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211Sd~~fi . ~/ - / ....
No. 13475PISTON AND RING ASSvY FRICTION STUDIES
IN CU1JTINS 903 ENGINECoNmTACT DAAE07-84-C-R134
JUNE 1989DONALD J. PATTERSONIKEVIN M. MORRISON
GEORGE B, ScHwAmRZ
DEPARTMENT OF MECHANICALENGINEERING AND APPLIED MECHANICS
TH UNIVERSITY OF MICHIGANANN ARBOR, MICHIGAN 48109-2121AND
U.S. ARw rANK-AUOMOTI VE CO•vAND
By WARREN, MICHIGAN 48397-50
APPROVED FOR PUBLIC RELEASE:
DISTRIBUTION IS UNLIMITED
U.S. ARMY TANK-AUTOMOTIVE COMMANDRESEARCH, DEVELOPMENT &
ENGINEERING CENTERWarren, Michigan 48397-5000
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6a. NAME OF PERFORMING ORGANIZATION 6b. OFFICE SYMBOL 7a. NAME
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State, and ZIP Code)2250 G.G. Brown LaboratoryAnn Arbor, Michigan
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NUMBERSPROGRAM I PROJECT TASK WORK UNITWarren, Michigan 48397-5000
ELEMENT NO. NO. NO. ACCESSION NO.
11. TITLE (Include Security Classification)
Piston and Ring Assembly Friction Studies in Cummins 903 Engine
(u)
12. PERSONAL AUTHOR(S)Patterson, Donald J., Morrison, Kevin M.,
and Schwartz, George B.
13a. TYPE OF REPORT 13b. TIME COVERED. 14. DATE OF RE;ORT (Year,
Month, Day) 15. PAGE COUNTFIAL .FROM Oct. 84TOOct. 8&.
Jun58
16. SUPPLEMENTARY NOTATION
17. COSATI CODES 18. SUBJECT TERMS (Continue on reverse if
necessary and identify by block number)FIELD GROUP SUB-GROUP
Friction, Piston, Piston rings, Uncooled Diesel
19. ABSTRACT (Continue on reverse if necessary and identify by
block number)
Piston and ring assembly friction has been measured in a single
cylinder Cummins 903 diesel.The engine was motored and fired,
cooled and uncooled. For uncooled operation, plasmasprayed chromium
oxide ring and liner coatings were employed with a synthetic
lubricant.The Instantaneous IMEP and Fixed Sleeve methods were used
for the friction measurement ona crank angle by crank angle basis,
with a cycle average of about 1.5 to 4 psi fmep. Con-siderable
effort was expended in developing the measurement techniques, with
a major efforton the Instantaneous IMEP method. In a parallel
effort a bench type, heated, piston ringand liner wear simulator
was developed. This permitted rapid screening of promisingcandidate
materials for uncooled engine tests. The plasma sprayed chromium
oxide coatingswere found to be best.
20. DISTRIBUTION/AVAILABILITY OF ABSTRACT 21. ABSTRACT SECURITY
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Code) 22c. OFFICE SYMBOLE. Schwartz (313)574-5656 AMSTA-RGRD
DD Form 1473, JUN 86 Previous editions are obsolete. SECURITY
CLASSIFICATION OF THIS PAGEUnclassified
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PREFACE
The very important role of the Cummins Engine Company,especially
Ralph Slone and Malcolm Naylor is gratefullyacknowledged. They
supplied virtually all of the enginehardware, some experimental
equipment, and the basic pistonand ring laboratory fixture.
Furthermore, the authors thank Professor Zu-Wei Cui ofZhejiang
University, China, and Professor Kenneth Ludema ofThe University of
Michigan, for their assistance withdevelopment of the piston and
ring simulator and theanalysis of the results. Also, we wish to
acknowledge thecontributions of Guy Babbitt, graduate student, for
his workin designing, constructing, and evaluating the
Fixed-Sleevemethod for the Cummins 903 engine.
We also thank Jack Brigham and Fred Rowe for their
expertassistance in design and construction of the test
equipment.Most importantly, we thank the Army-Tank Automotive
Commandfor their financial and technical support. Special note
ismade of the important contributions of Dr Walter Bryzik,
andErnest Schwarz. They put the program together andcoordinated the
Cummins and University of Michigan efforts.
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TABLE OF CONTENTS
Section Page
1.0. INTRODUCTION .................................... 18
2.0. OBJECTIVE ............................... ....... 19
3.0. CONCLUSIONS AND OBSERVATIONS .................... 203.1.
Instantaneous IMEPMethod ....................... 203.2.
Fixed-Sleeve Method ............................. 213.3. Ring and
Liner Beinch Test ....................... 21
4.0. RECOMMENDATIONS .................................. 224.1.
Instantaneous IMEP Method ....................... 224.2.
Fixed-Sleeve Method ......... .................... 224.3. Ring and
Liner Bench Test ....................... 23
5.0. DISCUSSION ...................................... 235.1.
Background ................................... 235.2. Design
.......................................... 245.2.1. Instantaneous
IMEP Method ..................... 245.2.2. Fixed-Sleeve Method
........................... 325.2.3. Ring and Liner Bench Test
..................... 325.3. Implementation
.................................. 385.3.1. Implementation of the
Instantaneous IMEP
Method ........................................ 38
5.3.1.1. Engine Installation ...................... 385.3.1.2.
Grasshopper Linkage Design.................. 405.3.1.3. Cylinder
Pressure-Transducer............. 495.3.1.4. Strain-Gauged
Connecting Rod.......... 495.3.1.5. Data Acquisition
......................... 555.3.2. Implementation of Fixed-Sleeve
Method......... 585.3.2.1. Implementation on the 4.1-Litre Engine
...... 585.3.2.2. Additional Details ......................
615.3.2.3. Implementation on the Cummins 903 Engine .... 615.3.3.
Ring and Liner Bench Test ..................... 705.4. Testing
......................................... 705.4.1. Testing With the
Instantaneous IMEP Method .... 705.4.1.1. Procedures
....................... 705.4.1.2. Results on the Cummins 903
Engine ........... 725.4.2. Testing With the Fixed-Sleeve Method
.......... 895.4.2.1. Procedures ..................................
895.4.2.2. Calibration ................................. 895.4.2.3.
Fixed-Sleeve Results on 4.1-Litre Engine .... 905.4.2.4. Testing
With the Cummins 903 Engine ......... 1055.4.3. Ring and Liner
Bench Test ..................... 1125.4.3.1. Baseline Ring/Liner
Results ................. 114
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TABLE OF CONTENTS (Continued)
5.4.3.2. Titanium Carbide Ring and Chrome CarbideLiner Coatings
.............................. 115
5.4.3.3. Plasma-Sprayed Chromium Oxide Ring and LinerCoatings
........... .... .................... 120
5.4.3.4. Comparison With Cameron Plint ...............
1205.4.3.5. Comparison With Engine Results ..............
1275.4.3.6. Interface Oil Quantity and Quality
Considerations .............................. 1275.4.3.7.
Simulator Repeatability ..................... 1335.4.3.8.
Photographic Results from Engine Tests ...... 133
LIST OF REFERENCES .................... ........ ..........
154
DISTRIBUTION LIST ................................... Dist-6
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LIST OF ILLUSTRATIONS
Figure Title Page
5-1. Single-Cylinder Cummins 903 Engine Equippedfor
Instantaneous IMEP Method .................. 25
5-2. Stain-Gauged Connecting Rod .................... 28
5-3. Grasshopper Linkage ............................ 29
5-4. Typical Cylinder Pressure, Connecting Rod,and Inertia
Forces ............................. 30
5-5. Piston and Ring Assembly Friction Force,Velocity and Power
Dissipation ................. 31
5-6. Fixed-Sleeve Design for the 4.1-LitreGasoline Engine
............. ... ............... 34
5-7. Cylinder Pressure (upper), Strain-GaugeVoltage (center),
and Resulting FrictionForce (lower), WOT, 1000 RPM, Motoring
......... 35
5-8. Schematic Showing Essential Features ofBench-Test Simulator
for Ring and Liner Wearand Friction .............................
....... 37
5-9. Photograph of Layout Board for DesigningGrasshopper Linkage
......................... 41
5-10. Photograph of Completed Grasshopper Linkage .... 42
5-11. Lower-End Bracket, Side View ................... 43
5-12. Lower-End Bracket, End View .................... 44
5-13. Oil-Pan Modifications .......................... 45
5-14. Oil-Pan Spacer .................................. 46
5-15. Photographs of Lower-End Bracket (upper)and Oil-Pan
Modifications (lower) .............. 47
5-16. Grasshopper to Connecting Rod AttachmentBracket
........................................ 48
5-17. Pressure-Transducer Sleeve ..................... 50
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5-18. Sleeve and Head Assembly ....................... 51
5-19. Pressure-Transducer Location in Head ........... 52
5-20. Photographs of Pressure-Transducer ............. 53
5-21. Photograph of Machined Connecting Rod .......... 54
5-22. Data Acquisition System and Display ............ 56
5-23. Crankangle Encoder Installed on Front of Engine 57
5-24. Schematic of Data Acquisition System ........... 59
5-25. Block Diagram for Data Acquisition System ...... 60
5-26. Photograph of Fixed-Sleeve Assembly for 4.1-Litre Gasoline
Engine .......................... 62
5-27. Components of the Fixed-Sleeve Method for theCummins 903
Engine ............................. 64
5-28. Original Strain-Gauge Bridge Noise, No BridgeExcitation
........................... 64
5-29. Same as Figure 5-28 Except with Excitation,10 lbm Weight
Applied Intermittently ........... 65
5-30. Same as Figure 5-28, Except 2 lbm Weight Added. 65
5-31. Same as Figure 5-30, Except 10 kHz Filter ...... 66
5-32. Same as Figure 5-30, Except 30 kHz Filter ...... 66
5-33. Same as Figure 5-32, Except No Load Applied .... 67
5-34. Fourier Transform of Figure 5-33 ............... 67
5-35. Fourier Transform of Figure 5-33, HigherFrequencies
.................................... 68
5-36. Original Signal, Except IBM Monitor Unplugged.. 68
5-37. Bridge Calibration, Volts Versus Weight Appliedto
Strain-Gauged Collar ........................ 69
5-38. Brake Specific-Fuel Consumption DuringBreak-In: BSFC
units, lbm/bhp-hr ............... 73
5-39. Motoring Torque During Break-In ................ 74
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5-40. Fuel Injector Inlet Pressure During Break-In... 75
5-41. Friction Force with Low (102 F) and High(200 F) Oil and
Water Temperatures, SAE 40Oil, 200 RPM, Normally Aspirated
............... 77
5-42. Friction Force Trace Including Error fromCrankshaft
Magnetism - 1200 RPM, 200 Waterand Oil, Naturally Aspirated
................... 79
5-43. Strain-Gauge Signal Without BridgeExcitation Before and
After Reduction ofMagnetic Interference, 1200 RPM ................
