, breakup length was defined as previous method [1]. The multihole nozzle, which is injected vertically, sprays injected from each four nozzle holes are generated one spray. To the contrary, as shown in Fig. 7 (b), sprays are injected from each four nozzle holes like that the nozzle, which was shown in Fig. 7 (a). Since this nozzle has four nozzle holes with inclination angle of 45 deg., it is necessary to measure the liquid core length of each sprays along the spray injected with inclination angle. Breakup length L b of this nozzle was calculated by the following equation; L b = L m / cos θ. The disintegration behavior of spray was photographed by scattering light illumination method. Spray angle was defined as spray boundary, and it was measured by images of photographed sprays. Droplet size and its distributions were measured by a narrow angle forward scattering type LDSA particle analyzer at 120 mm downstream from the nozzle exit. It gives Sauter mean diameter that is spatially averaged along a line through the spray. Test Nozzles Schematic of structure of the atomization enhancement nozzle as mentioned before (Figure 2) and configuration of it by three dimensional image are shown in Figs. 8and 9, respectively. Structure of the atomization enhancement nozzle invented in the previous study is that the bypass, which is connected between the upstream chamber correspond to the sac chamber of the actual Diesel injector and the gap, which was made at middle of the nozzle hole. Swirling flow occurs in the gap by incoming from the bypass. Schematic of test nozzles is shown in Fig. 10, and configuration of atomization enhancement nozzle by three dimensional image is shown in Fig. 11. The test nozzles are the multi-hole nozzle, which is separated four nozzle holes to one nozzle hole at outlet of the nozzle hole. Figure 10 (a) shows the nozzle with sharp inlet shaped nozzle (called Nozzle-S). Figures 10 (b) and (c) show the nozzles, which was dressed with round inlet cutting at inlet or outlet of the multi-hole nozzle (called Nozzle-R di, R do, respectively). Figure 10 (d) shows new developed nozzle, which was inclined angle of 45 deg. at nozzle holes to injection direction (called Nozzle-I). Total sectional area of nozzle holes at the outlet of the nozzle hole is same values independent of geometric shapes of inlet and outlet of the nozzle hole. Test nozzles were used sectional area of the nozzle hole upstream from the gap equals total sectional areas of nozzle holes downstream from the gap A 2 mm 2 (A 1 = A 2 Correspond to Sac Chamber Bypass Nozzle Hole Upstream from Gap Gap Nozzle Holes Downstream from Gap (1) Nozzle Hole Upstream from Gap (2) Gap (Installed at Middle of Single Hole Nozzle) (3) Nozzle Holes Downstream from Gap Figure 8. Schematic of structure of atomization enhancement nozzle. (Reproduced from Fig.2) Nozzle Holes : Detail by 3D Image Nozzle Hole Bypass Upstream from Gap Gap Downstream from Gap Figure 9. Configuration of atomization enhancement nozzle by three dimensional image. mm 2 ), and total sectional areas of nozzle holes downstream from the gap A 2 is larger than sectional area of the nozzle hole upstream from the gap A 1 mm 2 (A 2 > A 1 mm 2 ). Results and Discussion Effects of Inlet and Outlet Shapes of Nozzle Hole Downstream from Gap on Atomization and Flow Characteristics The effects of inlet and outlet shapes of the nozzle hole downstream from the gap on dispersion of spray and disintegration behavior of spray are shown in Fig. 12. As shown in Fig. 12, spread of spray of Nozzle-R di, that is, the nozzle, which is dressed with round inlet cutting at inlet of the multi-hole nozzle, becomes largest compared with spread of sprays of Nozzle-S and Nozzle-R do. Effects of inlet and outlet shapes of the nozzle hole downstream from the gap on breakup length and spray angle are shown in Figs. 13 and 14, respectively. As shown in Fig.13, breakup length becomes short with an increase in injection pressure P i until about P i =6 MPa, independent of inlet and outlet shapes of the nozzle hole. When P i is over about P i =6 MPa, breakup

