Measurement and Visualization of Spray
Characteristics of a Fuel Injector under Different
Operating Temperatures and Pressures
Edward J. Timm, Thomas R. Stuecken and Harold J. Schock
Engine Research Laboratory, Michigan State University, East Lansing, MI
ROUGH DRAFT
REVISION 2
10-23-02
ABSTRACT
Laboratory experiments with a fuel port fuel injector were conducted to determine the influence of
fuel type, temperature, and system pressure on the nature of a fuel spray produced with a
manifold fuel injection system. The motivation for this study comes from the vastly different
component gasoline blends that exist worldwide. These wide variations in fuel quality present
many challenges to the automotive industry including issues related to cold start and engine
calibration. Radial scans of the fuel spray profiles were measured using a 1-component Phase
Doppler Anemometer (PDA) system. Spray profiles were performed on 27 different combinations
of fuel type, temperature and system pressure. The three different fuels included: a 48 kPa (7
psi) and 90 kPA (13 psi) RVP butane enhanced fuel and a specially blended 54 kPa (7.8 psi)
RVP pentane enhanced fuel. Droplet measurements were conducted at temperatures of 24 C, 18 C and –29 C and at fuel system pressures of 300, 400, and 500 kPa. The results show that
fuel droplet size is affected by fuel type and temperature. Increasing the fuel system pressure
decreases the fuel droplet size for all fuels and temperatures examined. High-speed flow
visualization of the spray patterns confirms the results obtained with the PDA system. Increasing
the fuel system pressure to reduce droplet size is expected to result in enhanced evaporation and
improved engine cold ambient startability.
INTRODUCTION
Worldwide variation in fuel quality can present many different challenges to the automotive
industry. Engine performance in automobiles depends on many different factors, one of which
includes fuel spray quality. Fuel spray quality can be defined as the degree of atomization and
uniformity of the droplet size distribution. Smaller droplets evaporate and move with the airflow
easier. Fuel spray quality has a decisive effect on mixture formation and combustion in the
gasoline engine, which can affect engine starting, performance and emissions.
Two important characteristics of fuel are its volatility and octane number, which is defined as the
resistance to self-ignition (Stone 1999). Volatility is defined as the volume percentage of fuel that
is distilled at or below fixed temperatures. Fuel that is too volatile and is used during high
ambient temperatures can vaporize in fuel lines and cause vapor lock in carbureted engines.
Sufficient fuel volatility is critical in cold ambient climates, where cold starting problems of long
cranking times can result in scuffing of cylinder liners and engines that will not start.
In the U.S., fuel volatility is expressed in terms of the Reid Vapor Pressure (RVP). The method
for measuring RVP is defined in ASTM Procedure D323. The Environmental Protection Agency
in the U.S. has set maximum Federal and State RVP standards for conventional gasoline. For
example in Michigan, during the months of June, July and August, the maximum RVP for
conventional gasoline is 54 kPa (7.8 psi) compared to 62 kPa (9.0 psi) during the month of May.
Environmental and ambient conditions can also add additional levels of variation to fuel spray
quality. Fuel that is stored in above ground vented tanks is highly susceptible to the loss of
volatile components, especially if stored for long periods of time. The loss of volatile components
can result in difficult engine starting.
Over the last several years, General Motors and other manufacturers has conducted fuel quality
surveys to provide fuel data for worldwide engine calibration. From the survey data, developing
trends and shortcomings related to fuel quality have been identified and are used to help
eliminate potential problems with engine performance. As stated previously, sufficient fuel
volatility or RVP is critical for cold-start performance, especially in winter. An example of a typical
survey (showing the range of RVP for 10 large cities located in China) is presented in Figure 1.
Based upon the ranges of RVP values within and among the cities, calibration of engines for cold
starting is especially complicated.
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Figure 1 – Range of measured RVP for fuel sampled in 10 large cities located in China,
1999.
The objective of this work involves determining the effect of fuel type, temperature and system
pressure on the spray particle size distribution of a common fuel port fuel injector. Specifically,
we intend to evaluate the extent to which changing the system pressure enhances the formation
of small droplets, which should evaporate more readily under cold ambient conditions.