80
5-44. Motoring Piston and Ring Friction, 1200RPM, 29.17 PSIA
Manifold Pressure, 200 FWater and Oil, Friction MEP = 3.03 PSI
......... 82
5-45. Firing Piston and Ring Friction, 1200 RPM,29.17 PSIA
Manifold Pressure, 200 F Waterand Oil, Friction MEP = 2.25 PSI
............... 84
5-46. Instantaneous Crank Speed at 1200 RPM,Firing, 30 In. Hg.
Boost ....................... 85
5-47. Results Shown in Figure 5-45 BeforeCorrected for
Instantaneous Speed Variation .... 86
5-48. Motoring Piston and Ring Friction, 1200RPM, 30.01 PSIA
Manifold Pressure, UncooledOperation, Friction MEP = 2.97
PSI,Synthetic Lubricant ............................. 87
5-49. Firing Piston and Ring Friction, 1200 RPM,29.91 PSIA
Manifold Pressure, UncooledOperation, Friction MEP = 1.55
PSI,Synthetic Lubricant .................... 88
5-50. Calibration Curve Showing Increasing andDecreasing
Pressure ............................ 91
5-51. Strain-Gauge Signals Overlapped for FourConsecutive
Traces, 1000 RPM, Motoring, WOT .... 92
5-52. Friction Force Versus Crank Angle Motoringand Firing, 1000
RPM, Part Load: Note MajorDifference After TDC Firing
.................... 93
5-53. The Influence of Engine Speed Under FiringOperation, 1000
RPM, WOT: M.V.P. IndicatesMaximum Piston Velocity Crank Angle
............ 95
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5-54. The Effect of Water and Oil TemperaturesUnder Motoring
Operation, 1000 RPM, WOT:T.P. Indicates Transition Point
............... 95
5-55. Comparison Between Honed and Machined Liners,1000 RPM,
Motoring, WOT ........................ 97
5-56. Friction Without Oil Ring, Various CompressionRings
Removed, 500 RPM, Motoring, WOT .......... 98
5-57. Friction with Oil Ring, Various CompressionRings Removed,
500 RPM, Motoring, WOT .......... 99
5-58. Histogram of Friction Mean EffectivePressure for Various
Ring Combinations,From Data of Figures 5-55 and 5-56 ..............
101
5-59. Comparison of Fixed-Sleeve (upper) andInstantaneous IMEP
(lower) Methods,Motoring, 1000 RPM, SAE 50 Oil, 14.39 PSIAManifold
Pressure, 104 F Water, 130 F Oil ...... 103
5-60. Comparison of Fixed-Sleeve (upper) andInstantaneous IMEP
(lower) Methods, Firing,1000 RPM, SAE 30 Oil, 8.39 PSIA
ManifoldPressure, 176 F Water, 220 F Oil ............... 104
5-61. Comparison of PR FMEP Results for the TwoMethods: (The
Fixed-Sleeve Results areConsistently Higher)
........................... 106
5-62. Piston and Ring Friction by Fixed-SleeveMethod, Cummins
903 Engine, 100 RPM, SAE 40Oil, Motoring, 175 F Water, 195 F
Oil,Friction MEP = 4.08 PSI ........................ 107
5-63. Noise Generated by Magnetic.Fields, NoBridge Excitation,
100 RPM ..................... 108
5-64. Data of Figure 5-62 Corrected for MagneticInterference
..................................... 109
5-65. Noise Generated by Magnetic Fields, No BridgeExcitation,
1000 RPM ............ . ...... .. 110
5-66. Piston and Ring Friction by Fixed-SleeveMethod, Cummins
903 Engine, 1000 RPM, SAE 40Oil, Motoring, 175 F Water, 195 F
Oil,Friction MEP = 4.85 PSI, Corrected forMagnetic
Noise..................-.. ... ...... .i i
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5-67. Friction Coefficient Versus Crank Angle forBase Engine
Materials, Normal Force 85.4 N,268 RPM, 35 C Test Temperature
................. 115
5-68. Proficorder Trace of Worn Baseline LinerTested Against
Chromium Plated Ring,Mineral Oil: Scale Vert = 0.51 um/div,Horiz =
2.5 mm/div, Sample Interval of 7.4 um.. 115
5-69. Average Friction Coefficient During Test,Baseline Engine
Materials, Lubricated .......... 116
5-70. Average Friction Coefficient Over Test,Titanium Carbide
Ring on Chromium CarbideLiner, No Lubrication
.......................... 117
5-71. Average Friction Coefficient Over Test,Titanium Carbide
Ring on Chromium CarbideLiner, Synthetic Lubricant
..................... 118
5-72. Proficorder Roughness Traces of Plasma-SprayedChromium
Carbide Liners, Before and After Two-Hour Test Against Titanium
Carbide PlasmaSprayed Ring, Scale: vert = 0.25 um/div, Horiz= 0.1
mm/div, Sample Interval of 1.0 um ........ 119
5-73. Proficorder Traces Showing Wear ScarGeometry on Worn
Chromium Carbide LinerSamples, Two-Hour Test, Scale: vert =
5.0um/div, horiz = 1.0 mm/div, Sample Intervalof 7.0 um
...................................... 121
5-74. Average Friction Coefficient Over Test,Chromium Oxide Ring
on Chromium OxideLiner, No Lubricant ............................
122
5-75. Average Friction Coefficient Over Test,Chromium Oxide Ring
on Chromium OxideLiner, Synthetic Lubricant .....................
123
5-76. Proficorder Roughness Traces of PlasmaSprayed Chromium
Oxide Liners, Before andAfter Two-Hour Test Against Chromium
OxidePlasma-Sprayed Ring, Scale: vert = 0.25um/div, Horiz = 0.1
mm/div, Sample Intervalof 1.0 um
...................................... 124
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5-77. Proficorder Traces Showing Wear ScarGeometry on Worn
Chromium Oxide LinerSamples, Two-Hour Test, Scale: vert =
5.0um/div, horiz = 1.0 mm/div, Sample Intervalof 7.0 um
...................................... 125
5-78. Ring and Liner Wear Coefficients fromCameron Plint Tests:
Solid and Dashed LinesShow Variations of Ring and Liner Wear
withTemperature for Conventional Materials (CrPlated Ring, Gray
Iron Liner) with aCommercial CE/SF 15W40 \Mineral Oil
BasedLubricant; Points are for Various CeramicCoatings; Captions
Refer to Ring Material,Liner Material, and Lubricant
Combination;Cr203, and Cr3C2 are Plasma-Sprayed;TiC is
Plasma-Sprayed with CaF2, Ni, and Cr;SCAis Silica-Chromia-/Alumina
Slury Coating .... 126
5-79. Profilometer Traces From Engine TestedPiston Rings
.......................... ......... 129
5-80. Profilometer Traces From Engine Tested Liners.. 130
5-81. Right and Left (+) Side FrictionCoefficient Over Test
Before Side-to-SideLubrication Balance. CE/SF 15W40 MineralOil,
Chrome Plated Ring, Gray Iron Liner,149 C, 180 N Load, 500 RPM
..................... 131
5-82. Same as Figure 5-81, Except After Partial-Lubrication
Balance ............................ 132
5-83. Same as Figure 5-81, Except After Full-Lubrication Balance
............................ 134
5-84. Same as Figure 5-83, Except SDL-1 SyntheticLubricant
...................................... 135
5-85. Cr203 Coated, Unworn ........................... 137
5-86. Cr2C3 Coated, Unworn ........................... 137
5-87. Cr203 Coated, 2 Kg Load Knoop Indenter ......... 139
5-88. Cr2C3 Coated, Worn, 1 Kg Load Knoop ............ 139
5-89. Cr203 Coated, 2 Kg Load Knoop Indenter ......... 140
5-90. Cr2C3 Coated, 2 Kg Load Applied ................ 140
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5-91. Cr203 Coated, Many Axial and Radial Cracks ..... 141
5-92. Cr203 Coated, Many Axial and Radial Cracks ..... 141
5-93. Cr2C3 Coated, Light Areas are Worn ............. 143
5-94. Cr2C3 Coated, Top of Peaks Show Scratches ...... 143
5-95. Cr203 Coated, Worn, More Bumps Still Exist ..... 144
5-96. Cr203 Coated, Slightly Worn .................... 144
5-97. Photographs of Wear and Friction BenchSimulator
..................................... 145
5-98. Cr203-Dipped Coating, Unworn ................... 147
5-99. Cr203-Dipped Coating, Unworn, 0.1 Kg Load ...... 147
5-100. Cr2C3 Coating, Unworn ......................... 148
5-101. Cr2C3 Plasma-Sprayed Coating, Unworn .......... 148
5-102. Cr2C3 Plasma-Sprayed Coating, Unworn .......... 149
5-103. Cr203-Dipped Coating, Run Dry, 266 RPM ........ 149
5-104. Cr2C3 Plasma-Sprayed Coating, Run Dry ......... 150
5-105. Cr203-Dipped Coating, Synthetic Oil ........... 150
5-106. Cr203 Plasma-Sprayed Coating, Syntheticoil
............................................ 151
5-107. Cr2C3 Plasma-Sprayed Coating, Syntheticoil
........................................... 153
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LIST OF TABLES
Table Title Page
5-1. Cummins 903 V-8 Engine Information .............. 26
5-2. Cadillac 4.1-Litre V-8 Engine Information ....... 33
5-3. Automated Features of Simulator ................. 71
5-4. Summary of Average Break-In Data ................ 76
5-5. Steps Taken to Minimize Magnetic Noise .......... 81
5-6. Simulator Material Couples and Data ............. 113
5-7. Uncooled NTC-250 Ring and Liner Coatings ........ 128
5-8. Side-to-Side Repeatability Comparison ........... 136
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1.0. INTRODUCTION
This research at the University of Michigan was aimed
atsupporting the advanced technology diesel program of theU.S. Army
Tank Automotive Command, working with the CumminsEngine Company.