6 Nozzle-S, S Nozzle-S, R di One of test nozzle: Three dimensional 3D images Figure 11. Configuration of atomization enhancement nozzle by three dimensional 3D image. Nozzle-S, S (An example) Nozzle-S Nozzle-S, I : Part Nozzle-I Nozzle Types S, S S, R di S, R do Hole Number: N=4 Hole Diameter: D 1 =0.6 mm, D 2 =0.3 mm (N=4) Pitch Circle Diameter of Nozzle Hole: D p =3.0 mm Round Inlet Curvature: R=0.2 mm Injection Pressure: P i max. =8.0 MPa Figure 12. Effects of inlet and outlet shapes of nozzle hole downstream from gap on spread of spray and disintegration behavior of spray. (a) Nozzle-S, S (c) Nozzle-S, R do (b) Nozzle- S, R di (d) Nozzle-S, I Figure 10. Schematic of test nozzles and details of nozzle hole downstream from gap. length keep almost constant length with an increase in P i independent of inlet and outlet shapes of the nozzle hole. Breakup length of Nozzle-R di becomes shortest compared with Nozzle-S and Nozzle-R do at all injection pressure regions. As shown in Fig. 14, spray angle becomes large gradually with an increasing in injection pressure. When spray angle was compared at maximum injection pressure of P i =8 MPa, spray angle of Nozzle-R di becomes large about 60 p.c. compared with one of Nozzle-S. It can be seen that microscopic view point, breakup length and spray angle of Nozzle-R di become slightly

7 Breakup Length L b mm N=4, n=4, D b =0.2 mm, D bp =1.2 mm D 1 =0.6 mm, D g =4.0 mm D 2 =0.3 mm (N=4), D p =3.0 mm A 1 =A 2 mm 2 2 : Nozzle-S, S : Nozzle-S, R do : Nozzle-S, R di Injection Pressure P i MPa Figure 13. Effect of inlet and outlet shapes of nozzle hole downstream from gap on breakup length. Sauter Mean Diameter D 32 um N=4, n=4, D b =0.2 mm D 1 =0.6 mm, D g =4.0 mm D 2 =0.3 mm (N=4), D p =3.0 mm P i max. =8.0 MPa 10 S, S S, R di S, R do Nozzle Types Figure 15. Effect of inlet and outlet shapes of nozzle hole downstream from gap on Sauter mean diameter. Spray Angle S A deg N=4, n=4, D b =0.2 mm, D bp =1.2 mm D 1 =0.6 mm, D g =4.0 mm D 2 =0.3 mm (N=4), D p =3.0 mm A 1 =A 2 mm 2 30 : Nozzle-S, R di : Nozzle-S, R do : Nozzle-S, S Injection Pressure P i MPa Figure 14. Effect of inlet and outlet shapes of nozzle hole downstream from gap on spray angle. Volumetric Flow Rate Q cm 3 /s N=4, n=4, D b =0.2 mm, D bp =1.2 mm D 1 =0.6 mm, D g =4.0 mm D 2 =0.3 mm (N=4), D p =3.0 mm 10 : Nozzle-S, R About Half di : Nozzle-S, R do of P i max. : Nozzle-S, S Injection Pressure P i MPa Figure 16. Effect of inlet and outlet shapes of nozzle hole downstream from gap on volumetric flow rate. short and large, which were compared with ones of Nozzle-R do. Variations of injection pressure on Sauter mean diameter at 120 mm downstream from the nozzle is shown in Fig. 15. Sauter mean diameter becomes small monotonically with an increasing in injection pressure Sauter mean diameter is almost same values at arbitrary injection pressure independent of inlet and outlet shapes of the nozzle hole. Moreover, Sauter mean diameter of 20 μm order are obtained at maximum injection pressure of P i max. =8 MPa independent of inlet and outlet shapes of the nozzle hole. Thus, since breakup length and spray angle of Nozzle-R di are obtained excellent atomization characteristics, Sauter mean diameter is obtained almost same characteristics. It is guessed that measurement point of Sauter mean diameter separates from nozzle exit 120 mm, atomization of spray droplets are completed at measurement point independent of inlet and outlet of nozzle holes. Thus, since breakup length and spray angle of Nozzle-R di are obtained excellent atomization characteristics, Sauter mean diameter is obtained almost same characteristics. It is guessed that measurement point of Sauter mean diameter separates from nozzle exit 120 mm, atomization of spray droplets are completed at measurement point independent of inlet and outlet of nozzle holes. Effects of inlet and outlet shapes of the nozzle hole downstream from the gap on flow characteristics are shown in Fig. 16. As shown in Fig. 16, volumetric flow rate increases monotonically with an increasing in injection pressure and almost same volumetric flow rate compared with arbitrary injection pressure independent of inlet and outlet shapes of the nozzle hole. Volumetric flow rate of Nozzle-S, R di are largest at all injection pressure regions compared with Nozzle-S and Nozzle-S, R do. Moreover, volumetric flow rate of Nozzle-S, R di is obtained about 20 p.c. larger than Nozzle-S,S at all in-

