SS symmetry
Article
Effect of Zinc Oxide Nano-Additives and Soybean
Biodiesel at Varying Loads and Compression Ratios
on VCR Diesel Engine Characteristics
Rakhamaji S. Gavhane 1 , Ajit M. Kate 2 , Abhay Pawar 3 , Mohammad Reza Safaei 4,5,6, * ,
Manzoore Elahi M. Soudagar 7 , Muhammad Mujtaba Abbas 7 , Hafiz Muhammad Ali 8 ,
Nagaraj R Banapurmath 9 , Marjan Goodarzi 10 , Irfan Anjum Badruddin 11 , Waqar Ahmed 7 and
Kiran Shahapurkar 12
1
2
3
4
5
6
7
8
9
10
11
12
*
Department of Mechanical Engineering, Amrutvahini College of Engineering, Sangamner,
Ahmednagar 422608, India; rakhmaji.gavhane@avcoe.org
Department of Mechanical Engineering, Zeal College of Engineering and Research, Pune 411041, India;
ajit.kate@zealeducation.com
Department of Mechanical Engineering, D Y Patil College of Engineering, Ambi Talegaon Tal Maval,
Pune 410506, India; abhay.pawar@dyptc.edu
Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam
Faculty of Electrical—Electronic Engineering, Duy Tan University, Da Nang 550000, Vietnam
Department of Civil and Environmental Engineering, Florida International University, Miami, FL 33174, USA
Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur 50603,
Malaysia; manzoor@siswa.um.edu.my (M.E.M.S.); m.mujtaba@uet.edu.pk (M.M.A.);
Hva80013@siswa.um.edu.my (W.A.)
Mechanical Engineering Department, King Fahd University of Petroleum and Minerals (KFUPM),
Dharan 31261, Saudi Arabia; hafiz.ali@kfupm.edu.sa
Department of Mechanical Engineering, B.V.B. College of Engineering and Technology,
KLE Technological University, Vidyanagar, Hubli 580031, India; nr_banapurmath@kletech.ac.in
Sustainable Management of Natural Resources and Environment Research Group, Faculty of Environment
and Labour Safety, Ton Duc Thang University, Ho Chi Minh City 700000, Vietnam;
marjan.goodarzi@tdtu.edu.vn
Research Center for Advanced Materials Science (RCAMS), King Khalid University, P.O. Box 9004,
Abha 61413, Kingdom of Saudi Arabia; irfan@kku.edu.sa
Department of Mechanical Design and Manufacturing Engineering, School of Mechanical, Chemical and
Materials Engineering, Adama Science and Technology University, Adama 1888, Ethiopia;
kiranhs1588@astu.edu.et
Correspondence: mohammadrezasafaei@duytan.edu.vn; Tel.: (+1)-502-657-9981
Received: 10 May 2020; Accepted: 5 June 2020; Published: 22 June 2020
Abstract: The present investigation is directed towards synthesis of zinc oxide (ZnO) nanoparticles
and steady blending with soybean biodiesel (SBME25) to improve the fuel properties of SBME25 and
enhance the overall characteristics of a variable compression ratio diesel engine. The soybean biodiesel
(SBME) was prepared using the transesterification reaction. Numerous characterization tests were
carried out to ascertain the shape and size of zinc oxide nanoparticles. The synthesized asymmetric
ZnO nanoparticles were dispersed in SBME25 at three dosage levels (25, 50, and 75 ppm) with sodium
dodecyl benzene sulphonate (SDBS) surfactant using the ultrasonication process. The quantified
physicochemical properties of all the fuels blends were in symmetry with the American society for
testing and materials (ASTM) standards. Nanofuel blends demonstrated enhanced fuel properties
compared with SBME25. The engine was operated at two different compression ratios (18.5 and 21.5)
and a comparison was made, and best fuel blend and compression ratio (CR) were selected. Fuel blend
SBME25ZnO50 and compression ratio (CR) of 21.5 illustrated an overall enhancement in engine
characteristics. For SBME25ZnO50 and CR 21.5 fuel blend, brake thermal efficiency (BTE) increased
by 23.2%, brake specific fuel consumption (BSFC) were reduced by 26.66%, and hydrocarbon (HC),
Symmetry 2020, 12, 1042; doi:10.3390/sym12061042
www.mdpi.com/journal/symmetry
Symmetry 2020, 12, 1042
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CO, smoke, and CO2 emissions were reduced by 32.234%, 28.21% 22.55% and 21.66%, respectively;
in addition, the heat release rate (HRR) and mean gas temperature (MGT) improved, and ignition
delay (ID) was reduced. In contrast, the NOx emissions increased for all the nanofuel blends due to
greater supply of oxygen and increase in the temperature of the combustion chamber. At a CR of 18.5,
a similar trend was observed, while the values of engine characteristics were lower compared with
CR of 21.5. The properties of nanofuel blend SBME25ZnO50 were in symmetry and comparable to
the diesel fuel.
Keywords: soybean biodiesel; zinc oxide nanoparticles; compression ratio; VCR engine performance;
emissions
1. Introduction
The global increase in fuel consumption and dependence on petroleum, and the increasing costs
due to higher demand, have sparked interest in alternate and sustainable energy sources [1]. Developing
nations are highly dependent on fossil fuels, particularly for their industrial and transport sectors [2].
Currently, due to an inadequate supply of fossil fuels, increasing global prices for crude oil and
environmental factors have led to renewable energy sources becoming increasingly more important [3,4].
Vegetable oils have certain comparable diesel fuel properties and are known to have several advantages
over fossil fuels, such as being environmentally friendly, nontoxic, and biodegradable, and thus
help in establishing environmental balance [5,6]. Their cetane number and vaporization pressure is
almost equivalent to that of diesel. Biodiesel contains extra oxygen atoms in its molecular structure,
which contribute oxygen that assist in enhanced fuel combustion. Nonetheless, despite the numerous
advantages of biodiesel, it has certain disadvantages, such as high viscosity, poor cold flow properties
and characteristics, and lower heating value [1,7,8]. A recently developed technique to improve
combustion characteristics and fuel properties is through the addition of fuel additives. The past
decade has witnessed a rise in the utilization of alcohol-based additives in biodiesel fuel blends, such as
ethanol, butanol, heptanol, and diethyl ether [9–11]. Alcohol-based additives supply more oxygen in
the combustion chamber to reduce emissions, however, due to the formation of a lean mixture it lowers
the calorific value, which, combined with higher auto ignition temperatures and lower lubrication
properties, results in engine deterioration and reduced performance characteristics. Hence, researchers
have explored the potential of micro- and nanoparticle additives. Microparticle additives assisted
in improving the engine characteristics, but they tend to agglomerate. Nanotechnology has found a
suitable place in many industrial applications, such as engineering, agricultural and medical science,
biotechnology, and transport. Nanoparticle additives exhibit higher thermophysical properties and ease
of miscibility in any base fluids [12–16]. Previous investigators reported nanoparticle additives to be
exceptionally effective in reducing the agglomeration in comparison with microparticles and improve
engine characteristics due to the large surface air-to-volume ratio, high thermophysical properties, high
combustion velocity, and high thermal conductivity [17–19]. In addition, the addition of nanoparticles
to base fluids improves the physiochemical properties, in the form of higher flash point, fire point,
cloud point, and calorific value, and lower density and viscosity of the base fluid [1,7,14,20–23]. Table 1
shows the effect of nanoparticles in different fuel blends. Recent studies on the effect of nanoparticles
and biodiesel in diesel engines reported an enhancement in combustion characteristics, such as cylinder
pressure, heat release rate (HRR), and mean gas temperature (MGT), and reduced the ignition delay
(ID) period for metal and carbon-based nano-additives, such as carbon nanotubes, graphene oxide,
Cu2 O, FeCl3 , CeO2 , Co3 O4 , Al2 O3 , TiO2 , and ZnO.
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Table 1. The effect of nanoparticles in different fuel blends.
Biofuel Blends
Biodiesel
Dosage of NPs
Engine Type
Application Output
D (80%) + BD (20%)
Dairy scum
oil methyl
ester
Graphene oxide
20 ppm
40 ppm
60 ppm
D (80%) + BD (20%)
Pongamia oil
methyl ester
FeO
30 nm and
Ferrofluid
100 nm
SC, DI, 4-S, CI engine, 23◦ BTDC, WC,
17.5 CR, 3 FI nozzles
D (40%) + BD (30%)
+ ethanol (30%)
Palm oil
methyl ester
ZnO
250 ppm
SC, DI, 4-S, CI engine, 23◦ BTDC, WC,
17.5 CR, 3 FI nozzles
D (70%) + BD (20%)
+ ethanol (10%)
Castor oil
methyl ester
γ-Alumina
10 ppm
20 ppm
30 ppm
SC, DI, 4-S, CI
Engine, 23◦ BTDC
HCC, AC, 17.5 CR 3 FI nozzles, 0.3 mm
dia. FI holes, 661 cc
BD (91%) + 50 mL
DEE
Jatropha
methyl ester
CNT
50 ppm
SC, DI, 4-S, CI
Engine, 26◦ BTDC
HCC, AC, 17.5 CR 3 FI nozzles
•
•
•
•
•
•
•
•
•
•
Dosage level of 40 ppm of GNPs increased the BTE, HRR and
reduced the BSFC, ignition delay.
