# Estimating the exergy efficiency of engine using nanolubricants

**ABSTRACT** Friction is an effective factor in the reduction of the exergy efficiency in engines. In this study, the effects of using nanolubricants on friction reduction, thereby increasing the engine exergy... [more]Friction is an effective factor in the reduction of the exergy efficiency in engines. In this study, the effects of using nanolubricants on friction reduction, thereby increasing the engine exergy efficiency, have been investigated. First, studies done on exergy, engine lubrication and friction reduction with nanolubricants have been reviewed. Based on these studies the mathematical formula for estimating the exergy efficiency of an engine that uses nanolubrication was derived. Finally, it has been found that adding CuO nanoparticles to SF oil has the greatest effect on the exergy efficiency improvement and the maximum amount of this improvement is 4.6%.

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**ABSTRACT:**Solar energy is a clean, abundant and easily available renewable energy. Usage of solar energy in different kinds of systems provides scope for several studies on exergy analysis. In the present work, a comprehensive literature review has been carried out on exergy analysis of various solar energy systems. The systems considered under study are solar photovoltaic, solar heating devices, solar water desalination system, solar air conditioning and refrigerators, solar drying process and solar power generation. The summary of exergy analysis and exergetic efficiencies is presented along with the exergy destruction sources.Renewable and Sustainable Energy Reviews 01/2012; 16(1):350-356. · 5.63 Impact Factor - SourceAvailable from: Mahdi GhazviniRenewable and Sustainable Energy Reviews 01/2011; · 5.63 Impact Factor
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**ABSTRACT:**Renewable energy sources can be a good substitute of the fossil fuels which are being terminated fast. Nowadays biomass and biofuels are considered because of their environment friendly characteristics and their ability of supplying much more energy. An alternative means to select the most efficient and convenient biomass, is exergy analysis. The present paper has reviewed the existent surveys on the exergy analysis of different kind of biomass included the woody biomass, herbaceous and agricultural biomass, aquatic biomass, contaminated biomass and industrial biomass. The most common thermochemical processes are investigated and the efficiency of the different process and various kinds of biomass are determined.Renewable and Sustainable Energy Reviews 01/2012; 16(2):1217-1222. · 5.63 Impact Factor

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Exergy efficiency; Nanolubricants; Engine friction;

Keywords:

© Sila Science. All rights reserved.

1. Introduction

During the past two decades, exergy analysis has been attractive to many scientists,

researchers and engineers in many different areas. Exergy analysis is determination the maximum

theoretical amount of operation capability of system in many applications [1, 2]. One of the most

important applications of exergy analysis is, it can be implemented to reduce losses and

destructions and therefore the efficiency of system can be evaluated [3, 4]. For example, exergy

analysis is able to be used for reducing losses and minimizing irreversibilities in engines. One of

the best methods of reducing irreversibilities; especially irreversibilities related to friction; is to

improve the quality of lubrication in engines. A simple way to improve quality of lubricants is to

add some additives to standard engines oil, and in this case the nanoparticles are useful additives

[5]. Results of researches conducted in recent years show that adding nanoparticles provides

special properties for materials, including friction reduction through mending effect, rolling

effect, third body material transfer, ball bearing effect, colloidal effect, protective film [5, 6].

_____________

∗Corresponding author : Tel:+60-010-298-2705; Fax:+60-010-298-3541.

Email address: mohammadnejad_mostafa@yahoo.com (M. Mohammadnejad).

Energy Education Science and Technology Part A: Energy Science and Research

2011 Volume (Issue) 27(2): 447-454

Estimating the exergy efficiency

of engine using nanolubricants

M. Mohammadnejad*, M. Ghazvini, F. S. Javadi, R. Saidur

University of Malaya, Department of Mechanical Engineering, 50603 Kuala Lumpur, Malayasia

Received 12 October 2010; accepted 19 December 2010

Abstract

Friction is an effective factor in the reduction of the exergy efficiency in engines. In this study, the

effects of using nanolubricants on friction reduction, thereby increasing the engine exergy efficiency, have

been investigated. First, studies done on exergy, engine lubrication and friction reduction with

nanolubricants have been reviewed. Based on these studies the mathematical formula for estimating the

exergy efficiency of an engine that uses nanolubrication was derived. Finally, it has been found that

adding CuO nanoparticles to SF oil has the greatest effect on the exergy efficiency improvement and the

maximum amount of this improvement is 4.6%.

Exergy

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448 M. Mohammadnejad et al. / EEST Part A Energy Science and Research 27 (2011) 447-454

In this study, it has been focused on the possible exergy efficiency improvement in engines by

using nanolubricants in reducing rubbing friction. Related equations of friction losses and exergy

for engine have been performed to estimate exergy efficiency using nanolubricant. Firstly, the

thermodynamic equation of friction losses in engine and also the relationship between exergy and

thermodynamic properties of system have been provided, and then the required information about

friction coefficient of nanolubricants has been mentioned. Finally with combining both of them

the exergy efficiency of engines using nanolubricant has been estimated in different temperature

in comparison with engines using standard lubricant.

