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The Effect of Fuel Sulfur
and Jacket Temperature
on Piston Ring Wear
as Determined by
Radioactive Tracer
By
M. POPOVICH
Professor of Mechanical Engineering
and
R. W. PETERSON
Standard Oil Company of California Fellow
BULLETIN NO. 33
JULY 1953
Engineering Experiment Station
Oregon State College
Corvallis
I
THE Oregon State Engineering Experiment Station was
established by act of the Board of Regents of the College
on May 4, 1927. It is the purpose of the Station to serve the
state in a manner broadly outlined by the following policy:
(1)To stimulate and elevate engineering education by
developing the research spirit in faculty and students.
(2) To serve the industries, utilities, professional engineers, public departments, and engineering teachers by making
investigations of interest to them.
(3) To publish and distribute by bulletins, circulars, and
technical articles in periodicals the results of such studies, surveys, tests, investigations, and research as will be of greatest
benefit to the people of Oregon, and particularly to the state's
industries, utilities, and professional engineers.
To make available the results of the investigations conducted by the Station three types of publications are issued.
These are:
(1) Bulletins covering original investigations.
(2) Circulars giving compilations of useful data.
(3) Reprints giving more general distribution to scientific
papers or reports previously published elsewhere, as for example, in the proceedings of professional societies.
Single copies of publications are sent free on request to
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copies, or copies to others, are sent at prices covering cost of
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For copies of publications or for other information address
Oregon State Engineering Experiment Station,
Corvallis, Oregon
The Effect of Fuel Sulfur
and Jacket Temperature
on Piston Ring Wear
as Determined by
Radioactive Tracer
By
M. PopovIcH
Professor of Mechanical Engineering
and
R. W. PETERSON
Standard Oil Company of California Fellow
BULLETIN NO. 33
JULY 1953
Engineering Experiment Station
Oregon State College
Corvallis
Foreword and Acknowledgmenfs
The problem of engine wear has been the object of research by
engine manufacturers and oil companies for many years. Modern
internal combustion engines are limited in economical service life
by ring and cylinder bore wear. Most engines require overhaul
because oil consumption becomes excessive and power loss consider-
able, both factors being due to ring and cylinder wear. Through
continued research the major causes of engine wear can be determined and methods developed appreciably to extend the service life.
The authors are grateful to the California Research Corporation for helpful information regarding experiences in applying the
radioactive piston ring wear test methods and to the Atlantic Re-
fining Company for granting permission to use the test method
which they originated and patented. The Shell Oil Company also
contributed valuable information and suggestions.
Acknowledgment is made to the Engineering Experiment Station for providing supplies and equipment for the work. The junior
author expresses his personal gratitude to the Standard Oil Company
of California for having sponsored his advanced studies by means
of a Research Fellowship.
The authors also express appreciation to the Isotopes Division
of the Atomic Energy Commission for valuable information contributed.
Table of Contents
Page
I. SUMMARY AND INTRODUCTION
1.
5
Summary ---------------------------------------------------------------------------5
Introduction -------------------------------------------------------------------- 5
II. THEORY OF RING AND CYLINDER WEAR
6
Friction ---------------------------------------------------------------------------- 6
2.
1.
2.
3.
4.
Abrasion --------------------------------------------------------------------------
III. WEAR TEST METHODS
1.
2.
3.
6
Corrosion ------------------------------------------------------------------------ 6
Scuffing ---------------------------------------------------------------------------- 7
----------------------------------------------
7
Physical Measurement of Rings and Cylinder Bore -- 7
Chemical Analysis of Lubricating Oil -------------------------- 8
Radioactive Piston Rings ---------------------------------------------- 8
IV. OBJECTIVES OF THIS WORK
V. APPARATUS
----------------------------------
9
-------------------------------------------------------------------- 10
The Engine and Accessories ---------------------------------------2. Counting Equipment -----------------------------------------------------3. Shipping and Storage ---------------------------------------------------4. Handling and Shielding -----------------------------------------------5. Monitoring Instruments -----------------------------------------------1.
10
11
12
13
13
VI. RADIATION SAFETY
VII.
-----------------------------------------------------14
PROCEDURF ---------------------------------------------------------------------- 16
1. Test Conditions -------------------------------------------------------------- 16
Operation ------------------------------------------------------------------------ 17
3. Iron Loss and Decay Corrections ---------------------------------- 17
2.
VIII.
RESULTS
---------------------------------------------------------------------------- 19
IX. CONCLUSIONS ---------------------------------------------------------------- 22
X. RECOMMENDATIONS -------------------------------------------------- 22
XI. BIBLIOGRAPHY -------------------------------------------------------------- 24
lllustratons
Page
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Test Engine and Auxiliary Equipment
10
Radioactivity Measuring Equipment ---------------------------- 11
Radioactive Ring Shipping Container -------------------------- 12
Piston Shielding Jig and Ring Handling Tools ---------- 13
Radiation Safety Instruments -------------------------------------- 14
Effect of Fuel Sulfur on Ring Wear ---------------------------- 19
Typical Curves for Wear Rate Determination ---------- 21
------------------------
3
The Effect of Fuel Sulfur and Jacket
Temperature on Piston Ring Wear
as Determined by Radioactive Tracer
By
M. PoPovIcH
Professor of Mechanical Engineering
and
R. W. PETERSON
Standard Oil Company of California Fellow
I. Summary and Introduction
1. Summary. Investigation of piston ring wear was made using
fuels of various sulfur contents and varying water jacket temperature. Tests were made in a single-cylinder, water-cooled Lauson
engine fitted with two irradiated compression rings. Wear rates
were determined by finding the amounts of radioactive iron in the
crankcase lubricating oil by means of a geiger counter.
