**3.1 Characteristics of the incoming air flow**

Velocity profiles of the incoming air flow in the test channel were measured in three representative cross-sections in the presence and in the absence of spray using three dimensional (3-D) Laser Doppler Velocimetry (LDV) system. This system consisted of two transceivers oriented 90 degrees apart, which were installed on the rail connected to the 3-D remotely controlled traversing mechanism. This system optically accessed test section from the orifice plate (X=0) to the coordinate X<25mm. To obtain velocity measurements incoming air was seeded with 3-5mkm alumina particles. Results of measurements are presented on Figure 6 in the form of the mean and RMS velocity profiles. It is clear that the mean and RMS velocity profiles are of trapeze-shape form typical for turbulence flow in tubes. Presence and absence of spray did not produce any significant differences in velocity profiles. No significant differences in the profiles were indicated while measured across the test channel 5mm upstream (*z/d~ 10*) and 20mm downstream (*z/d~40*) of the point of injection.

Fig. 6. Characterization of the crossing air velocity field in the test section

### **3.2 Characteristics of injectors**

66 Advanced Fluid Dynamics

Images of the fuel jet exiting from both injectors in the absence and in the presence

Results of the spray penetration measurements obtained by processing of images

Velocity profiles of the incoming air flow in the test channel were measured in three representative cross-sections in the presence and in the absence of spray using three dimensional (3-D) Laser Doppler Velocimetry (LDV) system. This system consisted of two transceivers oriented 90 degrees apart, which were installed on the rail connected to the 3-D remotely controlled traversing mechanism. This system optically accessed test section from the orifice plate (X=0) to the coordinate X<25mm. To obtain velocity measurements incoming air was seeded with 3-5mkm alumina particles. Results of measurements are presented on Figure 6 in the form of the mean and RMS velocity profiles. It is clear that the mean and RMS velocity profiles are of trapeze-shape form typical for turbulence flow in tubes. Presence and absence of spray did not produce any significant differences in velocity profiles. No significant differences in the profiles were indicated while measured across the test channel 5mm upstream (*z/d~ 10*) and 20mm downstream (*z/d~40*) of the point of

Development of the empirical correlations for spray penetration into the cross flow

Z=-5mm Particle Seeding, Spray Off Z=-5mm Particles Seeding Spray On Z=20mm Particles, Spray Off

**0**

(a) Mean velocity b) Velocity RMS

Fig. 6. Characterization of the crossing air velocity field in the test section

**0 5 10 15 20 25 30 Distance-X, mm**

Z=-5mm Particle Seeding, Spray Off Z=-5mm Particles Seeding Spray On Z=20mm Particles, Spray Off

**4**

**8**

**% Z RMS Velocity**

**12**

**16**

obtained at different Weber numbers and different momentum ratios

**3. Results and discussion** 

Droplet sizes

injection.

**Velocity, m/s**

This section consists of several parts including Characteristics of the incoming air flow;

Hydraulic characteristics

of the crossing air flow

Locating of the jet breakup position

**3.1 Characteristics of the incoming air flow** 

**0 5 10 15 20 25 30 Distance-X, mm**

Characteristics of the tested fuel injectors which include:

The main difference between the investigated injectors was shape of the surface between the plenum and the injection orifice.

Fig. 7. Schematics of the tested injectors

One injector had sharp edge as shown on the Fig 7-a and the other one had smooth transition path from the plenum to the orifice (i.e., round edge, see Fig 7-b). Their hydraulic characteristics presented on the Fig. 8 reflect this difference in the injector's internal shape.

Specifically, discharge coefficient . . 2 *inj fuel inj fuel d A P m C* of the sharp edge orifice was

relatively constant *Cd~0.75* in the tested range of *ReD* numbers while the discharge coefficient of the round edge orifice is *Cd~0.96* at the Reynolds numbers exceeding *ReD=10,000 (Pinj*.>60psi) which is relevant to the current study.

Fig. 8. Hydraulic characteristics of the tested injectors (*ReD*=*fuelDinj.Ufuel /fuel)*

Effect of injector geometry on jet disintegration was first demonstrated without cross flow of air. Images of the fuel jets injected from both injectors into the atmosphere are presented on the Fig. 9. It is clearly seen that the jet coming out of the sharp edged orifice disintegrated forming spray structures, ligaments and droplets (see Figure 9-a) while jet injected from the round edge orifice was relatively smooth and intact (Figure 9-b).

A closer look on these fuel jets without cross flow in a near field (see Figure. 10) reveals that the jet injected from the sharp edge orifice expands and disintegrates while the jet from the round edge orifice shows the development of the hydrodynamic instabilities (see Figures 10 a and 10-b respectively). This observation suggests that internal turbulence created by the sharp edge at the entrance of the cylindrical orifice (*L/D*~10) dramatically change jet boundaries and may lead to the differences in spray creation especially when the mechanism of the jet disintegration in the cross flow at elevated Weber numbers (*We*>200) is "shearing". In fact images of the fuel jets shown on the Figure 11 clearly indicate that significant scale difference in liquid border structure on the outer edge of the jet remain

Fuel Jet in Cross Flow – Experimental Study of Spray Characteristics 69

The above mentioned difference in the outer border structure of the jet can potentially influence size of the created droplets. In fact, sharp edged injector used in the current study produces larger droplets as indicated on the counter plots of the Sauter Mean Diameter

both tested orifices (sharp and round edged) on the Figure 12 (-a and –b respectively). Measurements were undertaken using PDPA in the representative cross-section of the spray located 60 orifice diameters downstream of point of injection (*z/d=60*) where spray was fully developed at the same flow conditions (*We=*1000 and *q~*20) for both orifices. Comparison of the SMD along the center line in the same plane (*z/d=60*) presented in the Figure 13 reveals ~10% larger droplets on the periphery of the spray produced by the sharp edge orifice.

