UNIVERSITI TEKNIKAL MALAYSIA MELAKA

INVESTIGATE THE VISCOSITY OF USED ENGINE OIL

BEFORE AND AFTER FILTRATION AND ENHANCE BY

NANOPARTICLES

This report is submitted in accordance with the requirement of Universiti Teknikal

Malaysia Melaka (UTeM) for the Bachelor of Mechanical Engineering Technology

(Maintenance Technology) with Honours.

by

NUR HAFIZAH BINTI ABDUL AZIZ

B071310039

890715-08-5464

FACULTY OF ENGINEERING TECHNOLOGY

2016

__________________________ _________________________

Tarikh: ______________________ Tarikh:_____________________

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

TAJUK: Investigate the Viscosity of Used Engine Oil Before and After Filtration and Enhance by Nanoparticles SESI PENGAJIAN: 2016/17 Semester 1 Saya NUR HAFIZAH BINTI ABDUL AZIZ mengaku membenarkan Laporan PSM ini disimpan di Perpustakaan Universiti Teknikal Malaysia Melaka (UTeM) dengan syarat-syarat kegunaan seperti berikut: 1. Laporan PSM adalah hak milik Universiti Teknikal Malaysia Melaka dan penulis. 2. Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan

untuk tujuan pengajian sahaja dengan izin penulis. 3. Perpustakaan dibenarkan membuat salinan laporan PSM ini sebagai bahan

pertukaran antara institusi pengajian tinggi.

4. **Sila tandakan ( )

BORANG PENGESAHAN STATUS LAPORAN PROJEK SARJANA MUDA

SULIT

TERHAD

TIDAK TERHAD

(Mengandungi maklumat yang berdarjah keselamatan atau

kepentingan Malaysia sebagaimana yang termaktub dalam

AKTA RAHSIA RASMI 1972)

(Mengandungi maklumat TERHAD yang telah ditentukan oleh

organisasi/badan di mana penyelidikan dijalankan)

Disahkan oleh:

Alamat Tetap:

NO. 1A, Jalan Ngah Sudin,

Kampung Ulu Chepor,

31200 Chemor, Perak.

Cop Rasmi:

** Jika Laporan PSM ini SULIT atau TERHAD, sila lampirkan surat daripada pihak

berkuasa/organisasi berkenaan dengan menyatakan sekali sebab dan tempoh laporan PSM ini perlu

dikelaskan sebagai SULIT atau TERHAD.

DECLARATION

I hereby, declared this report entitled “Investigate the viscosity of used engine oil before

and after filtration and enhance by nanoparticles” is the results of my own research

except as cited in references.

Signature : …………………………………………

Author‟s Name : Nur Hafizah Binti Abdul Aziz

Date : …………………………………………

APPROVAL

This report is submitted to the Faculty of Engineering Technology of UTeM as a partial

fulfilment of the requirements for the degree of Bachelor of Mechanical Engineering

Technology (Maintenance Technology) with Honours. The member of the supervisory is

as follow:

………………………………..

(Dr. Muhammad Ilman Hakimi Chua Bin Abdullah)

ABSTRAK

Pada masa kini, pelincir yang digunakan khususnya pada suhu yang tinggi

kebiasaannya menunjukkan perubahan peningkatan kelikatan minyak pelincir yang

telah digunapakai. Antara faktor yang menyebabkan kelikatan minyak pelincir

terjejas kebiasaannya disebabkan oleh pengoksidaan, digradikasi, kehadiran air dan

lain-lain lagi. Justeru itu, minyak enjin yang digunakan kebiasaannya akan menjadi

bahan buangan sahaja. Peningkatan sisa minyak enjin yang telah digunakan semakin

meluas terutamanya dalam aplikasi industry pada masa kini. Walau bagaimanapun,

sisa minyak ini boleh digunakan semula dengan peranan nanopartikel. Ini kerana,

nanopartikel boleh meningkatkan sifat-sifat kimia minyak pelincir dengan lebih baik

jika dibanding dengan bahan tambahan yang digunakan pada masa kini, terutama

dari segi kelikatan minyak tersebut. Kajian dijalankan bagi mengkaji kelikatan

nanopartikal yang ditambah di dalam minyak terpakai sebelum dan selepas ditapis.

