This study investigates the effects of graphene nanoparticle (GNP) additives on the performance and emissions of biodiesel blends made from jatropha and karanja oils in a compression ignition engine. Results indicate that adding 50 mg/l GNP improved brake thermal efficiency by 4.77%–7.17% and reduced NOx emissions by 8%–14%, but higher GNP proportions negatively impacted combustion and performance. The research highlights the potential of biodiesel and GNP as eco-friendly alternatives to conventional diesel fuel.

1. Special Issue: ICCEMME-2021
International J of Engine Research
1–11
Ó IMechE 2022
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DOI: 10.1177/14680874221097574
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Investigation of combustion,
performance, and emissions of
biodiesel blends using graphene
nanoparticle as an additive
Michael G Bidir1
, Millerjothi Narayanan Kalamegam1
,
Muyiwa S Adaramola2
, Ftwi Y Hagos3
and Ramesh Chandra Singh4
Abstract
Effective utilization of biofuels is believed as one of the vital potential sustainable energy resources in current years.
Over the last two decades, it has lured the attention of many researchers in the automotive sector to find the solution
to problems of global warming, depletion of fossil and fluctuation of fuel prices, and growing reliance on imported energy
sources. This experimental investigation aims to assess the impact of graphene nanoparticles (GNP) on the performance
and emissions of a compression ignition engine fuel with Jatropha (J20), and Karanja (K20) blends contrasted with that of
neat diesel. This research work used a single-cylinder, four-stroke, water-cooled, naturally-aspirated direct injection die-
sel engine. It was coupled to an eddy current dynamometer with a rated output of 3.5 kW at a speed of 1500rpm.
Samples of GNP in mass fractions of 50 and 100 mg/L were prepared, and their physicochemical properties were evalu-
ated. Measurements were collected to examine the performance and exhaust releases. In addition, the combustion indi-
cators, including in-cylinder pressure, heat release rate, and mean gas temperature, have been studied and analyzed. The
experimental result has shown that by adding 50 mg/L GNPs in K20 and J20, the brake thermal efficiency improved by
about 4.77%–7.17%, respectively, compared to their base blends. The maximum smoke level was detected to be about
43% at full-load for both biodiesels at 50 mg/L GNP proportion. NOx concentration has also considerably decreased to
about 8%–14% for GNP added blends compared to J20 and K20 biodiesel operations. However, a higher proportion of
GNP added blends affects the combustion rate and substantial drop in the engine’s performance at maximum load.
Keywords
Graphene nanoparticle, biodiesel blends, diesel engine, performance, emissions, combustion
Date received: 22 September 2021; accepted: 11 April 2022
Introduction
Energy is a driving force for the global economy. The
energy and global economic patterns have been similar
over the years. On the other hand, the transportation
industry is a significant industry that heavily influences
the economy, accounting for 5% on average of the
gross domestic products (GDP).1
In the drive toward a
sustainable economy, countries diversify energy sources
in both transportation and stationary power plants.2
Compression ignition engines are the primary power
conversion technologies being utilized in public and
freight transport in the transportation sector and off-
grid power generation for agriculture, heavy-duty, off-
road applications. Controlling the developing energy
1
School of Mechanical and Industrial Engineering, EiT-M, Mekelle
University, Mekelle, Tigray, Ethiopia
2
Department of Environmental Science and Natural Resource
Management, Norwegian University of Life Sciences, Norway
3
Department of Mechanical and Industrial Engineering, College of
Engineering, Sultan Qaboos University, Al-khod, Sultanate of Oman
4
Department of Mechanical Engineering, Delhi Technological University,
Delhi, India
Corresponding authors:
Michael G Bidir, School of Mechanical and Industrial Engineering, EiT-M,
Mekelle University, P.O. Box 231, Mekelle, Tigray, Ethiopia.