The results indicate that corrosion is an important factor in
the wear process at low jacket temperatures and with sulfur present
in the fuel. At jacket temperatures above 150 F the corrosive effect
of sulfur is virtually eliminated. The results obtained agree not only
with those published by some other investigators but also with field
experience.
2. Introduction. The effect of operating variables on engine
wear, specifically piston ring and cylinder wear, has been the objective of exhaustive research by engine manufacturers, oil companies, and allied industries for many years. The useful life of the
present-day engine is largely determined by power loss and oil consumption, both caused by ring and cylinder wear. The life of the
bearings and other moving parts is possibly twice that of rings and
cylinders. This indicates that in order to lengthen the economical
service life of modern engines, the objective of research must be
to find the major causes of this wear and ways of reducing it. To
realize the importance of prolonging engine life and reducing fuel
and oil consumption, one needs only consider the motorized age in
which he lives.
A great deal of progress has been made toward this objective
and some important facts have been discovered. Engine manufacturers have approached the wear problem with research directed
toward improved engine design. Oil companies have been developing
'-.-"-
6
.-..,. ..,-
ENGINEERING EXPERIMENT STATION BULLETIN 33
new lubricating oils to combat wear. This research has been carried
on in accurately controlled laboratory dynamometer tests and fullscale field service tests, both equally important in the progress made
thus far. Advanced research and correlation and verification of
previous research are greatly needed. The numerous operating variables that could affect ring and cylinder wear give relatively unlimited opportunities for further research.
II. Theory of Ring and Cylinder Wear
The processes by which wear of rings and cylinders occurs in
internal combustion engines are complex. Authorities on this subject, however, generally agree that wear occurs by the following
processes: (1) friction, (2) abrasion, (3) corrosion, (4) scuffing.
1. Friction. Wear by friction is the cutting or deforming
action of the ring passing over the cylinder wall surface. Irregulari-
ties on each surface will cut or deform the other surface at the
points of contact where the oil film is breeched. This action will
actually remove the irregularities and increase the contact area,
thus improving the load-carrying ability of the surfaces. During the
break-in period this type of wear is desirable, but after the surfaces fit properly it should be brought to a minimum. It is probable
that surface finish, material properties, and oil viscosity are the
major factors in friction wear. The surface finish governs the number
of irregularities in the surface. Hardness of the materials affects
the depth of surface penetration by irregularities and hence the
amount of cutting. Oil viscosity determines how close the two surfaces apprbach each other or how small an irregularity will penetrate the oil film and cut the other surface.
2. Abrasion. By abrasive wear is meant the friction wear
caused by foreign particles between the rubbing surfaces. These
particles may be brought in with the intake air or carried in the
lubricating oil. Well-designed oil and air filters reduce this type of
wear, but under adverse atmospheric conditions some particles may
still find their way into the engine. It is reasonable that, in addition
to the factors affecting friction wear, the quantity, size, shape, and
hardness of foreign particles affect abrasive wear. Abrasive wear
differs from friction wear in that the harder surface will wear more
because the abrasive particles embed themselves in the softer material.
3. Corrosion. Corrosive wear is, as the name implies, a chemical
process. It is a result of acid attack of metal surfaces by certain
products of combustion of fuel or lubricating oil contaminants or
oxidation products. Any acid-forming substance can cause this type
PISTON RING WEAR AS DETERMINED BY RADIOACTIVE TRACER
7
of wear, but it appears that sulfur and its acids are the major offenders. The corrosive wear tests that have been conducted indicate
that the cylinder wall temperature is the critical factor. Other factors
that could affect corrosive wear are oil film thickness, oil acidity or
alkalinity, cylinder pressures and temperatures, and material com-
position. Oil film thickness could affect corrosion by acting as a
protective covering which hinders the acid particles from contacting
the metal surface. Oil alkalinity could retard corrosion by neutralizing the acids before they reach the metal. Cylinder wall temperatures could influence the chemical reaction rate, increasing it as the
temperature rises. But more important, cylinder wall temperatures
could affect the amount of condensation or adsorbed water on the
metal surfaces, and hence the effectiveness of acid causing the corrosion.
4.
Scuffing. Scuffing is wear caused by the welding of points
on the two surfaces and subsequent tearing away of the welded
junctions. High surface temperatures and clean metallic contact
are the main factors that initiate scuffing. Any oil film, of course,
will aid in preventing scuffing by separating the surfaces. Once the
surface is roughened by scuffing, wear rates will be high because of
friction wear. Scuffing is critical during break-in since there are
high temperatures and thin oil films between the surfaces. High
temperatures, high pressures, rubbing velocities, and distortion also
add to the possibility of scuffing. Scuffing may be hindered by higher
viscosity lubricants which provide a film that is more difficult to
penetrate. Dust or any other abrasive particles present greatly aggravated scuffing. Considerable work has been done on metal coatings
and finishes to prevent scuffing. The exact properties that make such
materials resistant to scuffing have not been fully determined.
III. Wear Test Methods
One of the most difficult problems to circumvent in engine
wear research is that of measuring the small quantities of iron involved to determine the effect of any set of operating conditions.
The three methods used at present are discussed in the following
text.
Physical measurement of rings and cylinder bore.
Chemical analysis of lubricating oil for iron content.
Radioactive piston rings.
1.
Physical measurement of rings and cylinder bore. This
method requires very long and, consequently, expensive periods of
8
ENGINEERING EXPERIMENT STATION BULLETIN 33
operation (more than 500 hours) to obtain wear measurable with
micrometers, dial indicators, and feeler gages. Over such long
periods of time, it is hard to maintain constant conditions; therefore the isolation of variables and reproducibility of results are diffi-
cult. Also, differences in material composition and surface finish
in different engines, even of the same type, affect wear, further
complicating the evaluation of wear data.