8 jection pressure regions. In case of Nozzle-S, R di, volumetric flow rate of Nozzle-S at maximum injection pressure of P i max. =8 MPa is obtained at about half injection pressure of P i =4 MPa (P i =4.5 MPa), and flow characteristics is improved significantly. In general, when the nozzle, which was dressed with round inlet cutting at inlet of the nozzle hole, was used, it is well known that although volumetric flow rate is improved, atomization characteristics are getting worse with an increase in volumetric flow rate. Moreover, it is expected that although excellent atomization characteristics is obtained at low-injection pressure, volumetric flow rate at low-injection pressure becomes less than one of high-injection pressure. However, from these results, it can be seen that the nozzle, which was dressed with round inlet cutting at inlet of the nozzle hole, both atomization characteristics and flow characteristics are improved significantly. From these results, it was cleared that Nozzle-R di, which was dressed with round inlet cutting at inlet of the nozzle hole, was used, both spray characteristics and flow characteristics are improved. The reasons are considered as follows. Schematics of liquid flow in nozzle holes and the gap with cavitation and swirling flow; effects of geometric shapes of the nozzle hole downstream from the gap are shown in Fig. 17. Except of inlet shape of the nozzle hole structures of the atomization enhancement nozzle are same. It is guessed that in case of Nozzle-S, R di, liquid flow with large disturbance of occurrence of cavitation and strong swirling flow in the gap are easy to come into the nozzle hole downstream from the gap compared with Nozzle-S, S. Therefore, it is considered that strong disturbance with swirling flow hardly reduces at there, issuing spray dispersed to radial direction. Effect of Existence of Inclination Angle of Nozzle Hole Downstream from Gap on Spray Characteristics In order to more disperse spray and droplet of spray, the nozzle, which was inclined angle of 45 deg. at the nozzle hole to injection direction (Nozzle-S, I) and consists of atomization enhancement element, was used. In case of Nozzle-S, I, considerably excellent spray characteristics were obtained comparing with ones of Nozzle-S, R di that excellent spray characteristics were obtained as the facts above-mentioned. The effect of existence of inclination angle of nozzle hole on disintegration behavior of spray and dispersion of spray is shown in Fig. 18. As shown in Fig. 18, although spray of Nozzle-S, I exists a few of heterogeneous regions, spread of spray becomes large dramatically and it is obtained solid cone spray. In spite sprays are injected from the nozzle hole, which is divided one nozzle hole into four small nozzle holes, the spray dispersed considerably wide like that an actual multi-hole Diesel injection nozzle, for instance, hole numbers of four. The effects of existence of inclination angle of the nozzle hole downstream from the gap on breakup length at the maximum injection pressure of P i max. =8 (a) Nozzle-S, S Nozzle Types S, S S, I (b) Nozzle-S, R di Figure 17. Schematics of liquid flow in nozzle holes and gap with cavitation and swirling flow. and generation (Effects of swirling of geometric flow shapes in the of gap nozzle are almost hole same phenomena. downstream from gap.) Hole Number: N=4 Hole Diameter: D 1 =0.6 mm, D 2 =0.3 mm (N=4) Pitch Circle Diameter of Nozzle Hole: D p =3.0 mm Inclination Angle of Nozzle Hole: 45 deg. Injection Pressure: P i max. =8.0 MPa Figure 18. Effects of existence of inclination angle of nozzle hole on disintegration behavior of spray and dispersion of spray.