Email: Michael.gebreyesus@mu.edu.et
Ftwi Y Hagos, Department of Mechanical and Industrial Engineering,
College of Engineering, Sultan Qaboos University, P.O. Box 50, Al-khod,
P.C. 123, Sultanate of Oman.
Email: f.hagos@squ.edu.om

2. utilization of diesel-fueled engines without adversely
influencing the economy and environment has become
a significant challenge. Biofuel is being considered as a
useful inexhaustible source as partial or complete sub-
stitution of diesel fuel. It is a commercially viable, prac-
tically feasible, ecologically friendly, and efficiently
accessible alternative fuel.3
The current energy scenario is vigorously dependent
on non-renewable energy sources, prompting a world-
wide concern of the environment. Diesel engine contri-
butes hugely to environmental pollution; nonetheless, it
remains the better preference for heavy-duty vehicles,
farm machinery and stationary applications.4
These
engines give two-third of the energy needed for
American agricultural machines, and a comparative
circumstance is predominant in other countries where a
large number of the farm motors are running on diesel
fuel.5
The thermal efficiency of heat engines is directly
proportional to their compression ratio. Compression
ignition engines operate at a higher compression ratio;
they are inherited with higher thermal efficiency.
On the other hand, their combustion strategy is oper-
ated under a heterogeneous mixture that enables them
to perform at an overall lean mixture. As a result, their
fuel economy is better than their spark-ignition counter-
parts. Other advantages of compression ignition engines
are producing more torque, the ability to withstand high
vibration and extreme conditions, fewer engine compo-
nents, thereby less maintenance requirement.
Despite these all advantages, diesel engines are under
great scrutiny due to their emissions of harmful gases
and particulate matter. The principal emissions from
compression ignition engines are oxides of nitrogen
(NOx) (predominantly NO and NO2), hydrocarbon
(HC), carbon monoxide (CO), and particulate matter
(PM). The discharges of HC and CO are relatively low
in diesel engines. The reduction is due to lean opera-
tion. According to the report by Res
xitoğlu et al.6
NOx
accounts for over 50% of the pollutants released from
diesel engines. There are two types of NOx formation
mechanisms: thermal NOx and fuel bound NOx. The
fuels for internal combustion engines, fuel bound NOx
is negligible. The nitrogen in the air inducted into the
combustion chamber has no role in the combustion
reaction when the adiabatic flame temperature is below
1540°C. As shown in Figure 1, a strong bond of nitro-
gen breaks at higher temperatures, and it reacts with
free oxygen, resulting in thermal NOx. Besides their
health effects on humans, NOx can react with other che-
micals in the air to form ozone and particulate matter.
The majority of particulate matter formed in diesel
engines is from the agglomeration of partially burnt
hydrocarbons. Compared to spark-ignition engines,
compression-ignition engines produce a higher concen-
tration of particulate matter. Exhaust gas from diesel is
black smoke due to the soot component of the particu-
late matter, which accounts for up to 50% of the total
composition. Besides the soot, soluble organic fractions
and inorganic fraction constituents make up the
remaining composition. The soluble organic fractions
are sourced from heavy hydrocarbons that are attached
to the soot. The formation mechanism of the particu-
late matter depends on the source. The particulate mat-
ter from the fuel is formed when the heavy component
of hydrocarbons cannot vaporize and properly mix
with air, a partial combustion result. Other PM sources
are partial burning of lubricating oil and other foreign
substances in the combustion chamber.
An expanding exhaust emission norm throughout the
planet has constrained energy experts to investigate new
strategies or expand current techniques to lessen dis-
charges. Engine producers and scientists are urged to look
for exhaust emission regulating procedures and elective
fuel sources to fulfill the fuel emergency and strenuous
exhaust emission guidelines. To this specific circumstance,
biodiesel has a prominent role in advancing elective fuel
utilized as neat or mixed with diesel fuel.8
Despite the numerous benefits of biodiesel like bio-
degradation, non-harmfulness, outstanding lubricity,
environmentally friendly, and renewable nature, it is
not widely utilized owing to its higher viscosity, poor
vaporization, and lower heating value that could
decrease ignition efficiency and prompts great size of
NOx discharge when utilized in compression ignition
diesel engines (CIDE).9
Numerous research studies
have demonstrated that incorporating metallic oxide
nanoparticles (NPs) into biodiesel diminishes NOx dis-
charge and progresses its burning attributes.