2. Chemical analysis of lubricating oil. Because the second
method yields results in shorter periods of operation (about 100
hours), many of the problems encountered in the first method are
eliminated. Laboratory analysis of oil samples is necessary, and
sampling procedure is critical. Oil changing and accounting for
iron lost due to oil consumption are also problems, but these can be
solved without much difficulty. It is also necessary to assume that
the iron worn from other engine parts is of negligible quantity, a
simplification which is usually reasonable.
Radioactive piston rings. The third and most recently de3.
veloped method involves the use of radioactive rings on the piston.
Since special geiger counters can detect accurately radioactive iron
in the lubricating oil in concentrations as low as one part per million,
wear rates under set operating conditions can be established in as
little as 12 hours. Thus, variables can be isolated more effectively
and in addition an engine may be used to obtain all the data necessary
for the determination of the effect of one variable on wear without
influence of time and engine condition on results. The disadvantages
of the expensive radiation measuring instruments required and the
precautions necessary to protect personnel from radiation hazards
are more than offset by the time and money saved in operation. The
Atomic Energy Commission has made the irradiation of piston rings
convenient and inexpensive since the development of the istopes
division at the Oak Ridge National Laboratories. The use of this
method yields results only on ring wear; since the rings are exposed to the same conditions as the cylinder walls, however, the ring
wear should be an excellent index of the effect of operating variables.
The radioactive ring wear method was originated by Atlantic
Refining Company in 1940. At that time it was somewhat impractical,
mainly because the only source of radioactive materials was from the
cyclotron. The characteristic short life and weak activity of most
isotopes produced in a cyclotron were the principal disadvantages.
Since World War II, the availability of irradiation service from
the reactor at Oak Ridge has rendered this method a greatly improved means of measuring engine wear.
PISTON RING WEAR AS DETERMINED BY RADIOACTIVE TRACER
9
The method consists of irradiating a standard piston ring in the
reactor for one month to bring it to a relatively high level of activity,
although only one atom in a billion becomes the radioactive iron
isotope, Fe59. The ring is then installed in the engine with special
tools. As the ring wears under the set conditions, the radioactive
iron particles are carried into the lubricating oil. Periodically, samples
of oil are drained from the crankcase and a very sensitive immersion
type geiger counter is used to determine the activity of the oil. By
comparing measured activity to that of a standard solution of known
iron content, the quantity of ring iron in the oil sample can be calculated. The total amount of oil in the engine and the rate of oil
consumption must be known to complete the calculation of total iron
worn from the ring. The engine is operated under a certain set of
conditions until the rate of increase of total ring iron in the oil
becomes constant, thus establishing a definite wear rate. A more
detailed description of these procedures and calculations is given
later in the report.
IV. Objectives of This Work
Of the four processes discussed in the theory, wear due to
corrosion appears to be the most controversial. Disagreement
among investigators demonstrates the need for more information.
A survey of previous research shows that little work has been
done on wear rates with various fuel sulfur contents and cylinder
wall or jacket temperatures. For this reason, it was decided to hold
all other conditions constant while varying fuel sulfur content and
jacket temperature. The results could then be plotted as wear
rates versus jacket temperature for each fuel sulfur content. Fuel
sulfur contents of 0.0%, 0.3%, and 0.75% and jacket temperatures from 110 F to 180 F were selected. The range from 0.0%
to 0.3% covers commercial gasoline fuels. The 0.75% sulfur content was chosen to determine the relative increase in wear with
abnormal sulfur content. The sulfur-free fuel gave a corrosionfree basis for determining the effect of corrosive wear alone.
Actually, the sulfur-free fuel contained about 0.01% sulfur.
The radioactive ring method was chosen as the most advanced
and convenient means for obtaining the wear measurements in
this test. Also, it was desired to initiate the relatively new radioactive tracer method at Oregon State College to progress in the
field of engine research. As much data as possible were obtained
on operating procedures and techniques to help in further research.
The tracer method gives almost unlimited possibilities for further
engine wear research.
10
ENGINEERING EXPERIMENT STATION BULLETIN 33
V. Apparafus
1. The engine and accessories. The engine used (Figure 1)
for this test was a Lauson 2 in. by 2 in., 4 cycle type LF 822.
The engine was loaded by a dc generator connected to heating coils
u
Figure 1. Test Engine and Auxiliary Equipment
capable of dissipating the engine's 2.7 hp at 1,800 rpm. A gravity
flow fuel system was used for dependability. Cooling was accomplished by a heat exchanger supplied with city water. The engine was
equipped with a water pump and control valve to circulate and control the flow of cooling water through the jacket and heat exchanger.
Control valves on the exchanger supply and engine system were
manipulated in such a manner that the water temperature rise through
the engine was about equal at the various jacket temperatures. An
PISTON RING WEAR AS DETERMINED BY RADIOACTIVE TRACER 11
external oil sump shown under the engine was used to facilitate
sampling and temperature control. The "power stat" at the left
supplied current through the ammeter to a heating coil wrapped
around the oil sump. About four amperes through a 12 ohm coil
were necessary for the maximum oil temperatures used. A rightangle mercury-in-glass thermometer indicated the sump temperature.
The sump was so constructed that the oil was drained down to exactly
the same level each time samples were taken, thus leaving the same
quantity of oil in the engine for operation while measuring the radio-
activity of the sample. A gage glass on the sump was marked at a
level corresponding to a known initial weight of oil. Then the oil
loss could be determined by weighing the sample each time. The
sample weight was approximately two-thirds of the total weight of
oil in the engine.
Figure 2. Radioactivity Measuring Equipment.
2. Counting equipment. Figure 2 shows the containers and
instruments that were used for determining the activity of the oil
samples. The glass cylinder on the right is the oil sampling cylinder.
