Effect of Exhaust Gas Recirculation (EGR) on Diesel Engine Oil – impact on wear
Oyelayo Ajayi, Robert Erck, Ali Erdemir, George Fenske, and Irwin Goldblatt*
*BP-Global Lubricant Technology, Wayne, NJ
14th DEER Conference, Dearborn, MI August 4-7, 2008
Background Exhaust gas recirculation (EGR) is an effective means to reduce NOx emission from diesel engine
EGR will contaminate engine oil – Increase of oil soot loading – Increase in oil total acid number (TAN)
EGR will result in durability problem for many lubricated engine components due to accelerated wear
Goal: Mitigate detrimental impact of EGR on engine components through materials, surface and lubricant technologies.
2 Approach Characterize and quantify effect of EGR on lubricant degradation – Physical, chemical, etc.
Evaluate impact of lubricant degradation on friction and wear behavior
Develop and evaluate material and surface technologies for improved friction and wear performance in EGR environment
Develop and evaluate advanced lubricant formulation for EGR – Impact of regulation
3 Oil Degradation – physical
Used oils from Cummins M-11 engine tests were characterized
A (New oil) B C D
Viscosity at 100 ºC (cSt) 14.40 14.39 14.55 14.86 (start of engine test) Viscosity at 100 ºC (cSt) - 24.95 42.91 120.52 (end of engine test) Total Acid Number 1.1 3.81 2.08 2.36 (TAN) Total Base Number 10.43 8.42 6.11 5.33 (TBN) Soot Content (%) 0 6.9 9.0 12.0
4 Oil Degradation
140 12
y = m1 + m2*x^m3 TAN 120 Value Error TBN m1 12.597 3.8445 10 m2 0.0050762 0.0065194 100 m3 4.0059 0.50887 Chisq 16.728 NA 8 R2 0.99758 NA 80 6
60 TAN/TBN
Viscocity (cSt) Viscocity 4
40 2
20
0 03691215 0 02468101214 Soot Content (%) Soot Content (%)
TAN and TBN variation as ¾ Oil viscosity increases as 4th power expected. of soot content. Non of used oils reached cross ¾ Oxidation may also contribute to oil over point. thickening. ¾ Soot content of 4.5% limit in engine tests.
5 Oil Degradation – Additives
Used oils from Cummins M-11 engine tests chemical composition (ppm) characterized by standard spectrochemical analysis Element A (New oil) B C D
Iron (Fe) 1 119 147 58 Chromium (Cr) < 1 18 25 10 Molybdenum (Mo) < 5 6 < 5 < 5 Phosphorus (P) 1247 750 756 304 Zinc (Zn) 1356 1111 945 843 Calcium (Ca) 3992 1096 3058 999 Magnesium (Mg) 14 10 10 4
- Increase iron content from wear - Decrease in additive content – additive depletion
6 Soot (Solid) Particles
Insoluble solid particles in used oil consist of many components. - Carbon, iron oxide, metallic wear debris
Variety of sizes and shapes
7 Preliminary Friction and Wear Test
Test configuration: Four-ball (ASTM D 4172)
Balls: ½” diameter M50 steel
Load: 73 N
Speed: 1200 rpm
Lubricant: New and used oil from Cummins M-11 engine test Duration: 1 hour
8 Friction Results
A B C D
0.3
0.2 Friction Coefficient Friction
0.1
0 0 102030405060 Time (min)
Friction coefficient nearly constant for duration of test for all oils
Periodic spike in friction for all the used oils
9 Friction Results
0.2 Average friction for used oil slightly lower than for clean 0.15 oil – Effect of viscosity 0.1 increase on fluid film
0.05 – Carbon soot acting as solid lubricant 0 ABCD Test Oil
10 Wear Results
12 Substantial increase in 10 wear in tests with used 8 oils
6 – Oil degradation leads to less protection of
4 rubbing surfaces • Change in chemistry 2 • Presence of solid 0 particles ABCD Test Oil
11 Wear Results
12.0 12.0
y = -3.752 + 3.6301x R2= 0.9858 10.0 10.0
8.0 8.0
6.0 6.0
4.0 4.0
2.0 2.0
0.0 0.0 02468101214 1.01.52.02.53.03.54.04.55.0 Soot % Total Acid Number (TAN)
For the limited data points in the present study Wear volume not dependent on soot content Wear appears linearly dependent on TAN
12 Wear Mechanism – clean oil
Evidence of abrasive and oxidative wear Formation of surface films – reaction with lubricant additive
13 Wear Mechanisms – used oil
Oils B & C Oil D
For used oils B and C, wear similar – primarily abrasive, with less surface films For used oil D, in addition to abrasion, evidence of corrosion and scuffing – Higher TAN (corrosion) and soot content (scuffing). – Soot interferes with lubricant entrainment into the contact
14 Conclusions
Exposure of oil to EGR during diesel engine testing resulted in accelerated degradation of oil – Increase in soot content resulting in significant increase in oil viscosity – Increase TAN and more rapid decrease in TBN
– Oil additive depletion
Although the used oil reduced the average friction during a four-ball bench-top test, wear was increased by about two orders of magnitude compared to new oil.
In the tests with used oils, predominant wear mode is abrasion, aided by corrosion. – Scuffing was also observed in test with 12% soot content.
No clear trend correlation can be established between bench-top friction and wear testing and wear during engine test.
15 The End
Thank you !
This work was supported by the Office of Vehicle Technologies of the U.S. Department of Energy under contract DE-AC02-06CH11357
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