Dengan merujuk kepada ASTMD2270, indeks kelikatan sampel kemudiannya dikira

dan di nilai berdasarkan keputusan yang diperoleh. Akhir sekali, sebagai

pengesahkan kepada keputusan ujikaji yang dijalankan, „flash point‟ bagi tiap sampel

dikenalpasti dengan merujuk kepada ASTM D3828. Keputusan dari ujikaji yang di

jalankan menunjukkan sampel yang di campur dengan nanopartikal dapat

mengurangkan kelikatan kinetik sebanyak 3-7% pada suhu 40°C dan 2-8% pada

suhu 100°C. Bagi indeks kelikatan pula, sampel-sampel yang melalui proses

penapisan sebanyak tiga kali menunjukkan peningkatan sebanyak 5.5% dengan

graphite mencatat indeks kelikatan paling tinggi melebihi minyak terpakai dengan

0.61%.Manakala, keputusan „flash point‟ yang diperoleh menunjukkan nilai lebih

rendah dari nilai rujukan dengan nilai „flash point‟ paling rendah, 145.5°C, dan

156°C mencatat suhu tertinggi untuk sampel flash.

ABSTRACT

Currently, most of the lubricants used were reflected in high temperature applications

which usually increase the possibilities of the lubricant viscosity been distorted. The

symptom for viscosity distorted usually caused by oxidation, degradation, the

presence of water and such that lead to this problem. Therefore, the used engine oil

will become a waste. This waste increase day by day as the engine oil are wide been

used especially in industrial application. However, this waste oil can be re-used by

enhancement of nanoparticles. Nanoparticles could improve for the better lubricant

chemical properties compared to the currently used additives, especially for the

viscosity characteristic. Thus, testing was conducted in order to investigate the

viscosity of used engine oil before and after filtration with enhancement of

nanoparticles. The viscosity index of prepared samples was calculated and evaluated

according to ASTM D2270. The flash point of the samples was determined in order

to verify the result obtained according to ASTM D3828. Result shows reduction of

the kinematic viscosity value around 3-7% at 40°C and 2-8% at 100°C compared to

the pure used engine oil. The viscosity index for the prepared samples with three-

time filtration process indicated the highest value compared to the other by 5.5%

increment. And, graphite mark as the highest viscosity index value that exceeds the

viscosity index of used engine oil by 0.61%. The lowest value of prepared sample

flash point obtained is 145.5°C, with 156°C mark as the highest flash point of the

sample.

DEDICATION

This thesis I dedicate to my beloved parents.

ACKNOWLEDGEMENT

All praise is due to Allah for giving me strength and ability to understand,

learn and complete this thesis. I would like to express my deep gratitude and

appreciation to Dr. Muhammad Ilman Hakimi Chua bin Abdullah as my supervisor,

for his constant guidance and encouragement, without which this work would not

have been possible. Also, for given his valuable time, advice, criticism and

correction to this thesis from the very beginning up to the end of the writing. For his

unwavering support, I am truly grateful. I am also grateful to all of the lecturers in

the Fakulti Teknologi Kejuruteraan who have thought and guided me during the

years of my study, especially En. Mohd Sulhan bin Mokhtar, my academic advisor

(PA), for his support toward the successful completion of my studies.

I would also like to express my heartfelt gratitude to my beloved parents,

Abdul Aziz bin Talot @ Talib, and Ma Hairiah binti Amer Moehd Isa for their

endless love, encouragement, and support that made me possible to face the entire

obstacle in life. I am also thankful to all my siblings, Abdul Murshid, Nur Liana,

Muhammad Bukhari, Munirah, and Usamah for their supports end encouragement.

My thanks are also addressed to all of my fellow BETM members, especially

Rumaisa, Haya, Suhaida, Baizura, Lieyana, and Munirah, for their time and help

while completing this thesis. Not forgotten, all of the Team PSM Dr. Ilman members

that help in collecting information, sharing their knowledge and opinion while

preparing this thesis.

