Paper ID ICLASS6-171 Spray and Mixture Properties of Group-Hole Nozzle for D.I. Diesel Engines Keiya Nishida 1, Shinsuke Nomura 2 and Yuhei, Matsumoto 3 ICLASS-26 Aug.27-Sept.1, 26, Kyoto, Japan 1 Assosiate Professor, Graduate School of Engineering, University of Hiroshima, nishida@hiroshima-u.ac.jp 2 Alumni, Shikoku Electric Power Company, nomura11412@yonden.co.jp 3 Graduate Student, Graduate School of Engineering, University of Hiroshima, yuhmatsu@hiroshima-u.ac.jp ABSTRACT Reducing nozzle hole size is of advantage for the atomization and evaporation of the fuel spray in a D.I. Diesel engine. However the hole diameter reduction is usually accompanied with a decrease in the spray tip penetration, thus worsening the fuel spatial distribution and fuel air mixing. In this paper, the group hole nozzle concept, which solves the problem resulting from the reduction of the hole diameter, is examined. Compared to the conventional multi hole nozzle, the group hole nozzle has a series of group of holes, and each group consists of two small holes with a small spatial interval and a small angle. The spray was injected into a high pressure and high temperature nitrogen gas in a constant volume vessel by a common rail injection system. The spray and mixture properties of the group hole nozzle were investigated by the ultraviolet and visible Laser Absorption Scattering (LAS) technique as well as the high speed schliren video imaging, and compared with those of the single hole nozzle with the same total cross sectional area of the injection hole(s). Key Words: Fuel Spray, Diesel Engine, Mixture Property, Group Hole Nozzle, Laser Diagnostics, Laser Absorption Scattering Technique 1. INTRODUCTION Using a nozzle with small holes together with high injection pressure facilitates better fuel atomization and evaporation, thus reducing the particulate emission formed in a D.I. Diesel engines [1]. However, the spray properties usually change so that the spray tip penetration is weakened as the hole diameter decreases, usually resulting in poor spatial distribution of the fuel [2]. For meeting the demand in order that the reduction of the nozzle hole diameter does not adversely affect the spray tip penetration and spatial distribution of the fuel, the concept of the group hole nozzle was proposed by Denso corporation [3]. Compared to the conventional multi hole nozzle, the difference is that the group hole nozzle has a series group of holes, and each group consists of two small holes which were very closely located and parallel to each other, or with a small diverging or converging angle between two holes. It is expected that the reduction of nozzle hole size improves the fuel atomization and evaporation. In addition, the very closely located holes induces the spray to spray interaction and affects the ambient gas entrainment into the spray. Such spray dynamics can help to hold the spray momentum and maintain the spray tip penetration. In this study, for examining the spray and mixture properties of the group hole nozzle, the ultraviolet and visible Laser Absorption Scattering (LAS) imaging technique [4, ] as well as the high speed schlieren video imaging were adopted to determine liquid and vapor phase concentration distributions as well as the spray tip penetration and the spray angle. The mixture properties, such as mass of ambient gas entrained, mass of fuel vapor and mean equivalence ratio, were obtained using the LAS measurements. It is demonstrated in the paper that how the group hole concept compensates the spray tip penetration comparing to the single hole nozzle having the equivalent cross sectional area, how the spray angle changes, and to what degree the ambient gas entrainment and fuel evaporation are affected. 2. EXPERIMENTAL APPARATUS AND PROCEDURES Investigation of the spray and mixture properties of the group hole nozzle and the conventional single hole nozzle were implemented by using the ultraviolet and visible LAS technique as well as commonly used high speed schlieren video imaging. The LAS technique is an in-house quantitative diagnostic and can simultaneously provide two-dimensinal concentration distributions of the vapor and liquid phases in a Diesel like fuel spray [4, ]. Fig.1 Experimental Apparatus