Adding nanoparticles into diesel fuel substantially
affecting the fuel qualities and combustion attributes.
It aids efficient mixing of fuel particles and offers adja-
cent interaction that enables the circulation of reactants
to the external and enhances the reaction.10,11
Adding
magnesia nanoparticles (NPs) to neat diesel fuel has
revealed a considerable decrease in kinematic viscosity,
flash point properties, and pollutant releases.12
Similarly, the effect of the addition of MnO2 and MgO
to diesel fuel properties was studied. Adding 8 and
16 mmol/L displayed an improvement in the fuel’s visc-
osity, flash point, and cloud point properties.13
An
experiment carried out using CeO2 nanoparticles in
biodiesel with a dose of 20 and 800 ppm caused a
reduction of HC and NOx releases by 40% and 30%,
respectively, and substantial enhancement in engine
efficiency.14
An investigation to examine the effect of
Al2O3 NPs incorporation to diesel-biodiesel-ethanol
mixtures on diesel engine emission and performance
attributes shows a decrease in HC and CO emissions
and a rise in NOx and smoke opacity releases. A
decreased peak pressure and heat release rate (HRR)
was reported from the combustion results.15
A test runs
in a diesel engine using CNT, and Al2O3 additives with
diesel-biodiesel blends demonstrated a rise in thermal
efficiency and decrease in exhaust discharges contrasted
to pure diesel-biodiesel mix.16
Correspondingly, the
impact of CeO2 and CNT mix on B5 and B20 fuels at
the proportion of 30, 60, and 90 ppm dosage were
examined on a diesel engine. The result showed an
2 International J of Engine Research 00(0)

3. increase in the power and torque by 7.81% and 4.91%,
respectively. Similarly, a reduction is reported in CO,
HC, NOx, and soot emission discharges by 38.8%,
18.9%, 71.4%, and 26.3%, respectively.17
The literature has anticipated that the biodiesel
derived from renewable sources oil can undoubtedly
substitute conventional diesel fuel when the fuel’s visc-
osity is moderated by mixing it with neat diesel fuel or
by heating the biodiesels.18–20
Jatropha and Karanja
oils are abundantly available, and their non-edible
nature makes them candidates as sources for biodiesel
production. Those bio-oils can be used as replacement
fuels for CIDE, extensively utilized in transportation,
agriculture, and reinforcement for power-producing
purposes. In conclusion, this experiment investigated
the practicality of utilizing jatropha and Karanja bio-
diesel and their mixes with graphene nanoparticles
(GNPs) as working fuels in diesel engines. The biodie-
sels were produced from jatropha and Karanja seeds by
transesterification procedure. The principal intention of
the experimental work was to examine the effects of 50
and 100 mg/L doses of GNPs as an additive with mixed
proportions of Jatropha 20% (J20) and Karanja 20%
(K20) biodiesel. An experiment was conducted to study
combustion parameters, including in-cylinder pressure,
net heat release rate (NHRR), and mean gas tempera-
ture (MGT). The performance characteristics were also
examined based on brake thermal efficiency (BTE),
brake-specific fuel consumption (BSFC), and exhaust
gas temperature (EGT). Emission levels including CO,
UHC, NOx, and smoke opacity have been measured
and analyzed. The findings were then contrasted against
the outcomes of conventional diesel fuel.