Piston and ring assembly friction,scuffing, and wear are expected
to be stumbling blocks tothe development of commercial, and even
laboratory advancedtechnology engines, versions of which are
expected to beminimally cooled. In such engines, liners may
reachtemperatures in the range of 500-600 C. At thesetemperatures,
liquid lubricants decompose rapidly. Wear,scuffing, excessive
friction, and general destruction ofpiston and ring rubbing
surfaces may be expected.Consequently, a measure of piston and ring
assembly (PRA)friction, together with assessment of the wear and
scuffingof rubbing surfaces, are needed engine-development
tools.
The problem is that there are no well-established techniquesthat
give the piston and ring assembly friction, as theengine runs under
loaded conditions. Furthermore,conventional bench-type wear testers
do not lend themselvesto total screening of advanced technology
engine ring andliner components because of geometrical and
environmentaldifferences between bench and engine tests. The
chiefproblem is duplication of the top-ring reversal
temperature,load and lubrication environment.
At the University of Michigan, a PRA friction
measurementtechnique, termed the Instantaneous IMEP method, had
beendeveloped prior to this program and reported by Uras
inReferences 1-6. In that earlier work, it had produceduseful
results in running gasoline engines. The initialthrust of the
present program was to apply that technique toa minimally cooled,
advanced-technology engine. The Cummins903 engine was selected. A
single-cylinder version wasused.
Because of possible experimental limitations of theInstantaneous
IMEP method and the absolute necessity ofdetermining reliable PRA
friction data, it was decided topursue an alternate method as well.
That method, aderivative of so-called moveable bore methods, is
termed theFixed-Sleeve method. Its development had started in
anearlier program at Michigan using a gasoline engine. Thatearlier
work was reported by Ku in References 7 and 8. Inthe present
program, the Fixed-Sleeve method was applied toa second Cummins 903
single-cylinder engine, and some ofthat work was reported in
Reference 9.
To support their work on low-heat rejection engines, Cummins
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had begun development of a bench-test simulator to permitrapid
screening of materials with respect to piston and ringfriction and
wear. Rapid screening is desirable, sinceengine test are relatively
complicated, time consuming, andexpensive. That work was
transferred to Michigan to supportthe present research program.
Further development of thatfixture has occurred and is reported
herein, as well inReferences 13 and 15.
A good deal of the material in this report was included
inProgress Reports to the U.S. Army, References 10 - 12.These
reports contain more detail on some topics.
In the sections that follow, the overall program discussionis
organized into three segments. They are:
1. Instantaneous IMEP Method2. Fixed-Sleeve Method3. Ring and
Liner Bench Test
Motoring and firing friction results are reported on the
903engine with the Instantaneous IMEP method, including resultswith
ceramic-coated rings and liner, synthetic lubrication,and uncooled
engine block. Motoring results are reportedwith the Fixed-Sleeve
Method. A variety of results from thebench-test fixture are
reported, including various ceramiccoatings and lubricants. A
comparison with Cameron Plintwear data, as well as engine worn
samples is made. Micro-scopic examinations of fresh and worn
surfaces are included.The piston and ring assembly friction has
been reported asthe quotient of the friction work per 720 crank
angle degreeengine cycle divided by the cylinder displacement. This
istermed the PR MEP and is reported in units of psi.
2.0. OBJECTIVE
The objective of this research was to quantify the pistonand
ring friction of advanced technology, low-heat rejectionengines.
This mission involved:
1. Development of measuring techniques.
2. Evaluation of advanced materials including ceramics.
3. Evaluation of lubricant effects includingsynthetics.
4. Development of experimental screening methods forfriction and
wear of piston and ring-rubbingsurfaces.
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3.0. CONCLUSIONS AND OBSERVATIONS
The measurement of instantaneous piston and ring friction ina
turbocharged, firing engine is a difficult challenge.Only near the
end of the program were successful frictionmeasurements made in a
firing engine with the InstantaneousIMEP method and in a motored
engine with the Fixed-Sleevemethod. On the other hand, the
bench-test simulator provedrelatively easy to operate, and much
data was obtained onceramic-coatings, synthetic lubrication and
high-temperatureservice.
Below are conclusions and observations for the various
experimental methods within this program.
3.1. Instantaneous IMEP Method
The Instantaneous IMEP method appeared to give reasonablevalues
for PRA friction in the 903 engine with intake airboost. The
technique is promising for revealing significantchanges in
friction, or the appearance of unusual frictionforces, such as
those associated with an engine failure. Onthe other hand, it may
be difficult to quantify smallfrictional changes because of the
lack of sensitivity of themethod. A major advantage of the method
is that nosignificant engine modifications are required. Thus
thedata obtained correctly reflects the engine design. Noother
technique has this advantage. Some specificobservations were:
1. Firing and motoring PRA friction were similar undermotoring
and firing conditions. Friction was in theboundary or mixed regime
near the dead centers andappeared relatively hydrodynamic
midstrokes. With cooloil (high viscosity), the friction was higher,
but morehydrodynamic. Warm engine PR MEP values ranged fromabout
1.5 to 4 psi.
2. The synthetic lubricant gave lower friction than
theconventional SAE 40 oil in conventional,
cooled-engineoperation.
3. Friction with an uncooled block and syntheticlubricant was
similar in character to that of the baseengine with cooling and
conventional motor oil, whenmotoring. Firing results looked
similar, but the PR MEPvalues were unreliable.
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3.2. Fixed-Sleeve Method
Some difficulties were experienced in adapting this methodto the
Cummins 903 engine. As a result, limited data wereobtained. PR MEP
was 2.34 psi at 1000 rpm, motoring underwarmed-up engine
conditions. Results looked similar tothose obtained with the
Instantaneous IMEP method.
Below are some observations and conclusions.
1. Repeatability and the ability to differentiate smallfriction
differences appear excellent. On the otherhand, a special liner is
required; thus enginemodifications are necessary which themselves
may modifybase engine friction characteristics. The methodappears
to be readily adapted to engines with liners,such as the Cummins
903 engine.
2. The Fixed-Sleeve method permits relatively rapidchange of
piston, ring, and liner variables, andcalibration is relatively
straight forward. Designvariables can be investigated relatively
quickly.
3. This method is projected to be very useful forevaluating bore
roundness, straightness, and surfacefinish effects. It will also be
useful for evaluatingnew piston or ring designs.
4. The location of the strain-gauges, away from theheat and
cylinder stresses, suggests that this methodmight be more easily
used to measure friction inuncooled engines than the Instantaneous
IMEP method.
3.3. Ring and Liner Bench Test
Below are some conclusions and observations on the benchtest
simulator for piston and ring wear, and friction.
1. In unlubricated tests, the titanium carbide,chromium carbide
pair was a poor combination, whereasthe chromium oxide pair was
exceptional. The simulatortests correlated directionally with the
Cameron Plintresults and were in qualitative agreement with
engineresults.
2. Lubricated tests demonstrated lower wear andfriction, as
expected. Careful control of lubricantfeed rate, targeting, and
spray pattern are required forgood repeatability and minimization
of side-to-sidevariations. Air atomization of the lubricant is
veryhelpful.
21
-
3. Additional work is needed to establish correlationbetween
bench-testers and running engines. Such workincludes development of
standard test procedures,parametric evaluations, and more
sophisticated surfaceanalysis of wear samples. A better knowledge
of thequantity and quality of the lubricant at the wearinterface of
running engines would be helpful inachieving a more correct
laboratory simulation.
4. Overall, it is concluded that the simulator is apromising
bench-test device for evaluating ring, liner,and lubricant
combinations for advanced technologyengines. While it will never be
possible to totallyeliminate engine testing, this efficient
benchsimulation should make the job of screening newmaterials, new
lubricants, and new designs moreefficient and cost effective.
4.0. RECOMMENDATIONS
4.1. Instantaneous IMEP Method
This method of measuring piston and ring assembly frictionworked
reasonably well on the boosted Cummins 903 engine.Problems were
encountered developing the instrumentation,especially solving the
problem of magnetic noise. Finally,results looked reasonable. This
method is projected to bevery useful for evaluating friction and
friction-relatedproblems in uncooled engines.
4.2. Fixed-Sleeve Method
The progress of this method was slow, since the major effortwas
on the Instantaneous IMEP method. By program end, afirst-generation
design had been implemented on a motoringengine. Some problems with
strain-gauge lead wiring weresuspected. The signal to noise ratio
was poor. It wasconcluded that a new design was needed which
would:
1. Eliminate the threaded liner hold-down in favor of aclamped
design.
2. Use a thinner section on which the strain-gaugeswere
applied.
3. Route the strain-gauge wires to produce less of anantenna
effect.
4. Demagnetize all the moving parts in the crankcase.
22
-
4.3. Ring and Liner Bench Test
The ring and liner bench-test fixture worked quite well
asdeveloped within this program. It should prove useful as
ascreening tool for rings, liners, materials and lubricants.The
number of engine tests required should therefore, bediminished
considerably. A number of organizations haveexpressed interest in
obtaining the simulator.
5.0. DISCUSSION
5.1. Background
The Instantaneous IMEP technique had been developed at
theUniversity of Michigan prior to the start of the presentprogram.
It had produced useful results on running gasolineengines. The
initial thrust of the present program was toapply that technique to
the minimally cooled, advancedtechnology diesel engine.
The first step was to apply the technique to the
productionCummins 903, and a one-cylinder engine was set-up
andinstrumented for this. Once a successful result wasobtained, the
approach was applied to the same engine with"low-heat rejection
components" and run under "low-heatrejection operation." That
effort is described in par.5.2.1., 5.3.1, and 5.4.1.
Early in the program, it was found that the
instrumentationsignals needed for the Instantaneous IMEP method
were quitenoisy with the 903 engine. In addition, it was
anticipatedthat the differencing of the large numbers derived from
thisturbo-charged engine would make precise frictionquantification
quite difficult. Prior to the start of thisprogram, the
Fixed-Sleeve method had been initiated on anautomotive-type
gasoline engine. That technique workedextremely well on the
Cadillac 4.1-litre V-8 engine, whichhad a die cast aluminum block
and iron liner. That work wasreported in references 7 and 8.
The success on the gasoline engine, coupled with concernsfor
precision of the Instantaneous IMEP technique, led us toapply the
Fixed-Sleeve method to a second Cummins 903single-cylinder engine.
The design implementation isdescribed in this report, but the test
results, obtainedprior to the end of this program, were
disappointing. Nouseful results were obtained, although the
approach stillappears attractive. A summary of the design and
results ofthe earlier work on the gasoline engine, together
withextension to the 903 engine are included in this report.