TABLE OF CONTENT

ABSTRAK I

ABSTRACT II

DEDICATION III

ACKNOWLEDGEMENT IV

TABLE OF CONTENT V-VII

LIST OF TABLES VIII

LIST OF FIGURES IX-X

LIST ABBREVIATIONS, SYMBOLS AND NOMENCLATURES XI-XII

CHAPTER 1: INTRODUCTION 1

1.1 Introduction 1-2

1.2 Problem Statement 2-3

1.3 Objective 3

1.4 Scope of Work 3

CHAPTER 2: LITERATURE REVIEW 4

2.0 Literature Review 4

2.1 Background of Lubricant 4-5

2.1.1 Introduction of Lubricant 5-8

2.1.2 Type of Lubricant 8-10

2.1.2.1 Petroleum Based Oil 11-13

2.2 Polyalphaolefins (PAOs) 13-14

2.2.1 Characterization 14-16

2.2.2 Used Engine Oil 16-18

2.2.3 Purification of Waste or Used Engine Oil 18-20

2.3 Nanoparticles 20

2.3.1 Nanoparticles as Additive 21

2.3.2 Effect of Nanoparticles in Chemical or Physical Oil

Properties

21-24

2.4 Lubricant Viscosity 25

2.4.1 Dynamic Viscosity 25

2.4.2 Kinematic Viscosity 26

2.4.3 Viscosity Index 26-27

2.5 Viscosity Improver 28

2.5.1 Effect of Nanoparticles in Viscosity Properties 28-29

2.5.2 Effect of Nanofluid on the Viscosity Index 29-30

2.5.3 Effect of Viscosity with Temperature 30-31

CHAPTER 3: METHODOLOGY 32

3.0 Introduction 32-33

3.1 Material Selection 33

3.1.1 Engine Oil (SN 0W-20) 34

3.1.2 Nanoparticles 35

3.1.2.1 Hexagonal Boron Nitride (hBN) Nanoparticles 35-36

3.1.2.2 Alumina (Al2O3) Nanoparticles 36-37

3.1.2.3 Graphite Nanoparticles 38

3.2 Sample Preparation 39

3.2.1 Filtration 39

3.2.1.1 ASTM D7317 39-41

3.2.2 Sample Composition 42-43

3.2.3 Ultrasonic Homogenizer 43-44

3.3 Testing Method 44

3.3.1 Viscosity Testing 45-47

3.3.1.1 ASTM D2270 48

3.3.2 Flash Point 48-49

CHAPTER 4: RESULTS AND DISCUSSION 50

4.0 Results and Discussion 50

4.1 Effect of used engine oil's kinematic viscosity enhances by

Nanoparticles

50-52

4.1.1 Kinematic viscosity analysis at 40°C 53-55

4.1.2 Kinematic viscosity analysis at 100°C 55-56

4.2 Effect of used engine oil's viscosity index enhances by

Nanoparticles 56-57

4.2.1 Analysis of viscosity index 58-59

4.3 Effect of used engine oil's flash point enhances by Nanoparticles 59-60

4.3.1 Analysis of flash point 60-62

CHAPTER 5: CONCLUSION AND RECOMMENDATIONS 63

5.0 Conclusion 63-64

5.1 Recommendations 64

REFERENCES

65-78

APPENDICES

A List of Respondents

79-80

LIST OF TABLES

Table Title Page

2.1 Elastohydrodynamic characteristic 7

2.2 Group of Mineral Based Oil 13

2.3 Evaluation of polyalphaolefin properties group 15

2.4 Classifications of used engine oil and it source 17-18

2.5 Effect of nanoparticles in physical oil properties 22-24

3.1 SN 0W-20 performance criteria 34

3.2 Characteristic of -BN, -BN, and -BN 35

3.3 Characteristic of hexagonal boron nitride and cubic boron nitride 36

3.4 Characteristic of alumina (Al2O3) alpha and alumina (Al2O3)

gamma

37

3.5 Characteristic of graphite 38

3.6 Centration of samples 42

3.7 Composition of samples 43

3.8 Test condition of flash point 49

4.1 The average of kinematic viscosity, cSt at 40°C and 100°C 51

4.2 The viscosity index of the prepared samples 57

4.3 Flash point of the prepared samples 60

LIST OF FIGURES

Figure Title Page

2.1 Lubricant regimes 6

2.2 Hydrodynamic layer 6

2.3 Stribeck curve 8

2.4 Crystalline structure of graphite 9

2.5 Application methods for solid lubricant 9

2.6 Saturated and unsaturated bond 10

2.7 Type of mineral oils 11

2.8 Polyalphaolefins chemical structure 14

2.9 Different type of force in filtration process 20

2.10 Scar resistance behavior for Fe nanoparticles, Cu nanoparticles,

and Co nanoparticles

22

2.11 Graph of Kinematic viscosity versus temperature characteristic 27

2.12 Graph of kinematic viscosity evaluation 27

2.13 Kinematic viscosity measured at 40ºC and 100 ºC 29

2.14 The oil properties comparisons between SAE 15W40 with hBN

and Al2O3 nanoparticles

30

2.15 Viscosities (cSt) at 40°C and 100°C of n-paraffins of chain length

C11 to C44

31

2.16 Log viscosities (cSt) of n paraffins of chain length chain length C11

to C44

31

LIST OF FIGURES

Figure Title Page