Material and methods
Experimental test fuel blends
Seven test fuel samples were designated for the experi-
ment in this research work. Table 1 represents the
details of the experimental test fuel blends used and
tested on the CIDE to investigate the performance,
combustion, and emissions attributes. The letters D, J,
and K represent diesel, jatropha biodiesel and karanja
biodiesel, respectively, and GNP for graphene nano-
particles. The GNP used in the current study was for-
mulated through synthetic oxidation manufactured by
the improved Hummers’ approach at Addnano
Technologies.
Three stages of the experimental study were carried
out in the current analysis. The virgin oils of jatropha
and Karanja were prepared. Their biodiesel was pro-
duced through the esterification process by 20% (by-
weight) methanol and utilizing NaOH with a mass frac-
tion of 0.5% (by weight) as catalysts via the transesteri-
fication procedure. The produced biodiesels were mixed
with neat diesel fuel to form the diesel-biodiesel blends
(J20 and K20), and the characteristics of the physico-
chemical potential of the blends were tested based on
ASTM D6751 standards. In the second step, a mass
fraction of 50 and 100 mg/L GNP (graphene nanoparti-
cle) was combined with the base blend fuels to form
nanoparticle incorporated blend fuel (J20GNP50,
J20GNP100, K20GNP50, and K20GNP100), and the
physicochemical properties were analyzed. Then, the
combustion, performance, and discharge attributes of
GNP added mixed fuels were explored and contrasted
with the neat diesel fuel to assess the enhancements in
the performance and exhaust discharge qualities.
Physicochemical analysis
The significant physicochemical properties of test fuel,
such as calorific value, cetane index, flash point, den-
sity, viscosity, and sulphur content, were characterized
based on ASTM D6751 standard for D100, J20,
J20GNP50, J20GNP100, K20, K20GNP50, and
K20GNP100. The measured physicochemical proper-
ties of test fuel samples and their contrast against the
standard limits are addressed in Table 2.
Experimental setup and procedure
The engine used for the experimental work was a sin-
gle-cylinder, four-stroke, water-cooled, vertically-
Figure 1. Temperature dependency in NOx formation
mechanisms in combustion processes.7
Table 1. Test fuel blends formulation.
S. No. Type of blend Description
1 D100 Diesel
2 J20 Jatropha biodiesel 20% + Diesel 80%
3 J20GNP50 Jatropha biodiesel 20% + Diesel
80% + GNP 50 mg/L
4 J20GNP100 Jatropha biodiesel 20% + Diesel
80% + GNP 100 mg/L
5 K20 Karanja biodiesel 20% + Diesel 80%
6 K20GNP50 Karanja biodiesel 20% + Diesel
80% + GNP 50 mg/L
7 K20GNP100 Karanja biodiesel 20% + Diesel
80% + GNP 100 mg/L
Bidir et al. 3

4. mounted, naturally-aspirated direct-injection diesel
engine (DIDE). The engine produces a rated power of
3.5 kW at a constant speed of 1500 rpm with a com-
pression ratio of 18:1. The schematic diagram of the
investigational test arrangement and engine descrip-
tions are given in Figure 2 and Table 3, respectively.
The engine is mounted with an eddy current dynam-
ometer for load application and engine speed control.
The load conditions of 0%, 25%, 50%, 75%, and full-
load ratings are considered variations in the test. The
functional boundaries were attuned by electronic means
with a controller board linked to the CIDE. It tends to
be run through a display unit connected to the control
board. The presentation unit was employed for showing
the estimations of the boundaries. The exhaust releases
data of HC, CO, CO2, and NOx were collected by
means of an AVL Di-gas analyzer, and the smoke opa-
city was gathered via AVL 437 smoke meter. To avoid
atmospheric condition interference, tests have been
scheduled at the same time of the days with weather
conditions uniform throughout. The engine has to sta-
bilize first and operate at a steady state before experi-
mental data to be collected. The engine has to run with
diesel fuel till the engine oil and coolant temperatures
stabilize, then after fuel switchover is taken place. Data
collection starts after the engine is maintained to run
for over 5 min. Three sets of data were collected for
each experimental setting, and an average value has
been used reporting.
