Influence Of Compression Ratio On The Operating Attributes Of Palm Oil Powered Diesel Engine … ·...

Influence Of Compression Ratio On The Operating Attributes Of Palm

Oil Powered Diesel Engine With Alumina Nanoparticles

R Selladurai1 T Sakthivel

2 C Chinnasamy

3*Dr M Subramanian

4

1 Lecturer (Senior Grade), Mechanical Engineering, PSG Polytechnic College, Coimbatore

2 Lecturer, Mechanical Engineering, PSG Polytechnic College, Coimbatore

3 Assistant Professor, Mechanical Engineering, SNS College of Technology, Coimbatore

4 Professor of Mechanical Engineering, SNS College of Technology, Coimbatore.

* Corresponding author E-mail: [email protected] Mob: +91-9994866851

Abstract

The present study emphases on experimentally investigating the performance, emission, and

combustion characteristics of single cylinder direct injection diesel engine fuelled with Palm

Methyl Ester (PME) along with Aluminium Oxide (Al2O3) nano-sized particles in the mass

fractions of 100 and 200 ppm by varying the Compression Ratio (CR) from 15 to 18. The

test output reveals that by the dispersion of nanoparticles as well as by increasing the CR,

considerable improvement in Brake Thermal Efficiency (BTHE) and a reduction in Brake

Specific Fuel Consumption (BSFC) could be observed against all test fuel blends as a result

of better combustion attributes. The addition of both PME and nanoparticles minimized the

emission constituents like Carbon Monoxide (CO), Hydrocarbons (HC), and smoke opacity

significantly compared to diesel. The introduction of alumina nanoparticles into PME

marginally reduces the EGT and NO emissions. A marginal rise in cylinder pressure and a

slight reduction in Heat Release Rate (HRR) is observed while increasing the CR from 15 to

18. Overall, the engine exhibits improved working behavior with curtailed pollutants by the

addition of alumina nanoparticles at a CR of 18 compared to PME.

Keywords

Compression ratio, diesel engine, alumina nanoparticles Palm biodiesel

Pramana Research Journal

Volume 8, Issue 7, 2018

ISSN NO: 2249-2976

http://pramanaresearch.org/1

mailto:[email protected]

Introduction

The petroleum products continue to dominate the world energy market as they discover

numerous applications in the field of transportation and industrialization. The enormous usage

roots two severe threats one leads to depletion of fossil fuel reserves and other causes critical

environmental hazards owing to pollutants released from fossil fuels. The use of biofuels

extracted from vegetable oils, animal fats, and waste cooking oil furnishes a solution for foresaid

issues [1]. The In-cylinder modifications are better preferred over after treatment systems for

curtailing the deleterious emissions from a diesel engine since they require high primary cost and

space to accommodate [2]. The emission constituents such as CO, HC, Particulate matter, and

smoke opacity are lesser for biodiesel powered engine compared to conventional diesel fuel.

However, the discharge of NOx emissions from biodiesel powered engine is higher than diesel

due to inherent oxygen content [3-7].

The eminent fact is that the CR of diesel engine directly influences the working outputs of the

engine since it amends the entire combustion chamber geometry. The upper latent heat of

vapourization, lower cetane number, and higher self-ignition temperature of diesel fuel makes it

flexible to raise the CR in diesel engines [8]. The combustion noise can be reduced by varying

the CR [9]. The performance attributes like BTHE and BSFC are improved and pollutants like

CO and particulate matter are decreased with increase in NO emissions and EGT by increasing

the CR [10]. The CO2 emissions and delay period is decreased by increasing the CR from 14 to

18 [11].

The dispersion of potential nanoparticles into diesel or biodiesel improves the engine output

characteristics by enhancing the surface area between reaction mixtures [12]. The boosted

catalytic activity ameliorates the combustion and ignition outputs of the engine [13]. The

nanoparticles keep the various surfaces active enhancing the reactivity between fuel molecules



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[14]. The addition of nano additives improves the fuel properties like calorific value and cetane

number owing to enhanced surface area/volume ratio and evaporation characteristics [15]. The

dispersion of alumina and cerium oxide nanoparticles into PME, improves the BTHE close to

diesel and significant reduction in emission constituents like CO, HC, and smoke is observed

along with a marginal reduction in NO emissions [16]. The combustion attributes like peak

pressure, HRR is lowered by the addition of nanoparticles into PME [17].

Owing to previous reports, the CR significantly contribute to engine output and the nanoparticles

have potential properties to improve the engine output. Henceforth, the present study is devoted

to examine the engine working characteristics by varying the CR from 15 to 18 by dispersing

alumina nanoparticles into PME in the mass fractions of 100 and 200 ppm.