3.1 Methodology flow chart 33

3.2 TME image of Alumina (Al2O3) alpha and Alumina (Al2O3) gamma 37

3.3 Schematic diagram of paper filtration apparatus 41

3.4 Figure of paper filtration apparatus 41

3.5 Schematic diagram of ultrasonic homogenizer 44

3.6 Viscometer with water bath 46

3.7 Schematic diagram of Brookfield viscometer DV II + PRO 47

3.8 Small scale closed cup flash point tester 49

4.1 Graph of the kinematic viscosity at temperature of 40 °C and 100

°C versus samples prepared

52

4.2 The agglomeration of the prepared sample 54

4.3 Samples with hexagonal Boron Nitride nanoparticles 54

4.4 Samples with graphite nanoparticles 55

4.5 Samples with aluminum oxide nanoparticles 55

4.6 Graph of the viscosity index versus the prepared samples 58

4.7 Graph of the flash point versus the filtration process 62

LIST OF ABBREVIATIONS, SYMBOLS AND

NOMENCLATURE

Al2O3 - Alumina

API - American Petroleum Institute

ASTM - American Society of the International Association for Testing and Materials

BN - Boron nitride

C - Viscometer constant, mm³/s)

C - Carbon

CH - Carbon-hydrogen

CI - Compression-ignition

Co - Cobalt

cP - Centipoise

cSt - Centistokes

Cu - Copper

CuO - Copper oxide

EHL - Elastohydrodynamic

Fe - Ferrum

H - The kinematic viscosity at 40 ºC of an oil of 100 viscosity index that

have the same value as the kinematic viscosity at 100 ºC of the oil

that the viscosity index to be calculated, mm²/s

hBn - Hexagonal boron nitride

HL - Hydrodynamic lubrication

Hz - Hertz

L - The kinematic viscosity at 40 ºC of the oil that the viscosity index to

be calculated, mm²/s

m - Meter

m - Mass

mL - mililiter

Ƞ - Dynamic / Absolute viscosity, pa-s

ºC - Celsius

ºF - Fahrenheit

P - Pressure, Pa

P - Poise

p - Density, g/cm³

PAOs - Polyalphaolefins

s - Second

Sn - Tin / stannum

t - Time, s

TiO2 - Titanium oxide

U - The kinematic viscosity at 40 ºC of oil with the value of viscosity

index is 0 and having the same kinematic viscosity at 100 ºC as the

oil whose viscosity index is to be calculated, mm²/s

USA - United State of America

v - Volume

VI - Viscosity Index

vol.% - Volume friction

- Rotational speed, rps

- Kinematic viscosity, cSt

CHAPTER 1

INTRODUCTION

1.0 Introduction

Lubricant has been used for many years as a substance to reduce wear and

friction between the surface areas. Different kind of lubricant properties is

formulated in order to optimize the key performance features. Lubricant can be

classified into three categories; the solid lubricant, semi-solid lubricant, and liquid

lubricant. The three different type of liquid lubricant in used is synthetic, mineral oil

and bio-based oil, which are choose based on the application critical parameter. In

order to optimize the lubricant to it desired characteristic, additive are used to scatter

the molecule of the lubricant. Therefore, wear, friction, corrosion and others can be

reduced, (Zhang et al., 2009). Synthetic oil is synthetically designed for a specific

sub-atomic piece with a customized and uniform structure where the molecules are

saturated with carbon‐hydrogen (CH) bonds.

Due to the saturated CH bonds in synthetic oil, the lubricant has more

advantage compared to mineral oil in withstanding higher temperature, good

viscosity, have better oxidative stability and high load-carrying capacity. However,

in any lubricant oil mixture, suitable added substances should be incorporated to

upgrade certain properties, such as oxidation strength, friction reduction, wear,

hostile to erosion, and strength against organic attack. Therefore, the lubricant ought

to have the capacity to keep the added substance fix the certain properties as desired

in operating order, (Mortier et al., 2010). Most of the applied lubricant nowadays

lubricate for high temperature applications which cause most of this lubricant face

distortion in oil viscosity. Nanoparticles are viewed as solutions to re-used distorted

lubricant by enhancing the lubricant with nanoparticles.