The calorific value increased while the viscosity reduced.
The emissions, CO, HC and smoke reduced.
The NOx emission slightly increased.
Improves the peak HRR, BTE.
Reduction in NOx emissions.
BSFC reduces for Nanofuel blends.
Reduction in CO, HC, PM, smoke.
Reduction of BSFC, HRR and cylinder pressure.
Decrease in CO, NOx, smoke and BTE.
Increases the calorific value.
•
•
Improved BTE, Cylinder pressure and heat release rate.
Lower HC, CO emissions, BSEC.
•
•
•
•
•
The CO, HC and NOx reduced in comparison with neat diesel.
Enhanced combustion attributes, micro explosion of
fuel droplets.
Improved BTE and reduced BSFC.
Accelerates the burning rate, lowers the ID and HRR.
Improves the peak HRR, BTE.
Reduces the NOx, smoke and HC.
Avoids the accumulation of non-polar complexes on the
cylinder wall.
Catalytic effect of NPs and micro explosion improved BTE,
HRR and cylinder gas pressure.
Better atomization and rapid evaporation.
NOx was reduced.
Supply of excess O leads in lower CO and HC.
•
•
•
Improved BTE, Cylinder pressure and heat release rate.
Lower HC, CO emissions, BSEC.
Lower NOx emissions.
•
23◦ BDTC,
SC, DI, 4-S, CI engine,
17.5 CR, 3 FI nozzles
WC,
D (70%) + BD (10%)
+ ethanol (20%)
(Diesterol- E20)
Castor oil
methyl ester
Ceria and CNT
25 ppm
50 ppm
100 ppm
CI, WC, DI, 1500 rpm, 19:1, 23◦ BTDC
BD + (200 and 500
ppm
of Ethanox)
Calophyllum
Inophyllum
Methyl Ester
ZnO
50 ppm
100 ppm
2-C, DI, 4-S, CI
Engine, 23◦ BTDC, WC, 18.5 CR, 5 FI
nozzles, 1670 cc
D (70%) + BD (20%)
+ ethanol (10%)
Jatropha
methyl ester
γ-Alumina
10 ppm
20 ppm
30 ppm
SC, DI, 4-S, CI
Engine, 23◦ BTDC
HCC, AC, 17.5 CR, 3 FI nozzles, 0.3 mm
dia. FI holes, 661 cc
•
•
•
•
•
•
Ref.
[7]
[24]
[25]
[26]
[27]
[28]
[29]
[30]
D: Diesel; BD: Biodiesel; WC: Water Cooled; SC: Single Cylinder; AC: Air Cooled; 4-S: Four Stroke; DI: Direct Injection; CI: Compression-Ignition; FI: Fuel Injector; CR: Compression ratio;
BTDC: Before Top Dead Center.
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Özgür et al. [31] investigated the combined effect of the addition of 25 and 50 mg/L of MgO and
SiO2 nanoparticles in diesel. The authors observed that the addition of nanoparticles in diesel fuel
lowered the NOx and CO, and increased the engine performance marginally. Soudagar et al. [7,32]
studied the influence of graphene oxide and Al2 O3 nanoparticles (20, 40, and 60 ppm) in dairy
scum methyl ester and honge oil methyl ester. Sodium dodecyl sulfate surfactant was used for
nanoparticle stabilization of nanofuel in the base fluid and the ultrasonication process was carried out
for proper blending of fuel blends. The authors reported an enhancement in the overall combustion
and performance characteristics, and reduction in hydrocarbon (HC), CO, and smoke opacity, of a
conventional mechanical fuel injection system diesel engine for the all the nanofuel blends in contrast
to B20 fuel. Karthikeyan et al. [33] performed a related study introducing ZnO nanoparticles to canola
biodiesel. They observed that for the B20+ZnO fuel blends, the brake thermal efficiency (BTE) increased,
and HC and CO decreased, in comparison with neat B20. The influence of alumina (Al2 O3 ) nanoparticles
on biodiesel blends was investigated by Venu and Madhavan [34]. The authors reported the Al2 O3 in
biodiesel reduced the brake specific fuel consumption (BSFC), NOX , HC, and carbon dioxide despite
the increased emission of CO. Sajith et al. [35] studied the influence of CeO2 nanoparticles in biodiesel
fuel blends. In order to achieve optimum efficiency, different dosing levels of CeO2 nanoparticles
(20, 40, 60, and 80 ppm) were used. The impact of CeO2 nanoparticles on compression-ignition (CI)
engine efficiency, thermophysical properties of the fuel, and emissions characteristics were investigated.
The authors reported a decline in the NOx and HC emissions and enhancement in the overall engine
characteristics. Keskin et al. [36] reported the influence of nanoparticles on specific fuel consumption
(SFC) and emission characteristics of diesel engines. The MnO2 and MgO nanoparticles were added to
the diesel at concentration levels of 8 and 16 µmol/L. The physiochemical properties of diesel fuel were
enhanced due to addition of the nanoparticles. The addition of combined nano-additives reduced CO
by 16%, smoke opacity by 29%, and the SFC by 4.16%, whereas a 10% increase in NOx emissions was
recorded. Consequently, the previous literature suggests that the addition of nanoparticle additives to
biodiesel fuel enhances the overall diesel engine characteristics and the fuel properties. Studies have
been carried out using fixed engine variables by numerous investigators.
Regarding environmental pollution due to the addition of nanoparticles in fuel, limited research
is available concerning the traces of nano-additives in engine exhaust emissions. Deqing Mei et al. [37]
reported CeO2 in diesel fuel enhances the combustion process, while a high dosing level of nano-CeO2
can cause early ignition, which can lead to escaping of nanoparticles through the exhaust. However,
the authors found only a trace of nanoparticles and an insignificant effect on particulate matter (PM)
emission. Qibai et al. [38] investigated the effects of Al and carbon nanoparticles in a diesel-biodiesel
blend; the exhaust gases were passed through diesel particulate filters (DPFs), and slight traces of
aluminum, oxygen, carbon, and silicon were found. Toxic effects of nanoparticles on animals include
crossing cell membranes and inhaled NPs can reach the blood and target sites such as the heart, blood
cells, and liver [1]. The information on these pathways is limited, but the actual number of particles
that move from one organ to another can be significant, depending on exposure time [39]. Studies on
the environmental pollution caused by nanoparticles as fuel additives are limited, hence there is a
scope for further study.
The objective of the current research is to investigate the combined effect of nanoparticle additives
and biodiesel fuel blends at varying compression ratios and loads in a variable compression ratio
(VCR) diesel engine. The study delves into the potential of a ZnO nanoparticle and soybean biodiesel
blend. The soybean biodiesel (SBME25) is blended with synthesized zinc oxide nanoparticles at
varying blending ratios of 25, 50, and 75 ppm. This study facilitates and proposes a direction for future
research and commercialization of all aspects of nanotechnology in biodiesel fuels in diesel engine
applications. In addition, this study enables the selection of optimal and most suitable compression
ratios for enhancement of diesel engine characteristics.
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2. Material and Methods
2.1. Production of Soybean Biodiesel
A Gas Chromatography Mass Spectrometer (GCMS/MS) Shimadzu, Japan (TQ 8030) was used to
analyze the free fatty acid (FFA) percentage in the soybean oil. Table 2 shows the FFA composition of
soybean biodiesel.
Table 2. Fatty acid composition of soybean oil.
Fatty Acid
Carbon Chain
Composition (wt.%)
Palmitic
Stearic
Oleic
Linoleic
Linolenic
C 16:0
C 18:0
C 18:1
C 18:2
C 18:3
11.24
4.15
23.69
51.66
6.89
The preparation of biodiesel was carried out at Apex innovations laboratory, India. In the
esterification method, the soybean oil was heated with sulfuric acid at 70 ◦ C and methanol in an
air-oven for about 60 min to eliminate the moisture. In the subsequent step, i.e., the transesterification
reaction, the solution was mixed with sodium hydroxide at 6:1 M and heated at 60 ◦ C for about 60 min.
The mixing and heating processes were carried out on a magnetic stirrer rotating at a constant speed of
500 rpm. Then, the solution was transferred to a separating funnel and kept steady for 24 h. After 24 h,
a clear distinct layer was visible, distinguishing the glycerol and biodiesel. The lower layer containing
glycerol was drained and the upper layer was extracted and washed using warm water. The liquid
was dried to obtain soybean biodiesel.
2.2. Synthesis and Characterization of Zinc Oxide Nanoparticles
The zinc oxide nanoparticles were synthesized using the aqueous precipitation method as
previously reported Haniffa et al. [40] and Li Yuan et al. [41]. Initially, 0.5 M zinc nitrate (Zn(NO3 )2 )
was added of drop by drop to 0.5 M of sodium carbonate (Na2 CO3 ) solution under vigorous stirring.
