EPA/AA/TDG/94-04
Technical Report
Spray Characteristics of Single- and Three-Hole
Nozzle Injectors in Ambient Air and
in a Motored Single-Cylinder Test Engine
by
Jeffrey P. Hahn
Fakhri J. Hamady
Ronald M. Schaefer
November 1994
NOTICE
Technical Reports do not necessarily represent final EPA
decisions or positions. They are intended to present technical
analysis of issues using data which are currently available. The
purpose in the release of such reports is to facilitate the
exchange of technical information and to inform the public of
technical developments which may form the basis for a final EPA
decision, position, or regulatory action.
U. S. Environmental Protection Agency
Office of Air and Radiation
Office of Mobile Sources
Office of Regulatory Programs and Technology
Technology Development Group
2565 Plymouth Road
Ann Arbor, MI 48105
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Table of Contents
Page
Number
I. Summary 1
II. Introduction 1
III. Experimental Facilities 1
IV. Results and Discussion 1
V. Conclusion 4
VI. Recommendations and Future Efforts 9
VII. Acknowledgements 9
VIII. References 9
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I.
The high-speed/high-resolution imaging system was used to
evaluate two mid-pressure (15 MPa) fuel injector nozzles in ambient
air and in a motored single-cylinder test engine. The nozzles are
designed for use in the EPA/NVFEL program to develop clean and
efficient engines that use alternative fuels.
This report is part of an ongoing investigation to analyze the
transient spray characteristics for direct-injection type fuel
injectors. The experimental results compare a single-hole and a
three-hole nozzle and conclude that both of these injector nozzles
yield similar spray patterns and atomization and could be
particularly useful for combustion systems where injection into a
piston bowl is required.
II. Introduction
This work is a continuation of the work described in report
EPA/AA/TDG/94-03 with the analysis focused on two similar nozzles.
For background information, please refer to the previous report.
III. Experimental Facilities
The basic experimental facilities and procedures are described
in detail in Technical Report EPA/AA/TDG/94-03.
In this report the imaging location for the in-cylinder
visualization is different from that described in the previous
report. Figure 1 shows the engine assembly and the spark-plug
adaptor where the image carrier was located to take all the in-
cylinder pictures that are displayed in this report.
Figure 2 shows the two-nozzle assemblies that are evaluated in
this report. The nozzles are inwardly opening needle valves
actuated by the pressure acting against a spring force. All of the
nozzle design parameters are the same with the exception of the
needle swirl vanes and the number of holes. The injectors were
operated exclusively on alcohol fuel at a pressure of 15 MPa.
IV. Results and Discussion
The spray behavior and performance of the two injector nozzles
were compared and analyzed based on the following:
• Spray visualization in ambient air;
• Spray visualization in motored engine;
• Spray droplet size measurements; and
• Fuel flowrate.
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Spark plug
Injector
Image.
carrier
Camera
adapter
-ring
Rulon ring
Laser light sheet
Cylinder
Drum camera
Cylinder
head
Piston
Quartz
insert
Piston
extension
Base engine
Figure 1 Optical engine assembly showing image carrier
and high speed drum camera
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Swirl
vanes
Enlarged view
(no scale)
Vertical
vanes
(a) Single-hole (b) Three-hole
Figure 2 Mid-pressure injector nozzle assemblies
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The high-speed imaging was performed at 5000 frames/second
(fps) for both ambient and in-cylinder conditions. The spray
droplet sizes were measured with the Malvern particle sizer.
Droplet measurements were performed only in ambient air due to the
Malvern system limitation to take in-cylinder measurement because
of window fouling.
The ambient air photographs of the spray patterns from the two
nozzles (Figure 3) show little discernable difference between the
spray features. One possible scenario which was considered was
that the individual sprays from the three-hole nozzle would
coalesce downstream of the nozzle and result in larger droplet
formation, but the pictures show no evidence of significantly
larger droplets from the three-hole nozzle in either the ambient or
in-cylinder conditions.
The droplet size measurements (Figure 4) illustrate a
difference between the two nozzles, but the limitations of the
measurement method and technique prevent a definitive comparison
from being made based on the Malvern measurements. Because of the
spray densities, only a portion of the perimeter of the spray can
be measured with the Malvern equipment leading to extrapolations
and uncertainties of the overall spray quality. Since both nozzles
had Sauter mean diameter (SMD) readings on the average of 10
microns, we shall assume that both nozzles have comparable, and
quite good, droplet size characteristics. A more advanced
measurement technique is required to make a more reliable
comparison of the particle sizes of the two nozzles.