Preparation and characterization of fuel blends

The biodiesel reported in this study is produced from non- edible Palm oil using a standard

alkaline transesterification process in which the glycerides are physically separated from the raw

oil. The conversion yield of raw oil into Palm methyl ester (PME) could be obtained as 94%. The

nanoparticles procured with an average particle size of 36 nm are accurately weighed and

dispersed into PME in the mass fractions of 100 and 200 ppm using an ultrasonic vibrator (make:

Hielscher, Model: UP4005). The detailed properties of Al2O3 nanoparticles are presented in table

1. The morphology of nanoparticles is studied using Scanning Electron Microscope (SEM). The

shape of the nanoparticles is found to be spherical with an average size of 80-90 nm as

photographed in figure 1.



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Table 1 Properties of Al2O3 nanoparticles

Item Value

Purity (%) 99.9

Average Particle Size (nm) 36

Thermal Conductivity (W/m-

K) 35

Density (g/cm3) 3.79

Specific heat (J/kg-K) 878

Figure 1 SEM image of Alumina nanoparticles

The stability of dispersed solid nanoparticles inside a biodiesel is a huge concern and is

evaluated by measuring the potential difference between the base liquid fuel (biodiesel) and

dispersed medium (nanoparticles).



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The repulsive force between molecules should always be greater than attraction force in order to

maintain the nanoparticles stable inside the base fuel. In this concern, a surfactant (SONOPULS-

HD2070) is added to improve the stability of nanoparticles inside the base fuel. The alumina

nanoparticles were found to be stable inside PME for more than 5 days.

Properties of test fuel blends

The properties of each test fuel blend are measured using various standard instruments and

ASTM standards were adapted to each property variable. The density and net calorific value of

the fuel are measured using hydrometer and Bomb calorimeter respectively. The kinematic

viscosity is measured at a temperature of 40°C using redwood viscometer. The flash point of

each fuel blend is measured by exposing the test fuel to a spark in closed cup apparatus and the

cetane number of the fuel is measured using ignition quality tester. The Physical- chemical

properties of each test fuel and their respective ASTM standards can be referred from table 2.

Table 2 Properties comparison of test fuel blends

Density (g/cm3)

Net Calorific value (KJ/Kg)

Kinematic Viscosity @40°C (cSt)

Flash Point (°C)

Cetane Number

Diesel 0.838 44500 2.5 74 51

JME 0.895 39500 5.2 88 55

JME+Al

100ppm 0.892 39494 5.24 89 56

JME+Al

200ppm 0.891 39490 5.26 89 57

Engine configurations

The test rig comprises of a single cylinder, four stroke, VCR (Variable Compression Ratio)

water cooled diesel engine.



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The engine is operated at a constant speed of 1500 rpm and loaded via eddy current

dynamometer. The photographic view of experimental setup is depicted in figure 2. The other

detailed specifications of the engine can be referred from table 3. A pressure transducer (make:

PCB Piezotronics) protruded inside the combustion chamber senses the in-cylinder pressure,

cylinder temperature, Heat Release Rate (HRR) etc.., and converts into a digital electric signal

which is interfaced to computer through high-speed data acquisition device visualized using the

enginesoft software. The combustion attributes are quantified against crank movement angle

which is measured using a crank angle encoder. The emission constituents such as CO and HC

are measured on dry basis and the concentration of NO emissions are measured by

chemiluminescence method using a chemical sensor fitted in the four gas emission analyzer

(make: HEPHZIBAH) and the smoke opacity is quantified using smoke meter (make: AVL) by

using optics based folded geometry. The Exhaust Gas Temperature is measured using

chromelalumel (K-type) RTD make PT 100 type thermocouple.

Table 3 Engine Specifications

Parameter Specification

Type of Engine Kirloskar (Model: 240PE) Single Cylinder

Variable Compression Ratio DI Diesel Engine.

Bore & Stroke 87.5 × 100mm

Compression ratio range 12 to 18

Cubic capacity 0.661 liters

Fuel Injection timing 230 BTDC

Rated power 3.5 KW @ 1500rpm

Injection pressure 210 bar

Crank angle encoder Resolution of 1 Deg, Speed of 5500 RPM

ECU PE3 Series ECU, Model PE3-8400P

Type of Cooling Water cooled

Type of Loading Eddy Current Dynamometer with water cooling

.



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Figure 2 Experimental setup

Experimental conditions

The compression ratio is varied from 15 to 18 after feeding each test fuel blend by tilting the

cylinder block vertically using the locknuts provided (figure 3) without interrupting the engine

operation. While varying the compression ratio, the stroke volume remains unchanged and the

clearance volume inversely varies with respect to CR as tabulated in table 4. All the output

parameters were measured under steady state conditions at 50% of the load. Each output

parameter is measured three times to validate the repeatability and average of it is considered for

the analysis.