9 MPa and spray angle are shown in Figs. 19 and 20, respectively. As shown in Fig. 19, breakup length of Nozzle-S, I becomes short about 30 p.c. compared with one of Nozzle-S, R di. As shown in Fig. 20, spray angle becomes slightly large until about injection pressure of about P i =6 MPa at Nozzle-S, R di and Nozzle-S, I. When injection pressure increases over about P i =6 MPa, variations of spray angle are almost the same tendency as variation of breakup length, and even though injection pressure more increases, spray angle becomes almost constant until maximum injection pressure of P i max. =8 MPa. When spray angle was compared at maximum injection pressure of P i max. =8 MPa, spray angle of Nozzle-S, I becomes large dramatically and it becomes large about three times lather than one of Nozzle-S, R di, and it becomes over 100 deg. The developed nozzle with inclination angle of nozzle holes in this study of Nozzle-S, I, which was separated one nozzle hole from four small nozzle holes Breakup Length L b mm Spray Angle S A deg N=4, n=4, D b =0.2 mm, D bp =1.2 mm D 1 =0.6 mm, D g =3.6 mm D 2 =0.3 mm (N=4), D p =3.0 mm D pu =2.4 mm, D pd =3.0 mm, P i =8.0 MPa Nozzle-S, S Nozzle-S, I Nozzle Types Figure 19. Effects of existence of inclination angle on breakup length (P i max. =8 MPa) N=4, n=4, D b =0.2 mm, D bp =1.2 mm D 1 =0.6 mm, D g =3.6 mm, D 2 =0.3 mm (N=4) D p =3.0 mm, D pu =2.4 mm, D pd =3.0 mm Nozzle-S, I Nozzle-S, S Injection Pressure P i MPa Figure 20. Effects of existence of inclination angle on spray angle. at the same sectional area of nozzle holes, considerably large spray angle was obtained compared with the actual multi-hole Diesel injection nozzle. Conclusions (1) Spread of spray of Nozzle-S, R di (with round inlet cutting of multi-hole nozzle) becomes largest compared with Nozzle-S, S (sharp inlet shape nozzle) and Nozzle-S, R do (with round outlet cutting of multi-hole nozzle). (2) Breakup length of Nozzle-S, R di is the shortest compared with Nozzle-S, S and Nozzle-S, R do, spray angle of Nozzle-S, R di becomes large about 60 p.c. compared with one of Nozzle-S, S. (3) Sauter mean diameter is obtained almost same values of 20 μm order, and droplet size distribution, frequency of arbitrary droplet size and frequency of minimum and maximum size droplets diameter are almost same values at maximum injection pressure of P i =8 MPa independent of inlet and outlet shapes of the nozzle hole. (4) Volumetric flow rate of Nozzle-S, R di are largest at all injection pressure regions compared with Nozzle-S, S and Nozzle-S, R do. (5) Nozzle-S, R di is able to improve spray characteristics and flow characteristics. (6) When spray angle was compared at maximum injection pressure of P i =8 MPa, spray angle of Nozzle-I becomes large dramatically and it becomes large about three times compared with Nozzle-R di. Acknowledgements This work was partly supported by Japan Society for the Promotion of Science (JSPS) KAKENHI (C) Grant Number Moreover, this research was partly supported by the Ministry of Education, Culture, Sports, Science and Technology (MEWT) MEXT- Supported Program for the Strategic Research Foundation at Private Universities. The authors wish to express their thanks for supporting this research. Nomenclature A 1 Sectional area of nozzle hole upstream from gap A 2 Total sectional area of nozzle hole downstream from gap D Hole diameter D 1 Hole diameter upstream from gap D 2 Hole diameter downstream from gap D 32 Sauter mean diameter D b Bypass diameter D bp Pitch circle diameter of bypass D g Gap diameter D p Pitch circle diameter of nozzle hole downstream from gap