Soon after separation from the solution using vacuum filtration technique by washing and rinsing three
times with distilled water and then ethanol, the precipitate was dried in an air circulating oven at 80 ◦ C
for 2 h. The oven-dried powder was calcined to 500 ◦ C for 3 h to obtain zinc oxide nanopowder. Finally,
for a period of 5 h the nano powder was ball-milled at 200 rpm to obtain fine zinc oxide nanoparticles.
Figure 1 illustrates a flow chart showing the synthesis of zinc oxide nanoparticles using the aqueous
precipitation method.
Field emission scanning electron microscope (FESEM) analysis was used to determine chemical
composition and visualize the surface morphology of ZnO nanoparticles. The analysis was performed
using a Bruker XFlash 6I30, USA. Figure 2 represents the SEM image of ZnO nanoparticles at 25,000×
magnification. The synthesized ZnO nanoparticles had Rosette and irregular crystal structures with a
wurtzite hexagonal phase, in agreement with previous literature [42,43].
X-ray powder diffraction (XRD) was used to evaluate the crystallinity (phase identification) by
comparison with the integrated intensity of a previously reported pattern to that of the observed sharp
peaks of the synthesized zinc oxide nanoparticles. The XRD analysis is shown in Figure 3a; the analysis
was carried out using a Bruker D8 VENTURE, USA. The calculated hkl values for the peaks observed
for ZnO nanoparticles at 2θ = 32.45◦ (100), 34.64◦ (002), 36.57◦ (101), 48.52◦ (102), 56.43◦ (110), 62.66◦
(103), 66.36◦ (200), 68.13◦ (112), 69.44◦ (201), 72.32◦ (004), and 77.73◦ (004). A sharp peak was observed
at 36.57◦ (101), which indicates the crystallinity of ZnO nanoparticles; the peaks reported in the current
investigation were closer to the characteristic peaks reported by [44,45]. Figure 3b shows the UV-Vis
absorption spectra; ultra-violet absorption for ZnO nanoparticles confirms absorbance at a wavelength
of 365.47 nm, between the characteristic range of 350 to 380 nm [44].
Symmetry 2020, 12, 1042
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Figure 1. A flow chart of the synthesis of zinc oxide nanoparticles through the aqueous
precipitation method.
μ at 25,000× magnification level.
Figure 2. FESEM at 3 µm
θ
Symmetry 2020, 12, 1042
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ZnO nanoparticles
Absorbance (a.u.)
365.47 nm
320
340
360
380
400
420
440
460
480
500
520
540
560
Wavelength (nm)
(a)
(b)
(c)
Figure 3. Characterization tests: (a) XRD analysis; (b) UV-Vis Absorbance; (c) TEM at 100 nm
magnification.
The main objective of transmission electron microscopy (TEM) analysis is to produce high
magnification images of the internal structure of a sample. Figure 3c illustrates the TEM image at
100 nm and magnification level of 20,000×. The TEM analysis is also used to collect data on crystalline
structures, contamination, stress, and internal fractures inside materials [44]. Initially, the ZnO
nanoparticles were dispersed in ethanol. The structure of ZnO nanoparticles was found to be hexagonal
wurtzite and the size of the nanoparticles was in the range of 15–40 nm.
2.3. Preparation and Physiochemical Properties of Nanofuel Blends
A scale was used to measure precise quantities of zinc oxide nanoparticles. The ZnO nanoparticles
(25, 50, and 75 mg/L) were mixed with 10 mL of distilled water. Sodium dodecyl sulfate (SDS) surfactant
was added for surface modifications and stabilization, to reduce the possibility of coagulation and
coalescence, and to reduce the surface tension. Surfactants tend to position themselves at the interface
between the nanoparticles and the base fluid, where it establishes a degree of continuity between the
Symmetry 2020, 12, 1042
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nanoparticles and fluids. The ultrasonication process was carried out for steady blending; initially the
ultrasonication bath was used to blend the solution with an agitation time of 60 min. Later, the different
nanofluid blends were blended using an ultrasonication probe at a frequency of 15–30 Hz for 20 min.
After the zinc oxide nanofluids were prepared they were transferred to the SBME25-diesel fuel blend,
and heated and steadily mixed using a magnetic stirrer at 60 ◦ C for 30 min to remove traces of water
molecules. Then, the same ultrasonication processes were carried out for a steady dispersion of zinc
oxide nanoparticles in SBME25 biodiesel–diesel fuel blend. Figure 4 illustrates the comprehensive
steps involved in the preparation of nanofuel.
Figure 4. The comprehensive steps involved in the preparation of nanofuel.
The experiments were conducted in various lab facilities available in Maharashtra and Karnataka,
India. The detailed description of the equipment, procedure, and lab setup was presented in previous
articles by Soudagar et al. [7,32] on the addition of graphene oxide and Al2 O3 nanoparticles in dairy
scum oil methyl ester and honge oil methyl ester. The physiochemical properties of the test fuel blends
are demonstrated in Table 3. The analysis indicates the addition of zinc oxide nanoparticles to soybean
biodiesel increases the calorific value and cetane number and demonstrates comparable diesel fuel
properties. The fuel blend SBME25ZnO50 demonstrated overall improvement in the physicochemical
properties. The analyzed results were within the ASTM D6751 standard for biodiesel.
−
−
−
−
−
−
−
−
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Table 3. Physicochemical properties of fuel blends.
Properties
Unit
ASTM
Standards
Test Limit
ASTM D6751
Diesel
SBME25
SBME25ZnO25
SBME25ZnO50
SBME25ZnO75
Density
Calorific value
Kinematic Viscosity
Specific Gravity
Cetane Number
Flash Point
Pour Point
Cloud Point
Sulphur content
Water content
kg/m3 at 15 ◦ C
kJ/kg
cSt at 40 ◦ C
gm/cc
◦C
◦C
◦C
% w/w
% vol
D4052
D5865
D445
D891
D613
D93
D97-12
D2500-11
D5453
D2709
860–900
Min. 35,000
1.9–6
0.87–0.90
Min. 40
>130
−15 to 16
−3 to 12
0.05
0.05% vol
810
45,000
2.12
0.811
51
55
−4
−2
0.005
-
845.66
41,684
3.56
0.825
48.66
65.71
−6
4.5
0.012
Trace
845.87
43,400
3.52
0.820
52.55
62.87
−5
3.5
0.0156
Trace
846.22
44,800
3.525
0.821
53.74
60.47
−5.65
3.54
0.0162
Trace
846.84
43,850
3.531
0.824
53.15
61.87
−5.6
3.57
0.0188
Trace
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2.4. Uncertainty Analysis of Expected Errors
Uncertainty analysis is an organized set of procedures followed for calculation of errors in
experimental data. The inaccuracies occur due to the error in electronic and mechanical components,
environmental factors, and human miscalculations. The data is gathered in ideal conditions,
and specifications and details of all the components are available. Measurement errors from several
different sources are classified into bias and precision errors; throughout the experimentation the bias
errors remain constant. In this work, the estimation of experimental uncertainty and the evaluation of
standard errors in the measurements were derived using the method proposed by Moffat et al. [46].
Table 4 illustrates the uncertainty and accuracy levels of calculated engine parameters.
Table 4. Uncertainty and accuracy levels of calculated engine parameters.
Parameters
Accuracy (±)
Uncertainty (%)
Brake power (KW)
Brake thermal efficiency (%)
Brake specific fuel consumption (%)
Heat release rate (J/◦ CA)
Carbon monoxide emission (%)
Nitrogen oxide emission (ppm)
Hydrocarbon emission (ppm)
Exhaust gas temperature (◦ C)
Mean gas temperature (◦ C)
Smoke meter (HSU)
±0.01%
±10 ppm
±10 ppm
±1
±1
±0.22
±0.28
±0.31
±0.24
±0.18
±0.24
±0.14
±0.15
±0.35
±0.25
In addition, the propagation of errors was studied using standard deviations by plotting error
bars, where error bars were derived considering the average of six readings. The propagation of
uncertainty for various factors are determined depending on two or more independent parameters is
carried out using Equation (1):
s
Uy
y
=
ux1
x1
!2
+
u 2
x2
x2
+ .................. +
u n
xn
xn
(1)
where Uy : uncertainty; y: testing value; x1 , x2 ,..., xn : evaluated parameter; and the uncertainty of
emissions is Uy = Resolution
Range .
The overall uncertainty of the engine characteristics is calculated using Equation (2):
s
Overall uncertainty = ±
Uncertainty % o f (BTE2 + BSFC2 + CO2 + NOx2 + HC2
)
+smoke2 + HRR2 + MGT2 + EGT2
= ± 1.82 (2)
2.5. Test Engine Setup
The engine used in the current investigation is a variable compression ratio (VCR), Kirloskar make,
single cylinder diesel engine. All the experiments were carried-out at Apex innovation laboratory,
India. The engine was coupled to a five-gas analyzer and smoke meter. The combustion chamber used
in the current investigation was hemispherical; compression ratios were varied without stopping the
VCR engine and the readings were derived using enginesoft software. A Data Acquisition System
(DAQ) and Labview software was used as an interface between the computer and the engine sensors
(air and fuel flow, temperatures, and load measurement sensors). Table 5 illustrates the specification of
the VCR test engine used in the current investigation.
