EPA/AA/TDG/93-05
Technical Report
Spray Characteristics of
Two Types of Fuel Injectors
by
Jeffrey P. Hahn
Fakhri J. Hamady
Karl H. Hellman
March 1993
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
Regulatory Programs and Technology Division
Technology Development Group
2565 Plymouth Road
Ann Arbor, MI 48105
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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
ANN ARBOR. MICHIGAN 48105
OFFICE OF
AIR AND RADIATION
MEMORANDUM
SUBJECT: Exemption From Peer and Administrative Review
FROM: Karl H. Hellman, Chief
Technology Development Group
TO: Charles L. Gray, Jr., Director
Regulatory Programs and Technology Division
The attached report entitled "Spray Characteristics of Two
Types of Fuel Injectors," (EPA/AA/TDG/93-05) describes the results
of our continuing in-house study of fuel injector properties. A
laser diffraction technique was used to quantify the fuel spray
droplet sizes and volume concentration for two different types of
fuel injectors.
Since this report is concerned only with the presentation of
data and its analysis, and does not involve matters of policy or
regulations, your concurrence is requested to waive administrative
review according to the policy outlined in your directive of April
22, 1982.
Concurrence:
Cfiarles L. Gray, J./ Director, RPT
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Table of Contents
Page
I. Introduction ...................... 1
II. Spray Measurements .................. 1
III. Fuel Injectors .................... 1
IV. Characteristics of the Liquid Fuel Spray ....... 3
V. Summary ........................ 5
VI. Future Directions ................... 9
VII. Acknowledgments .................... 9
VIII. References ....................... 9
APPENDIX A - Malvern Series 2600 Particle Sizer ...... A-l
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I. Introduction
The Technology Development Group (TDG) of the Regulatory
Programs and Technology at the EPA National Vehicle and Fuel
Emissions Laboratory (NVFEL) has evaluated the spray
characteristics of two types of fuel injectors intended for
possible application in alcohol-fueled automotive engines. This
report is part of TDG's ongoing research program on time resolved
spray analysis and combustion processes utilizing high-speed flow
visualization and laser diffraction techniques. The two types of
injectors which were studied are a standard gasoline pintle-type
port fuel injector and an air-assist poppet valve injector
previously developed at NVFEL, which is based on an injector used
in a swirl chamber Diesel engine. Nitrogen is used as an atomizing
fluid rather than air in this work. The spray analyses were
performed using a Malvern Series 2600 particle size analyzer.[1]
This analyzer is used to measure the particle size distribution and
volume concentration of liquid droplet sprays. The 'measurements
were taken as the injectors were injecting into the atmosphere at
different fuel injection pressures. Experimental results showed
that the air-assist poppet valve injector generated finer particles
compared with the pintle-type injector.
II. spray Measurements
The Malvern Series 2600 Laser Diffraction System is a non-
intrusive optical measurement instrument used to characterize
liquid or solid particles. A detailed description of the Malvern
system is included in Appendix A. Due to the periodic nature of
the fuel injector events, a Malvern PS51 pulsed spray synchronizer
[2] was used to control both the fuel injection and measurement
timing for the experiment. The synchronizer controls the injection
period and duration and also sends a delayed trigger signal to the
measurement unit relative to the beginning of the injection event
which ensures that the actual particle size measurement occurs when
the fuel spray intercepts the measurement region. A dynamic output
mode of the Malvern system allows the user to determine the
appropriate trigger delay for the given injector location.
Ill. Fuel Injectors
The port injector used in this study is a Nippondenso pintle-
type injector which is used in Nissan products (see Figure 1) .
This injector was operated in its stock configuration at a fuel
injection pressure of 50 psi. The test fuel was methanol.
The air-assist poppet valve injector is a modified Lucas
Microjector (see Figure 2) . The Lucas Microjector is a direct
injection Diesel injector with an outwardly opening poppet which
was used in the U.S. market in some GM passenger car swirl chamber
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Pintle nozzle itaowtng
vmlve
views of ptnlle ooota
orifice ihowmf vmivt Mm lifUd
0.015 in. (kft) «otl 0.031 ia. (nghl)
Pimte
Vilvc needle
Return spnn|
Figure 1 Cross section of pintle type fuel injector
Closed
original
ClOMd
modified-i
Closed
modified-ii
Closed
modified-iii
no*
Figure 2 Cross section of poppet type fuel injector
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-3-
Diesels. The Microjector poppet and nozzle body were modified to
provide a wider spray angle for this injector. The modifications
also resulted in less wetted surface area downstream of the valve
seat in the nozzle body which should reduce the injected droplet
size. Three separate poppet valve and nozzle body combinations
were used in the £ests. Nitrogen was used rather than air for the
atomizing process and the injected fuel was methanol. The nitrogen
and methanol were metered to the Microjector through individual
pintle injectors mounted on a yoke upstream of the Microjector.