Inside it, supported and centered by a specially constructed frame, is
ENGINEERING EXPERIMENT STATION BULLETIN 33
12
the immersion type geiger counter. The center cylinder is for washing
the counter and was filled with white gasoline. The one on the left
is the standard solution cylinder with its top and bottom counter
centering rings. The instrument on the right is a RCL Mk 13 Mod
1 scalar that actually performs the counting operation. The standard
solution cylinder was filled to nearly the same level as the oil sampling
cylinder to expose the counter surface geometrially the same each
time an activity count was taken. Before the test was started, fresh
oil was put in the sampling cylinder and a count taken. This was the
background count and was subtracted from all oil sample activity
counts. Because it affects the background, the standard solution was
not in the vicinity of the counter when the operator was counting
oil samples. Since the background count varies over long periods,
the value subtracted was actually an average of several counts. The
counting time used was three minutes, which gave a good average
count and still did not require the oil being out of the engine for
excessive time.
Figure 3. Radioactive Ring Shipping Container
3.
Shipping and storage. For shipping the irradiated rings
a special container shown at right in Figure 3 was made. It surrounds
the rings with two inches of lead. The step construction eliminated
PISTON RING WEAR AS DETERMINED BY RADIOACTIVE TRACER 13
any cracks through which radiation could travel. Studs and wing
nuts hold the lid securely on the base. Handles were provided on the
lid for removal. The box at left contained the lead container during
shipment. It was made of double thicknesses of three-quarter inch
plywood and was assembled by glue and wood screws. The frame on
the top was for shipping cards. The container design had to be approved by the Bureau of Explosives. Approval of this container is
shown by the permit number on the lid. The shipping weight was
about 85 pounds.
Figure 4. Piston Shielding Jig and Ring Handling Tools.
4. Handling and shielding. The picture shown in Figure 4
was taken looking from the back side of the jig. The operation of
placing the rings on the piston was shielded by the two inch thick
lead bricks shown and observed through mirrors. This prevented
unnecessary exposure to the body but did not protect the hand
and forearm. The tool at left is a commercial ring expander with
long handles. The tool on the right is an ordinary ring compressor,
also with long handles. The piston was carried and placed in the
engine with the second tool.
5.
Monitoring instruments. The instrument on the left in
Figure 5 is a minometer sold by the Victoreen Instrument Company.
Inserted in the minometer is a pocket ionization chamber. An ionization chamber ready for use is shown in the center. The minometer
14
ENGINEERING EXPERIMENT STATION BULLETIN 33
Figure 5. Radiation Safety Instruments.
and pocket chamber measure the dosage from gamma and x-rays.
To operate the instrument a charge is placed on the chamber by the
minometer and as the radiation ionizes the gas in the chamber, the
charge leaks off. After a period of exposure, the amount of discharge
is measured by the minometer on a scale calibrated in roentgens.
The instrument at right is a RCL Mark 11 Model 10 portable geiger
counter. It is used for detecting small amounts of radioactive contamination. It does not measure dosage, but is useful in examining
clothes, tools, hands, etc., for contamination.
VI. Radafiori Safety
The use of radioactive materials raises the problem of protecting operating personnel from the physical hazards of harmful
radiation. Even though the radiation from the rings is not extremely
dangerous, it cannot be ignored. With some reasonable precautions
and special handling equipment, the danger is virtually eliminated.
The physiological effects of radiation are rather complex, and new
information is being compiled constantly. The figures stated in this
report are mostly Atomic Energy Commission (AEC) specifications
PISTON RING WEAR AS DETERMINED BY RADIOACTIVE TRACER 15
from the AEC isotopes Catalog. There is a great amount of information on this subject that Could be included here; however, only the
data that are essential in this type of work will be discussed.
The unit used to define radiation dosage is the roentgen and is
based on the ionizing effect of the radiation on a gas. Sources of
radiation from the rings are beta and gamma rays. To determine
physical dosage, both radiations can be considered the same and
measured in the same units. The accepted safe level of dosage is
0.1 r (roentgen) per 8-hour day or 0.3 r per week of either type
of radiation. The dosage can be measured conveniently with pocket
ionization chambers in conjunction with a minometer or pocket
dosimeters. A portable geiger counter is also helpful in detecting
contamination but does not give indications of dosage. A survey
meter is an excellent instrument for both detection and dosage indication but is expensive. Use of ionization chambers with the minometer and a portable geiger counter is normally quite satisfactory for
protection of personnel.
Beta rays are easily stopped by most material, but since gamma
rays are very penetrating, several inches of lead are required to
stop them effectively. For this reason, personnel should be shielded
from the rings as much as possible to minimize the dosage when
handling the rings or working around the engine. The beta rays
or particles constitute a hazard only if ingested into the body or
absorbed through the skin because their penetrating power is low
and their path in air is short. Even though the activity of the oil
is low, skin contact should be avoided. To eliminate any possibility
of absorption into the body, rubber gloves should be used because
skin contact is almost inevitable regardless of how carefully the oil
is handled, Of course, direct handling of the rings is extremely
dangerous. In general, the best protection from any type of radiation is distance, since intensity decreases as the square of the distance.
Some actual measurements made during this test are as follows.