Figure 5 illustrates the pictorial view of the test engine used in the current investigation. The heat
release rate was estimated using the data for 600 crank angle values. The compression ratio was varied
by the tilting block arrangement, in which the compression ratio could be varied without stopping
the engine. The arrangement consisted of compression ratio indicator and compression ratio adjuster
Symmetry 2020, 12, 1042
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with a lock nut and six Allen bolts. For varying the compression ratio, the Allen bolts were slightly
loosened, and the adjuster lock nut was loosened. Further, the adjuster was rotated to set a desired
compression ratio according to the compression ratio indicator, and then locked using a lock nut.
The chosen compression ratios in the current investigation were 18.5 and 21.5.
Table 5. Test Engine Specifications.
Number of Strokes
4
Fuel type
Cylinder
Rated Power
Speed
Cylinder diameter
Load indicator
Fuel tank
Exhaust Gas Recirculation
Piezo sensor
Temperature sensor
Load sensor
Rotameter
Dynamometer
Model
Make
End flanges both sides
Air gap
Torque
Hot coil voltage
Continuous current (amp)
Cold resistance ohm
Diesel, Biodiesel, and Nanofuel
Single, Water cooled
3.5 KW
1500 rpm
87.5 mm
Digital, Range 0–50 Kg, Supply 230 V air cooled
Volume 15 liters with glass fuel metering column
Water cooled, Stainless Steel, Range 0–15%
Range 5000 PSI, with low noise cable
RTD, PT100 and Thermocouple, Type K
Load cell, type strain gauge, range 0–50 Kg
Engine cooling 40–400 LPH; Cal. 25–250 LPH
AG10
Saj test plant rig
Cardon shaft model 1260 type
0.77 mm
11.5 Nm
60 V
5
9.8
Figure 5. Variable compression ratio (VCR) test engine setup.
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3. Results and Discussions
In this section, the combustion, performance, and emission characteristics of the diesel engine are
investigated. The effect of nanofuel blends and compression ratios of 18.5 and 21.5 on heat release rate,
ignition delay, BTE, BSFC, and mean gas temperature, and CO, NOx, HC, CO2 , and smoke emissions
are reported. A constant speed of 1500 rpm, injection timing (IT) of 23.5◦ BTDC (before top dead
center), and five loads were maintained. Table 6 illustrates the factors considered and employed in the
current investigation.
Table 6. Engine parameters.
Factors Considered
Parameters Employed
Engine
Combustion Chamber (CC)
Injection Pressure (IP)
Fuel Injector (FI) holes
Injection timing (IT)
Speed
Compression Ratio (CR)
Fuel
Variable Compression Ratio (VCR)
Hemispherical (HCC)
220 bar
4 holes, 0.25 mm dia.
23◦ BTDC
1500 rpm (constant)
18.5, 21.5
Diesel, SBME25, SBME25ZnO25, SBME25ZnO50, SBME25ZnO75
3.1. The Effect of Zinc Oxide Nano Additives and Soybean Fuel Blend on the Engine Performance
3.1.1. The Effect of SBME25-ZnO Nanofuel Blends on Brake Thermal Efficiency (BTE) at Different
Compression Ratios
Figure 6 illustrates the variation of BTE at varying loads. The results demonstrate that the BTE of
the VCR diesel engine was enhanced at all dosage levels of zinc oxide nanoparticles. The zinc oxide
nanoparticles promote complete combustion of the fuel charge when compared with biodiesel fuel
blends. Equations (3) and (4) illustrates the estimation of BP and BTE, respectively:
BP =
0.785 × N × (W x 9.81) × Arm lenght
2πN (W × R)
2πNT
=
=
kW
60000
60000
60000
BTE =
BP × 3600 × 100
%
kg
Fuel f low hr × Cv
(3)
(4)
Brake thermal efficiency for all tested fuels with different compression ratios at variable load is
presented in Figure 7a,b. BTE increased with an increase in load up to 80%, then exhibited a slight
reduction at 100% load. At maximum load and CR 21.5, the BTE increased by 11.592% (SBME25ZnO25),
23.2% (SBME25ZnO50), and 19.024% (SBME25ZnO75) compared to SBME25 fuel. Diesel fuel exhibited
a BTE value that was 29.64% lower with 18.5 CR at 80% load. All fuel blends showed lower BTE values
compared to diesel due to lower calorific value, lower brake power, and higher BSFC. In addition,
the BTE value fell with a reduction in compression ratio. All tested fuels showed a reduction in
BTE values: 9.88% (diesel), 15.4% (SBME25ZnO25), 6.15% (SBME25ZnO50), 11.1% (SBME25ZnO75),
and 20.5% (SBME25) with a compression ratio of 18.5 compared to a CR of 21.5, due to lower
compression temperature, which resulted in poor combustion of fuel. BTE is directly proportional to
compression ratio [47]. Brake thermal efficiency showed an enhancement with an increase in loads
and lower heat losses at higher engine load [48]. The metal zinc oxide nanoparticles improved the
combustion process by reducing its duration and ignition delay, and increased in-cylinder temperature
and pressure, and high HRR subsequently increased the BTE [49,50]. Zinc oxide nanoparticles act as a
potential catalyst due to their high reactive surface area during the combustion process, which leads to
a micro explosion of fuel droplets resulting in improved combustion characteristics, such as cylinder
pressure and high heat release rate, therefore increasing the BTE.
(
×
)
.
×
Symmetry 2020, 12, 1042
40
Compression ratio: 18.5:1
28.547
26.227
27.415
28.478
30.557
25.714
23.63
22.58
20.36
21.87
18.847
16.477
16.79
12.89
14.189
8.63
10
13 of 31
24.412
24.7
18.92
19.786
10.41
11.64
12.884
15
×
Engine: VCR 4S with EGR
Injector: 4 holes, 0.25 mm dia.
Engine Speed:1500 rpm
IP: 240 bar, IT: 23.5°btdc
CC: Hemisperical
25
20
×
)×
.
29.647
30
Fuel Blends
Diesel
SBME25ZnO25
SBME25ZnO50
SBME25ZnO75
SBME25
13.57
Brake Thermal Efficiency (%)
35
× (
×
5
0
20%
40%
60%
80%
100%
Load
(a)
45
Engine: VCR 4S with EGR
Injector: 4 holes, 0.25 mm dia.
Engine Speed:1500 rpm
IP: 240 bar, IT: 23.5°btdc
CC: Hemisperical
27.657
22.71
23.225
25.1
25.923
27.2
28.623
30.498
28.954
30.955
25.894
23.996
20.95
18.56
19.452
12.3
13.479
13.11
14.856
15
21.66
22.677
20
26.784
28.892
30
25
Compression ratio: 21.5:1
31.285
35
15.58
Brake Thermal Efficiency (%)
40
Fuel Blends
Diesel
SBME25ZnO25
SBME25ZnO50
SBME25ZnO75
SBME25
10
5
0
20%
40%
60%
80%
100%
Load
(b)
Figure 6. The variation of BTE at compression ratios of (a) 18.5 and (b) 21.5.
14 of 31
0.398
0.41
0.422
0.35
0.295
0.238
0.245
0.242
0.264
0.251
0.256
0.271
0.295
0.289
0.298
0.3
0.315
0.33
0.318
0.315
0.334
0.352
0.378
0.39
0.368
0.4
Fuel Blends
Diesel
SBME25ZnO25
SBME25ZnO50
SBME25ZnO75
SBME25
Engine: VCR 4S with EGR
Injector: 4 holes, 0.25 mm dia.
Engine Speed:1500 rpm
IP: 240 bar, IT: 23.5°btdc
CC: Hemisperical
Compression ratio: 18.5:1
0.5
0.415
Brake Specific Fuel Consumption (kg/kWh)
Symmetry 2020, 12, 1042
0.2
0.1
0.0
20%
40%
60%
80%
100%
Load
0.27
0.234
0.245
0.198
0.221
0.231
0.253
0.278
0.298
0.312
0.232
0.245
0.282
0.2969
0.309
0.315
0.284
0.264
0.3
Fuel Blends
Diesel
SBME25ZnO25
SBME25ZnO50
SBME25ZnO75
SBME25
Engine: VCR 4S with EGR
Injector: 4 holes, 0.25 mm dia.
Engine Speed:1500 rpm
IP: 240 bar, IT: 23.5°btdc
CC: Hemisperical
0.248
0.354
0.352
0.4
0.37
0.385
0.415
Compression ratio: 21.5
0.33
Brake Specific Fuel Consumption (kg/kWh)
(a)
0.2
0.1
0.0
20%
40%
60%
80%
100%
Load
(b)
Figure 7. The variation of BTE at compression ratios: (a) 18.5 and (b) 21.5.