23
-
(See par. 5.2.2., 5.3.2, and 5.4.2.)
Parallel to the above-engine program, a laboratory benchtest
friction and wear simulator was developed to assesssurface damage,
wear, and friction between liner segmentsand reciprocating ring.
This simulator allowed rapidscreening of candidate materials. The
basic reciprocatorwas designed by Cummins. It was extensively
modified andcomputer controlled at Michigan. The progress on
thisportion of the program has been rapid, and considerable datahas
been taken with this rig. The simulator has become auseful
screening device for selecting promising, high-temperature engine
materials and lubricants. This portionof the program is summarized
in par. 5.2.3., 5.3.3. and5.4.3. The simulator is discussed in
references 13 and 15.
5.2. Design
Discussed below is the design of the various experimentalmethods
explored within this program. These are:
1. Instantaneous IMEP Method2. Fixed-Sleeve Method3. Ring and
Liner Bench Test
5.2.1. Instantaneous IMEP Method. The Instantaneous IMEPmethod
employs a force balance between the measured cylinderpressure
force, the compressive force in the connecting rod,the inertia
force and the friction force. Considering thecomponents of these
forces acting along the cylinder axis,the sum of the other three
equal the friction force of thepiston, rings and piston pin
assembly. Figure 5-1 shows thesingle-cylinder version of the
Cummins 903 V-8 enginemodified for the Instantaneous IMEP method.
The large pipeemanating from the cylinder-head region is a vent for
thecrankcase. This provides atmospheric pressure on thebackside of
the piston. A crankangle encoder is mounted onthe front of the
engine. Simultaneous measurements ofcylinder pressure and rod
compressive force are made at eachcrank angle over the entire
cycle. Table 5-1 gives relevantengine information about the
production Cummins 903 engine.
In applying this method, inertia forces are commonlycalculated
from the well-known theoretical equation,assuming a constant
crank-speed. As discussed later, forthis one-cylinder engine, and
where inertia forces are quitelarge, crank-speed variation must be
taken into account inthe calculation of the inertia forces. In the
determinationof the inertia forces, it is necessary to consider
thereciprocating mass of the piston, rings, the pin, and
thatportion of the connecting rod which reciprocates with the
24
-
Figure 5-1. Single-Cylinder Cummins 903 Engine Equipped for
Instantaneous IMEP Method
25
-
Table 5-1. Cummins V8-903 Engine Information
Bore 139 mm
Stroke 121 mm
Connecting Rod Length 208 mm
Displacement 903 cu in
Compression Ratio 15.5:1
Closed-Deck Iron Block
Wet-Cast Iron Liner (Removable)
26
-
piston. As reported in reference 1, a distributed model ofthe
connecting rod inertia is necessary, since it was foundthat the
error associated with the use of a lumped model wasexcessive.
Figure 5-2 shows the strain-gauged connecting rod used withthe
Instantaneous IMEP method. Pairs of 90 degree rosettesare installed
on either side of a machined section locatedat approximately
one-third of the connecting rod web lengthnear the small end. Wires
from the strain-gauges, powersupply, and thermocouple, to measure
the bridge temperature,are attached to the connecting rod. From the
connectingrod, the wires are routed exterior to the engine by the
useof a grasshopper linkage shown in Figure 5-3. More detailof the
implementation of the Instantaneous IMEP technique isgiven in
Section 5.3.1.
For purposes of illustration of the method, Figure 5-4
showssignals for Instantaneous IMEP method measurements made on
atwo-litre gasoline engine at 800 rpm motoring, partthrottle. The
top trace is the cylinder pressure, thecenter trace is the
compressive force in the co-necting rod,and the lower trace is the
inertia force. Note that thestrain-gauge signal includes abrupt
jumps at thi deadcenters, indicated by the circles in the figure
Thesejumps arise from the change in static friction as the
pistonreverses direction. Differencing these forces to obtainpiston
ring assembly friction results in the top curve ofFigure 5-5. This
curve shows piston-ring assembly frictionforce as a function of
crank angle. The static frictionreversals at the dead centers are
very apparent.
It is difficult to determine the factors that contribute tothe
shape of the friction force curve. This is because thecurve
reflects the skirt, the three piston rings, and thepiston pin
friction. Each component is operating in asomewhat different
lubrication regime. Near the deadcenters, the piston rings dominate
the friction results.There, the rings operate in the mixed or
boundary•ubrication regime. In midstroke, probably all
componentsire operating in the hydrodynamic regime.
The frictional work associated with these forces resultsfrom the
product of friction force times piston velocity.The velocity is
shown in the center portion of the figure.The power is shown at the
bottom of Figure 5-5. The areaunder the curve of power versus
crankangle is the totalenergy loss due to friction. The frictional
work, dividedby the displacement of the cylinder, has been termed
thefriction mean effective pressure (fmep) of the piston andring
assembly, (PR FMEP).
27
-
Figure 5-2. Stain-Gauged Connecting Rod
28
-
Figure 5-3. Grasshopper Linkage
29
-
I- Intake --4 Compression .-Expansion4-- Exhaust --I
2.000
.0,500 .05 .000-
"• 1.500"0 70
0.000[
2.0
06!-• 90
S 180
0.
270
I. .. ± . J L..... I ,1 .. , I0 7" 2w 37r 4w
Crank Angle (rod.)
Figure 5-4. Typical Cylinder Pressure, Connecting Rod,
andInertia Forces
30
-
1-Intake ---- Compression "Expansion - Exhaust -160
" 80OU~
COC
~ 0z U160
4
Z' 222>- 0
C 00o• 2
0_
4
240
3: 200
12a..9160-
U0.
80 80
.o 40
0 I I I I
0 7r 27r 37r 4,
Crank Angle (rod.)
Figure 5-5. Piston and Ring Assembly Friction Force,Velocity and
Power Dissipation
31
-
5.2.2. Fixed-Sleeve Method. The Fixed-Sleeve method is
aderivative of a class of what is termed "movable bore"methods. It
was implemented on a 4.1-litre gasoline engine(7), and considerable
data were obtained. Table 5-2 givesrelevant engine information for
that engine. A briefcomparison of the two methods, simultaneously
implemented onthe 4.1-litre engine, may be found on page 64
under"Comparison of the Fixed-Sleeve and Instantaneous IMEPmethods
on the 4.1-Litre engine."
Figure 5-6 shows a cross section of the Fixed-Sleeve design.The
original 4.1-litre engine liner, which had an 88 mm boreis fitted
with a smaller 80 mm sleeve which is attached tothe outer liner by
a pair of lock nuts located at the bottomof the assembly. Piano
wire in tension is used near the topof the assembly to pilot the
inner sleeve so that it doesnot touch the outer liner. O-rings are
used to sealcombustion gas, water and oil. Cooling water is
permittedto circulate between the two sleeves. Strain-gauges
aremounted on both inner and outer surfaces of the
necked-downsection near the bottom of the outer liner.
The outer liner, which is essentially identical to theproduction
liner, is supported in the engine in theconventional way between
the top of that liner and thesupport lip. Thus the inner liner is
positioned like astandpipe, the top of which is shortened slightly
so that itcannot contact the cylinder-head. Acting on the
innersleeve are the sum of the cylinder pressure force acting onthe
rim and the friction force. An example of these forcesis shown in
Figure 5-7. The upper figure shows cylinderpressure while motoring
at 1000 rpm, wide open throttle.The center figure shows the
strain-gauge signals, and thelower figure shows the friction force
as a function ofcrankangle. This is found by differencing the two
uppersignals.
5.2.3. Ring and Liner Bench Test. The ring and liner benchtest
simulator provides a rapid means of screening candidatering, liner,
and lubricant combinations under simulatedengine conditions. The
rig simulates the most severe wearand friction conditions in the
engine, namely directly aftertop dead-center, where piston speed is
low, and loads andtemperatures are high. The simulator incorporates
acomplete piston ring positioned in a disk- shaped holder.The ring
ends are held together by pins and clamped to thenominal gap
clearance. The holder with ring reciprocateswith a stroke of 2.54
cm, and portions of the ring areloaded by two liner segments placed
180 degrees apart. Eachstationary liner segment is about 3.8 cm
long and 0.7 cmwide. It is cut from a finished liner. The ring
holder is
32
-
Table 5-2. Cadillac V8-4.l-Litre Engine Information
Bore 88 mm
Stroke 84 mm
Connecting Rod Length 134 mm
Displacement 4100 cc
Compression Ratio 8.5:1
Closed-Deck Iron Block
Wet-Cast Iron Liner (Removable)
33
-
88.8"
---- 80.00
UPPER O-RING
WIRE CLAMP
SUPPORTING WIRE
0"CYLINDER LINER
SUPPORTINGSLEEVE
SUPPORT LIP
LOWER O-RING
STRAIN GAGES
COPPER WASHER
LOCK NUT
Figure 5-6. Fixed-Sleeve Design for the 4.1-Litre
GasolineEngine
34
-
"u 1200- MOTORING AT 1000 RPM(WOT)
,., 900-a..
La 600-zZ-
300-C")
- 100
600-
z450-
i-
3000LL
i-,
400-z
200,0
, -------------I0U0
200-
400 INTAKE I COMPRESSION I EXPANSION I EXHAUST180 360 540
720
CRANK ANGLE (DEG)
Figure 5-7. Cylinder Pressure (upper), Strain-Gauge
Voltage(center), and Resulting Friction Force (lower),
WOT, 1000 RPM, Motoring
35
-
powered by a 1.34 kw d.c. electric motor that is speedcontrolled
by a SCR controller. Load is applied to thering, liner interface by
means of an air cylinder and leverarm arrangement. Provision is
made for lubricant spray atthe wear interface, and the entire unit
may be heated to ashigh as 550 C, in order to simulate low-heat
rejectionengine top-ring reversal temperatures.
Data obtained from the simulator include friction force as
afunction of stroke and average friction coefficient as afunction
of time. As is often done after such tests, linersamples may be
analyzed for wear volume, surface finish, andother meaningful wear
parameters. Simulator results areavailable for both right and left
wear interfaces.
Figure 5-8 shows a schematic of the simulator. Bypressurizing
the air cylinder, ring loads are applied whichcan simulate the high
pressures experienced in highlyturbocharged engines under peak
pressure conditions.Maximum reciprocating speed is limited to 700
rpm by inertiaforces. In effect the simulator attempts to duplicate
themost severe ring and liner condition; namely low speed, highload
at TDC firing. Most testing to date has been at speedsbelow 500
rpm. Very high speed operation, if desired wouldrequire addition of
a reciprocating balance mechanism.