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Figure 3 Locknut setup for varying the CR

Table 4 Cylinder volume variations with respect to CR

Compression Ratio

Stroke Volume (cm3)

Clearance Volume (cm3)

Method of variation

15 661 44.06 Actual C.R

16 661 41.31 Block lowered by 0.46 mm





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Results and discussion

The operation of CI engine was found to be smooth while operating with PME fuel as well as

with an addition of alumina nanoparticles. The variation trends of operating attributes such as

performance, emission, and combustion are discussed here.

Variation of performance attributes

Figure 4 illustrates the variation trends of performance attributes such as BTHE and BSFC for

various test fuels under varying compression ratios from 15 to 18. The dispersion of

nanoparticles into PME100, improves the BTHE and tends to get closer to diesel during lower

CR operations and it moves 0.76% greater than diesel when the CR is raised to 18. The

improvement could be attributed to enhancement in combustion attributes owing to an enhanced

surface area to volume ratio and the boosted catalytic activity between reaction mixtures. Further,

with an increase in CR from 15 to 18, the BTHE improved under all test fuel blends owing to an

achievement of near complete combustion as the fuel injected to a compressed air which is at

elevated temperature and pressure [18,19]. The addition of alumina nanoparticles into PME

reduces the BSFC up to 6.09% while comparing with PME100. This could be probably

attributed to ameliorated catalytic effect resulting in less fuel consumption to generate the

adequate power. With an increase in CR, the ignition attributes of the mixture are improved as

the pressure and temperature inside the cylinder raises which makes easy and efficient energy

conversion resulting in minimized BSFC under all fuel blends.



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Figure 4 Variations of BTHE and BSFC

Emission characteristics

The variation of emission constituents like CO, HC, NO and smoke opacity against varying

compression ratios for various test fuel blends are discussed here.

Variation of CO emissions

Figure 5 depicts the variation trends of CO emissions for various test fuels under varying

compression ratios. The concentration of CO emissions sharply decreases up to 50.43% by the

replacement of diesel with PME. The combustion is better progressed due to oxidation

characteristics of biodiesel. Further reduction in CO emissions up to 17.54% could be noticed by

the addition nanoparticles into PME due to shortened ignition delay and catalytic activity caused

by nanoparticles [3]. The increase in CR tends to achieve near complete combustion which

further reduces the CO emissions for all test fuel blends [18]. The minimum CO emission

concentration could be observed as 0.094 % of vol. for PME 100+Al200 at a CR of 18.



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Figure 5 Variation of CO emissions

Variation of HC emissions

The variation of HC emissions for various test fuel blends under varying CR’s is illustrated in

figure 6. The exorbitant supply of oxygen from PME benefits in achieving near complete

combustion and reduces the HC emissions up to 28.12%. The addition of nano additives into

PME further reduces the HC emissions up to 21.7%. The nanoparticle enhances the combustion

by supplying adequate oxygen to minimize the partially burnt mixture [16]. The nanoparticle

also causes secondary atomization and distributes the fuel more significantly across the volume

of the chamber [15]. The increase in CR enables better combustion due to the high temperature

of the compressed air and reduces the charge dilution resulting in a marginal reduction of HC

emissions. The lowest HC emission could be observed as 18 ppm for PME100+Al200 at a CR of

18.



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Figure 6 Variation of HC emissions

Variation of EGT and NO emissions

Figure 7 illustrates the variation trends of NO emissions with respect to varying CR’s for various

test fuel blends. An increase in concentration of NO emission could be noticed up to 9.6% during

lower CR’s and up to 20.6% during higher CR operations for PME compared to diesel. This is

due to higher heat release rate resulting in exorbitant combustion temperature. However, the

addition of nano additives into PME causes a marginal reduction up to 8.24%. This could be

attributed to shortened Ignition delay, reduced peak pressure, and maximum rate of pressure rise

[3]. At lower CR’s the combustion takes place comparatively at a lower temperature causing less

NO emissions [18]. With an increase in CR, the combustion temperature and pressure increases

as clearance volume is squeezed resulting in formation of higher concentration of NO emissions

for all fuel blends.



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The increase in CR from 15 to 18 causes the NO emissions to raise up to 36.08% for PME. The

EGT increases up to 6.62% for PME compared to diesel. However, by the addition of 200 ppm

nanoparticles, the EGT is marginally reduced up to 2.64% owing to better combustion attributes

and shortened ignition delay. The increase in CR results in exorbitant flame temperature causing

higher EGT across all test fuel blends as shown in figure 8.