EXPERIMENTAL METHODS
In order to thoroughly evaluate the quality of a fuel spray produced with a manifold injection
system, two different types of laser diagnostic techniques were used to evaluate the spray
characteristics. The spray characteristics were measuring using a 1-D Particle Dynamics
Analysis system (PDA) and a high-speed flow visualization system. A structured 3x3x3 testing
matrix was developed using three different test parameters to capture the variation in fuel spray
quality. These included fuel type, fuel system pressure and temperature.
Table 1 shows the
different fuel types, temperatures and pressures comprising 27 combinations, which were in the
study.
Table. 1 3x3x3 Test Matrix for Radial Profile Scans
Fuel
Temperature
Fuel System
Pressure
Fuel Type
24 C
300 kPa
GM6134-M (48 kPa, 7 psi RVP, Butane Enhanced)
-18 C
400 kPa
GM6135-M Butane (90 kPa, 13 psi RVP, Butane Enhanced)
-29 C
500 kPa
Simulated China Fuel (54 kPa, 7.8 RVP, Pentane Enhanced)
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TEST SETUP
To determine the fuel spray characteristics of the fuel injector under different operating
temperatures and pressures, a temperature-controlled chamber was constructed to house a
nitrogen pressurized fuel vessel and the fuel injector assembly, Figure 2. A Sigma Systems
Corporation model M30MM temperature control unit was used to ensure the tests were
performed at the same temperature. This device has both heating and cooling elements and
programmable controller, which allows the temperature to be controlled within  0.1 C. A second
chamber was attached to the side of the unit to house the injector and enable it to project the fuel
out of the chamber for measurement. A fuel recovery system was used to collect the fuel during
a test and to remove fuel vapors from the measurement area. The fuel injector sprayed fuel into
ambient air in an area that allowed for laser and optical measurements.
Figure 2 – Test setup used for PDA and high-speed flow visualization.
1-D PDA SYSTEM
The system used to measure the fuel droplet size was a 1-component Dantec Dynamics’ Particle
Dynamics Analysis system and operated in the forward scattering mode. The system consists of
the following components presented in Table 2. The PDA system can perform non-intrusive
measurements simultaneously of the size and the velocity of individual spherical particles in
liquids and gaseous flows.
Phase Doppler anemometry is based on light-scattering
interferometry and therefore requires no calibration. The measurements are performed at the
intersection of focused two laser beams, which define the measurement volume. The two laser
beams create an interference fringe pattern of alternating light and dark planes. As particles pass
through the intersection, light is scattered onto multiple detectors, which converts the optical
signal into an electrical signal representing a Doppler burst. The signal processor measures the
phase difference between the Doppler signals from the multiple detectors and calculates the
particle diameter.
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A radial scan with the PDA system was performed at a fixed distance of 100 mm from the injector
tip. The PDA measurements were conducted for points every 2 mm along a line that was
perpendicular to the injector electrical connector direction. Prior to each radial scan, the pressure
chamber was filled with test fuel and placed in the temperature-controlled chamber. The fuel was
then allowed to reach the desired testing temperature by monitoring a thermal couple inside the
pressure chamber. Before each radial scan the injector was allowed to run several minutes to
remove any air and residue of old fuel in the injector line. The fuel system operating conditions
used in the laser diagnostic tests are presented in Table 3.
Table 2. PDA equipment
PDA Equipment
Model or Type
Signal Processor
Multi PDA 58N80
Detector Unit
Fiber PDA
Transmitting Optics
85 mm Fiberflow
Transmitting focal length
310 mm
Beam Separation
50 mm
Receiving Optics
FiberPDA
Receiving focal length
400 mm
Laser Power
300 mW, Ar-ion
Scattering Angle
30 degrees
Table 3. Fuel System Operating Conditions
System Condition
Ambient Pressure
1.0 bar
Ambient Temperature
21 C 2 C
Fuel Delivery per Injection
15.0 mg
Fuel Logic Pulsewidths
5 ms
Injection Repetition Rate
10 Hz
Fuel Pump System
Nitrogen Pressurized Bladder
HIGH-SPEED FLOW VISUALIZATION SYSTEM
A high-speed flow visualization system was used to visualize the fuel spray pattern downstream
of the fuel injector into ambient air. The high-speed flow visualization system consists of a 55watt copper vapor laser (CVL), high-speed 35-mm drum camera, synchronization system and
optics. The CVL is a gas discharge device of 55-watt average output power. The laser emits
short pulses with a pulse duration of approximately 30ns and a pulse jitter of 3 ns. The laser
beam (5.08 cm in diameter and of Gaussian power) is directed toward the area of interest by a
set of circular mirrors 10.16 cm in diameter. A cylindrical lens and mirror are used to focus the
beam into a light sheet approximately 1 mm thick. The laser light sheet provides enough
scattered light off the fuel droplets to expose the films required for the high-speed flow
visualization.