The friction force is transduced by strain-gauges mounted onboth
right and left arm pivots. This not only permits anindependent
friction measurement at both wear locations, butalso eliminates
unwanted bearing friction, inertia force,and noise from vibration
which were characteristic ofearlier designs.
As desired, lubrication is provided by means of water
cooledstainless steel tubes through which a pressurized air andoil
mixture pass. The oil is provided as a spray mistdirected to the
rubbing surfaces. A peristaltic pump,capable of precise, variable
feed rate, is used to controloil quantity. A double wall,
insulated, stainless steeloven surrounds the liner samples and
ring. Electric heatersare used to produce high temperatures. Heater
control is bymeans of the computer (IBM XT compatible), which
cycles theheaters. Thermocouples are employed at several
pointswithin the oven to indicate temperature. An angle encoderwith
250 pulses per revolution is used to tell the computerwhen to
sample the strain-gauge force.
36
-
VARIABLE SPEED a STROKE
MACHINE FRAME NEEDLE BEARING
AIR CYLINDER
THRUST BEARINGSTRAIN GAGES
SPSON ING
iLINER SECTION•
Figure 5-8. Schematic Showing Essential Features of BenchTest
Simulator for Ring and Liner Wear andFriction
37
-
5.3. Implementation
Below is discussed the implementation of the variousexperimental
methods conducted within this program. Theseare:
1. Instantaneous IMEP Method2. Fixed-Sleeve Method3. Ring and
Liner Bench Test
5.3.1. Implementation of the Instantaneous IMEP Method.
5.3.1.1. Engine Installation. A single-cylinder Cummins
903engine was obtained from Cummins Engine Company for thisprogram.
The engine was one of several made by Cummins forresearch purposes.
It was constructed from a V-8 by cuttingthe block in such a manner
as to leave two cylinders at theflywheel end of the engine. The
crank, front end, cylinder-head, and fuel injection system were
appropriately modified.Figure 1 showed the engine installed in Room
249 of the W.E. Lay Automotive Laboratory at the University of
Michigan.
In this modified engine, only one cylinder was working. Theother
did not compress, due to a large hole placed in thepiston crown.
Additional weight was placed on the pistonpin to preserve engine
balance. By this means, a fairlysmooth running single-cylinder
engine is obtained.
The engine was installed and coupled to a 600 HP G.E.Electric
Dynamometer. The dynamometer was improved with theaddition of a 500
lbm maximum capacity load cell and aDaytronics Model 3270
strain-gauge conditioner/indicator toreplace an existing "LINK"
pneumatic system. One of thestrain-gauge conditioner filter
selections was modified tohave a cut off frequency of about 0.2 Hz
so that thedynamometer output torque was averaged over a longer
periodof time. This reduced low-frequency torque fluctuationswhich
had made it difficult to get steady torque readings.The dynamometer
speed controls were tuned thoroughly by G.E.personnel.
A system to convert the existing test cell engine coolantsystem
from a total loss tap water type system to a closed50/50 antifreeze
system was designed and installed. Thissystem used a 2 HP coolant
pump which was provided byCummins. A BCF 5-030-03-024-004, 24",
2-pass heat exchangerwas purchased and installed to separate the
coolant solutionfrom the tap water coolant. An identical unit was
installedfor the oil system. Pneumatic temperature controllers
wereused for control of the coolant, oil, and inlet
airtemperatures. These were available in the laboratory.
38
-
Control valve bodies, with the proper flow coefficients,were
installed. The smallest capacity units (Cv=0.5) gavebest
temperature control.
Oil-pressure supply to the engine was provided by a 2 HPpump. An
adjustable pressure regulator was added in aby-pass configuration,
to allow accurate control of oilpressure. It was found that the
piping from the pump outletto the heat exchanger, and on to the
engine, had to be aslarge as possible (1" was used); otherwise, the
pressureloss though the system dropped oil pressure below
anacceptable level at the highest flow rate with the highestoil
temperature. A dry sump oil reservoir was needed toavoid dragging
the grasshopper linkage through the oil.
An intercooler unit modified from a multicylinder engine wasused
to preheat the pressurized intake air. This was donein order to
simulate air temperatures encountered in
theturbocharged/intercooled multicylinder engine (240oF). Heatwas
provided by steam at a pressure of about 30 psig. Thissteam was
provided by a 40 kW electric mini-boiler in theequipment room above
the test cell. The steam outlettemperature was monitored by the
pneumatic controllertemperature sensor in the intake pipe, and the
controllerregulated the flow of steam through the control valve.
Bothoil and coolant system heat exchangers were equipped withsteam
lines and traps, so that heat could be added whenrunning motoring
tests, and prior to starting.
Pressure in the intake manifold of up to 50 inches ofmercury
gauge pressure was provided by two screw-type ai,compressors. One
was 40 hp. This was the regular builc •'gsupply (110 psig). The
second was an auxiliary unit of :0hp placed above the test cell and
was used only when theengine was run with boosted intake pressure.
Air flow tothe engine was measured by a critical flow orifice
systemconsisting of five orifices in parallel. The air-floworifices
were calibrated with a 10 cu. ft. air bell. Alarge Heise gauge was
installed upstream to monitor pressurethere. A 35 psi relief valve
was installed in the line tothe intake manifold for safety reasons.
Two-inch compressedair lines ducted the air from the compressors.
Two low-resistance rayon air filters were installed to filter
theair.
A variable speed fuel pump system was provided by Cummins.The
pump was equipped with a small needle valve bypassingthe pump
output for fine pressure adjustment. Coarseadjustment was provided
by controlling the speed. A CoxInstrument Model 402 weigh scale was
used to measure flow.
39
-
Exhaust back pressure was controlled by a manually
operatedvalve. An 80 in. Hg. well type manometer was installed
tomonitor the back pressure.
5.3.1.2. Grasshopper Linkage Design. The purpose of thistwo-bar
linkage is to fully support a wiring harnesscontaining a number of
wires from their point of attachmenton the connecting rod to a
stationary point on the engine.From there, the wires are connected
to external circuitry.Below are design criteria:
1. Minimize swing angles al, a2, a3 for minimum wire
twist.
2. Minimize link lengths for better clearance.
3. Minimize acceleration of the joints to minimizestresses.
4. Optimize geometry that will allow motion through allangles
without interference with block and minimizemodifications of the
oil-pan.
The specific design was made with the assistance of a full-scale
layout board, Figure 5-9 This was constructed ofcardboard upon a
full-scale drawing of the block. Pins andguides permitted rotary
and reciprocating motion. Linklengths and attachment points were
selected to avoidinterferences and to minimize the swing angles.
The topswing angle al, is usually the largest, with some
occasionalwire breakage experienced with angles as large as
90degrees. Angles less than 70 degrees are much preferred.Computer
analysis of these linkages showed that the maximumacceleration is
at the pivot point a2, which is the "elbow."This occurs just before
the piston reaches bottom center.Figure 5-10 shows the completed
linkage.
Figures 5-11 and 5-12 show the bracket design for holdingthe
bottom (fixed) end of the grasshopper linkage in themodified
oil-pan. The modified oil-pan is shown in Figures5-13 and 5-14. A
photograph of the bracket holding thefixed pivot of the grasshopper
linkage is shown in Figure5-15, upper. Figure 5-15, lower, shows a
photograph of themodified oil-pan. Figure 5-16 shows the bracket
attachingthe grasshopper linkage to the big end of the
connectingrod.
40
-
Ný
Figure 5-9. Photograph of Layout Board for Designing
Grasshopper Linkage
41
-
?17
Figure 5-10. Photograph of Completed Grasshopper Linkage
42
-
• � �0 7, 0U K a 0pPAI
L -L I L
""14P FORIid.2S 111AP Eý I
xI I. so4M0zs".0s 9I j
AWADS SOL NO
,J ,
0,6z " BRACK..•ET SSE" O .CioAtLULt( 6. Er- H) A D- ,' o,,u' kj
I : ", ,,
Fi-gur'e 5-11. L~ower'-End Br'acket., Side View
43
-
_,E FT 5 E. .0_0" CU MM INS
5.00 0 BRACKET
.0.004
r1 r
0.80 "O.5""L
II0.710 0~.1 0 1 .754
Figure 5-12. Lower-End Bracket, End View
44
-
CU/ktH/M5 0ziL- PPW 5PIPCE5-
I"
-
CUMMI[NS PAIN MODIFICATIONS
ExT &PAW
-4-- o i.5
4.6
-
* I . . . .t• !
Figure 5-15. Photographs of Lower-End Bracket (upper) andOil-Pan
Modifications (lower)
47
-
CONNECTING ROD. BRACKET
O. WI4o"I . ........ ... 4.00" ..... .. .. )..J o. €b40" Cl•
.. . . -0.30.N l, I I ', ! ,. ,i , f,.oo" .. .. .... r -
--....... - •:"- - "+:• .
T _ I... .....,, - I. '° "0'
S.T, 0. . . . . 5
0. 4OO "
-1
0.1501
2.10 RAO I D
' 3i" 75 - - T"
Figure 5-16. Grasshopper to Connecting Rod AttachmentBracket
48
-
The final Grasshopper linkage design parameters were:
Top member length 6.90"Bottom member length 6.00"Swing angles al
65 deg
a2 57 dega3 56 deg
Upper pivot pin relative X = +3.188"to connecting rod big end Y
= -1.375"centerline (rod vertical)
Bottom pivot pin relative X = +2.15"to crank center Y =
-11.96"
This linkage was satisfactory in that it never broke, andthe
wires it carried never broke.
5.3.1.3. Cylinder Pressure-Transducer. A key aspect of
theInstantaneous IMEP method is the correct measurement of
thecylinder pressure at each crank angle. Our experienceindicates
that the Kistler 7061 transducer is the bestavailable. This is a
water-cooled unit, requiring a 14 mminstallation hole. The
transducer was installed in avirtually flush mounted manner in the
Cummins 903 cylinderhead. The transducer was contained in a 303
stainless steelsleeve. This prevented engine oil and coolant
fromcontacting the transducer and cable connections. A
coppercompression washer provided a seal against cylinderpressure.
The transducer installation, including sleeve,are shown in Figures
5-17 to 5-19. Figure 5-20 presentsphotographs showing the
installation of the pressuretransducer into the cylinder-head.