Symmetry 2020, 12, 1042
15 of 31
3.1.2. The Effect of SBME25-ZnO Nanofuel Blends on Brake Specific Fuel Consumption (BSFC) at
Different Compression Ratios
Figure 7a,b show the variation of BSFC and loads for various fuel blends at different compression
ratios. The BSFC is reduced with an increase in engine load. The lowest BSFC value with 21.5 CR
0.198 Kg/kWh for SBME25ZnO50 is obtained at 100% engine load. On average, the BSFC values were
0.258 Kg/kWh (diesel), 0.262 Kg/kWh (SBME25ZnO50), 0.2896 Kg/kWh (SBME25ZnO75), 0.304 Kg/kWh
(SBME25ZnO25), and 0.329 Kg/kWh (SBME25) at 21.5 CR. All ternary fuel blends showed reduction in
BSFC: 20.37%, 12.18%, and 7.82% for SBME25ZnO50, SBME25ZnO75, and SBME25ZnO25, respectively,
compared to SBME25. The minimum BSFC value was recorded with zinc oxide (50 ppm) as a fuel
additive. SBME25ZnO50 showed higher BSFC value 0.245 Kg/kWh with 18.5 compression ratio at 100%
engine load. The average BSFC values for all tested fuels increased with a decrease in compression
ratio. All tested fuels showed a rise in the BSFC for 18.5 compression ratio: 14.47% (diesel), 8.94%
(SBME25ZnO25), 15.46% (SBME25ZnO50), 4.48% (SBME25ZnO75), and 13.7% (SBME25), compared to
21.5 compression ratio. At higher load, BSFC values are reduced due to less heat loses and a smaller
amount of fuel is required to obtain specific brake power [51,52]. A similar increase in BSFC with an
increase in compression ratio has been reported by various researchers [48,53,54]. Biodiesel with fuel
additive (ZnO) showed significant reduction in BSFC due to improved combustion characteristics.
Nanoparticle enhanced the air–fuel mixing, micro explosion of fuel droplets, and secondary atomization,
resulting in lower BSFC. The combustion process is improved with the use of ZnO as a fuel additive
(oxidizing agent) due to its high calorific value, shorter ignition delay, and more reactive surface
area [49]. Dahad et al. [55] and Deepak et al. [56] reported a similar reduction in BSFC with the use of
zinc oxide as a fuel additive in a diesel engine.
3.2. The Effect of Zinc Oxide Nano-Additives and Soybean Fuel Blend on Engine Emissions
3.2.1. The Effect of SBME25-ZnO Nanofuel Blends on Carbon Monoxide (CO) Emissions at Different
Compression Ratios
The variation in carbon monoxide emissions and loads for all tested fuels at different compression
ratio is presented in Figure 8a,b. Carbon monoxide emissions are produced due to incomplete
combustion during the combustion process. All tested fuels showed reduction in carbon monoxide
emissions, with the exception of diesel, due to the presence of extra oxygen molecules, which results in
complete conversion of CO to CO2 [57]. SBME25ZnO50 showed the lowest CO emissions among all
tested fuels due to the presence of extra oxygen and reactive surface area (ZnO), which leads to high
in-cylinder temperature and pressure resulting in complete combustion. On average, the CO emissions
were reduced by 41.08%, 31.44%, and 18.66% for SBME25ZnO50, SBME25ZnO75, and SBME25ZnO25
ternary blends, respectively, compared to SBME25. All tested fuels showed an increase in CO emission
values: 20.85% (diesel), 19.87% (SBME25ZnO25), 4.23% (SBME25ZnO50), 6.53% (SBME25ZnO75),
and 14.45% (SBME25) with compression ratio of 18.5 compared to a compression ratio of 21.5. This
was due to a lower compression temperature, which resulted in poor combustion of fuel. A similar
result has been reported by Sharma et al. [58], in which an increase in the compression ratio resulted in
an increased air temperature, leading to a reduction in the ignition delay period and CO emissions due
to complete combustion.
Symmetry 2020, 12, 1042
0.44
16 of 31
Engine: VCR 4S with EGR , Injector: 4 holes, 0.25 mm dia.
Engine Speed:1500 rpm, IP: 240 bar, IT: 23.5°btdc CC: Hemisperical
SBME25
0.22
0.151
0.38
Compression ratio: 18.5:1
0.33
0.161
0.172
0.188
0.396
0.22
0.198
0.0638
0.348
0.0805
0.092
0.105
0.128
SBME25ZnO50
0.261
0.211
0.153
0.174
0.0472
0.48
0.0625
0.0795
0.0838
SBME25ZnO25
0.35
0.36
0.16
0.44
0.115
0.124
0.157
0.189
0.175
0.151
SBME25ZnO75
0.229
0.258
0.17
0.172
0.086
0.0625
0.336
0.309
0.06
0.075
0.088
0.098
0
20%
40%
60%
0.0782
0.0884
0.0921
SBME25ZnO50
0.252
0.201
0.168
0.084
0.144
0.0456
0.300
0.150
0.0608
0.0772
0.0821
SBME25ZnO25
0.225
0.1
0.000
Diesel
0.22
0.00
0.142
0.28
0.2112
0.105
0.24
0.112
0.145
0.178
0.075
0.33
0.11
Carbon monoxide emissions (% vol.)
Carbon monoxide emissions (% vol.)
0.174
0.12
0.1365
0.344
0.295
SBME25ZnO75
0.261
0.24
Compression ratio: 21.5:1
0.099
0.348
0.087
SBME25
0.297
0.11
0.087
Engine: VCR 4S with EGR , Injector: 4 holes, 0.25 mm dia.
Engine Speed:1500 rpm, IP: 240 bar, IT: 23.5°btdc CC: Hemisperical
0.21
0.176
0.154
0.088
80%
Diesel
0.264
100%
0.000
0.05
0.062
0.074
0.086
0
20%
40%
60%
Load
Load
(a)
(b)
0.141
80%
100%
Figure 8. The variation of carbon monoxide at compression ratios: (a) 18.5 and (b) 21.5.
3.2.2. The Effect of SBME25-ZnO Nanofuel Blends on Hydrocarbon (HC) Emissions at Different
Compression Ratios
HC emissions for diesel, SBME25ZnO25, SBME25ZnO50, SBME25ZnO75, and SBME25 at variable
load with different compression ratios are shown in Figure 9a,b. HC emissions are mainly affected
by fuel characteristics, fuel spray properties, and different engine operating conditions. The average
HC emissions at CR 21.5 were 0.131, 0.139, 0.147, 0.1530, and 0.189 g/kWh for SBME25ZnO50, diesel,
SBME25ZnO75, SBME25ZnO25, and SBME25, respectively, from minimum to maximum engine loads.
All ternary fuel blends showed reduction in HC emissions compared to a neat biodiesel–diesel blend.
Overall, significant reductions in HC emissions for a compression ratio of 21.5 of 30.83%, 22.12%, and
18.76% were observed for SBME25ZnO50, SBME25ZnO75, and SBME25ZnO25, respectively, compared
to SBME25. The fuel blend SBME25 showed maximum HC emissions due to its viscous attributes,
which resulted in poor fuel spray characteristics and led to incomplete combustion. All fuels tested at
CR 18.5 showed higher HC emissions compared to CR 21.5. HC emissions are mainly affected by the
air–fuel mixture and the air-to-fuel equivalence ratio from rich to lean mixture. A similar increase in HC
emissions due to a lower compression ratio was reported by Sharma et al. [58]. All tested fuels showed
an increase in CO emission values: 12.58% (diesel), 12.26% (SBME25ZnO25), 14.35% (SBME25ZnO50),
8.27% (SBME25ZnO75), and 20.48% (SBME25) with a compression ratio of 18.5 compared to 21.5 CR.
Symmetry 2020, 12, 1042
17 of 31
Engine: VCR 4S with EGR , Injector: 4 holes, 0.25 mm dia.
Engine Speed:1500 rpm, IP: 240 bar, IT: 23.5°btdc CC: Hemisperical
Engine: VCR 4S with EGR , Injector: 4 holes, 0.25 mm dia.
Engine Speed:1500 rpm, IP: 240 bar, IT: 23.5°btdc CC: Hemisperical
SBME25
0.332
0.166
0.1795
Hydrocarbon Emission (g/kW-h)
0.19
0.2642
0.176
SBME25ZnO75
0.20
0.145
0.05
0.158
0.155
0.148
0.1517
SBME25ZnO50
0.210
0.182
0.138
0.1508
0.14
0.138
0.138
0.126
0.084
SBME25ZnO25
0.25
0.20
0.15
0.21
0.156
0.164
0.1614
0.1709
0.1702
0.126
Compression ratio: 21.5:1
0.179
0.19
0.2
0.21
0.168
SBME25ZnO75
0.135
0.135
0.108
0.145
0.155
0.191
0.1454
0.1472
0.1442
0.1454
0.135
0.145
0.152
0.131
0.128
0.154
0.158
0.165
0.132
0.16
SBME25ZnO50
0.198
0.128
0.132
0.122
0.142
0.099
SBME25ZnO25
0.192
0.168
0.142
0.120
Diesel
0.136
0.151
0.1412
0.165
Diesel
0.170
0.153
0.063
0.000
0.162
0.144
0.10
0.189
0.17
0.189
0.1914
0.10
0.168
0.198
0.154
0.083
0.25
0.15
0.191
0.242
Hydrocarbon Emission (g/kW-h)
0.249
0.254
SBME25
0.220
Compression ratio: 18.5:1
0.1335
0.135
0
20%
0.1264
0.137
0.145
0.152
0.119
0
20%
40%
Load
(a)
60%
80%
100%
40%
60%
80%
100%
Load
(b)
Figure 9. The variation of hydrocarbon emissions at compression ratios: (a) 18.5 and (b) 21.5.