For energy saving, exergy and energy analysis have been applied to some utility sectors such

as chillers, refrigerators and room air conditioners in some recent research [3, 7-9]. Also using

renewable energies especially solar energy, wind energy and biofuel energy has received more

attention than before [10-16]. On the other hand there are many researches in different areas of

nanotechnology [17, 18], but there is no work on estimating exergy efficiency improvement of an

engine with the lubricant which contains nanoparticles. The objective of this work is to estimate

the exergy efficiency of an engine using nanolubricants.

2. Studies done on exergy and engines lubrication

2. 1. Exergy equation related to system

The concept of exergy is stated according to both first and second laws of thermodynamic.

Exergy is known as the maximum amount of generated work by a system or flow, up to when the

system or flow reaches to equilibrium with reference environment. When a system or flow is not

completely in stable equilibrium with environment, it changes. Exergy is a measure for

evaluating this change. In actual process a part of exergy destroys due to irreversibilities [19].

In exergy analysis it is necessary to be specified the characteristics of reference environment

including temperature , pressure and chemical composition [20]. In general exergy efficiency is a

measure of approach to the ideal case. Therefore, the result of exergy analysis is useful for

determining that how much the efficiency of a system can be improved [19].

In fact the aim of exergy analysis is to determine the causes and to calculate the magnitude of

exergy losses. The exergy of a thermodynamic system (regardless of exergy associated with

kinetic and potential energy) is determined by Eq. 1:

where T0 is the temperature of environment and S0 , h0 are the initial entropy and enthalpy of

system respectively. Q is the heat rejected to the cool medium (the waste heat) [21].

2. 2. Theory of engine lubrication

In estimating the magnitude of friction of different engines it is necessary to identify the

friction coefficient of lubricants. The analysis of friction behavior in lubricants can be done with

Stribeck curve, which has been shown in Fig. 1.

Fig. 1 shows the variations of friction coefficient as a function of the combined variables of

(1)

)1 ()()(

0

000

H

T

T

QSSThh

−+−−−=

ψ

Page 3

on [24-27]

[22]

M. Mohammadnejad et al. / EEST Part A Energy Science and Research 27 (2011) 447-454 449

Fig. 1. Stribeck curve and the regime of lubricants

rotation speed, the viscosity of lubricant and normal force (ην/p). Totally this figure illustrates the

relationship between friction coefficient and lubricant condition [5]. When rotation speed is low

and normal force is high (ην/p is low), the friction coefficient is completely related to the

properties of contacting surface, and this regime is called Boundary lubrication. But the

Hydrodynamic lubrication regime occurs when the rotation speed is high and normal force is low

(ην/p is high ), the friction coefficient is related to the properties of lubricant film [5, 23]. This

type of lubrication regime occurs in engine bearing, between piston skirt and cylinder liner and

between piston rings and liners for high sliding velocity. Between these two regimes there is a

regime which the friction coefficient of lubricant is related to both of contact surfaces properties

and lubricant film, which is called mixed lubricati

3. Studies done on friction reduction by nanolubricant

In research that has been already done [6], three types of nanoparticles (Cuo, TiO2, Nano-

diamond ) were added into two different types of standard lubricating oils ( SF and base oil ) for

analyzing the variations of friction coefficients (the difference between SF and base oil is, SF oil

has friction reduction and anti wear additives in similar viscosity grade ). The weight percent of

each nanoparticles additives (Cuo , TiO2, Nano-diamond) is 0.1 in both standard lubricating oils

[23]. The friction coefficient of SF oil with and without nanoparticles additives have been shown

in Fig. 2. The X-coordinate shows temperature of lubricant, and displays the passed time from the

start of the test. The friction coefficients of the SF oil with nanoparticles, specially the CuO and

TiO2 additives, are lower than the SF oil without nano additives.

After 10 minutes from the start of the test, when the temperature increases above 50 0C,

friction coefficient of SF oil containing CuO becomes lower than the other two nanoparticles.

The maximum friction coefficient reduction, in this case, is about 18.4% in comparison with the

SF oil without nanoparticles [6]. Fig. 3 shows the friction coefficients of base oil with and

without nanoparticles.

As can be seen in this figure the friction coefficient of the base oil containing CuO is reduced,

whereas by adding nano-diamond this improvement does not exist. In addition the average of

reducing friction coefficient in case of adding CuO to base oil is 5.8% [6]. According to

mentioned research, CuO additive has the greatest effect on reducing friction coefficient of

standard oil.

.

.

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450 M. Mohammadnejad et al. / EEST Part A Energy Science and Research 27 (2011) 447-454

Fig. 2 . Friction coefficient of SF oil with and without nanoparticles [6].

Fig. 3 . Friction coefficients of base oil with and without nanoparticles [6].