(a) Sharp edged injector (b) Round edged injector

Round Edged Orifice

Sharp Edged Orifice

Fig. 12. Sauter Mean Diameter (SMD) in the cross plane of the spray at z/d=60 for tested

0 5 10 15 20 **X (mm)**

Fig. 13. Comparison of the SMDs along the central plane at z/d=60

<sup>32</sup> / , with *Di* – diameter of the individual droplet) presented for

*<sup>i</sup> <sup>i</sup> <sup>i</sup> <sup>i</sup> SMD <sup>D</sup> <sup>D</sup> <sup>n</sup> <sup>D</sup> <sup>n</sup>* <sup>3</sup> <sup>2</sup>

injectors

0

10

20

**SMD (micron)**

30

40

while jets are injected into the cross flow. Size of the outer border structures on the jet exiting from the round edge orifice (Figure 11-b) is at least ten times smaller and more organized than on the jet exiting from the sharp edged orifice (Figure 11-a).

(b) Round edged injector

Fig. 9. Images of the fuel jet injected into the atmosphere (no cross flow) from injectors

Fig. 10. Zoom in the liquid jets injected into the atmosphere (no cross flow) from injectors

Fig. 11. Images of the fuel jet injected into the cross-flow of air at We=1000, momentum flux ratio *q=20* and *Re=14,700*.

68 Advanced Fluid Dynamics

while jets are injected into the cross flow. Size of the outer border structures on the jet exiting from the round edge orifice (Figure 11-b) is at least ten times smaller and more

(a) Sharp edged injector

(b) Round edged injector

(a) Sharp edged injector (b) Round edged injector

(a) Sharp edged injector (b) Round edged injector

Fig. 11. Images of the fuel jet injected into the cross-flow of air at We=1000, momentum flux

ratio *q=20* and *Re=14,700*.

Fig. 10. Zoom in the liquid jets injected into the atmosphere (no cross flow) from injectors

Fig. 9. Images of the fuel jet injected into the atmosphere (no cross flow) from injectors

organized than on the jet exiting from the sharp edged orifice (Figure 11-a).

The above mentioned difference in the outer border structure of the jet can potentially influence size of the created droplets. In fact, sharp edged injector used in the current study produces larger droplets as indicated on the counter plots of the Sauter Mean Diameter *<sup>i</sup> <sup>i</sup> <sup>i</sup> <sup>i</sup> SMD <sup>D</sup> <sup>D</sup> <sup>n</sup> <sup>D</sup> <sup>n</sup>* <sup>3</sup> <sup>2</sup> <sup>32</sup> / , with *Di* – diameter of the individual droplet) presented for both tested orifices (sharp and round edged) on the Figure 12 (-a and –b respectively). Measurements were undertaken using PDPA in the representative cross-section of the spray located 60 orifice diameters downstream of point of injection (*z/d=60*) where spray was fully developed at the same flow conditions (*We=*1000 and *q~*20) for both orifices. Comparison of the SMD along the center line in the same plane (*z/d=60*) presented in the Figure 13 reveals ~10% larger droplets on the periphery of the spray produced by the sharp edge orifice.

Fig. 12. Sauter Mean Diameter (SMD) in the cross plane of the spray at z/d=60 for tested injectors

Fig. 13. Comparison of the SMDs along the central plane at z/d=60

Fuel Jet in Cross Flow – Experimental Study of Spray Characteristics 71

in Figure 15-b by application of the threshold that was set to the intensity of the image which corresponds to the sharp fall in intensity of the liquid jet. The edge of this binary field was tracked to obtain the complete boundary of the liquid jet (see Figure 15-c). The farthest point on this boundary from the center of the orifice is defined as the CBP in this study. This CBP position was averaged over 150 images. Figure 15-d shows the averaged image of the liquid jet obtained using this technique with crosses indicating individual CBPs and circle

Figures 16-a and -b show the coordinates of the mean location of the CBP in the direction of fuel injection (*X*) and airflow (*Z*) downstream of the orifice respectively. Data of all four experimental series demonstrate the same effect of the CBP approximation to the orifice with the growth of momentum flux ratio (*q*). Two competing factors control position of the CBP: (1) Increase of the liquid jet velocity with the growth of *q* and (2) acceleration of the jet disintegration with the growth of the liquid velocity and thus its internal turbulence. This competition is clearly indicated by the maximum on the graph, which shows *X/d* coordinate of CBP on the Figure 16-a. This effect is much stronger for the sharp edged orifice at higher temperature of the crossing air flow. This fact supports hypothesis of the influence of internal turbulence of liquid jet upon the location of CBP because of possibility of cavitation at increased temperature of the injector internal surfaces caused by the high temperature of

(a) Raw image (b) Binary field

(c) Boundary with indicated CBP (d) Averaged image and CBP location

Fig. 15. Methodology for locating the column breakup point (CBP)

indicating the average CBP location for the investigated operating conditions.

the crossing air.
