Effect of Recirculation (EGR) on Diesel – impact on wear

Oyelayo Ajayi, Robert Erck, Ali Erdemir, George Fenske, and Irwin Goldblatt*

*BP-Global 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

„ EGR will contaminate engine oil – Increase of oil 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 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 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) 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 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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