The LAS optical system together with the constant volume vessel and the fuel injection system are shown in Fig. 1. A pulsed Nd:YAG laser radiates second harmonic visible light (32nm) and the fourth harmonic ultraviolet light (266nm) simultaneously. After being collimated by the beam expander and made coaxial, the beams were directed to the fuel spray, which was injected by a common rail injection system into a constant volume vessel filled with a high pressure and high temperature nitrogen gas. After being attenuated by the spray, the beam was separated into two wavelengths, and the two beams were focused to the CCD tips in the cameras, that is, the incident light extinction images of the fuel spray at 32nm and 266nm were taken by the CCD cameras. The image data were forwarded to the computers for the LAS image processing. Dimethylnaphthalene (DMN) was used as an LAS test fuel simulating the Diesel fuel, which has the physical properties similar to the Diesel fuel and strongly absorbs the 266nm ultraviolet light and does not absorb the 32nm visible light. According to the Lambert-Beer s law, at the 266nm absorbing wavelength, totaling the optical thickness due to vapor absorption and the optical thickness due to droplet scattering gives the total optical thickness of the DMN spray measured by the CCD camera. While, at the 32nm non-absorbing wavelength, the optical thickness due to droplet scattering alone equals the total optical thickness of the DMN spray measured by the CCD camera. It has been proven experimentally that the optical thickness of droplets at the two wavelengths is nearly identical in the DMN spray[4]. Therefore, the vapor optical thickness can be obtained by subtracting the optical thickness at 32nm from the optical thickness at 266nm. The concentration distribution of the vapor phase is deduced by the LAS image processing of the vapor optical thickness, and the liquid phase by the optical thickness at 32nm due only to the droplet scattering. For the shot to shot spray variation, the LAS image processing was made using the average of eight spray images under the same experimental condition. 3. NOZZLE SPECIFICATIONS AND EXPERIMENTAL CONDITIONS The schematic structures of the group hole nozzle and the single hole nozzle used in this study are shown in Fig. 2. These nozzles are to simulate the fuel spray injected from one of the multi holes and one group hole of the multi group holes. The nozzle specifications are listed in Table 1. The nozzle SH/.16-1.2 identifies the single hole nozzle having the hole diameter D=.16mm and the length L=1.2mm, which was used for the reference. The group hole nozzle DH/.113-1.2-deg indicates the dual hole, each hole diameter D 1 =D 2 =.113mm, the hole length L=1.2mm and the angle between two holes α=deg. The total cross sectional area of two holes is the same as the reference holes α of the group hole nozzle is changed to +deg., + deg., single hole nozzle SH/.16-1.2. An angle between two holes α of the group hole nozzle was changed to +deg., +deg., which are called as the diverging group hole, and deg., deg. called as the converging group hole. The interval (wall thickness) between two holes is B=.287mm at the hole inlet, kept constant for all nozzles. SH/.113-1.2 is the single hole (a) Single-Hole Nozzle (b) Group-Hole Nozzle Fig.2 Nozzle Structures Table 1 Nozzle Specifications Table 2 Orifice Diameter D 1 mm Orifice Diameter D 2 mm Length L mm Interval B mm Experimental Conditions Angle Between Orifice α deg. SH/.113-1.2.113-1.2 - - SH-.16-1.2.16-1.2 - - DH/.113-1.2-().113.113 1.2.287 DH/.113-1.2-(+).113.113 1.2.287 DH/.113-1.2-(+).113.113 1.2.287 DH/.113-1.2-(-).113.113 1.2.287 - DH/.113-1.2-(-).113.113 1.2.287 - Ambient Gas Ambient Temperature Ta, K 833 Ambient Pressure P a, MPa 4. Test Fuel Fuel Injection System Injection Pressure P inj, MPa 9 Injection Duration t inj, ms.8 Injection Mass M inj, mg Nitrogen Laser Shot Timing t s, ms ASOI.8, 1. 