Table 8 The mean values, standard deviations, and *p values after conducting specific laboratory tests of used engine oils.

From: Degradation of anti-wear additives and tribological properties of engine oils at extended oil change intervals in city buses

 

Bus ID

 

2378

{1}

2384

{2}

2400

{3}

2414

{4}

2420

{5}

N

3

3

3

3

3

4-ball test

Wear scar diameter [mm]

x̅

(SD)

1.932

(0.066)

4.041

(0.053)

2.107

(0.039)

1.980

(0.012)

1.974

(0.057)

Elemental analysis

Iron

[Fe]

x̅

(SD)

62.75

(0.83)

76.14

(0.06)

96.37

(0.81)

75.87

(0.58)

131.7

(0.10)

Copper

[Cu]

11.3

(0.10)

4.48

(0.09)

9.30

(0.02)

2.14

(0.14)

5.26

(0.17)

Molybdenum [Mo]

366

(9)

417

(21)

384

(22)

387

(11)

419

(11)

Zinc

[Zn]

1544

(6)

1077

(1)

1576

(6)

1405

(1)

1579

(0)

Phosphorus

[P]

1001

(13)

759

(26)

1082

(24)

907

(14)

1116

(37)

Sulfur

[S]

3616

(9)

2809

(34)

3504

(26)

3594

(23)

3570

(17)

FTIR

Phos. antiwear

[A/cm]

x̅

(SD)

− 16.76

(0.03)

− 17.63

(0.06)

− 19.85

(0.05)

− 11.50

(0.05)

− 16.67

(0.05)

Soot

[A/cm]

0.413

(0.00)

0.816

(0.01)

0.492

(0.01)

0.509

(0.00)

0.828

(0.01)

 

{5}–{4}

{5}–{3}

{5}–{2}

{5}–{1}

{4}–{3}

{4}–{2}

{4}–{1}

{3}–{2}

{3}–{1}

{2}–{1}

p-value

0.999

0.504

< 0.001

0.825

0.059

< 0.001

0.774

< 0.001

0.010

< 0.001

p-value

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

0.996

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

0.170

0.126

0.999

0.015

0.999

0.228

0.535

0.170

0.650

0.021

< 0.001

0.851

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

0.482

< 0.001

0.001

< 0.001

< 0.001

0.006

< 0.001

0.015

< 0.001

0.723

0.037

< 0.001

0.197

0.005

< 0.001

0.787

< 0.001

0.001

< 0.001

p-value

< 0.001

< 0.001

< 0.001

0.183

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

0.452

< 0.001

0.154

< 0.001

< 0.001

< 0.001

< 0.001

< 0.001

  1. N number of samples tested, x̅ arithmetic average, SD standard deviation, *p value resulting from the application of Tukey’s post-hoc test.
  2. Oil groups (e.g., {5}–{4}) represent a comparison between two distinct oil samples. Analyzing the results for individual samples helps identify similar oils or distinguish those that differ.
  3. Significant values are in bold.
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