Two rings weighing 9.5 grams each were shipped in a lead container
and arrived at the test site at a level of activity that produced a dosage
rate of 4 r/hr at a distance of six inches. This allowed an exposure
of six minutes at one foot while installing the rings. One minute per
ring was ample time for placing the rings on the piston held in a
special jig. Installing the piston and rod in the engine took two
minutes. For additional safety, one person performed the first opera-
tion and another the second. After the piston was placed in the
engine, a full day elapsed before the rod was connected to the crank-
shaft and the engine made ready for operation. During the two
hours necessary for last assembly, 0.02 r was measured by ionization
16
ENGINEERING EXPERIMENT STATION BULLETIN 33
chambers on the wrists of both hands. The shielding provided by
the cylinder block reduced the dosage considerably. During this
same day, the standard solution containing 200 mg of the iron was
made. At the end of this day the wrist chambers registered 0.05 r or
half the safe daily dose. The special tools for handling the rings
were constructed in such a way that the hands were one foot away
from the radioactive material. The whole operation was entirely
safe because the specified dosage is based on whole body exposure,
and dosages measured were to the hands and forearms.
After the engine was in operating condition, measurements were
taken around the engine to determine the safe time in this vicinity.
At an average radius of four inches around the engine cylinder
and head, the dosage rate was 0.1 r/day. During the first day of
operation the dosage measured by wrist and shirt pocket chambers
was 0.04 r in 16 hours. Succeeding days showed less exposure as the
engine required less attention. Ionization chambers placed adjacent to
the standard solution and typical oil samples containing about 6 mg of
radioactive iron showed about 0.003 r/hr.
Disposable paper towels were used to wipe up any oil drops
around the engine or sampling containers. Hands and shirt sleeves
were checked repeatedly for any trace of contamination, and none
was detected. Because of the rings in the engine, it was necessary
to be at least 30 feet away when checking hands or clothes. In the
vicinity of the engine the geiger counter read 1,000 to 2,000 counts
per minute. A reverse flow muffler was used on the exhaust system
to trap any contaminated solids. To check exhaust, a porous paper
was placed at the muffler outlet to filter the gases. No contamination
was detected at this point.
Considering the over-all operation, it was completely safe. Some
precautions taken were possibly unnecessary but nevertheless wise.
Any precaution that would reduce exposure, even though already
below the safe limit, was considered worth while.
VII. Procedure
1. Test conditions. After the authors obtained proper authorization through the Atomic Energy Commission and Federal Bureau
of Explosives, two standard compression rings for the Lauson engine
were sent to the Oak Ridge National Laboratory for irradiation.
Also, six 200 mg segments of the ring material were irradiated with
the rings for use as standards of radioactivity. Eight weeks elapsed
from shipment to receipt of the rings and standards. The standard
solution was made by dissolving one of the segments in a 1 to 12
PISTON RING WEAR AS DETERMINED BY RADIOACTIVE TRACER 17
sulfuric acid solution and then diluting 1 to 20 to reduce the activity
count. The final solution was then comparable in iron content to
the oil samples. The rings were installed in the engine with the special
tools described in the preceding chapter. The fuel with various
sulfur content was made by mixing carbon disulfide with sulfur-free
white gasoline. The lubricating oil used was an ASTM Reo-7-48
reference oil. The constant conditions held were as follows:
50%
Load
Speed
1,800 rpm
155 F
Oil Sump Temp
(65
Octane)
White Gas + CS2
Fuel
25° BTDC
Ignition Timing
13.5 to 1
A/F Ratio
85 F
Intake Temp
2. Operation. Since new rings were used and the cylinder
walls were honed, a break-in run was necessary. This period of
operation was continued until the activity count of the oil indicated
that a normal wear rate had been established. After changing oil,
the regular runs with no-sulfur fuel were started, first setting the
high jacket temperature of 180 F, and successively 160 F, 145 F,
130 F, and 110 F. The engine was run a minimum of five hours before
taking the first oil count on any condition to eliminate the effect of
the previous conditions. Ring iron wear was measured at two- and
three-hour intervals, depending on the wear rate. A running plot
of ring iron in the oil versus hours was kept during each run. Four
points in a straight line were set as the requirement to establish
the wear rate, usually over a period of 12 hours or more. This
process was repeated for each fuel sulfur content. When the fuel
was changed, a considerably longer time was allowed for the conditions to take effect. Also, the oil was changed after each run to
eliminate the possibility of dirty oil affecting wear.
3.
Iron loss and decay corrections. It was necessary to
correct for iron loss due to oil consumption. This was accomplished
by assuming that all the oil lost during an interval contained the same
quantity of iron as the oil at the end of that interval. This is a close
approximation because the oil lost by the rings contains a higher
concentration of ring iron than the oil in the sump because of its
proximity to the wear region. Thus, assuming a higher-than-average
iron concentration for the interval is justified. Total oil quantity was
fixed at the time of taking the first sample for each run by filling the
oil sump to a predetermined mark on the sump gage glass. Then, with
constant oil temperature, oil consumption was found with sufficient
18
ENGINEERING EXPERIMENT STATION BULLETIN 33
accuracy by the decrease in weight of successive oil samples. The
last factor considered was the radioactive decay of the standard
solution. This is necessary because the half life of Fe59 is only 47
days. Radioactivity counts on the standard solution were taken at
one-day intervals at the beginning of the test. Using these values
and the half life of 47 days, a semilog plot of counts per minute
per mg (cpm/mg) versus days was constructed to provide the
standard activity count for the rest of the test. This curve was based
on the theoretical exponential decay of radioactive materials and
conveniently plots a straight line on semilog graph paper.
Applying the previously mentioned factors, the total ring iron
in the oil was calculated in the following manner.
Let: W = Total weight of oil in engine at time of first sample
w = Weight of sample taken
C
C3
Radioactivity count of sample taken, cpm
= Specific radioactivity of standard solution from
curve, cpm/mg
RI = Total iron worn from the rings, mg.