Table 2. Physicochemical analysis of test fuel samples.
Test parameters Test
method
D100 J20 J20GNP50 J20 K20 K20 K20 Limits
GNP100 GNP50 GNP100
Calorific value (MJ/kg) ASTM D240 43.6 41.8 42.9 42.3 41.2 42.4 41.9 –
Cetane index ASTM D976 50.0 52.0 54.2 56.3 51.3 53.0 55.4 46 Min (D100)
51 Min (BD)
Flash point (°C) ASTM D93 58.0 67.0 64.0 62.0 65.0 63.0 61.0 55 Min (D100)
123 Min (BD)
Density at 15°C (g/mL) ASTM D1298 830 832 834 854 831 838 847 820–860 (D100)
800–900 (BD)
Sulphur content (% by mass) ASTM D129 48.00 0.051 0.059 0.040 0.01 0.01 0.01 50 Max (D100)
10 Max (BD)
Kinematic viscosity at 40°C (cSt) ASTM D445 2.51 2.92 3.52 3.81 3.03 3.51 3.92 2–4.5 (D100)
3.5–5 (BD)
Table 3. Test engine specifications.
Parameters Specification
Engine type Kirloskar, four-stroke, single-cylinder, water-cooled, naturally-aspirated, VCR diesel engine
Bore 3 stroke length (mm) 87.5 3 110
Connecting rod length (mm) 234
Displacement volume (cc) 661.45
Rated power 3.5 kW at 1500 rpm
Compression ratio 18:1
Pressure transducer Range 350 bar with low noise cable
Crank angle encoder 1°, 5500 rpm speed, with TDC pulse
Data acquisition system I USB-6210, 16-bit, 250 kS/s
Temperature sensor RTD type, PT100 thermocouple, K type
Dynamometer Eddy current type, maximum load of 7.5 kW
Figure 2. Experimental engine setup schematic diagram.
4 International J of Engine Research 00(0)

5. Results and discussions
Combustion characteristics
Heat release rate. Heat release rate (HRR) examination
is among the techniques used to fully understand the
engine combustion chamber’s combustion mechanism.
It is expressed in a Joule per degree of the crankshaft
rotation angle (J/°CA). The combustion characteristics
are discussed in this test regarding the start of combus-
tion (SOC). The SOC was attained from the HRR ver-
sus crank angle diagram in this experimental work.
Combustion duration (CD) shows the advance of com-
bustion in a cycle. It is defined as the time range
between the start of combustion (SOC) and the end of
combustion (EOC).15
SOC is considered the crank
angle in which abrupt HRR happens, whereas EOC is
the crank angle where 90 % combustion occurs.
The HRR of jatropha and Karanja biodiesel blends
are given in Figure 3 at full-load conditions. From the
figure, it can be noticed that the premixed combustion
(area beneath the first high-pitched peak in the HRR
illustration) of the J20GNP50 mixture was much higher
than the other blended fuels. The SOC for J20GNP50
was observed to be at 8° bTDC. The peak HRR of the
blend was recorded at 7°aTDC of the power stroke and
was 47.46 J/°CA. Similarly, the SOC for K20GNP50
was observed at 7° bTDC. The peak HHR of the blend
was recorded at 7° aTDC of the power stroke and was
44.87 J/°CA. It can be observed that the HRR of J20
and K20 at 6° aTDC was recorded as 43.34 and 42.22 J/
°CA, respectively. Based on the comparison, the HRR
of the two blends is lower than their respective GNP
added bends of J20GNP50 and K20GNP50. The HRR
of GNP50 added blends of biodiesel-diesel fuels is bet-
ter than the GNP100 added blends of biodiesel-diesel
fuels. The GNP100 added blends encountered the prob-
lem of poor atomization, consequently lower HRR at
full-load engine conditions.
Mean gas temperature. Figure 4 demonstrates the mean
gas temperature (MGT) variation of various test fuel
mixtures of biodiesel with and without GNP as
additives.