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The 35-mm Cordin Drum Camera (Model 370) projects a continuous non-shuttered image onto a
one-meter length of 35-mm film. The one –meter length of film allows 50 full size 35-mm images
to be exposed. More images are possible by reducing the width of the image. In our setup, a
total of 90 images were recorded for each test.
A total of 12 different variations of fuel type, temperature and pressure were filmed. The
variations included; 1) all three fuels, 2) two temperatures 24 C and -29 C, and two fuel system
pressures, 300 and 500 kPa. After processing the film from each of the 12 tests, the film was
digitized and each individual frame stored in JPEQ format. The individual frames were then
assembled and processed into an animated movie for each variation.
RESULTS
RADIAL PROFILE SCANS
The results obtained with the 1-D PDA system provide many key drop size parameters such as
mean diameter (D10), area mean diameter (D20), volume mean diameter (D30), Sauter mean
diameter (D32), 90% fractional volume (Dv0.9), and fuel volume flow. In this paper, the radial
profiles will be compared using the Sauter mean diameter (SMD or D32). SMD is a means of
expressing the fineness of a spray in terms of the surface area produced by the spray. The SMD
is the diameter of a droplet having the same volume-to-surface area ratio as the total volume of
all the droplets to the total surface area of all the droplets.
The Sauter mean diameter (SMD) is calculated as:
N
D32 
D
3
i
i 1
N
D
i 1
where
(1)
2
i
D = diameter of droplet.
FUEL SYSTEM PRESSURE EFFECT
In comparing the radial profiles obtained with the PDA system, the GM6135-M (13 RVP) fuel is
considered to be the reference fuel for this study. The radial profile for the 13 RVP fuel at 24 C
for the three fuel system pressures is presented in Figure 2. The results show that as system
pressure is increased, the SMD decreases. The variation among the SMD values also decreases
(i.e. the profiles flatten out) as system pressure increases. For example, at 300 kPa, the SMD
values range from 107 to 140 microns compared to 91 to 108 microns at 500 kPa.
Similar results were obtained for the GM6134-M (7 RVP) and simulated China fuel at a fuel
temperature of 24 C, Figures 3 and 4. In each test, increasing the fuel system pressure reduced
the SMD profile values. At 300 kPa, the peak SMD value for the RVP 7 fuel was 152 microns
compared to 122 microns at 500 kPa. The simulated China fuel decreased from 160 to 125
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microns when the pressure was increased from 300 to 500 kPa. The variation among the SMD
values also decreased for both fuel profiles as fuel system pressure is increased.
The peak SMD value for this particular injector occurs at the radial location 2 mm from the
centerline. The shift from the centerline or spray skew is typical of many injectors and can cause
problems with fuel port targeting. Spray skew is defined as the angle and offset from the
theoretical position of the max flux point of the spray at inlet valve targeting position.
Figure 3 - Radial scan for SMD spray parameter profile, RVP 13 fuel at 24 C and all fuel
system pressures.
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Figure 4 - Radial scan for SMD spray parameter profile, RVP 7 fuel at 24 C and all fuel
system pressures.
Figure 5 - Radial scan for SMD spray parameter profile, Simulated China fuel at 24 C and
all fuel system pressures.
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FUEL TEMPERATURE, FUEL PRESSURE INTERACTION
The effect of fuel temperature on the SMD profiles for RVP 13 fuel is shown in Figures 5-7. At
300 kPa, the –18 and –29 C fuel had larger SMD values compared to the fuel at 24 C. The
SMD value for the 300 kPa system pressure at the radial location 2 mm from the centerline was
140 microns at 24 C compared to 152 microns at –18 C and 158 microns at –29 C. When
system pressure was increased to 400 and 500 kPa, the SMD values decrease, however there
still is a slight temperature effect, with the colder fuel having a higher SMD values near the center
of the profile.