Then at first sampling,
R1
WxC
vi x
C3
At intervals 1, 2, 3, etc,
rw
RI1
I
Lwi
C1 + (w-w1) C1
11
I
J
C31
rw
RI2
I
Lw2
C2 + (w-w1) C1 + (wi-w2) C2
11
I
J
C82
rw
RI3
I
C3 + (w-w1) C1 + (w1-w2) C2 + (w2-w3) C3
Lw3
Applying C31, C32, C33, etc, to all the terms in the brackets is not
exactly correct, but the decay is so slight and the oil consumption
is so small, being less than one per cent of the total oil, that the
error is negligible over short test periods. At low wear rates the cal-
culations can be simplified by using the first calculation at each
interval without sacrificing accuracy. By plotting RI, RI1, RI2, etc,
versus time in hours, the slope of the curve or wear rate in mg ring
iron per hour can be determined.
11
J
I
C33
PISTON RING WEAR AS DETERMINED BY RADIOACTIVE TRACER 19
VIII. RESULTS
The results of this test are shown graphically in Figure 6. It
can be seen that with 0.75% sulfur in the fuel, ring wear increases
nearly ten times as the jacket temperature is reduced from 160 F
to 110 F. At the low temperature, wear is increased nearly four
times by adding 0.75% sulfur to the fuel. With only 0.3% sulfur
it is still nearly twice the wear with sulfur-free fuel. The three curves
appear to converge to a minimum wear rate at 160 F, indicating that
the effect of sulfur is eliminated. This checks well with previous
research at other laboratories. H. R. Jackson, et al (8), of the
Atlantic Refining Company, report that the dew point temperature
of combustion gases is approximately 150 F. Below this temperature,
condensation of water vapor on the cylinder walls will occur, condensing larger quantities of vapor as the temperature decreases. Since
the oxides of sulfur are present in the combustion products, it is
probable that they combine with the water vapor to form highly
corrosive acids that attack the cylinder walls and rings. Above the
dew point, no condensation will occur, and the acids do not attack
the metal surfaces. If condensation of the acid on the surfaces is
the major cause of corrosive wear, the wear should be fairly constant above the dew point. This is borne out quite well by the curves,
and it appears that condensation is necessary to cause corrosion of
the metal. The wear above the dew point, then, must be caused by
friction and abrasion.
1.25
I
I
ONE-CYLINDER LAUSON ENGINE
155 F SLIMe
800 RPM 1/2 LOAD
1.00
0
1
0.01 PERCENT SULFUR
0.75
o
a.
0
0.30 PERCENT SULFUR
0.75 PERCENT
SULFUR
0.50
0.25
0.00
105
125
145
85
165
JACKET WATER TEMPERATURE - DEGREES
F
Figure 6. Effect of Fuel Sulfur on Ring Wear.
20
ENGINEERING EXPERIMENT STATION BULLETIN 33
Considering the high temperatures normally associated with the
combustion chamber of an internal combustion engine, it may require some exercise of the imagination to become convinced that a
dew point has been reached on internal surfaces. The cast iron of
which rings and cylinders are made is a fairly porous material
and would therefore tend to adsorb gaseous substances. It seems
reasonable that water vapor along with the oxides of sulfur could
be adsorbed by the metal during the combustion of fuel and condensed at the end of the exhaust stroke or beginning of the compression stroke as long as jacket temperatures remained low. High
jacket temperatures should discourage condensation and also reduce
the quantity of gases adsorbed.
Ellis and Edgar (4) in recent tests have effectively reduced
corrosive wear by the use of alkaline lubricating oils. Their objective
was not to prevent the acids from forming but to cover the metal
surfaces with a protective layer that would neutralize the acids
before they reached the ring and wall surfaces. Their tests were
highly successful. However, these tests did not indicate whether the
acids were formed in the process of combustion and then condensed
on the rings and walls or whether the corrosive gases are present
in an adsorbed layer in the metal surfaces awaiting condensation of
water vapor to start corrosion.
A result of the work at Oregon State College which appears to
support the adsorbed layer explanation is the reduction of high
temperature wear by higher fuel sulfur content. It is conceivable that
sulfur, being a high pressure additive in its free state and in certain
organic compounds, could, in the absence of water, reduce friction
and abrasive wear. The sulfur compounds formed during combustion
could possibly combine with the oil film to form a high pressure
additive that would reduce friction wear under this mild scuffing con-
dition. These data shown on the curve could be in error due to the
low wear rates, but this is unlikely because the points are quite consistent, and some were reproduced by check runs.
The no-sulfur curve should essentially show friction and abrasive wear at all jacket temperatures investigated. The slight dip in
the curve indicates an optimum oil viscosity for best lubrication.
Even though the oil sump temperature was held constant, viscosity
of the oil film on the cylinder wall was undoubtedly influenced by
wall temperature. The comparatively sharp rise in this curve above
160 F was checked twice, as shown by the two points, and seems to
be correct. However, it is possible that the non-additive reference
oil used has lubricating qualities at higher temperatures inferior to
those of a heavy duty oil. This high temperature wear increase is
PISTON RING WEAR AS DETERMINED BY RADIOACTIVE TRACER 21
also evident, but to a smaller degree, in the 0.3% and 0.75% curves.
Reduced viscosity apparently increases friction and abrasive wear in
the absence of metal-protecting additives.
The curves shown in Figure 7 are typical of the running plot
of data that was kept during the test. The break-in wear curve is
particularly interesting. The extremely high wear rate is caused by
scuffing as the ring and wall surface irregularities are cut away.
The engine appeared to be broken in at eight hours running, but
this was somewhat misleading. The runs immediately following were
erratic, and consistent data were obtained after more hours of
operation. Typical wear rate determination plots are shown by the
other two curves. The first section of the curves shows the residual
effects disappearing. The last section shows the wear rate being
established. In some cases, more time was required to eliminate the
residual effects. It was also found that it was necessary to fill the
25
ONE-CYLINDER LAUSON ENGINE
15SF SUMP 800 RPM V2 LOAD
20
a.