Figure 7 Variation of NO emissions



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Figure 8 Variation of Exhaust Gas Temperature

Variation of smoke opacity

The variation of smoke opacity for various fuel blends under varying CR’s is illustrated in figure

9. The poor atomization and mixture formation of PME owing to higher viscosity results in

increased smoke emissions up to 16.6% compared to diesel. However, a marginal reduction in

smoke could be seen while increasing the CR across all test fuels due to rapid combustion and

betterment of air-fuel mixture formation. The addition of alumina nano-sized particles improves

the combustion attributes resulting in minimized smoke concentrations to a maximum of 12.9%

due to rapid evaporation and shortened ID [17]. The minimum smoke concentration could be

recorded as 38% for PME100+Al200 at a CR of 18.



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Figure 9 Variation of Smoke opacity

Combustion characteristics

Variation of ignition delay

The Ignition delay is measured between the point of fuel injection (23˚ Before TDC) and start of

combustion where the negative heat release is started transforming into a positive value. The

Ignition delay is prolonged up to 19% for PME compared to diesel which is attributed to longer

and poor atomization of the air-fuel mixture resulting in longer diffusive combustion. However,

by the addition of nanoparticles into PME, the ID is shortened up to 18.7% as a result of

improved ignition properties of nanoparticles initiating the combustion early. The increase in CR

increases the cylinder temperature causing the combustion to initiate at an early crank angle and

decreases the ID up to 31.5% across all test fuel blends. The least ID could be witnessed for

PME 100 + Al 200 at a CR of 18 as depicted in figure 10.



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Figure 10 Variation of Ignition Delay

Variation of in-cylinder pressure

The variation of in-cylinder pressure with respect to crank angle for the CR’s of 15 and 18 at

50% of load is shown in figure 11 & 12 respectively. Due to longer ID and enhanced premixed

phase of combustion, the peak pressure raised from 47.86 to 49.45 bar and 50.73 to 55.39 bar for

the CR’s of 15 and 18 respectively. The introduction of nanoparticles into PME shortens the ID

due to improved reactivity between fuel and air owing to catalytic effect and reduces the cylinder

pressure and peak pressure slightly. The peak pressure for PME100+Al100 and PME100+ Al200

is reduced from 48.64 to 48.24 bar and from 53.5 to 52.1 bar during the CR’s of 15 and 18

respectively and moved slightly away from TDC.



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Figure 11 Variation of Cylinder pressure at a CR of 15

Figure 12 Variation of cylinder pressure at a CR of 18



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Variation of heat release rate

The Net Heat Release Rate with respect to the crank angle at 50% of the load for the CR’s of 15

and 18 are illustrated in figure 13 & 14 respectively. Due to longer diffusive combustion, the

heat release rate of PME is higher than diesel. The maximum HRR is raised from 42.09 to 47.14

J/˚CA and from 41.24 to 44.78 J/˚CA for the CR’s of 15 and 18 respectively. The addition of

nanoparticles enhances the pre-flame combustion and shortens the diffusive combustion period

leading to decrease of HRR from 47.14 to 45.45 J/˚CA and 44.78 to 41.82 J/˚CA for the CR’s of

15 and 18 respectively. The negative HRR could be seen for all test fuel blends due to heat losses

to cylinder surfaces. The increase in CR from 15 to 18 exhibits a slight reduction in HRR and the

peak HRR move slightly closer to TDC.

Figure 13 Variation of HRR at a CR of 15



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Figure 14 Variation of HRR at a CR of 18

Conclusions

The experimental investigation was carried out to study the influence of varying the

Compression ratio on the working attributes of a diesel engine at 50% of load fuelled with PME

and Al2O3 nanoparticles in various concentrations. The following conclusions could be drawn

from the experimental outcomes.

The increase in CR from 15 to 18 improves the BTHE as the fuel injected at elevated

temperature and pressure. The BTHE for PME100+Al200 is recorded as 28.58% which is

0.76% greater than diesel.

The BSFC reduced by 40.3% while increasing the CR from 15 to 18 across all test fuel

blends and by the addition of 200 ppm of alumina nanoparticles into PME, the BTHE

improved up to 8.6% at a CR of 18 and BSFC reduced up to 6.09% at a CR of 17.



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The emission constituents like CO, HC, and smoke opacity is minimized up to 35.17%, 28%,

and 24.07% with an increase in CR from 15 to 18. The minimum concentration of these

emissions could be observed for PME 100+Al 200 at a CR of 18.

The EGT and concentration of NO emission increase up to 10.36 and 36.08% respectively

with an increase in CR from 15 to 18 and marginal reduction of 2.64 and 8.24% in EGT and

NO emissions respectively could be seen with an addition of nanoparticles into PME.

The ID is shortened by the addition of nanoparticles as well as with an increase in CR. The

cylinder pressure and HRR marginally reduce by the introduction of nanoparticles into PME.

The engine exhibits better combustion and performance output along with curtailed

emissions by the dispersion of 200 ppm alumina nanoparticles into PME at a CR of 18.

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Influence Of Compression Ratio On The Operating Attributes Of Palm Oil Powered Diesel Engine … ·...

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