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
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
17 661 38.88 Block lowered by 0.54 mm
18 661 36.72 Block lowered by 0.62 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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