1.,3-Dimethylnaphthalence Common Rail Type SH/.113-1.2 2.98 SH/.16-1.2 6.2 DH/.113-1.2-().27 DH/.113-1.2-(+) - DH/.113-1.2-(+) - DH/.113-1.2-(-). DH/.113-1.2-(-).6 nozzle having the hole diameter D 1 =.113mm same as one of two holes of the group hole nozzle. This nozzle was prepared to investigate the effect of interaction between two sprays of the group hole nozzle on the spray and mixture properties, for example, to what degree the spray tip penetration of the group hole nozzle is increased comparing with the single hole nozzle SH/.113-1.2. Experimental conditions are shown in Table 2. The ambient gas is nitrogen whose temperature 833K and pressure 4.MPa are set as the ambient air condition at the fuel injection timing of the actual running engine. Dimethylnaphthalene is the LAS test fuel and was injected
by the common rail injection system at the injection pressure 9MPa. Injection duration was set to.8ms for all nozzles, consequently mass of fuel injected was slightly varied from.27mg to 6.2mg for the DH/.113 series group hole nozzles and the SH/.16 single hole nozzle. The mass of fuel injected for the SH/.113 single hole nozzle is 2.98mg, about the half of that of the SH/.16 single hole nozzle. Laser shot timing for the LAS measurement is.8ms after the start of injection (ASOI) which is.ms prior to the end of injection (EOI), and 1.ms ASOI which is.6ms after EOI. 4. RESULTS AND DISCUSSION 4.1 Spray Shape The spray shapes at 1.ms ASOI, which were taken as the optical thickness (incident light extinction, shadow) images in the LAS experiment, are shown in Figs. 3 and 4 (a) SH/.16-1.2 (b) SH/.113-1.2 Fig.3 Spray Shapes of Single Hole Nozzles at 1. ms ASOI for the single hole nozzles and the group hole nozzles, respectively. The spray area in each figure is colored in white as the high optical thickness, and the surrounding gas area is colored in black. The sprays for all single and group hole nozzles have rough, uneven and complicated boundaries, which are supposedly induced by puffing of fuel vapor clouds. Looking at the spray shapes for the single hole nozzles in Fig. 3, the SH/.16-1.2 nozzle has larger spray tip penetration than the SH/.113-1.2 nozzle. As shown in Fig. 4, the spray shapes of the DH/.113-1.2-(deg) group hole nozzle and the converging group hole nozzles, DH/.113-1.2-(-deg) and DH/.113-1.2-(-deg), are very similar to the SH/.16-1.2 single hole nozzle. However, the spray shapes of the diverging group hole nozzles, DH/.113-1.2-(+deg) and DH/.113-1.2-(+deg), are quite different from the others. As an angle between two holes increases, the spray penetrates less further and disperses widely. 4.2 Spray Properties Spray Tip Penetration The spray tip penetration was measured by the high speed schlieren video imaging. The results are shown in Figs. (a) and (b). The parallel group hole nozzle, DH/.113-1.2-(deg) shown in Fig. (a), has a little smaller but very close penetration comparing with the reference single hole nozzle, SH/.16-1.2, and much larger than the single hole nozzle, SH/.113-1.2. On the contrary, the diverging group hole nozzle, DH/.113-1.2-(+deg), has much smaller penetration than the reference single hole nozzle, SH/.16-1.2, which is almost same as the single hole nozzle, SH/.113-1.2. This may indicates that the degree diverging angle between two holes makes the penetrating dynamics of each spray independent. The spray tip penetration of the group hole nozzle with deg. diverging angle, DH/.113-1.2-(+deg) is in between the parallel group hole nozzle, DH/.113-1.2-(deg) and the diverging group hole nozzle, DH/.113-1.2-(+deg). The converging group hole nozzle, DH/.113-1.2-(-deg) shown in Fig. (b), has a little smaller but very close (a) DH/.113-1.2 (b) DH/.113-1.2 (c) DH/.113-1.2 (d) DH/.113-1.2 (e) DH/.113-1.2 -(deg) -(+deg) -(+deg) -(-deg) -(-deg) Fig.4 Spray Shapes of Group Hole Nozzles at 1. ms ASOI