3.2.3. The Effect of SBME25-ZnO Nanofuel Blends on Nitrogen Oxide (NOx) Emissions at Different
Compression Ratios
NOx emissions for all tested fuels with variable loads and different compression ratios are
presented in Figure 10a,b. NOx emissions increased with increase in engine load. High NOx emissions
were generated due to high in-cylinder temperature resulting from complete combustion. Extra oxygen
molecules in biodiesel and ternary blends enhanced the combustion process and resulted in the high
in-cylinder pressure and temperature that leads to higher NOx emissions. Average NOx emissions at a
compression ratio of 21.5 287.73, 290.77, 365.73, 412.51, and 456.14 ppm were obtained for SBME25, diesel,
SBME25ZnO25, SBME25ZnO50, and SBME25ZnO75, respectively, between 20% and 100% engine loads.
All ternary blends showed a slight increase in NOx emissions compared to diesel and biodiesel–diesel
blends due to high in-cylinder temperature and pressure. NOx emissions were increased by 27.10%,
43.36% and 58.52% at 21.5 CR for SBME25ZnO25, SBME25ZnO50, and SBME25ZnO75, respectively,
compared to SBME25. Ternary fuel blends improved the combustion process due to high oxygen
content in fuel additives as well as in biodiesel, which leads to shorter ignition delay due to high
cetane number [57,59]. At a compression ratio of 18.5, NOx emissions were reduced compared to the
engine tested at a higher compression ratio of 21.5. The combustion temperature was increased due
to a higher compression ratio because of the high oxygen intake that leads to improved combustion
phenomena and results in higher NOx emissions.
Symmetry 2020, 12, 1042
18 of 31
Engine: VCR 4S with EGR , Injector: 4 holes, 0.25 mm dia.
Engine Speed:1500 rpm, IP: 240 bar, IT: 23.5°btdc CC: Hemisperical
SBME25
Compression ratio: 18.5:1
420
265.84
280
140
62.48
Nitrogen oxide emissions (ppm)
680
640
361.44
300.44
81.74
680
350.45
378.12
457.786
SBME25ZnO25
290.56
340
70.85
600
340.65
370.41
0
SBME25ZnO75
420
210
272.14
75
330.68
365.47
380
264.844
60.89
0
20%
40%
Load
(a)
60%
80%
100%
251.77
58.25
363.465
455.408
312.671
352.47
442.786
135.65
Diesel
450
0
321.717
SBME25ZnO25
570
150
466.11
142.54
300
158.49
371.786
SBME25ZnO50
570
190
332.109
155.65
380
446.87
430.68
340.85
50.224
6000
271.97
67.54
240.84
300.69
630
190
Diesel
300
445.741
162.65
450
150
468.474
170.84
510
170
387.84
SBME25ZnO50
480
Compression ratio: 21.5:1
125.62
840
180.55
320
SBME25
300
150
310.71
90.55
Engine: VCR 4S with EGR , Injector: 4 holes, 0.25 mm dia.
Engine Speed:1500 rpm, IP: 240 bar, IT: 23.5°btdc CC: Hemisperical
450
SBME25ZnO75
340
160
438.48
140.58
510
170
325.75
357.17
600
Nitrogen oxide emissions (ppm)
560
250.88
310.68
350.66
405.74
135.89
55.67
0
20%
40%
60%
80%
100%
Load
(b)
Figure 10. The variation of nitrogen oxide emissions at compression ratios: (a) 18.5 and (b) 21.5.
3.2.4. The Effect of SBME25-ZnO Nanofuel Blends on Carbon Dioxide (CO2 ) Emissions at Different
Compression Ratios
The carbon molecules from the fuel combustion combines with the oxygen to produce carbon
dioxide emissions. Figure 11a,b show an increasing trend in CO2 emissions with increasing loading
conditions. For the compression ratio of 18.5, all the nanofuel blends lowered the carbon dioxide
emissions due to complete fuel combustion and lower generation of carbon molecules post combustion
process compared to the SBME25 fuel blend. In addition, a similar trend was observed for a compression
ratio of 21.5, however, lower carbon dioxide emissions were observed at a higher compression ratio due
to rapid combustion and enhanced micro-explosion process. At compression ratio of 21.5, fuel blend
SBME25ZnO50 showed lower carbon dioxide emissions compared to all fuel blends at maximum load.
The CO2 for 50 ppm of ZnO in SNME25 was lower by 21.66% and 2.36%, respectively, compared to
SBME25 and diesel fuel. This was due to the large surface area of ZnO nanoparticles enabling complete
combustion of hydrocarbon molecules [59,60].
Symmetry 2020, 12, 1042
SBME25
5.4
3.6
1.8
Carbon dioxide emissions (% vol.)
4.124
4.471
1.211
SBME25ZnO50
3.471
3.712
4.124
2.704
2.6
0.854
0.0
6.0
1.35
SBME25ZnO25
4.5
2.487
3.0
3.312
4.051
4.387
4.714
1.38
0.0
3.22
2.8
0.0
4.2
0.0
4.2
3.56
4.227
40%
Load
(a)
60%
80%
100%
4.25
3.25
3.45
2.1
SBME25ZnO50
4.003
2.42
0.7
1.11
SBME25ZnO25
4.18
3.75
3.85
3.1
3.4
3.72
40%
60%
80%
4.6
2.28
1.2
Diesel
4.2
0.0
20%
3.85
0.96
2.8
1.4
0.92
0
3.35
2.8
1.98
3.61
SBME25ZnO75
2.8
1.4
5.11
2.85
3.6
1.8
4.82
1.75
0.0
3.914
Compression ratio: 21.5:1
4.52
4.15
5.4
1.4
Diesel
4.2
0.0
0.0
3.854
2.257
0.0
1.4
1.8
3.714
3.9
SBME25
5.4
3.6
SBME25ZnO75
3.2
1.5
5.384
3.174
4.8
1.3
Compression ratio: 18.5:1
5.025
4.641
4.451
1.984
0.0
1.6
Engine: VCR 4S with EGR , Injector: 4 holes, 0.25 mm dia.
Engine Speed:1500 rpm, IP: 240 bar, IT: 23.5°btdc CC: Hemisperical
Engine: VCR 4S with EGR , Injector: 4 holes, 0.25 mm dia.
Engine Speed:1500 rpm, IP: 240 bar, IT: 23.5°btdc CC: Hemisperical
Carbon dioxide emissions (% vol.)
7.2
19 of 31
4.1
1.75
0.82
0
20%
100%
Load
(b)
Figure 11. The variation of carbon dioxide emissions at compression ratios: (a) 18.5 and (b) 21.5.
3.2.5. The Effect of SBME25-ZnO Nanofuel Blends on Smoke Emissions at Different
Compression Ratios
The smoke emissions for all tested fuels with variable loads and different compression ratios
are illustrated in Figure 12. The smoke emissions are produced due to incomplete combustion of
hydrocarbon particles in the combustion chamber, a rich air-to-fuel mixture, and poor fuel vaporization.
The SBME25 fuel blend produces higher smoke emissions due to lower calorific value and heat
release rate. In contrast, the biodiesel blends with ZnO nanoparticles improved the micro-explosion
phenomenon and air-to-fuel mixing, leading to lower smoke emissions. The smoke emissions for
compression ratios of 18.5 and 21.5 for SBME25ZnO50 fell by 19.95% and 22.54%, respectively, compared
with SBME25 and diesel fuel. The large surface area of the ZnO nanoparticles enhances the combustion
process resulting in complete fuel combustion. An increase in the compression ratio leads to better
air-to-fuel mixing and increases the temperature during the compression stroke. In addition, an increase
in the compression ratio reduces the dilution of the fuel charge by residual gases [61].
Symmetry 2020, 12, 1042
Engine: VCR 4S with EGR , Injector: 4 holes, 0.25 mm dia.