4. Mathematical formulation to estimat exergy efficiency of an engine using nanolubricants

Exergy of system without nanolubricantion:

Noting that the variation of temperature of system due to changing lubricant is negligible and

h = h(T). Exergy of system with nanolubrication :

(2)

(3)

)1 (][)(

0

000

H

causesother

to due

friction

todue

T

T

QSTSThh

−+∆+∆−−=

ψ

)1 (][)(

0

000

H

cuasesother

todue

friction

to due

′

T

T

QSTSThh

−+∆+∆−−=

′

ψ

Page 5

friction

todue

ST ∆

0

) 1 (M

−

f ′

f

M. Mohammadnejad et al. / EEST Part A Energy Science and Research 27 (2011) 447-454 451

where the notation ( .′) shows the properties of system with nanolubrication. From Eqs. 2 and 3:

Noting to this point internal energy of system due to friction changes negligibly [21].

where is friction coefficient of standard oil without nanoparticles and is friction coefficient

of nanolubricant.

Assuming :

f

=

M

f

′

From Eqs. 6 and 7:

From Eqs. 4 and 8, it can be resulted:

That in this Equation the term is related to engine and the term depends on

nanolubricant properties.

Based on research done [23], the amount of the exergy losses due to rubbing friction has been

estimated 20% of the exergy of system. Therefore from Eq. 5:

Then Eqs. 9 and 10 are combined:

′

ψ

Also the exergy efficiency is :

suppliedExergy

M2 .02 .1

−=

ψ

(4)

(5)

(6)

(7)

(8)

(9)

(10)

(11)

(12)

recoveredExergy

E=

η

][

00

cuasesother

todue

friction

todue

′

STST

∆+∆−=−

′ ψ ψ

friction

to duefriction

STW

∆=

0

ST

ST

f

f

W

W

friction

friction

′

∆

′

∆

=

′

=

0

0

friction

todue

friciton

todue

′

SMS

∆=∆

)1 (

0

MST

friction

todue

−∆=−

′ ψψ

ψ

2 . 0

0

=∆=

friction

todue friction

STW

Page 6

452 M. Mohammadnejad et al. / EEST Part A Energy Science and Research 27 (2011) 447-454

Exergy supplied is constant when the lubricant changes, thus :

ψ

η

E

From Eqs. 11 and 13 Eq. 14 is derived:

′

η

E

η′ : Exergy efficiency of engine using nanolubricant

E

η : Exergy efficiency of engine without nanolubricant

In Eq. 14, M can be calculated from Figs. 2 and 3 in different temperatures. Therefore it is

possible to evaluate the percentage of exergy efficiency improvement, in different temperature

for each type of nanolubricants. The achieved results have been displayed in Figs. 4 and 5.

Fig. 4. Exergy efficiency improvement using of engine nanolubricants (SF oil with CuO, TiO2,

Nano-diamond).

As can be seen in Fig. 4 adding CuO nanoparticles to SF oil has the greatest effect on the

improvement of exergy efficiency. The maximum amount of this improvement which occurs

around 80 0C is 4.6% . But on the other hand, adding nano-diamond to SF oil has the least effect.

The improvement of exergy for this nanolubricant is less than 1%.

Fig. 5 shows adding CuO nanoparticles to base oil has positive effect on the exergy efficiency

improvement. The maximum amount of this improvement is 2.3%; but on the other hand adding

nano-diamond to base oil has adverse effect on the exergy efficiency. In the worst condition the

exergy efficiency decreases to 3.8%.

The other result from Figs. 4 and 5 is that adding nanoparticles to SF oil provides better

condition for exergy efficiency in comparison with base oil.

ψ

η

′

=

′

E

M

E

E

2 . 0

−

2 . 1

=

η

(13)

(14)

Page 7

M. Mohammadnejad et al. / EEST Part A Energy Science and Research 27 (2011) 447-454 453

Fig. 5. Exergy efficiency improvement of engine using nanolubricants (Base oil with CuO,

Nano-diamod).

5. Conclusion

As the result of this study, the exergy efficiency improvement of an engine with

nanolubricants compared to one without nanolubricants can be calculated by using Eq. 14. With

this equation it has been found that adding CuO nanoparticles to SF oil has the greatest effect on

the improvement of exergy efficiency and the maximum amount of this improvement which

occurs around 80 0C is 4.6%. But on the other hand, adding nano-diamond to SF oil has the least

effect. The improvement of exergy for this nanolubricant is less than 1%.

It was also found that adding CuO nanoparticles to base oil has a positive effect on exergy

efficiency improvement, the maximum amount of improvement is 2.3%. On the other hand

adding nano-diamond to base oil has an adverse effect on the exergy efficiency. In the worst

conditions, the exergy efficiency decreases to 3.8%. Totally, it can be said that adding

nanoparticles to SF oil provides better conditions for exergy efficiency as compared to base oil.

Future studies should investigate other effects of nanotechnology on the performance of

engines.

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