10 D bd D pu D u I L L 1 L 2 L b L g L m L/D n N P a P i P i max. P n Q R di R do S S A θ Outlet pitch circle diameter of nozzle hole downstream from gap Inlet pitch circle diameter of nozzle hole downstream from gap Upstream chamber diameter Inclination Hole length Hole length upstream from gap Hole length downstream from gap Breakup length which was defined in this study Gap length Breakup length for spray of injection axis direction at nozzle with inclination angle (Nozzle-S, I) Ratio of hole length to hole diameter Bypass number Hole number Ambient pressure Injection pressure Maximum injection pressure Pressure in nozzle hole Volumetric flow rate Inlet shape of nozzle hole downstream from gap Outlet shape of nozzle hole downstream from gap Sharp edged nozzle Spray angle Inclination angle of nozzle hole Superscripts 1 Upstream 2 Downstream 32 Volume / Surface Area a Ambient A Angle b Bypass bp Pitch circle diameter of bypass di Inlet shape of nozzle hole do Outlet shape of nozzle hole g Gap i Injection i max. m n pd pu u Maximum injection pressure Breakup length for spray of injection axis direction at nozzle with inclination angle (Nozzle-S, I) Nozzle hole (Within gap and nozzle hole) Outlet pitch circle diameter of nozzle hole Inlet pitch circle diameter of nozzle hole Upstream References 1. Hiroyasu, H., Arai, M. and Shimizu, M., Break-up Length of a Liquid Jet and Internal Flow in a Nozzle, Proceedings Fifth International Conference on Liquid Atomization and Spray Systems ICLASS 1991, Wasinton DC, United States of America, July, 1991, pp Chaves, H, Knapp, M., Kubitzek, A., Obermeier, F. and Schneider, T., Experimental Study of Cavitation in the Nozzle Hole of Diesel Injectors Using Transparent Nozzles, SAE Technical Paper: No , (1995). 3. Tamaki, N., Nishida, K., Shimizu, M. and Hiroyasu, H., Effects of Cavitation and Internal Flow on Atomization of a Liquid Jet, Atomization and Sprays: Vol. 8, No. 2, (1998). 4. Arcoumanis, C. and Gavaises, M., Cavitation in Diesel Injectors: Modeling and Experiment, Proceedings Fourteenth Institute for Liquid Atomization and Spray Systems-Europe, Manchester, England, July, 1998, pp Tamaki, N., Shimizu, M. and Hiroyasu, H., Enhancement of the Atomization of a Liquid Jet by Cavitation in a Nozzle Hole, Atomization and Sprays: Vol. 11, No.2, (2001). 6. Tamaki, N., Effects of Cavitation in a Nozzle Hole on Atomization of Spray and Development of High- Efficiency Atomization Enhancement Nozzle, Proceedings 11th Internal Conference on Liquid Atomization and Spray Systems ICLASS 2009, Vail, Colorado, United States of America, July, 2009, CD-R, 6 pages. 7. Tamaki, N., Kato, A., Kato, K. and Imano, K., Improvement of Atomization Characteristics of Spray by Multi-Hole Nozzle for Pressure Atomized Type Injector, Proceedings 23rd Institute for Liquid Atomization and Spray Systems-Europe, Brno, Czech Republic, September, 2010, CD-R, 7 pages.