The one area where the two nozzles exhibit differing
performance is in the fuel flowrate. At 5-millisecond injector
pulse duration, the two nozzles have nominally the same flowrate,
but this can be attributed to the non-ideal behavior that our fuel
injector manifold displays at smaller pulse duration. For a 10-
millisecond pulse duration, the three-hole nozzle flows
approximately 35 percent more fuel (97 vs. 72 cubic millimeters per
injection) than the single-hole nozzle.
The in-cylinder images taken with the image carrier show the
three-hole nozzle injecting into a 1000-rpm motored single-cylinder
engine at two different injection timings (Figures 5 and 6). The
high penetration velocity of the spray causes the fuel to quickly
impinge upon the piston face for both injection timings. The
single-hole nozzle showed similar impingement behavior. With the
majority of the injected fuel impinging on the piston, a
quantitative assessment of the overall in-cylinder spray
atomization and evaporation cannot be made from the high-speed
images. The end of injection is also shown for both injection
timings. It should be noted that the end of injection is free of
large droplets which can be present for some injectors.
Photographs of the fuel sprays through the bottom of the piston are
not presented because no additional spray features were observed
with those photographs.
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0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6ms
(a) Single-hole nozzle
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 26ms
(b) Three-hole nozzle
Figure 3 Successive frames of one injection event at 5,000 fps injected from a mid-pressure injector
into the atmosphere at 15MPa injection pressure
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c/J
20
18
16
14
12
10
.2 8
Q.
O
Distance from nozzle = 5.0 cm
Nozzle type
A—-A Single-hole
•—• Three-hole
0 2 4 6 8 10
Time (ms)
Figure 4 Variation of droplet size with time from the start of injection
for the mid-pressure injectors in ambient air
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37.0° BTDC
27.4° BTDC
17.8° BTDC
13.0° BTDC
35.8° BTDC
26.2° BTDC
16.6° BTDC
11.8° BTDC
34.6° BTDC
25.0° BTDC
15.4° BTDC
10.6° BTDC
33.4° BTDC
23.8° BTDC
14.2° BTDC
9.4° BTDC
Figure 5 Selected frames of one injection event at 5000 fps and injection pressure of 15MPa from a
three-hole injector during compression stroke in a motored single-cylinder engine at 1000 rpm
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102.0° BTDC
92.4° BTDC
82.8° BTDC
78.0° BTDC
100.8° BTDC
91.2° BTDC
81.6° BTDC
76.8° BTDC
99.6° BTDC
90.0° BTDC
80.4° BTDC
75.6° BTDC
98.4° BTDC
88 8° BTDC
79.2° BTDC
74.4° BTDC
Figure 6 Selected frames of one injection event at 5000 fps and injection pressure of ISMPa from a
three-hole injector during compression stroke in a motored single-cylinder engine at 1000 rpm
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V. Conclusion
The results of the experimentation for the single- and three-
hole nozzles is that either nozzle could be used for a combustion
system which requires fuel delivery to a precise location, such as
injection into a piston bowl. The injector spray was not affected
by the in-cylinder charge motion (Note: The in-cylinder charge
motion is not known for this engine) due to the high spray momentum
and penetration velocity.
There was little qualitative or quantitative difference
between the two nozzles with the exception of the three-hole nozzle
having a higher fuel flowrate. The higher flowrate makes the
three-hole nozzle a more likely candidate of the two for use in the
direct injection engine applications.
VI • Recommendations and Future Efforts
The three-hole nozzle has desirable spray characteristics with
the exception of the high spray penetration. To control the spray
penetration, design changes to the nozzle can be considered
including increased swirl, reduced hole length to diameter (1/d)
ratio, and beveling of the outer edge of the nozzle hole, all of
which should increase the spray-cone angle and decrease the spray
penetration. A fast operating solenoid valve can also control the
spray penetration which gives sharp opening and closing of the
valve and shortens the injection duration.
_J
As stated in the results, the Malvern particle sizer has
limited accuracy and application when trying to compare fuel
injector sprays in ambient air. Additionally, the Malvern system
cannot be used in a motored test engine. To obtain accurate
quantitative results in both ambient air and in-cylinder,
consideration should be given toward acquiring a flow- and
particle-size measurement system which will work in both testing
environments. A Phase-Doppler particle analyzer system can perform
time-resolved measurements of spray droplet size and velocity both
in ambient air and in-cylinder. Mean drop size can then be
obtained in a burning and non-burning spray to assess the
reliability of data and to provide information on the droplet
evaporation rate.
VII. Acknowledgements
The authors would like to acknowledge the contributions of
Jennifer Criss and Lillian Johnson for their word processing and
editing support.
VIII.References
1. "High-Speed/High-Resolution Imaging of Fuel Sprays From
Various Injector Nozzles for Direct Injection Engines," Hamady,
F.J., J.P. Hahn, K.H. Hellman, and C.L. Gray, Jr., EPA/AA/TDG/94-
03, September 1994.
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