A Ruska Model 2400 HL dead weight tester was used tocalibrate
the pressure-transducer. Six calibrationpressures up to 300 psi
were applied. The procedure wasrepeated several times. Finally, the
curve of calibrationvoltage versus pressure was fit by the least
squares method.Subsequently, the pressure-transducer was used to
calibratethe strain-gauges applied to the connecting rod. This
gavean internally consistent calibration between the
cylinderpressure and strain-gauge signals. The Kistler Model
504E10charge amplifier was used with the Kistler transducer.
5.3.1.4. Strain-Gauged Connecting Rod. An integral part ofthe
Instantaneous IMEP method is to measure the compressivestress in
the connecting rod. This requires machining flatson the connecting
rod. Figure 5-21 shows the machined rodprior to application of the
gauges. The intent of themachining is to provide smooth surfaces
which are symmetricabout the neutral axis of the rod.
Micromeasurements strain
49
-
SII0
1.041L
I I g •t
I 4.508,
8.9 71 *[1 OI~ -RINiG GROOVE
8.175"og
x ,0
I I€ I :'
_._,______AT___________-___.NLo5•Sr
HEADTRANUCER SLEEVE0,"FOR CJJMMINS V-90OUNIVERSITY OF MICH IGA.
DIMENSIONS
Figure 5-17. Pressure-Transducer sleeve
50
-
SLEEVE - HEAC A M5'MBLY .... /FOR Ciji\IN5 V-90- /-/- -. VALVE
COVER
UNtVERSITT OF MICHIGAN/
6-13-8r,- FULL SCALE
I Iil I SLEEVE
SEAT FOR iO-RIN6'"
, .•,. - - -... . /,./ I
/ .. ".- I /,' - - .II
/. , /"~ I ""1.0.
1.750"- MILLED FLAT FORLOPPER /ASHER
TAPPED FOR 0.5 20
Figure 5-18. Sleeve and Head Assembly
51
-
-205
.~ .010
Figure 5-19. Pressure-Transducer Location in Head
52
-
Figure 5-20. Photographs of Pressure-Transducer
Installation
53
-
Figure 5-2 1. Photograph of Machined Connecting Rod
54
-
gauges Model WK-06-062TT-350 with resistance of 350 ohmswere
used. These are pairs of gauges mounted at rightangles.
After the gauges were applied and the rod installed, theengine
was motored for a few hours, in order to age thegauges. Then the
strain-gauges were calibrated twice asfollows. A one-inch thick
flat plate with two 14 mm tappedholes and one-inch spacer was
bolted to the cylinder blockdeck to allow introduction of
calibration pressure andmounting of the pressure-transducer. Steam
heated coolantwas circulated to control temperature during
calibration.The crankshaft was locked at two different crank
anglesusing brackets on the flywheel, and a nitrogen bottle wasused
to apply continuously increasing and decreasingpressure to the
piston. Stain-gauge and pressure-transduceroutputs were recorded
simultaneously, and then calibrationconstants were calculated from
this data. These constantsare the relationship between applied
force and voltageoutput, which together with bending and
temperaturecorrections are described in References 1 and 2.
AMicromeasurements Model 2310 strain-gauge amplifier wacaused.
5.3.1.5. Data Acquisition. The Instantaneous IMEP methodrequires
simultaneous measurement of cylinder pressuretransducer and
connecting rod strain-gauge voltages at onecrank angle degree
intervals. A data acquisitic: system wasdeveloped based on the IBM
PC-XT, which enabled thesemeasurements at engine speeds up to 3000
rpm, a computerdata acquisition rate of 18 kHz. Ultimately, the
dataacquisition rate was 20 kHz. A 12-bit resolution system
wasused. At this resolution the error caused by a variation ofone
bit is 0.25 percent, well within the objective of 1percent
accuracy. That is one part in 4096. Data for nineconsecutive engine
cycles were stored in memory for transferto a floppy disk. At the
same time, the friction force as afunction of crank angle, was
calculated and periodicallydisplayed on the a high-resolution (720
point up by 450down) monochrome monitor display screen (Figure
5-22). Inthis manner, it was possible to determine if the
data"looked right" as it was being acquired. A dot matrixprinter
with graphics capability allowed print out of testconditions, as
well as the monitor display.
Two Techmar Labmaster 2009 option TM-40-PGH analog todigital
conversion boards were installed in the IBM XT forthe data
acquisition. These were triggered by the opticalencoder mounted on
the engine crankshaft (Figure 5-23). Insome engine tests, a
commercial crank angle encoder, theLedex Model RC23-DM-360-5SE-1B,
was substituted. Sample and
55
-
a-Ho
Figure 5-22. Data Acquisition System and Display
56
-
00
Figure 5-23. Crankangle Encoder Installed on Front ofEngine
57
-
hold circuits on the A/D boards remember and hold thevoltage
until the next trigger signal, giving the computertime to acquire
the data. The circuit of this dataacquisition system is in Figure
5-24. Every other top dead-center pulse is removed, so that the
crank angle pulses canbe gated through, starting with TDC on the
intake stroke. Ablock diagram of the system software is shown in
Figure5-25. The main programs were written in Fortran with
anassembly language subroutine linked to the data collectionprogram
for fast data acquisition. This data acquisitionsystem was further
used for measuring the time intervalbetween crank angles, for
determining the speed variation ofthe crank, and in the data
acquisition of the Fixed-Sleevemethod.
5.3.2. Implementation of the Fixed-Sleeve Method.
5.3.2.1. Implementation on the 4.1-Litre Engine. Thisgasoline
engine is unique in that it is comprised of a diecast-aluminum
block into which are inserted cast-ironliners. It presented a very
convenient vehicle to implementthe Fixed-Sleeve method. In the
Fixed-Sleeve method thecylinder-head is not modified, except that a
flush mounted,water cooled, Kistler 7061 pressure-transducer was
installedin a manner similar to that described in 5.3.1.3.,
exceptthat it was installed through the front of the
cylinder-headin number 1 cylinder.
The cylinder block was modified in that a sleeve wasinserted
within a modified steel replica of the removableproduction liner.
Acting on this sleeve are both thefriction force of the piston and
rings and the combustiongas-pressure force acting on the upper rim
of the sleeve.That gas force, acting on about 6.5 square cm of rim
area,is then subtracted from the total, leaving the frictionforce
as a function of crank angle.
The combined gas and friction forces are measured by
full-strain-gauge bridge circuits uniformly spaced on both
insideand outside of the slender section (1.5 mm thick) of
thetailpiece of the outer liner. The gauges and method
ofapplication are similar to that described in 5.3.1.4. forthe
Instantaneous IMEP method. In this design, a total of16 active and
16 dummy gauges were used. The arrangementprovided temperature and
bending compensation and enoughsensitivity to resolve better than
one-pound force. Theproduction cylinder-head and gasket seal
against the outerliner as in the production engine. A smaller 80 mm
piston,provided by Cadillac engineering, and specially built
castiron liners, provided by SPX Corporation, were used with
anotherwise production engine, except that a carburetor and
58
-
2 133 12 CMOS Chips.4 11 (Starter Circuit)5 '1l 04024 - 7 Stage
Ripple Counter7 V a 4013 - Dual D-type Flip-Flop
4001 - Quad 2-input Nor Gates
Power Supplys1 - 5 (Starter Circuit &2 1 Photo Diode
power)
Sola Solids 84-05-210(5 volt, 1 amp)
0710)+5st Pressure
5..,10 Daughter
60t Mother Board .- #1
S~StrainFtý!ý0710H1 Starting Bus Address
IMother Board .
470 o h J2 pin 3
Frm]~ lo .o SYSTEM
oPhoto Diode Position 0coder
_- SCHEMATIC
ENGINE FRICTION DIAGRAMDATA ACQUISITION SYSTEM
Figure 5-24. Schematic of Data Acquisition System
59
-
Fortran Program
"GETDATA.FOR"
-Input Test Conditions
Fortran subroutine"UTecmar,,
Fortran Subroutine -Plots pressure and straingage inputs on
screen-Stores raw pressure
and
strain gage data on disk 1
Assembly language subroutino
"ADC.ASW'
-Operates A/D converter
and loads data to memory
Floppy________________
Disk
Storage
Fortran Program
"FRA2. FOR"-Take data from disk, calculates
and plots friction on screen.
-Stores friction, pistonvelocity and test conditionson disk
Figure 5-25. Block Diagram for Data Acquisition System
60
-
mechanical distributor were used for experimentalconvenience.
All cylinders were fired for the tests.
5.3.2.2. Additional Details. Referring to Figure 5-6,other
features of the design are: tensioned piano wire (0.5mm dia) near
the maximum side thrust region, to pilot theinner sleeve and keep
it from contacting the outer liner(which gives no axial
restriction.); soft silicon O-ringsfor isolating the cooling water
and combustion gases; andseveral holes between inner and outer
sleeves, to admitcooling water. The top of the inner sleeve was
shavedslightly to avoid any contact with the head. The twosleeves
were held together by a pair of lock nuts at thebase of the
assembly. With this design, both piston andliner can be changed
without disturbing the instrumentation.Figure 5-26 shows a
photograph of the Fixed-Sleeve assemblycomponents.
5.3.2.3. Implementation on the Cummins 903 Engine.
Basic Design and Instrumentation. A second
single-cylinderCummins 903 engine was set up in Room 246, for
theimplementation of the Fixed-Sleeve method. In all respectsthe
instrumentation and procedures were identical to thosedescribed for
the 4.1-litre engine. Each engine presents adifferent challenge
insofar as designing and applying theFixed-Sleeve method. Figure
5-27 shows a photograph givingan exploded view of the design
created for the Cummins 903.At the left is a collar which is
rigidly attached to theunderside of the block. That collar has a
necked-downsection with strain-gauges mounted inside and outside.
Thecollar and liner bottom are both threaded. The liner is
theninserted into the block and screwed into the collar,
whichsupports it rigidly at the bottom. The top of the liner
isspecially prepared as a separate piece, shown on the rightin the
figure. This piece is clamped to the block by thecylinder-head in
the same manner as the production engine.The liner and the top
piece have a concentric step and areallowed to slip relative to
each other. Sealing isaccomplished by two O-rings. Combustion gases
are sealed bya metal O-ring. A rubber O-ring is located just below
themetal ring.