Spray Tip Penetration S v (mm) Spray Tip Penetration S v (mm) 9 8 7 6 4 3 SH/.16-1.2 2 SH/.113-1.2 DH/.113-1.2-(deg) DH/.113-1.2-(+deg) DH/.113-1.2-(+deg).. 1. 1. 2. (a) Converging and Parallel Group Hole Nozzles and Single Hole Nozzles 9 8 7 6 4 3 2 DH/.113-1.2-(deg) DH/.113-1.2-(-deg) DH/.113-1.2-(-deg).. 1. 1. 2. (b) Diverging and Parallel Group Hole Nozzles and Single Hole Nozzles Fig. Spray Tip Penetration Spray Angle (deg.) Spray Angle (deg.) 3 3 2 2 1.. 1. 1. 2. (a) Converging and Parallel Group Hole Nozzles and Single Hole Nozzles 3 3 2 2 1 SH/.16-1.2 SH/.113-1.2 DH/.113-1.2-(deg) (Vertical) DH/.113-1.2-(deg) (Parallel) DH/.113-1.2-(+deg) (Vertical) DH/.113-1.2-(+deg) (Parallel) DH/.113-1.2-(deg) (Vertical) DH/.113-1.2-(deg) (Parallel) DH/.113-1.2-(-deg) (Vertical) DH/.113-1.2-(-deg) (Parallel).. 1. 1. 2. (b) Diverging and Parallel Group Hole Nozzles and Single Hole Nozzles Fig. 7 Spray Angles 3 Fig.6 (a) Vertical (b) Parallel View Directions of Group Hole Nozzle penetration comparing with the parallel group hole nozzle, DH/.113-1.2-(deg). Spray Angle The spray angle was defined as an angle between two lines connecting the nozzle tip and two (right and left) spray boundaries 2 mm apart from the nozzle tip. However, different from the single hole nozzle, the group hole nozzle is geometrically non-axisymmetric, that is, there are two view directions. As shown in Fig. 6, if the incident light comes from a direction vertical to the plane formed by the axes of two holes (group hole plane), the view direction is called Vertical in this study. Similarly, if the incident light comes from a direction parallel to the Spray Angle (Vertical) (deg.) 2 2 1 Measured Estimated DH.113-1.2-1 2 3 DH.113-1.2-4 6 DH.113-1.2-7 8 Fig. 8 Spray Angles for Group Hole Nozzles: Measured and Estimated from Single Hole Nozzle group hole plane, it is called Parallel. The vertical and parallel spray angles of the group hole nozzle, DH/.113-1.2-(deg) shown in Fig. 7 (a), are almost same with each other, therefore the spray of the parallel group hole nozzle can be assumed as axisymmetric. The parallel group hole nozzle, DH/.113-1.2-(deg), has the
spray angle very similar to the single hole nozzle, SH/.16-1.2. On the contrary, in the case of the diverging group hole nozzle, DH/.113-1.2-(+deg) in Fig. 7 (b), the vertical spray angle is much larger than the parallel spray angle. The parallel spray angle of the diverging group hole nozzle, DH/.113-1.2-(+deg), is very similar to the spray angle of the single hole nozzle, SH/.16-1.2. As shown in Fig. 7 (a), the spray angle of the single hole nozzle, SH/.113-1.2, is smaller than that of the single hole nozzle, SH/.16-1.2. The vertical spray angles of the diverging group hole nozzles were estimated by summing the spray angle of the single hole nozzle, SH/.113-1.2, and the angle between two holes. The vertical spray angle estimated by the above is the geometrical spray angle which does not include the interaction between the sprays from two holes. Comparisons of the vertical spray angle between the above estimation and the measurement are shown in Fig. 8. The measured vertical spray angles for the diverging angle degree to degree are smaller than (a) t s =.8ms ASOI (b) t s =1.ms ASOI Fig. 9 Equivalence Ratio Distributions of Liquid and Vapor Phases of Converging and Parallel Group Hole Nozzles and Single Hole Nozzle
the estimated ones. This implies that there is an interaction between two fuel jets from the group hole nozzle, where one fuel jet draws or entrains the other. The vertical and parallel spray angles of the converging group hole nozzle, DH/.113-1.2-(-deg) shown in Fig. 7 (b), are almost same with each other, therefore the spray of the converging group hole nozzle can be assumed as axisymmetric. The spray angle of the converging group hole nozzle, DH/.113-1.2-(-deg), is a little larger than the parallel group hole nozzle, DH/.113-1.2-(deg). This is supposedly due to more intense interaction between the fuel jets from two holes for the converging group hole nozzle than the parallel group hole nozzle. 