Recently, some studies in developing nanoparticles and nanotubes as another

sort of added substance material for oils been conducted due to their structure, size

and other special properties. Currently, nanofluid are new engineering lubricants,

which are produced using nanostructures technology, (Lee et al., 2009). Among the

nanofluid properties, the viscosity is an essential property since it demonstrates the

liquid's resistance. With the expanding of viscosity, the required vitality for pumping

and blending increase. Also, pumping power and weight drop are two key

components that rely on upon consistency, (Mahbubul et al., 2012). In this research,

the viscosity of used engine oil before, after filtration and enhance by nanoparticle

will be investigated. The viscosity index will be measured by using ASTM D2270 in

order to identify the viscosity index of samples prepared where the aim is for the

used engine oil with the enhance of nanoparticles give the same viscosity index as

pure engine oil.

1.1 Problem Statement

The growth of industrial technologies made the used engine oil as the most

plentiful material of waste available. Because of the application used for engine oil is

at high temperature, the viscosity, specific gravity and flash point properties will

reduce. Moreover, the disposes of the contaminant that comes from dirt or wear of

metal part disposed into the oil also lead to the degradation of oil properties, (Cooke,

1982). Thus usually, the used engine oil has low grade quality and can no longer

suitable to use. Moreover, the used engine oil is toxic and harmful to the

environment. Which the used engine oil can pollute around two hundred thousand

gallons of drinking water and cause damage to soil productivity for around forty

thousand square feet, (Suriani, 2014). Therefore, the responsible management is

needed in order to solve the problem regarding the disposal of waste.

Engine oil is usually used in high temperature equipment where the viscosity

of the lubricant is expanded because of vanishing of the light mixes, oil oxidation,

nitration and defilement by soot. Due to the build-up of engine oil temperature, the

viscosity of used engine oil will be distorted where the lower viscosity index of the

lubricant could increase the change of lubricant with the change of temperature.

However, with added of additive the viscosity index can be improved, the

viscosity of a fluid is utilized to depict the resistance of relative development

between stream layers. At the point when strong additives are included into lubricant,

fluid drag that follows up on a strong surface affects the liquid consistency and the

hydrodynamic weight. It has been reported that the state of an added substance

influences the sum of fluid drag, (Leal, 1980).

1.2 Objective

The objectives of this project are:

1. To investigate the viscosity of used engine oil before and after filtration

with enhancement of nanoparticles.

2. To evaluate the viscosity index of prepared sample by using ASTM D

2270.

1.3 Scope of Work

1. Investigating the viscosity of used engine oil before and after filtration

and enhance with different nanoparticles after been homogenize by the

ultrasonic homogenizer (Sartorius LABSONIC P).

2. Evaluating the viscosity index of the prepared sample using ASTM D

2270 Standard Practice.

CHAPTER 2

LITERATURE REVIEW

2.0 Literature Review

This chapter will cover all of the aspects needed that use as a review of the study

made for the final year project. In order to gain full knowledge on the study, this

chapter explains further information from lubricant background, type of lubricant,

polyalphaolefins (PAOs), nanoparticle, lubricant viscosity until viscosity improver.

All of this information is gathered from the journal, books, and article.

2.1 Background of Lubricant

Lubrication is first introduced centuries ago based on discoveries by

archaeological. During ancient Egypt time, in order to move the large and heavy

object, the olive oil is used as a lubricant. After few centuries, animal fat is

introduced as a lubricant in order to keep up demand from industrial that expanding.

The animal fat that being used are whales; especially sperm whale because it can

provide a large quantity of oily wax that can also be called as case oil. It is widely

used for almost everything from industrial purpose until household, such as lamp oil,

(Anderson, 1991).

According to Bradley‟s (1996) starting from the 1850s in Titusville,

Pennsylvania the world is introduced to petroleum when it is successfully drilled and

became the first petroleum well. In the 1920s, after a lot of different process and

development been made in order to boost up the quality of lubricant performance the

solvent refining are used as one of the effective solutions, (Wilson et al., 1994). After

a decade, the additive is then discovered before it is widely used in the 1940s to

enhance the lubricant properties and the start of regular lubricant analysis are made

in late 1940s in order to restrain from engine failure, (Bui, 1999).