Engine Speed:1500 rpm, IP: 240 bar, IT: 23.5°btdc CC: Hemisperical
SBME25
60
40
20
21.471
64
Compression ratio: 18.5:1
38.94
30.77
Smoke emissions (HSU)
16
SBME25ZnO75
16.67
60
32.971
24.81
15
SBME25ZnO25
18.78
64
27.478
0
43.178
39.471
15.86
0
22.48
20%
18.84
42.714
48.7
51.987
55.741
45.984
50.74
SBME25ZnO75
64
32
16
13.98
(a)
60%
80%
100%
38.9
29.178
45
30
10.556
18.452
13
24.65
41.96
24.71
44.92
49.35
39.667
48.786
45.24
51.644
32.64
15.9
Diesel
64
16
34.548
SBME25ZnO25
52
36.154
32
Load
21.64
58.412
SBME25ZnO50
60
15
55.741
44.6
35.678
48
29.197
40%
27.715
39
Diesel
32
18
52.64
26
48
16
47.48
13.741
35.971
Compression ratio: 21.5:1
54
27.84
21.891
51
17
SBME25
72
48
37.971
68
34
41.77
SBME25ZnO50
45
30
Engine: VCR 4S with EGR , Injector: 4 holes, 0.25 mm dia.
Engine Speed:1500 rpm, IP: 240 bar, IT: 23.5°btdc CC: Hemisperical
60.84
36
48
32
47.154
58.741
Smoke emissions (HSU)
80
20 of 31
12.36
0
19.79
20%
42.786
47.92
26.126
40%
60%
80%
100%
Load
(b)
Figure 12. The variation of smoke emissions at compression ratios: (a) 18.5 and (b) 21.5.
3.3. The Effect of Zinc Oxide Nano-Additives and Soybean Fuel Blend on Engine Combustion Characteristics
3.3.1. The Effect of SBME25-ZnO Nanofuel Blends on Ignition Delay at Different Compression Ratios
The ignition delay period is a critical phenomenon from the perspectives of preparation of the fuel
before being injected into the combustion chamber and selection of ideal injection timings. The ignition
delay period of a diesel engine is the time period between the start of injection and start of combustion.
The ignition delay period in the context of diesel engines is the period from the first charge of fuel
entering the combustion chamber to the period when the first flame propagates [62]. The ignition
delay period depends primarily on the ambient temperature. Due to fuel vaporization, the HRR curve
shows negative values prior to the start of combustion for diesel engines.
As it is evident from Figure 13a,b that the ignition delay period reduces with an increase in the
loading conditions due to a rise in the pressure and temperature for all the fuel blends. The rise in
pressure results in the mixture of molecules coming closely together, enhancing the chemical reactions
due to the active collisions of molecules, and resulting in a shorter ignition delay period. The higher
viscosity of soybean biodiesel results in poor atomization of fuel droplets, air-to-fuel mixing, and lower
flame cone angle, resulting in an increase in the delay period. The ZnO nanoparticles in SBME25 result
in a reduction in the ignition delay period due to enhancement of combustion rate and better premixed
combustion phase. At the higher compression ratio of 21.5, due to higher injection air-to-fuel mixture
in the combustion chamber, at the same injection timing and injection pressure, the ignition delay
period is lowered compared to 18.5 CR. At maximum load and compression ratio of 21.5, the values of
ignition delay period for SBME25ZnO concentrations of 50, 75, and 25 ppm, respectively, were 7.21,
8.125 and 8.786 ◦ CA, while at a compression ratio of 18.5 the values were 7.744, 8.125, and 9.174 ◦ CA.
At both compression ratios, the ignition delay period observed for SBMEZnO50 was lower than that
of all the fuel blends. At a compression ratio of 21.5 for the SBMEZnO50 fuel blend, reductions of
Symmetry 2020, 12, 1042
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25.02% and 5.38% were observed, and at a compression ratio 18.5, reductions of 23.47% and 2.18%
were observed, compared to SBME25 and neat diesel, respectively. This was due to the high catalytic
activity of zinc oxide nanoparticles, which enhance the combustion phenomena. However at higher
proportions of ZnO in the fuel blends, the ignition delay period slightly increases due to a negligible
increase in the viscosity.
11.15
11.52
10.12
10.21
9.174
7.744
8.22
7.917
8.214
8.88
8.57
9.15
9.51
9.25
9.68
10.14
9.94
10
10.842
11.541
11.05
11.514
11.25
Ignition Delay Period (°CA)
12.84
13.157
13.57
15
Fuel Blends
Diesel
SBME25ZnO25
SBME25ZnO50
SBME25ZnO75
SBME25
Engine: VCR 4S with EGR
Injector: 4 holes, 0.25 mm dia.
Engine Speed:1500 rpm
IP: 240 bar, IT: 23.5°btdc
CC: Hemisperical
Compression ratio: 18.5:1
5
0
20%
40%
60%
80%
100%
Load
(a)
10.87
11.421
8.125
7.21
7.62
7.77
8.21
8.786
8.84
9.014
9.64
9.845
9.62
10.021
10.842
9.58
10.04
10.68
11.12
10.82
11.142
11.654
12.51
13.24
12.971
Ignition Delay Period (°CA)
15
10
Fuel Blends
Diesel
SBME25ZnO25
SBME25ZnO50
SBME25ZnO75
SBME25
Engine: VCR 4S with EGR
Injector: 4 holes, 0.25 mm dia.
Engine Speed:1500 rpm
IP: 240 bar, IT: 23.5°btdc
CC: Hemisperical,
Compression ratio: 21.5:1
5
0
20%
40%
60%
80%
100%
Load
(b)
Figure 13. Variation of ignition delay period with load at compression ratios: (a) 18.5 and (b) 21.5.
Symmetry 2020, 12, 1042
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3.3.2. The Effect of SBME25-ZnO Nanofuel Blends on Mean Gas Temperature at Different
Compression Ratios
The mean value of the cylinder temperature of combusted and unburned gases present in the
combustion chamber during a cycle is known as mean gas temperature. Figure 14 illustrates the mean
gas temperature of fuel blends at varying crank angles at maximum load and compression ratio of 21.5.
The gases present in the cylinder are the blend of combusted and unburned air–fuel mixture. The mean
gas temperature ascertains the rate of combustion reaction of the fuel, and the desired value should be
nearer to the adiabatic temperature of the flame. The adiabatic flame temperature is achieved when
there is no loss in thermal energy and an adiabatic state is reached. At this point, maximum pressure is
reached, although the process of combustion is incomplete, and the combustion continues for another
few ◦ CA in the boundary of the combustion chamber. Peaks in the mean gas temperature for all the
fuel blends are observed from 370 to 385 ◦ CA, and the mean gas temperature for diesel is 1334.29 ◦ C at
380 ◦ CA. The nanofuel blend, SBME25ZnO50, exhibited a mean cylinder temperature of 1329.11 ◦ C
at 379 ◦ CA. Slightly lower values of mean gas temperature were observed for SBME25: the peak of
1301.87 ◦ C was seen at 380 ◦ CA due to viscosity and density.
@100 Load, 21.5 CR
Fuel Blends
Diesel
SBME25ZnO50
SBME25ZnO75
SBME25ZnO25
SBME25
Mean Gas Temperaure (°C)
1400
1200
1000
800
600
400
200
310
320
330
340
350
360
370
380
Crank Angle (°CA)
390
400
410
420
Figure 14. The mean gas temperature of fuel blends at varying crank angles at maximum load and
CR 21.5.
Symmetry 2020, 12, 1042
23 of 31
3.3.3. The Effect of SBME25-ZnO Nanofuel Blends on Heat Release Rate at Different
Compression Ratios
The first law of thermodynamics is used to evaluate the heat release rate (HRR), which is the
decrease in heat transfer and mass at cylinder pressure, and effective variations in volume at a closed
engine cycle. The contents of the cylinder are considered uniform with modeled properties in the
thermodynamic state and characterized by average values. The model is considered as having zero
dimension as no spatial variants are considered. In the current investigation, the experimental heat
release rate is determined using the first law-single zone model illustrated in Equation (5):
γh
dp
dQn
dQw
dV
1
=
×p
+
×V
+
dθ
γh − 1
dθ
γh − 1
dθ
dθ
(5)
where Tm is the mean in-cylinder temperature. γh is the specific heat, shown in Equation (6):
γh = 1.35 − 6 × 10−5 × Tm + 10−8 × Tm2
(6)
In Figure 15a,b, the heat release rate is averaged over 400 cycles for a smooth curve and to avoid
any irregularity in the combustion cycles that may occur in diesel engines fueled with low-ignition
biofuels. The HRR is negative during the ignition delay period, due to the cooling effect caused by
the vaporization of the fuel and loss of heat at the cylinder walls. Once the auto-ignition starts in
the combustion process, the heat release rate becomes positive and a rapid growth in the peak is
observed. The increase in the heat release rate for all the nanofuel blends is due to an enhanced cetane
number and lower ignition delay period, which assist in increasing the efficiency of the engine. At a
compression ratio of 21.5, all the fuel blends illustrated an enhancement in the heat release rate due to
higher pressure and combustion rate, leading to complete burning of the fuel charge and resulting in
higher energy output compared with the compression ratio of 18.5. The HRR for the SBME25 biodiesel
blend was lower than the other fuel blends due to the high molecular weight and low burning velocity.