0
I0
o
BREAK-IN 160 F JACKET O.0l
SULFUR
1.30 F JACKET 0.30
110 F JACKET 0.75
SULFUR
SULFUR
I-
o
0
-j
0
2
S
2
z
0
II
0
0
2
4
6
8
0
TIME - HOURS
12
14
16
Figure 7. Typical Curves for Wear Rate Determination
sump with fresh oil at the start of each run to obtain consistent
activity counts. This could be due to high iron concentrations and
foreign particles from previous runs affecting the wear. Also, the
accuracy of the geiger counter decreases with higher iron concentra-
tions. The possibility that foreign matter in the oil reduced the
activity count of the oil by shielding the iron particles is probably
remote.
In general, the results were quite satisfactory. The points fell on
reasonably smooth curves with the exception of the 0.3%-130 F,
22
ENGINEERING EXPERIMENT STATION BULLETIN 33
145 F points. The discrepancy of these points was not serious, however. The reproductibility was shown by the two points at 0.75%145 F and 0.0%-180 F.
Other theories on ring and cylinder wear are discussed in papers
listed in the bibliography.
IX. Conclusions
It can be concluded from this test that corrosion is an important
wear process at low jacket temperatures with sulfur in the fuel. Con-
ditions such as these are found in field service in start-stop shortrun driving. Commercial fuels contain between 0.1% and 0.2%
sulfur, and in this type of service average engine jacket temperatures are usually quite low. In long-haul work in which the engine
becomes thoroughly warmed, corrosive wear is virtually eliminated,
and friction and abrasion become the main factors in wear.
The no-sulfur curve shows that jacket temperature does not
have a very important effect on friction and abrasive wear within
normal operating limits. The variation detected can be attributed to
the change in oil viscosity on the cylinder walls with jacket temperature. The increase in wear above 160 F probably demonstrates the
need for additives in lubricating oils or for oils of more constant
viscosity. The non-additive reference oil used in this test apparently
did not have the best high temperature lubricating qualities.
The test indicates that for commercial fuels there is an optimum
jacket temperature for wear reduction. It appears that the range
from 150 F to 170 F water jacket is ideal for the Lauson engine.
This quantitative result from the Lauson engine can be applied to
other engines with reasonable accuracy because the conditions affecting dew point and condensation are comparable.
X. Recommendafions
Results obtained by the authors and by other investigators of
engine wear point out a number of outstanding subjects for further
research. Of special interest would be additional work in an attempt
to verify the results obtained at Oregon State College on the re-
duction in wear found by using high-sulfur fuels under certain
conditions. Such a study might contribute considerably to the knowledge of reaction mechanisms.
Neutralization of wear tendencies with high sulfur fuels under
adverse conditions by the use of alkaline additives in lubricating oils
PISTON RING WEAR AS DETERMINED BY RADIOACTIVE TRACER 23
warrants concentrated study. Results reported by Ellis and Edgar
(4) are apparently quite promising.
Tests using low-sulfur fuels over a wide range of loads, oil
viscosities, and atmospheric conditions should provide valuable infor-
mation on friction wear.
High additive content oils as well as "service station" additives
could be investigated with both low and high sulfur content fuels.
Of particular interest to the authors would be lubricating oils to
which molybdenum sulfide has been added.
Use of radioactive piston rings makes such investigations much
simpler, more rapid, and probably much more reliable. The use of
radioactive cylinder liners should also provide a valuable aid in wear
studies although these would considerably complicate radiation safety.
Of great interest and value would be determination of the ratios
of ring/cylinder bore wear under the various operating conditions.
The authors attempted total iron analyses of crankcase samples,
which, along with determination of ring wear by radioactivity measurements, should have provided some of the desired information.
To date results obtained have been inconsistent and are not considered
reliable.
24
ENGINEERING EXPERIMENT STATION BULLETIN 33
Xl. Bibliography
1.
2.
3.
Braendel, Helmuth G. Design features affecting wear. Paper presented
at the society of automotive engineers summer meeting, June 6, 1950,
at French Lick, Indiana. l2p.
Braendel, Helmuth G. Engine wear from scuff ing. Paper presented at
the society of automotive engineers summer meeting, June 6, 1950, at
French Lick, Indiana. Sp.
Brenneke, A. M., and A. J. Weigand. Piston rings and the wear problem.
Paper presented at the society of automotive engineers west coast
meeting, August 13-15, 1951, at Seattle, Washington. 5p.
4.
Ellis, J. C., and J. A. Edgar. Wear prevention by alkaline lubricating
5.
Glasstone, Samuel. Sourcebook on atomic energy, New York, Van nostrand,
6.
Guest, G. H. Radioisotopesindustrial applications. Toronto, Pitman, 1950.
7.
Jackson, H. R. Laboratory and field wear tests using radioactive tracers.
Paper presented at society of automotive engineers summer meeting,
June 1-6, 1952, at Atlantic City, New Jersey. 9p.
oils. Paper presented at the society of automotive engineers summer
meeting, June 1-6, 1952, at Atlantic City, New Jersey. l4p.
1950. 525p.
l8Sp.
8. Jackson, H. R. et al. Some phenomena of engine wear as revealed by
radioactive tracers. Paper presented at the society of automotive engineers fuels and lubricants meeting, Nov. 1, 1951, at Chicago, Illinois.
7p.
9.
Jeffrey, R. E., J. B. Duckworth, and E. J. Gay. Effects of sulfur in
motor gasoline on engine operation. Paper presented at the society of
automotive engineers summer meeting, June 4-9, 1950, at French Lick,
Indiana. lip.
10. Kavanagh, F. W. Engine wearcomparison of radioactive wear and
field measurements. Paper presented at the society of automotive engineers summer meeting, June 1-6, 1952, at Atlantic City, New Jersey.