4.3 Mixture Properties Liquid and Vapor Phase Equivalence Ratio Distributions The LAS image processing for obtaining the quantitative fuel concentration distributions in the spray requires the assumption of the axisymmetiry of the spray. Thus the optical thickness images of the sprays of the single hole nozzle, SH/.16-1.2 shown in Fig. 3, and the parallel and converging group hole nozzles, DH/.113-1.2-(deg), DH/.113-1.2-(-deg) and DH/.113-1.2-(-deg) shown in Fig. 4, which can be assumed to be axisymmetric, were analyzed. Figs. 9 (a) and (b) show the equivalence ratio distributions (contour maps) of the liquid and vapor phases in the cross section of the spray at t=.8ms and 1.ms ASOI, respectively. Each equivalence ratio distribution consists of the liquid phase (left) and the vapor phase (right). As t=.8ms ASOI is.ms prior to the end of injection (EOI), in the case of the single hole nozzle, SH/.16-1.2 for example, the liquid phase area with an equivalence ratio higher than 2. (colored in black) is seen around the spray axis from the vicinity of the nozzle to the middle of the spray. The vapor phase area with an equivalence ratio around.1 (colored in red) starts at the axial distance around 18mm from the nozzle and envelopes the liquid areas along the spray axis. Comparing with the single hole nozzle,sh/.16-1.2 described in the above, all group hole nozzles, DH/.113-1.2-(deg), DH/.113-1.2-(-deg) anddh/.113-1.2-(-deg), shortens the penetration of the liquid phase area with an equivalence ratio higher than 2. and the distance where the vapor phase area with an equivalence ratio around.1 starts. The shapes of the spray tips for the group hole nozzles are a little sharper than the single hole nozzle. There is not distinct differences in the liquid and vapor phase equivalence ratio distributions among the group hole nozzles, though the tip penetration decreases as an angle between two holes increases. At t=1.ms ASOI,.6ms after EOI as shown in Fig. 9 (b), the fuel evaporation proceeds, the liquid phase area decreases and the vapor phase area increases. The mixture properties over the entire spray, such as mass of ambient gas entrained, mass of fuel vapor and mean equivalence ratio, were deduced from Fig. 9 and are shown in the next section. Sauter Mean Diameter The LAS image processing of the evaporating fuel spray provides the sauter mean diameter (SMD). The SMDs of the spray at t=.8ms ASOI (.ms before EOI) are shown in Fig. for the single hole nozzles, SH/.16-1.2 and SH/.113-1.2, and the parallel and converging group hole nozzles, DH/.113-1.2-(deg), DH/.113-1.2-(-deg) and Sauter Mean Diameter D32 (μm) DH/.113-1.2-(-deg). The SMDs for the conversing group hole nozzle are smaller than that for the single hole nozzle, SH/.16-1.2, which has the cross sectional are of the hole same as the group hole nozzles. However, these group hole nozzles, SMDs are larger than that for the single hole nozzle, SH/.113-1.2, whose hole diameter is the same as one of the holes of the group hole nozzle. The group hole nozzle has a positive effect for decreasing the SMD comparing with the single hole nozzle with the single hole nozzle with the same cross sectional area of hole(s). On the contrary, the group hole nozzle has a negative effect for increasing the SMD comparing with the single hole nozzle whose diameter is same as one of the group holes. This is supposed by due to the interference effect (coalescence of droplets) between two jets from the group holes. Mass of Ambient Gas Entrained Fig. 11 shows temporal variations of the mass of ambient gas entrained into the spray for the single hole nozzle, SH/.16-1.2 and the parallel and converging group hole nozzles, DH/.113-1.2-(deg), DH/.113-1.2-(-deg) and 4 4 3 3 2 2 1 Ratio of Entrained Ambient Gas to Total Fuel M a /M f SH/.16 1 SH/.113 2 DH/.113 3 DH/.113 4 DH/.113-1.2-1.2-1.2-1.2-1.2 -(deg) -(-deg) -(-deg) 4 4 3 3 2 2 t=.8ms ASOI Fig. Sauter Mean Diameter for Converging and Parallel Group Hole Nozzles and Single Hole Nozzle at t=.8ms ASOI 1 SH/.16-1.2 DH/.113-1.2-(deg) DH/.113-1.2-(-deg) DH/.113-1.2-(-deg). 1. 1. Fig. 11 Mass of Ambient Gas M a Entrained to in Spray for Converging and Parallel Group Hole Nozzles and Single Hole Nozzle (A ratio of M a to total fuel in the spray M f is taken as the ordinate)