The nozzle spring was modified for this experiment to allow the
injector poppet valve to open at lower pressures than it would in
its stock configuration for Diesel applications. The air-assist
poppet valve injector was operated at pressures of 75, 100, and 135
psi in order to evaluate the effects of fuel pressure on the spray
characteristics.
IV. Characterization of the Liquid Fuel Spray
This section presents the fuel spray characteristics of
methanol fuel injected into the atmosphere with the following
injector configurations:
Pintle injector @ 50 psi
Air-assist injector with modified i poppet § 135 psi
Air-assist injector with modified ii poppet @ 135 psi
Air-assist injector with modified iii poppet @ 135 psi
Air-assist injector with modified iii poppet § 100 psi
Air-assist injector with modified iii poppet @ 75 psi
All practical sprays are comprised of drops of a variety of
sizes. There are many different ways in which the droplet size
distribution can be characterized. One way in which a spray can be
characterized is by use of the Sauter Mean Diameter (SMD) . The SMD
is the diameter of a drop that has the same surface-to-volume ratio
as the entire spray. The SMD has been found to be a very useful
indicator of the nature of a fuel spray for engine work and is the
measure we have chosen to use in this report.
The axial distributions of the SMD and volume concentration
from a pintle injector fuel spray are presented in Figure 3. Data
is shown for three different radial sections offset from the spray
centerline at an injection pressure of 50 psi. The profiles in
Figure 3(a) along the centerline downstream of the pintle nozzle
show an increase in the droplet size as the distance from the
nozzle increases. We attribute this behavior to the separated back
flow generated at the pintle valve and the counter rotating
vortical structure which proceeds downstream to cause droplets to
coalesce. This phenomenon is due to the dissipating energy of the
liquid jet caused by the vortical structure which dominates along
the spray centerline. Smaller droplets are found at the spray
periphery because of the higher liquid jet momentum which breaks
the liquid stream into smaller droplets.
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(a) Droplet size
1.0 2.0 3.0 4.0 5.0
Distance from nozzle tip (cm)
Sprays from a
pintle nozzle
1.20
(b) Volume concentration
Distance from nozzle tip (cm)
0.0
0.5 • 1.0
Offset from spray centerline (cm)
Figure 3 - Droplet size and volume concentration for pintle injector at 50 psi fuel
injection pressure
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-5-
Figure 3(b) presents the axial distribution of volume
concentration for the pintle injector at 50 psi. The profiles
indicate that the volume concentration is greatest along the spray
centerline; therefore, the concentration of large particles in the
spray is very high.
The SMD and volume concentration for an air-assist poppet
valve injector at an injection pressure of 135 psi are shown in
Figure 4. The profiles in Figure 4(a) indicate that the smallest
droplets are found along the spray centerline. As expected, this
is attributed to the high atomization of the higher air jet
momentum along the centerline which breaks the fuel stream into
smaller droplets. At the spray periphery near the nozzle/poppet
valve region, larger droplets are found due to fuel nozzle surface
interactions and droplet coalescence.
Figure 4(b) illustrates that the volume concentration at the
centerline of the air-assist injector spray is the greatest. The
profiles indicate that small droplets are most prevalent in the
air-assist injector's spray.
The effects of injector pressure on the SMD of the air-assist
injector are shown in Figure 5. It is apparent from this figure
that the increase in injection pressure enhances the atomization of
the fuel spray. Fewer data points are shown in Figures 5(c) and
5(d) because of the high extinction rate which prevented drop size
determination outside of the spray cone.
Spray droplet sizes for different nozzle/poppet valve
configurations with the air-assist injector are shown in Figure 6.
The nozzle/poppet valve configurations which were used are shown in
Figure 2. The results show that configurations with flat poppet
valves (modified i and ii) yielded slightly better performance than
did the pointed poppet valve (modified iii).
V.
Spray characteristics of pintle and poppet valve injectors
injected into the atmosphere have been measured using laser
diffraction measurements. Comparison of the spray results at
different fuel injection pressure and nozzle/poppet valve
configurations provided useful information on the controlling
parameters of the sprays. The following insights can be made:
1. The presence of atomizing air (nitrogen is used in this
study) has a significant effect on the spray characteristics.
2. The mean droplet size for the pintle injector is larger
than that from the air-assist poppet valve injector.
3. Spray characteristics for the two types of injectors are
dependent on fuel injection pressure and nozzle/poppet valve
configurations. Mean droplet size decreases with increasing
injection pressure.