Similar to the 4.1-litre engine, the collar was instrumentedwith
16 pairs of high-temperature strain-gauges. Eachbridge consisted of
eight gauges, four of which were equallyspaced on the inside
surface and the other four on theoutside. The bridges were wired so
that the gaugesmeasuring the circumferential, or hoop stresses,
providetemperature compensation. The gauges were wired to
minimizethe effects of bending loads. The gauges and wires were
61
-
Figure 5-26. Photograph of Fixed-Sleeve Assembly for 4.1-
Litre Gasoline Engine
62
-
covered with a thin layer of epoxy to protect them fromdamage
and temperature variations due to hot oil.
Calibration. The purpose of calibrating the fixture was
todetermine the following information:
1. Signal to noise ratio2. Causes of noise3. Repeatability4.
Linearity5. Gauge factor6. Magnitude of hysteresis caused by
O-rings
Signal to Noise Ratio. Figure 5-28 shows the noise presentwith
no excitation. Figures 5-29 and 5-30 show the sameconditions,
except that the excitation is applied, and10-(Figure 5-29) and 2-lb
weights (Figure 5-30) arealternatively placed on the collar. It can
be seen inFigure 5-30 that with no filtering, the noise level is
about1-2 lbf. Figures 5-31 and 5-32 show the same signal
(2-lbweight) when 10 kHz and 30 kHz low-pass filters are used.
Causes of Noise. Figure 5-33 is the same as Figure 5-32except,
no load is applied. Figure 5-34 shows a spectraldistribution plot
of Figure 5-33 obtained with a fastFourier transform (FFT). This
plot is used to detect any 60Hz component. It is seen that 60 Hz
and its harmonicsrepresents a sizable portion of the noise. Figure
5-35 isan spectral distribution of the same signal, but with
thesampling rate adjusted so that the FFT would include muchhigher
frequencies. The figure shows the presence of a 1700Hz signal and
its harmonics. After some investigation, itwas determined that the
IBM monitor was the source. Figure5-36 shows the signal with the
monitor unplugged.
Repeatability and Linearity. Repeatability is excellent,with no
observable difference from run to run. Linearity wasassessed by
putting successively heavier weights on thecollar. Figure 5-37
shows the result. The strain-gaugesare quite linear, and no
correction is anticipated.
Hysteresis. The hysteresis of the O-rings at theliner/top-ring
interface has been investigated atatmospheric pressure and room
temperature only. Nohysteresis was observed, a very desirable
result.Subsequently, it was found that the sleeve could not
beinserted with the lower cavity seals in place. It was thendecided
to cool the running engine with engine oil, andeliminate the seals.
Thus water was eliminated and norubber seals used.
63
-
Figure 5-27. Components of the Fixed-Sleeve Method for
theCummins 903 Engine
VOLTS
I *0.0 051.0
SECONDS
Figure 5-28. Original Strain-Gauge Bridge Noise, No
BridgeExcitation
64
-
0.02
-0 02-
-0.04-
-0.06-
SECONDS
Figure 5-29. Same as Figure 5-28 Except with Excitation,10 lbm
Weight Applied Intermittently
VOLTS ~ ''P
I ~I '-- ; oil
I I I0 20 40
SECONDS
Figure 5-30. Same as Figure 5-28, Except 2 ibm WeightAdded
65
-
SECONDS
Figure 5-31. same as Figure 5-30, Except 10 kHz Filter
VOLTS
-C. 0.
SECONDS
Figure 5-32. Same as Figure 5-30, Except 30 kHz Filter
66
-
0.021.
VOLTS
Sao 20•
--. 04'
- 3. O.S $
SECONDS
Figure 5-33. Same as Figure 5-32, Except No Load Applied
VOLg-6
I * I
HERTZ
Figure 5-34. Fourier Transform of Figure 5-33
67
-
VOLTS
I I I * *
HERTZ
Figure 5-35. Fourier Transform of Figure 5-33,
HigherFrequencies
VOLTS
0.00
-0.0
S I * I * I ..0.0 0. 0.4 0.3e 0.3
SECON-DS
Figure 5-36. Original Signal, Except IBM Monitor Unplugged
68
-
1.4-
1.2-
1.0-
+.8- + ++
Volts.6-
.4-
.2-
0 1020 40 60 80 100 120 140 160 180Weight, Lbm
Figure 5-37. Bridge Calibration, Volts Versus WeightApplied to
Strain-Gauged Collar
69
-
5.3.3. Ring and Liner Bench Test. The implementation ofthe ring
and liner bench-test involved not only thecalculation of friction
coefficient as a function of crankangle, as well as average
coefficient for the cycle, butalso implementing various process
control tasks. Frictioncoefficient is determined by dividing the
friction forcetransduced by the strain-gauges, by the normal load
providedby the air cylinder. Friction coefficient is calculated
andstored every 1.4 degrees of crank rotation. The
frictioncoefficient is also averaged over one revolution.
Theaverage coefficient, as a function of crank angle, isdisplayed
on the monitor screen for both right and leftsides and may be
recorded on a floppy disk at predeterminedintervals. Three cycles
are averaged prior to plotting andstoring. Upon completion of the
test, ring and linerprofiles may be measured to determine wear
volume, weightloss, and surface roughness, as part of an
overallassessment program. In the present study, liner and
ringroughness profiles were taken in the axial direction of
theliner and liner weight loss determined. Ring weight loss
isdifficult to determine, since only a small portion of thering is
worn.
For process control, as well as data acquisition andanalysis, a
computer system is employed. Speed, load andtest temperature, as a
function of time, are input for theprocess control function. The
simulator is capable ofunattended operation over the prescribed
cycle. While theresults presented herein are for tests of 2 and 4
hoursduration, tests of up to 20 hours have been
conducted.Automatic shut-down occurs if variables exceed
presetlimits. Periodically, friction data is taken, displayed onthe
screen, and stored on a flexible disk. Table 5.3 givesa list of the
computer controlled features.
5.4. Testing
Below is discussed the testing of the various
experimentalmethods conducted within this program. These are:
1. Instantaneous IMEP Method2. Fixed-Sleeve Method3. Ring and
Liner Bench Test
5.4.1. Testing With the Instantaneous IMEP Method.
5.4.1.1. Procedures. In testing with the InstantaneousIMEP
method both motoring and firing tests were run. Somemotoring tests
were run without compression, by installing aone inch thick steel
plate with a hole the size of thecylinder bore. Typically two data
runs were taken at each
70
-
Table 5-3. Automated Features of Simulator
Measurement and Control Features
Strain Gauge Force - Friction force stored digitally as
afunction of angular crank position
- Unit stops if friction coefficientexceeds specified
value(Important for scuffing tests)
Motor Speed - Speed monitored by angular positionsensor and
recorded
- Speed Controlled from 50 to 700 rpm- Independent
measurement.foroverspeed protection
Loading Force - Air cylinder pressure monitoredand recorded
- Pressure regulator motorized- Load constant or ramped up
to
about 650N
Oven Temperatures - Sample block temperaturemonitored for
control, and recorded
- Heaters cycled on and off based oncontrol equations
- Oven air sensed independently for
over-temperature protection- Temperature up to 6500C
System Integrity - Automatic shut-down after 10seconds if no
signals received fromcontroller
71
-
engine speed. Each run contained two sets of nineconsecutive
cycles and each set was taken about 1 minuteapart. Prior to tests
the engine was stabilize at the testcondition. Pressure and
strain-gauge signals were recordedsimultaneously using the data
acquisition system describedin 5.3.1.5. Results are presented in
Figure 5-41 through5-48, and are the average of 18 cycles. The use
of an 18cycle average arose from the characteristics of the
dataacquisition system, and did not reflect
additionalconsiderations. Eighteen cycles did provide very
repeatablefriction results, and there appeared to be no reason
toacquire additional data.
5.4.1.2. Results on the Cummins 903 Engine. Below is adiscussion
of the test results and some problem that wereencountered in
conventionally cooled engine tests and withSAE 40 lubricant. This
is followed by results from a cooledtest with ceramic-coating on
rings and liners, and SDL-1lubricant.
Baseline Engine Data. Data taken during the break-in of
thesingle-cylinder Cummins 903 engine are shown in Figures5-38,
5-39 and 5-40, and summarized in Table 5-4 togetherwith the test
conditions. Looking at Figures 5-38 and 5-39it is seen that the
bsfc increased about 0.01 units (2.5percent), and the motoring
torque increased about 4 lbf. ft.(13 percent) during the break-in.
This indicated a problemresulting in friction increase.
Subsequently, it was foundthat a large steel ring bolted to the top
of the dummybalance piston had worked its way against the cylinder
wall.This caused some light scuffing and friction increase.
Thesteel ring was modified and reinstalled, which solved
theproblem. A further problem is evident in Figure 5-40.
Fuelpressure increased during break-in. Ultimately, this wastraced
to swelling of the rubber fuel return line, which wasincased in a
flexible stainless braided covering. The linewas replaced. After
the initial problems were corrected, nonew problems arose. The
engine installation was judgedsatisfactory, since the performance
was similar to other 903single-cylinder engines built by Cummins
previously.
Piston Assembly Friction Without Compression. Figure 5-41shows
friction force, as a function of crankangle, under alow-speed
engine condition of about 200 rpm withoutcompression. There is no
pressure force across the pistonand, thus, the curves reflect the
strain in the connectingrod which gives the friction forces almost
directly, sincethe inertia forces are small at this speed. Results
arepresented for a relatively cool oil and water temperature of102
F and also a relatively hot oil and water temperature
ofapproximately 200 F. An SAE 40-grade oil was used.
72
-
CUMMINS DIESEL
.5 ', •s• d•--' -- .... "~m
.3
.2
.I
1 is 15 21 2S 30 5 413 45 53 55 6soENGINE HOURS
Figure 5-38. Brake Specific-Fuel Consumption DuringBreak-In:
BSFC units, lbm/bhp-hr
73
-
CUMMINS Di-SEL
0
18 1i i 20 25 30 35 46 4S Sm SS soENGINE HOURS
Figure 5-39. Motoring Torque During Break-In
74
-
CUHMINS DIESEL
1243 -. __ .--L ______,_ _-_ _- -
I120 - -
*
ins --- ----- 'A
I~nB• e
-,J40
26.