DH/.113-1.2-(-deg). Since there is a variation of the mass of fuel injected, in other words, the injection rate among the nozzles, as shown in Table 2, a ratio of the mass of ambient gas entrained to the mass of total (liquid and vapor phases) fuel in the spray, M a /M f, is adopted as an ordinate in order to clarify the ability of the nozzle in terms of the ambient gas entrainment into the spray. M a /M f for the parallel group hole nozzle, DH/.113-1.2-(deg), is larger than for the single hole nozzle, SH/.16-1.2. Among the group hole nozzles, M a /M f increases as an angle between two holes decreases. The difference between the group hole nozzles and the single hole nozzle becomes smaller as time proceeds. Mass of Fuel Vapor Fig. 12 shows temporal variations of the mass of fuel vapor in the spray. The ordinate is a ratio of the mass of fuel vapor to the total (liquid and vapor phases) fuel, M fv /M f, which is the similar manner to Fig. 11. M fv /M f for the parallel group hole nozzle, DH/.113-1.2-(deg), is larger than the single hole nozzle, SH/.16-1.2, and the diverging group hole nozzles are between them. It can be concluded that the parallel and converging group hole nozzles enhances the ambient gas entrainment into the spray and consequently promotes the fuel evaporation. Mean Equivalence Ratio Fig. 13 shows a mean equivalence ratio calculated by the mass of total (liquid and vapor phases) fuel and the mass of ambient gas entrained in the spray. At t=.8ms ASOI, a mean equivalence ratio varies among the nozzles due to the difference in the mass of fuel injected, in other words, the injection rate. However at t=1.ms ASOI, the all nozzles takes the similar mean equivalence ratio since the group hole effect, that is, the increase in the ambient gas entrained and the increase in the fuel vapor are compensated. Analysis of Group Hole Nozzle Effect using Single Hole Nozzle SH/.113-1.2 Result Two times of the mass of ambient gas entrained and two times of the mass of fuel vapor of the single hole nozzle, SH/.113-1.2, are considered to be the mixture properties which the group hole nozzle shows if there is not any effect of the interaction between the fuel jets from two holes. The comparisons of the mass of ambient gas entrained and the Equivalence Ratio of Total Fuel φ V+L Ratio of Entrained Ambient Gas to Total Fuel M a /M f 1..9.8.7.6..4.3.2.1 4 4 3 3 2 2 1 SH/.16-1.2 DH/.113-1.2-(deg) DH/.113-1.2-(-deg) DH/.113-1.2-(-deg).. 1. 1. Fig. 13 Mean Equivalence Ratio of Total Fuel (Vapor and Liquid Phases) for Converging and Parallel Group Hole Nozzles and Single Hole Nozzle SH/.113-1.2 (Estimated) DH/.113-1.2-(deg) DH/.113-1.2-(-deg) DH/.113-1.2-(-deg). 1. 1. Fig. 14 Mass of Ambient Gas Entrained in Spray for Group Hole Nozzles: Measured and Estimated from Single Hole Nozzle (A ratio of M a to total fuel in the spray M f is taken as the ordinate).6..4.3.2.1.. 1. 1. Fig. 12 Ratio of Mass of Fuel Vapor to Total Fuel in Spray for Converging and Parallel Group Hole Nozzles and Single Hole Nozzle Ratio of Fuel Vapor to Total Fuel M fv /M f.7 SH/.16-1.2 DH/.113-1.2-(deg) DH/.113-1.2-(-deg) DH/.113-1.2-(-deg).6..4.3.2.1.. 1. 1. Ratio of Fuel Vapor to Total Fuel M fv /M f.7 SH/.113-1.2 (Estimated) DH/.113-1.2-(deg) DH/.113-1.2-(-deg) DH/.113-1.2-(-deg) Fig. 1 Ratio of Mass of Fuel Vapor to Total Fuel in Spray for Group Hole Nozzle: Measured and Estimated from Single Hole Nozzle