The enhancement in heat release rate for the nanofuel blends is due to improved surface area, volume,
high ignition properties, and thermal conductivity. The maximum peaks observed for SBME25 ZnO
(25, 50, and 75 mg/L, respectively) at compression ratio 18.5 were 51.31, 58.97, and 62.26 J/◦ CA, while
the peaks for diesel and SBME25 were 66.72 and 49.12 J/◦ CA, respectively. The compression ratio of
21.5 illustrated a higher HRR due to higher burning velocity of fuel blends; the HRR values for 25, 50,
and 75 ppm of ZnO in SBME25 were 61.844, 70.44, and 65.854 J/◦ CA, respectively. The addition of zinc
oxide nanoparticles in the SBME25 biodiesel blend increases the HRR at both compression ratios due
to enhancement in oxygen content during combustion and atomization of fuel particles [33,56,60–65].
Table 7 illustrates the final results analysis of SBME25 and nanofuel blends.
Symmetry 2020, 12, 1042
24 of 31
@100% load, 18.5 CR
70
Fuel Blends
Diesel
SBME25ZnO50
SBME25ZnO25
SBME25ZnO75
SBME25
Heat Release Rate (°CA)
60
50
40
30
20
10
0
-10
-20
330
340
350
360
370
Crank Angle (°)
380
(a)
80
@100% load, 21.5 CR
Fuel Blends
Diesel
SBME25ZnO50
SBME25ZnO75
SBME25
SBME25ZnO25
Heat Release Rate (°CA)
70
60
50
40
30
20
10
0
-10
-20
320
330
340
350
360
Crank Angle (°)
370
380
390
(b)
Figure 15. The variation of heat release rate with ◦ CA at maximum load and compression ratios:
(a) 18.5 and (b) 21.5.
Symmetry 2020, 12, 1042
25 of 31
Table 7. The results analysis of SBME25 and nanofuel blends.
SBME25
Color
Code
Description
CR 18.5
CR 21.5
Decreases
Negative
Rise
Increases
Engine
Parameters
BSFC (kg/kWh)
BTE (%)
CO (% vol.)
HC (g/kWh)
CO2 (% vol.)
NOx (ppm)
Smoke (HSU)
ID (◦ CA)
HRR (◦ CA)
MGT (◦ K)
CR
18.5
0.295
20.36
0.38
0.2642
5.384
438.48
60.84
10.12
49.125
-
CR
21.5
0.27
23.23
0.28
0.21
5.11
430.68
58.412
9.64
58.97
1303.36
SBME25ZnO25
CR
18.5
0.264
23.63
0.35
0.21
4.714
445.741
55.741
9.174
51.312
-
(%)
10.508
16.56
7.895
20.514
12.44
1.62
8.334
9.347
4.426
-
CR
21.5
0.245
25.923
0.24
0.165
4.6
442.786
51.644
8.786
61.844
1311.97
SBME25ZnO50
(%)
9.25
11.592
14.28
21.45
9.98
2.27
11.58
9.72
4.841
0.66
CR
18.5
0.238
28.547
0.211
0.182
4.471
457.786
48.7
7.744
62.26
-
(%)
19.322
40.211
44.47
31.112
23.402
4.235
19.954
23.47
26.715
-
CR
21.5
0.198
28.62
0.201
0.142
4.003
455.408
45.24
7.21
70.44
1334.72
SBME25ZnO75
CR
18.5
26.66
0.245
23.2
26.277
28.21
0.295
32.234 0.1914
21.66
4.124
5.414 468.474
22.55
52.64
26.2
8.22
19.45
58.97
2.406
(%)
(%)
16.94
28.86
22.36
27.55
16.951
6.128
13.477
19.74
20.972
-
CR
21.5
0.234
27.65
0.229
0.16
4.25
466.11
49.35
8.125
65.854
1317.22
(%)
13.33
19.024
18.21
23.807
16.82
7.601
15.55
18.64
11.6
1.06
Symmetry 2020, 12, 1042
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4. Conclusions
The present study focuses on the effects of zinc oxide nanoparticles and soybean biodiesel blends at
different loads and varying CRs on a VCR, single cylinder engine with IT of 23◦ BTDC and at a constant
speed 1500 rpm. In the investigation, the engine was operated at two compression ratios of 18.5 and
21.5. Three nanofuel blends, SBME25ZnO25, SBME25ZnO50, and SBME25ZnO75, were prepared using
the ultrasonication process by varying the dosage levels of ZnO nanoparticles and sodium dodecyl
sulfate (SDS) surfactant. The following conclusions are drawn based on the obtained results:
1.
2.
3.
4.
The addition of ZnO nanoparticles to SBME25 enhanced the fuel properties, such as the calorific
value and cetane number, while the density and viscosity were comparable to SBME25.
The performance characteristics of the VCR engine were enhanced for the ternary fuel blends.
The dosage level of 50 ppm in SBME25 biodiesel and compression ratio of 21.5 increased the
BTE by 20.59% and reduced the BSFC by 20.37% compared with the SBME25 fuel blend due to
enhanced catalytic activity of zinc oxide nanoparticles.
The heat release rate and mean gas temperature of SBME25ZnO50 were comparable with diesel
fuel. The enhancement in the heat release rate is due to the micro-explosion phenomenon
occurring in the combustion chamber.
Emissions decreased with the addition of ZnO nanoparticles in the fuel blends. HC, CO,
smoke, and CO2 emissions were reduced by 30.83%, 41.08%, 22.54%, and 21.66%, respectively.
NOx emissions increased slightly due to excess oxygen in the combustion chamber.
The results and conclusion validate that ZnO nanoparticles in soybean biodiesel at a CR of
21.5 enhance performance and combustion, and reduce the emissions of a common rail direct
injection engine.
5. Recommendations for Future Research
Based on a recent comprehensive review of the effect of the addition of nanoparticles to fuel
blends on diesel engine characteristics by Soudagar et al. [1], the future research topics are suggested
as follows:
1.
2.
3.
4.
An extensive investigation of the surface reaction and engine wear on engine parts, such as the
combustion chamber, piston and piston rings, cylinder and cylinder linings, fuel injectors and
exhaust pipe, is required to confirm the reliability of nano-additives in a diesel engine.
The impact of metal-based nanoparticles used as fuel additives in diesel/biodiesel fuel on human
health should be examined before commercialization of the technology.
There is scope for further research on the effects of nanoparticles in exhaust emissions. This may
raise an issue related to environmental pollution caused by the addition of nanoparticles to diesel
and bio-diesel fuels.
Analysis of the cost and complexity in the preparation of nanoparticles, encompassing public
safety and economic feasibility, should be considered in future research. Furthermore, efforts
should be made in developing cost-effective and efficient nanoparticles.
Author Contributions: R.S.G.: Conceptualization, Methodology, Investigation, Writing-Original Draft; A.M.K.:
Supervision and Project administration and Resources; A.P.: Supervision, Project administration; M.R.S.: Project
administration, Review & Editing; M.E.M.S.: Design of the study, Conceptualization, Writing Methodology, and
Reviewing; M.M.A.: Interpretation of results, and Reviewing; H.M.A.: Formal analyses, Review & Editing; N.R.B.:
Review & Editing, Design and Analysis, Interpretation of results; M.G.: Review & Editing, Supervision; I.A.B.:
Conceptualization and Reviewing; W.A.: Review & Editing; K.S.: Review & Editing, Formal analysis. All authors
have read and agreed to the published version of the manuscript.
Funding: This work was funded by King Khalid University under the grant number R.G.P. 2/107/41.
Acknowledgments: The authors extend their appreciation to the Deanship of Scientific Research at King Khalid
University for funding this work through research groups program under grant number (R.G.P2/107/41).
Conflicts of Interest: The authors declare no conflict of interest.
Symmetry 2020, 12, 1042
27 of 31
Nomenclature
NPs
CRDI
CI
nm
g/kWh
CC
ATDC
FFA
ASTM
ID
CO2
NOX
BTE
SFC
IP
EGT
◦ CA
SBME
SBME25
ZnO25
SBME25
ZnO75
ZnO
SDS
IC
ppm
m
HCC
BTDC
CR
PP
HC
CO
PM
BSFC
Tw
IT
HRR
D100
SBME25
SBME25
ZnO50
Nanoparticles
Common rail direct injection
Compression ignition
Nanometer
Grams per kilowatt hour
Combustion chamber
After top dead center
Free fatty acid
American Society for Testing and Materials
Injection delay
Carbon dioxide
Oxides of nitrogen
Brake thermal efficiency
Specific fuel consumption
Injection pressure
Exhaust gas temperature
Crank angle (degrees)
Soybean methyl ester (Soybean biodiesel)
SBME25 and 25 ppm
ZnO NPs
SBME25 and 75 ppm
ZnO NPs
Zinc oxide
Sodium dodecyl sulfate
Internal combustion
Parts per million
Meter
Hemispherical combustion chamber
Before top dead center
Compression ratio
Peak pressure
Hydrocarbon
Carbon monoxide
Particulate matter
Brake specific fuel consumption
Wall temperature
Injection timing
Heat release rate
100% diesel
25% Soybean methyl ester blended with diesel
SBME25 and 50 ppm
ZnO NPs
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