I i s3 15 21 25 33 35 41 4S So SS soENGINE HOURS
Figure 5-40. Fuel Injector Inlet Pressure During Break-In
75
-
Table 5-4. Summary of Average Break-In Data
SCE V903 performance Data Baseline
Speed (rpm) 2600
Torque (ft-lbs) 135
Brake Hp 66.83
BSFC (lb/bhp-hr) 0.400
Fuel Rate (lb/hr) 26.85
A/F Ratio 30.50
In/Ex Mfld Press (in Hg) 50.5/50.5
Ex Mfld Press/In Mfld Press 1.00
Fuel Press (psi) 100-125
Oil Rifle Press (psi) 35
Oil Temp (-F) *240
Intake Mfld Temp (-F) 140
Ex Mfld Temp (-F) 810
Water Out of Cyl Head (-F) 185
Water Into Cyl Head (-F) 176
Blowby-in H20 3.0
Fuel Out of Cyl Head (-F) 135
Fuel Into Cyl Head (-F) 75
76
-
INTAKE COMP. POWER EXHAUST240
180
120
U-m
-J 60LUUJ
LL o
S60__ _ _
120
180
240 90 180 270 360 450 540 630 720
THETA (DEG)
Figure 5-41. Friction Force with Low (102 F) and High(200 F) Oil
and Water Temperatures, SAE 40Oil, 200 RPM, Normally Aspirated
77
-
It is evident that the greater viscosity in the lowertemperature
test produced a much more hydrodynamic characterto the resulting
friction. With the higher water and oiltemperatures, the friction
trace exhibits considerable mixedlubrication and may be viewed as
essentially a square waveof amplitude approximately plus or minus
20 lb force. Thepiston and ring assembly friction mean effective
pressurewas was 4.8 psi cold and 2.37 hot. The nearly
two-to-onedifference in friction results mainly from lower
frictionforces during the midstroke where the product of
frictionforce times velocity is especially high.
Occurrence of Magnetic Interference. At the University
ofMichigan, we have had considerable experience applying
theInstantaneous IMEP method to various gasoline engines.
Theapplication to the diesel engine was not expected to presenta
large problem, at least under motoring conditions.Consequently,
friction traces, such as that shown in Figure5-42, were entirely
unexpected. Figure 5-42 shows frictionforce as a function of
crankangle at 1200 rpm, motoring forthe 903 engine. In spite of our
best efforts, the dataappeared to be nonsense. After making a
number of changesin engine hardware and instrumentation, it was
finallyrealized that the strange result was coming from
magneticfields of the rotating crankshaft. The crank of this
enginehad been magnetized either during manufacture or
inspection.Strain-gauges and lead wires, including the wires on
thegrasshopper linkage, constitute conductors moving in
thatmagnetic field.
Figure 5-43 shows the strain-gauge bridge output signalbefore
and after reduction of the magnetic field, with nobridge input. The
voltages generated by the magnetic fieldwere dominating the signal.
A number of steps were taken tominimize this magnetic field effect,
which are summarized inTable 5-5. The extraneous signals were
minimized primarilythrough a combination of degaussing of the
crankshaft andmagnetic shielding. As a result, the extraneous
voltagebecame a relatively minor portion of the signal, which
couldbe measured at each engine speed without bridge excitation,and
the resulting noise subtracted from the strain-gaugesignal. The
relatively smooth curve shows the noise afterall reduction methods
were implemented.
Results After Elimination of Magnetic Noise. Havingresolved the
magnetic field problem, both motoring andfiring data were taken on
the Cummins 903 engine. Figure5-44 shows motoring results at 1200
rpm with one atmosphereboost pressure. In part, the remaining noise
on the traceresulted from the relatively high amplifier gain
required toamplify the strain-gauge signals from the rather
massive
78
-
INTAKE COM-P. POWER EXHAUST
240 -- m l180
120
La.
60
w
10 •
L)vvLL 60
120
24090 180 270 360 450 540 630 720
THETA MEG)
Figure 5-42. Friction Force Trace Including Error FromCrankshaft
Magnetism - 1200 RPM, 200 F Waterand Oil, Naturally Aspirated
79
-
INTAKE COmP. POWER EXHAUST
240
180
120- 20 ______
L-mdw 60
w
cc 60w cc7
120
180
24090 180 20 360 450 540 60 720
THETA MEG)
Figure 5-43. Strain-Gauge Signal Without Bridge ExcitationBefore
and After Reduction of MagneticInterference, 1200 RPM
80
-
Table 5-5. Steps Taken to Minimize Magnetic Noise
1. Install Mu Metal (high permability iron) shieldingover all
connecting rod wiring and connector.
2. Change wiring on connecting rod to give pairing ofsense wires
and excitation wires to remove loops.
3. Twist pairs of copper braid shielding on
grasshopperwires.
4. Demagnetize crankshaft as much as possible withhand- held
degausser.
5. Smooth sharp edges on crankshaft to remove
fieldconcentrations near grasshopper/connecting rod.
6. Measure signal at each speed without strain-gaugeexcitation,
so that any remaining noise can besubtracted from strain-gauge
signal.
81
-
INTAKE COMP. POWER EXHAUST240
180
m: . 60 Ik20
90 1 8 27K6.40 50 3 2
U.CS 60
LL cc
120
180
24 0-0 __90 ISO 270 360 450 540 630 720
THETA (DEG)
Figure 5-44. Motoring Piston and Ring Friction, 1200 RPM,29.17
PSIA Manifold Pressure, 200 F Water andOil, Friction MEP = 3.03
PSI
82
-
connecting rod of this engine. Compared to gasoline
engineexperience, the jumps at the dead centers are not
aspredominate. All in all, the friction appears to berelatively
hydrodynamic throughout the 720 degree stroke.Figure 5-45 shows
results of firing at 1200 rpm with oneatmosphere pressure boost.
Compared to motoring in Figure5-44, large differences may be noted
around top dead-centercompression. This large change between
motoring and firingsuggests that the technique will be useful for
identifyinglubrication problems in a low-heat rejection engine,
wherethe friction forces at top dead-center combustion mightbecome
very large. This firing curve exhibits someproblems, which are
artifacts of the measurements. Inparticular, on the power stroke,
the friction force drops toa negative level, which is
incorrect.
Accounting for Instantaneous Crank Speed. The inertiaforces of
Figures 5-44 and 5-45 were calculated based onmeasured
instantaneous crankshaft speed. Figure 5-46 showsa trace of
instantaneous speed at 1200 rpm firing with 30inches of mercury
boost pressure. The more than 50 rpmvariation in speed over the
cycle of this one-cylinderengine affects the inertia force
significantly. Thus,consideration of the effect of instantaneous
crank-speed isnecessary in this case. The friction trace is
distorted, asshown in Figure 5-47, if this is not done. Considering
theinstantaneous crank-speed of the engine is essential toobtaining
good friction results, if there is significantspeed variation such
as might be expected in engines withfew cylinders and heavy
reciprocating inertias.
Results With SDL-1 and Uncooled Operation. Figures 5-48 and5-49
show motoring and firing results with syntheticlubricant SDL-1 at
1200 rpm, intake manifold pressure of 30psia, about 40 psi bmep,
and without cylinder block cooling.These curves may be compared to
Figures 5-44 and 5-45, inwhich SAE 40-oil was used in the
conventionally cooledengine. The tests with SDL-1 were run using
chrome oxidering and liner coatings, whereas the data with SAE 40
usedproduction chrome-plated iron rings and Lubrited gray
ironliner. In comparing these results with those of the SAE
40lubricant, it is noticed that the PR FMEP is about the same(2.97
versus 3.03 psi) motoring, but is lower for the SDL-1(1.55 versus
2.25 psi) firing. Note that near TDCcompression, the SDL-I gave
higher friction in the mixed orboundary friction regime, which is
characteristic of thelubrication there, even for motoring. It is
not known whythe SDL-1 gave significantly lower firing friction
withuncooled operation. The result may be real, or it be due
tomeasurement inaccuracy. More study on tuis is needed.
83
-
INTAKE COMP. POWER EXHAUST240
180
120 r ty I
ww
120
240so 180 270 360 450 540 630 720
THETA (DEG)
Figure 5-45. Firing Piston and Ring Friction, 1200 RPM,29.17
PSIA Manifold Pressure, 200 F Water andOil, Friction MEP = 2.25
PSI
84
-
"1288
1278
S"1268
~ 1258 0 "
S 1248
S"1238
. 1228
1218
190
1188 188 360 540CRANK ANGLE (DEG)
Figure 5-46. Instantaneous Crank Speed at 1200 RPM, Firing,30
In. Hg. Boost
85
-
-NTKE COMP. POWER EXHAUST240 -4
ISO
t80
120 W
.-U, I./,:,
IJ W
,, > 60_ _ LI
U.L 0 -PA_ _ _
LL i
90 10 270 360 450 540 630 720
THETA (DEG)
Figure 5-47. Results shown in Figure 5-45 Before Correctedfor
Instantaneous Speed Variation
86
-
Intake Compression Expansion Exhaust
240
180
M 120-J
LýL 60
0cm
0c 60'(L
120
180
240 S0 it 27T 37T 47t
Crank Rngle (rad)
Figure 5-i Motoring Piston and Ring Friction, 1200 RPM,30.01
PSIA Manifold Pressure, UncooledOperation, Friction MEP = 2.97 PSI,
SyntheticLubricant
87
-
Intake Compression Expansion Exhaust
240
180
00 120-J
UL0U. 60
L A A
0 600
-4
120
180
2400 T2i 3n 47r
Crank Angle (rad)
Figure 5-49. Firing Piston and Ring Friction, 1200 RPM,29.91
PSIA Manifold Pressure, UncooledOperation, Friction MEP = 1.55 PSI,
SyntheticLubricant
88
-
General Comments on the Instantaneous IMEP Method.
TheInstantaneous IMEP method, when properly implemented, hasthe
potential of determining piston and ring assemblyfriction with good
accuracy over a large portion of the fullcycle. It is estimated
that about 90 percent of the cycleis reported with good accuracy.
At the very highestpressures and combustion temperatures the
uncertaintiesbecome greater. Thus about 10 percent of the crank
anglesof the cycle, around top dead-center combustion,
haverelatively high uncertainty with respect to friction
forces.
The method is projected to be able to assess changes infriction
coming about from engine or lubrication failures.The foregoing
statement is very significant, since often onewishes to anticipate
a problem as it develops. Therefore,even if the absolute values
with the Instantaneous IMEPmethod are less than perfect, the
indication of a relativechange is useful. A major plus for the
Instantaneous IMEPmethod is that essentially no engine
structuralmodifications are required. Our overall experience
withthis method, in both gasoline and diesel engines, shows thatit
has very good repeatability. Even with uncooled engineoperation,
there was no indication that the technique wouldnot work.
Unfortunately, this program t