mass of fuel vapor are shown in Figs. 14 and 1, respectively. The two times of the mass of mixture properties of the single hole nozzle, SH/.113-1.2, is expressed by 2x SH/.113-1.2. As shown in these figures, the mass of ambient gas entrained and the mass of fuel vapor for the group hole nozzles is smaller than the mass of 2x SH/.113-1.2. It can be concluded that, as compared with the single hole nozzle, SH/.113-1.2, the interaction between the fuel jets from two holes of the group hole nozzle has the effect of suppression of the ambient gas entrainment and fuel evaporation, though it has the effect of enhancement of the spray tip penetration.. CONCLUSIONS The group hole nozzle concept for the D.I. Diesel engine applications was examined experimentally in terms of the spray and mixture properties. The group hole nozzle used in this study has two small holes with a small spatial interval and a small angle. The single hole nozzle which has the same cross sectional area as the group hole nozzlewas also used for the comparison. The spray was injected into a high pressure and high temperature nitrogen gas in a constant volume vessel by a common rail injection system. The ultraviolet and visible Laser Absorption Scattering (LAS) imaging technique as well as the high speed schlieren video imaging were adopted to determine liquid and vapor phase concentration distributions as well as the spray tip penetration and the spray angle. Main results obtained in this study are summarized as follows. (1) The group hole nozzle with two parallel holes ( deg. angle between two holes) has slightly less spray tip penetration, greater mass of ambient gas entrained and more mass of fuel vapor compared to the single hole nozzle under the same total cross sectional area of the injection hole(s). (2) The group hole nozzle with a converging angle between two holes has the effect similar to the group hole nozzle with two parallel holes on the spray and mixture properties, that is, slightly less spray tip penetration, greater mass of ambient gas entrained and more mass of fuel vapor than the single hole nozzle with the same total cross sectional area of the injection holes, though they decreased as the converging angle between two holes increases. (3) The mass of ambient gas entrained and the mass of fuel vapor in the spray of the group hole nozzle with parallel holes and converging holes are a little smaller than the two times of the mass measured for the single hole nozzle whose diameter is the same as one of the group holes. It can be considered that the interaction between the fuel jets from two holes of the group hole nozzle has the effect of suppression of the ambient gas entrainment and fuel evaporation, though it has the effect of enhancement of the spray tip penetration as described in the above (1) and (2). (4) The group hole nozzle with a diverging angle between two holes shows spray behaviors quite different from the single hole nozzle. The spray tip penetration of the group hole nozzle is smaller than the single hole nozzle, and it decreases as the diverging angle increases. The spray angle taken from the vertical direction to the group hole plane is smaller than the summation of the angle between two holes and the spray angle of the single hole whose hole diameter is same as one of the group holes. It is supposed that there is an interaction between two fuel jets from the group hole nozzle, where one fuel jet draws or entrains the other. ACKNOWLEDGEMENTS The authors would like to express their appreciation to Mr. Takahiro Fukui, who worked for this study as an undergraduate student and is currently working with Honda Corporation, for his great efforts in conducting the experiment, to Denso corporation for their help in the injection system, and to NEDO, New Energy and Industrial Technology Development Organization, for their financial support. REFERENCES 1. Heywood, J. B., Internal Combustion Engine Fundamentals, McGraw-Hill, Inc. (1988). 2. Hiroyasu, H. and Arai, M., Structures of Fuel Sprays in Diesel Engines, SAE Paper, No.947 (199). 3. Tokuda, H., Itoh, S. and Kinugawa, M., DENSO Common Rail Technology to Successfully Meet Future, 26 Internationals Wiener Motorensymposium 2 (2) 4. Zhang, Y., Nishida, K. and Yoshizaki, T., Quantitative Measurement of Droplets and Vapor Concentration Distributions in Diesel Sprays by Processing UV and Visible Images, SAE Paper, No.21-1-1294 (21).. Zhang, Y., Yoshizaki, T. and Nishida, K., Imaging of Droplets and Vapor Distributions in a Diesel Fuel Spray via Laser Light Absorption Scattering Technique, Applied Optics, Vol.39, No.33 (2), pp.6221-6229.