Similar temperature effects were found for the RVP 7 fuel at a system fuel pressure of 300 kPa,
Figure 8. At the 2 mm radial location, the SMD was almost 20 microns larger for the fuel at –18
and –29 C compared to the fuel at 24 C. When the system pressure was increased to 400 kPa,
the RVP 7 fuel had similar profiles compared to the 300 kPa data, but the difference in the SMD
values at the 2 mm distance was only 10 microns between the different temperature fuels, Figure
9. At 500 kPa, the higher pressure on the RVP 7 fuel resulted in less of a temperature effect,
Figure 10.
The temperature and pressure effects for the simulated China fuel are presented in Figures 1113. At 300 kpa, there were only minor differences between the different temperature fuels. The
24 C had lower SMD values, but only at the –2 and 0 mm distance. When the pressure was
increased to 400 kPa, the overall SMD profile values decreased, however, the temperature effect
was not prominent. Similar results were obtained when the pressure was increased to 500 kPa.
Figure 6 - Radial scan for SMD spray parameter profile, RVP 13 fuel at 300 kPa and all fuel
system temperatures.
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Figure 7 - Radial scan for SMD spray parameter profile, RVP 13 fuel at 400 kPa and all fuel
system temperatures.
Figure 8 - Radial scan for SMD spray parameter profile, RVP 13 fuel at 500 kPa and all fuel
system temperatures.
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Figure 9 - Radial scan for SMD spray parameter profile, RVP 7 fuel at 300 kPa and all fuel
system temperatures.
Figure 10 - Radial scan for SMD spray parameter profile, RVP 7 fuel at 400 kPa and all fuel
system temperatures.
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Figure 11 - Radial scan for SMD spray parameter profile, RVP 7 fuel at 500 kPa and all fuel
system temperatures.
Figure 12 - Radial scan for SMD spray parameter profile, Simulated China fuel at 300 kPa
and all fuel system temperatures.
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Figure 13 - Radial scan for SMD spray parameter profile, Simulated China fuel at 400 kPa
and all fuel system temperatures.
Figure 14 - Radial scan for SMD spray parameter profile, Simulated China fuel at 500 kPa
and all fuel system temperatures.
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FUEL TYPE, PRESSURE AND TEMPERATURE INTERACTION EFFECT
The effect of fuel type on the SMD profile at a fuel temperature of 24 C and pressure of 300 kPa
is shown in Figure 14. The results show that the Simulated China fuel had the highest SMD
values followed by RVP7 and RVP 13. At the highest point of the profile, 2 mm, the SMD ranged
from 160 microns for the Simulated China fuel to 140 microns for the RVP 13 fuel. This
represents a 14 % difference in SMD between RVP 13 and the Simulated China fuel. At a
system fuel pressure of 400 kPa, the results were similar, with the Simulated China fuel having
the highest SMD, followed by RVP 7 and RVP 13, Figure 15. When the fuel system pressure is
increased to 500 kPa, the SMD values for all three fuels decreased, however both the Simulated
China and RVP 7 fuel had higher SMD profiles compared to the RVP 13 fuel, Figure 16.
When the fuel temperature was decreased to –18 C, the RVP 7 fuel had the highest SMD
followed by the Simulated China and RVP 13 fuels at both 300 and 400 kPa fuel system
pressure, Figures 17 and 18. When the pressure was increased to 500 kPa, all fuels had similar
SMD values at the highest point in the profiles, however, the simulated China fuel had the highest
SMD profiles, Figure 19.
At –29 C, the SMD profiles for all three fuels were nearly identical at the 300 kPa fuel system
pressure, except the RVP 7 fuel had a higher SMD value at the peak of the profile, Figure 20.
When the system pressure was increased to 400 and 500 kPa, the results were similar to the 300
kPa fuel system pressure, Figures 21 and 22. The profiles were similar, with the RVP 7 fuel
having the highest SMD at the peak of the profile.
Figure 15 - Radial scan for SMD spray parameter profile, all fuels at 300 kPa and 24 C fuel
system temperatures.
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Figure 16 - Radial scan for SMD spray parameter profile, all fuels at 400 kPa and 24 C fuel
system temperatures.
Figure 17 - Radial scan for SMD spray parameter profile, all fuels at 500 kPa and 24 C fuel
system temperatures.
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Figure 18 - Radial scan for SMD spray parameter profile, all fuels at 300 kPa and -18 C fuel
system temperatures.
Figure 19 - Radial scan for SMD spray parameter profile, all fuels at 400 kPa and -18 C fuel
system temperatures.
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Figure 20 - Radial scan for SMD spray parameter profile, all fuels at 500 kPa and -18 C fuel
system temperatures.