5p.
11.
Kunc, J. F., D. S. McArthur, and L. E. Moody. How engines wear.
Paper presented at the society of automotive engineers summer meeting,
June 1-6, 1952, at Atlantic City, New Jersey. 9p.
12. Manov, George G. The availability of radioisotopes and their application
to petroleum and automotive research. Paper presented at the
society of automotive engineers fuels and lubricants meeting, Nov. 1,
1951 at Chicago, Illinois. l4p.
13. Moore, C. C., and W. L. Kent. Wear measorements by physical, chemical,
or radioactivity methods. Paper presented at the society of automotive
engineers summer meeting, June 1-6, 1952, at Atlantic City, New
Jersey. 3p.
14. Pennington, John W. Piston ring and cylinder wear in diesel engines. Paper
presented at the society of automotive engineers tractor and diesel
engine meeting. Sept. 7-9, 1948, at Milwaukee, Wisconsin. l4p.
15.
Pinotti, P. L., D. E. Hull, and E. J. McLaughlin. Application of radioactive tracers to improvement of automotive fuels, lubricants, and
engines. 6P.
16. U. S. atomic energy commission. Isotopes catalog and price list no. 4.
Oak Ridge, Tennessee, USAEC isotopes division, March 1951. 75p.
PISTON RING WEAR AS DETERMINED BY RADIOACTIVE TRACER 25
OREGON STATE COLLEGE
ENGINEERING EXPERIMENT STATION
CORVALLIS, OREGON
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PISTON RING WEAR AS DETERMINED BY RADIOACTIVE TRACER 27
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THE ENGINEERING EXPERIMENT STATION
Administrative Officers
EDGAR W. SMITH, President, Oregon State Board of Higher Education.
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C. 0. HEATH, Engineering Materials.
G. W. HOLCOMB, Civil and Structural Engineering.
A. D. HUGHES, Heat Power and Air Conditioning.
J. G. JENsEN, Industrial Resources.
W. F. MCCULLOCH, Wood Products.
F. 0. MCMILLAN, Electrical Engineering.
Fam MERRYFIELD, Sanitary Engineering.
0. G. PAASCHE, Metallurgical Engineering.
W. H. PAUL, Automotive Engineering.
MIL0sH PopovscH, Mechanical Engineering.
M. C. SHEELY, Manufacturing Processes.
LOUIS SLEGEL, Machine Design.
E. C. STARR, Electrical Engineering.
C. E. THOMAS, Engineering Materials.
J. S. WALTON, Chemical Engineering.
Technical Counselors
R. H. BALDOCK, State Highway Engineer, Salem.
R. R. CLARK, Designing Engineer, Corps of Engineers, Portland District,
Portland.
R. W. COWLIN, Director, Pacific Northwest Forest and Range Experiment
Station, U. S. Department of Agriculture, Forest Service, Portland.
DAVID DON, Chief Engineer, Public Utilities Commissioner, Salem.
C. M. EVERTS, JR, State Sanitary Engineer, Portland.
F. W. LIBBEY, Director, State Department of Geology and Mineral Industries,
Portland.
PAUL B. MCKEE, President, Portland Gas and Coke Company, Portland.
B. S. Mos.Row, Engineer and General Manager, Department of Public Utilities
and Bureau of Water Works, Portland.
J. H. POLHEMUS, President, Portland General Electric Company, Portland.
S. C. SCHWARZ, Chemical Engineer, Portland Gas and Coke Company, Portland.
C.
K. STEmErr, Manager, Industries Department, Portland Chamber of
Commerce.
J. C. STEVENS, Consulting Civil and Hydraulic Engineer, Portland.
C. E. STRICKLIN, State Engineer, Salem.
Oregon State College
Corvallis
RESIDENT INSTRUCTION
Liberal Arts and Sciences
LOWER DIVISION (Junior Certificate)
SCHOOL OF SCIENCE (B.A., B.S., M.A., M.S., Ph.D. degrees)
Professional Schools
SCHOOL OF AGRICULTURE (B,S., B.Agr., M.S., M.Agr., Ph.D.
degrees)
SCHOOL OF BUSINESS AND TECHNOLOGY (BA., B.S., B.S.S. de-
grees)
SCHOOL OF EDUCATION (B.A., B.S., Ed.B., M.A., M.S., Ed.M.,
Ed.D. degrees)
SCHOOL OF ENGINEERING AND INDUSTRIAL ARTS (B.A., B.S.,
M.A., M.S., A.E., OLE., C.E., E.E., I.E., M.E., Min.E.,
Ph.D. degrees)
ScHooL OF FORESTRY (B.S., B.F., M.S., M.F., FE., degrees)
SCHOOL OF HOME EcoNoMIcs (B.A., B.S., M.A., M.S., M.H.Ec.,
Ph.D. degrees)
ScHooL OF PHARMACY (B.A., B.S., M.A., M.S., Ph.D. degrees)
Graduate School (M.A., M.Agr., M.S., Ed.M., M.F., M.H.Ec., A.E.,
OLE., C.E., E.E., F.E., I.E., M.E., MinE., Ed.D.,
Ph.D. degrees)
Summer Sessions
Short Courses
RESEARCH AND EXPERIMENTATION
General Research
Science Research Institute
Agricultural Experiment Station
Central Station, Corvallis
Astoria, Burns, Hermiston, Hood River, Medford, Moro, Union,
Pendleton Branch Stations
Klamath Falls, Milton-Freewater, Ontario, Oregon City, Redmond, The Dalles Experimental Areas
Engineering Experiment Station
Oregon Forest Products Laboratory
EXTENSION
Federal Cooperative Extension (Agriculture and Home Economics)
General Extension Division