This is when the development of synthetic lubricant is made in the 1950s and the

quality of base oil is upgraded dramatically in 1970s. The Group II base oil, one of

the groups in mineral oil, that widely used in the 1970s is classified officially into

groups by American Petroleum Institute (API) at 1990s and followed by Group III

until Group V accordingly. From the 2000s until today, thousands of studies still

continue to meet the requirement of better lubrication to optimize the performance

while reducing waste, cost and also environmentally friendly, (Kramer et al., 2001).

2.1.1 Introduction of Lubricant

Currently, the development of machinery technology is extended due to the

industrial demand which also lead to the evolution of lubricant. Lubricant is known

for decades as an important medium in machinery system. Lubricant is used to

reduce energy lost and machinery failure in the system. This application is viewed as

an approximately efficient in order to protect the equipment from wear and reducing

friction of the surface contact. Lubricating could also control other contamination

such as improve the coefficient of friction and heat withstand in the system.

Until today, many studies are made in order to fulfil the needs of current

machinery technology. It because lubricant is a must in order to extend the

machinery lifetime for modern machinery technologies. Therefore, the lubricant is

consists of additive and based fluid, where based fluid not only lubricates but also

acts as the additive carrier, (Rizvi, 2009). Some of the properties of lubricant are

viscosity, corrosion/oxidation stability, thermal solidity, viscosity index, flash point,

cloud point, pour point and etc. But because of lubricant has the limitation of their

properties which influence and reflects on its performance. The substances of

additive are added up in the lubricant to improve the properties of the lubricant based

on the application situation, (Choi et al., 2009).

Lubrication film is viewed as an important mechanism in the lubricant in order to

control the contamination in machinery systems and also protect the metal surface

from corrosion.

Figure 2.1: Lubricant regimes

(Source: www.substech.com, n.d)

Lubricant can be classified into three regimes, which are hydrodynamic

lubrication (fluid-film or thick-film lubrication), boundary lubricant (thin film

lubrication) and mixed lubrication (extreme pressure lubrication). Hydrodynamic

lubrication (HL) occurs when two surfaces are in sliding motion that is relatively to

each other but completely isolated by the liquid film. Thus, the surfaces are not in

contact with each other due to the liquid film. Therefore, the contact surfaces are

fully protected from friction and wear.

Figure 2.2: Hydrodynamic layer

(Source: www.cuiet.info/notes/chemistry/Lubricants, n.d)

Elastic deformations that occur when the surfaces are in rolling motion form

elastohydrodynamic lubrication (EHL). Even though EHL can withstand greater

pressure, it has a thinner liquid film form compared to HL. EHL is divided into hard

EHL and soft EHL. The characteristic of both EHL forms are summaries in the table

below, (Bernard et al., 2004).

Table 2.1: Elastohydrodynamic characteristic

Characteristic Hard EHL Soft EHL

Material type High elastic modulus

material

Low elastic modulus

material

Maximum pressure (Pmax) ~1 Gpa ~1Mpa

Minimum film thickness

(hmin)

>0.1µm ~1µm

(Source: Bernard et al., 2004)

Boundary lubrication occurs in the same case of hydrodynamic lubrication except

that the surface roughness of the composite is more than the standard thickness of it

liquid film formation. This lead to high friction, wears and other contamination

because of the asperities from both surfaces collides relatively to each other, (Hsu &

Gates, 2005).

Meanwhile, mixed lubrication presents in the middle between hydrodynamic and

boundary lubrication where even though the liquid film are separating the surface but

it still collides due to the surface asperities. According to Bernard et al. (2004)

Stribeck curve is a practical way in order to easily comprehend the different between

lubrication regimes of those three types of liquid film. It is widely known when

Stribeck finally found the explanation of friction that occurs in journal bearing.

Figure 2.3: Stribeck curve

(Source: Bernard et al., 2004)

The graph above is a result of steady state condition of lubrication film that

shows the coefficient of friction and the thickness of the lubricant film using the

Hersey number. The lubrication film thickness can be determined by using Hersey

number. The higher number of Hersey number mean the thicker lubricant film will

be and it can be calculated from the formula as below:

(2.1)

Where, Ƥ is for pressure in Pa, Ƞ is for absolute viscosity, pa-s, and is rotational

speed, rps.

2.1.2 Type of Lubricant

Being divided into the biological and non-biological origin, the lubricant can

also be used for some other different purpose aside from friction and constrain the

development of wear. The evolution of technology leads to the development of better

formulation lubricant. The enhancements of lubricant properties are used in order to

expand the application of lubricant. Lubricant can be classified into three categories

which are solid lubricant, semi-solid lubricant, and liquid lubricant.