Figure 21 - Radial scan for SMD spray parameter profile, all fuels at 300 kPa and -29 C fuel
system temperatures.
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Figure 22 - Radial scan for SMD spray parameter profile, all fuels at 400 kPa and -29 C fuel
system temperatures.
Figure 23 - Radial scan for SMD spray parameter profile, all fuels at 400 kPa and -29 C fuel
system temperatures.
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HIGH-SPEED FLOW VISUALIZATION
The pulse injection events were characterized for each fuel, pressure and temperature
combination. The individual frames (90 in total) were digitized, stored in JPEQ format then
assembled and processed into an animated movie. In order to visually compare the different
films, the 30th frame from each fuel, pressure and temperature combination was selected and
assembled into a single photograph. The individual photos were then compared to the actual
SMD data to see if they were in qualitative agreement.
The results from the high-speed flow visualization and SMD profile comparisons are shown in
Figures 23-28. The amount of light scattered from the droplets is dependent on the number and
size of droplets. Larger droplets scatter more light compared to smaller droplets, however a large
amount of smaller droplets will scatter more light than a few larger ones. In Figure 23, the
difference between the 24 C and –29 C RVP13 fuel at 300 kPa can be easily distinguished by
the amount and size of fuel droplets present. At the bottom of the spray cone for the 300 kPa, 29 C fuel, there are visibly larger droplets compared to the 300 kPa, 24 C fuel. This is
supported by the data presented in Figure 24, which shows that the SMD profile for the –29 C
fuel at 300 kPa is higher compared to the 24 C fuel. At 500 kPa, the number of droplets
compared to the 300 kPa fuel is easy to visualize. There is a slight difference in the SMD data
between the two fuel temperatures at 500 kPa, however it is difficult to visualize in the photo.
Similar results for the RVP 7 and simulated China fuels are shown in Figures 25 - 28. At 300
kPa, the difference between the 24 C and –29 C temperatures is evident by both the
visualization and the SMD data. Although there are some minor differences in the SMD data at
500 kPa, it is visually difficult to distinguish between the two different temperatures for both the
RVP 7 and simulated China fuel.
Figure 24 – High-speed flow visualization for RVP 13 fuel at 300 and 500 kPa fuel system
pressure and 24 and –29 C fuel temperature.
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Figure 25 - Radial scan for SMD spray parameter profile, RVP 13 fuel at 300 and 500 kPa
and 24 and –29 C.
Figure 26 - High-speed flow visualization for RVP 7 fuel at 300 and 500 kPa fuel system
pressure and 24 and –29 C fuel temperature.
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Figure 27 - Radial scan for SMD spray parameter profile, RVP 7 fuel at 300 and 500 kPa and
24 and –29 C.
Figure 28 - High-speed flow visualization for Simulated China fuel at 300 and 500 kPa fuel
system pressure and 24 and –29 C fuel temperature.
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Figure 29 - Radial scan for SMD spray parameter profile, Simulated China fuel at 300 and
500 kPa and 24 and –29 C.
SUMMARY AND CONCLUSIONS
The laboratory experiments to determine the effect of fuel type, temperature and system pressure
on spray quality using two laser based diagnostic techniques provided valuable information on
spray quality. The results from the radial profile scans suggest the following:

The type of fuel used in this study does have an effect on the fuel spray quality.

The temperature of the fuel has an effect on the fuel spray quality.

Increasing the fuel system pressure for any of the fuels reduced the SMD values and also
the variation among SMD values within a spray parameter profile.

Increasing the fuel system pressure decreases the differences in SMD profiles caused by
temperature and fuel type effects.
The results from the high-speed flow visualization indicated the following:

Individual frames from the high-speed flow visualization taken at the same time during an
injection event showed differences between different fuel temperatures and fuel system
pressures.

Spray patterns obtained with the high-speed flow visualization confirm the results
obtained from the spray pattern profiles.
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Based upon the results from the two laser diagnostic techniques in evaluated the different fuel
types, temperatures and system pressures, the following recommendation / observation can be
made:

Automotive manufactures and engine suppliers, located in various regions of the world,
are exposed to different or levels of variation, in the specifications of fuel. Potentially,
could enhance fuel injector performance and robustness, by increasing the fuel system
pressure to a level that decreases the variation with fuel type and ambient temperature.
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