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a _
II
5 u
E 1
S~
i
M
(a) Droplet size
2.0 3.0 4.0 5.0 6.0
Distance from nozzle tip (cm)
Sprays from a
nozzle with poppet valve
(b) Volume concentration
2.0 3.0 4.0 5.0 6.0
Distance from nozzle tip (cm)
.0
.0
2.0
° 3.0
Offset from injector axis (cm)
Figure 4 - Droplet size and volume concentration for an air-assist injector with modified
iii poppet valve at 135 psi Fuel injection pressure
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.
<0
10
I
CO
M
o
IQ
^
i
a
V)
(a) Spray centerline
100 i
90
80
70 {
60
50
40
30 i
20
10
0
1.0 2.0 3.0 4.0 5.0 6.0
(c) 2 cm off centerline
100
90 f
80 I
70
60
50
40
30
20
10
i
1.0 2.0 3.0 4.0 5.0 6.0
Distance from injector tip (cm)
(b) 1 cm off centerline
(d) 3 cm off centerline
100
90
80
70
60
50
40
30
20
10
1.0 2.0 3.0 4.0 5.0 6.0
Distance from injector tip (cm)
75 psi
a 1 00 psi
* 135 psi
Figure 5 - Effect of injection pressure on spray droplet size for an air-assist poppet valve
injector
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(a) Spray centerline
- 100
§ 90
| 80
r 70
* 60
1 50
c 40
— ^-_
P^\_ — ^^^-»
^^I:^5=— 0======*==^
0 2.0 3.0 4.0 5.0 6.0
(d) 3 cm off centerline
100 i
90
80
70
60
50
40
30
20
10
0
1
^_^
B^i
0 2.0 3.0 4.0 5.0 6.0
Distance from injector tip (cm)
Modified ii
— * Modified in
Figure 6 • Effect of nozzle/poppet valve configurations on spray droplet size from an air-
assist injector at 135 psi fuel injection pressure
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-9-
4. The air-assist poppet valve injectors have a higher
concentration of relatively small particles in their sprays than
does the pintle valve injector.
VI. Future Directions
As the demand for higher performance and lower emissions from
automotive engines is concentrated more on the combustion chamber,
our future efforts will focus on time resolved spray analysis and
combustion processes in an engine assembly. New concepts and
technology will be tested using both high-speed flow visualization
and laser diffraction techniques. Data will be incorporated in
automotive engine developments to promote clean combustion and
reduced emissions for future generation engines.
vii. Acknowledgments
The authors appreciate the efforts of Philip Dingle of Lucas
Automotive for providing the injectors to modify and also for
advice on how to modify the injectors. The authors also recognize
the efforts of Jennifer Criss for word processing and editing
support.
VIII.References
1. Malvern Instruments 2600 Series - User Manual.
2. Malvern Instruments Pulsed Spray Accessories.
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A--1
Appendix A
Malvern Series 2600 Particle Sizer
The Malvern Series 2600 laser diffraction particle sizer is an optical system that can be used for
particle size analysis of powders, aerosols and sprays. This system consists of a 2 mW He-Ne laser
(633nm wavelength) with a 9mm diameter beam, transmitter and scanning receiver mounted on the
opposite sides of an optical bench. The transmitter and receiver are interfaced to an IBM- compatible
personal computer. The receiver is equipped with a Fourier transform lens of 300 mm focal length to
focus on a semi-circular concentric diode array detector (31 diodes). The signal from each detector
diode proportional to the intensity of light falling on it is amplified and digitized and transferred to the
controlling computer, where it is analyzed.
The initial output consists of
light energy detected by each
diode, arranged in a histogram
from the innermost to the
outermost diode, as well as overall
beam intensity and obscuration.
The Malvern software can provide
calculated information such as the
Sauter mean diameter (SMD) and
other derived parameters including
volume concentration and specific
surface area. The particle size
distribution can also be presented
in a variety of graphical and tabular
results formats.
For our work with the fuel
injectors, the particle sizer can
detect volume sprays with particles
in the range of 0.5 to 564 microns
in three overlapping sub-ranges
with the standard system. The
Series 2600 instrument allows two
scattering models to be selected.
One is based on Fraunhofer diffraction
liquid (mil), and the second is based on
(pil) and particle-in-air (pia).
Printer
Laser
Scanning Amplifier
receiver
Fourier 'Detector
Particle* len*
Spatial filter
Diagram of System Configuration
Receiver cut-off
distance
Measured zone
of spray
Detector
plane
Printer Computer
Diagram of Laser Diffraction Experiment
which is better suited for liquid-droplet-spray (Ids) and metal-in-
anomalous diffraction which can be utilized for particle-in-liquid
The procedure to determine a grid pattern of the injector's particle size distribution was obtained
by placing the injector in a supporting frame which can be moved along the x-, y- and z-direction in the
vicinity of the particle sizer"s laser beam. The Intelligent Controls IC5460 was used to control the
injector pulse width and frequency while the sizer is acquiring data. Our experience so far is that an
individual particle size measurement takes approximately two minutes.
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