In general, the higher the heating value of the blend
is, the higher the MGT, which lessens the ignition delay
and ensures the maximum combustion of the test fuel
mix of the blend in the combustion cylinder. The MGT
in the cylinder’s combustion chamber for diesel fuel
was 889.4°C which was maximum compared with vari-
ous test fuel mixtures of biodiesels with and without
GNP as additives. For J20, the MGT was recorded as
797.6°C, lower than the MGT of diesel fuel but higher
than the MGT of K20, which was recorded as 796.4°C.
Similarly, J20GNP50 and K20GNP50 MGT blends
were recorded as 839.6 and 810.2°C, respectively, which
are much higher than the fuel blends without GNP.
The rise in mean gas temperature is mainly owing to
the warmer atmosphere created inside the combustion
chamber due to the higher energy content, cetane index,
and improved oxygen content, which primes to a rise in
the maximum cycle temperature. While the addition of
100 mg/L to the fuel blends resulted in lower MGT this
might be attributed to the higher density and kinematic
viscosity.
In-cylinder pressure. Figure 5 illustrates the measured in-
cylinder pressure data variation correlated to the crank
angle diagram for various blends of biodiesel with and
without adding graphene NPs at engine full-load
conditions.
It can be detected that in the condition of neat diesel
operation, the maximum cycle pressure found is about
50.4 bar, while for the J20 case, it is 43.3 bar. The K20
blends of biodiesel fuel operation display lower cycle
pressure related to diesel operation, which was recorded
as 42.0 bar. The maximum cylinder pressures for
Figure 3. The changes in heat release rate versus crank angle. Figure 4. Changes in mean gas temperature with crank angle.
Bidir et al. 5

6. J20GNP50 and K20GNP50 were detected as 45.14 and
43.38 bar, at 10.1 and 10.4°CA aTDC, respectively. The
increase in cylinder pressure might be owing to
improved energy content and cetane index, which
increases the temperature in the cylinder due to the
advance in the start of combustion and results in peak
pressure enhancement. From the figure, it can also be
noticed that for J20GNP100 and K20GNP100 blends,
the maximum cylinder pressure was 44.1 and 42.2 bar,
respectively, which was somewhat higher than the max-
imum cylinder pressure of J20 and K20 fuel blends,
respectively.
Engine performance characteristics
Brake thermal efficiency. The brake thermal efficiency
(BTE) specifies the chemical energy transformation
into helpful work at the engine output shaft. The diesel
fuel’s brake thermal efficiency is always more signifi-
cant than the biodiesel blends because of the higher
calorific value than the biodiesels.21
Figure 6 displays the BTE of the GNP mixtures of
jatropha and Karanja biodiesels at varying engine loads.
It can be seen that J20 and K20 revealed the lowest
BTE recording on average lower by 9.62% and 10.88%,
correspondingly as equated to neat diesel operation.
The decreased BTE for biodiesel blends can be associ-
ated with inferior energy content per unit size than neat
diesel. On the other hand, graphene nanoparticles added
blends of J20GNP50 and K20GNP50 displayed an
increase in BTE than J20 and K20 on average by 7.17%
and 6.88%, respectively. This is because the rise in
calorific value, cetane index, and fuel density indicates
better blends’ combustion efficiency. But, the BTE of
J20GNP100 and K20GNP100 decreases considerably
with an increase in the quantity of GPN (100 mg/L)
compared to J20GNP50 and K20GNP50. Because,
more quantity of GPN incorporation resulted in higher
viscosity and density of the blends subsequently irregu-
lar combustion and deprived atomization, hence pro-
ducing lower power.
Brake specific fuel consumption. Brake-specific fuel con-
sumption (BSFC) indicates the proportion of fuel utili-
zation rate to brake power production. In general, fuel
properties like higher heating value, viscosity and fuel
density, and fuel injection system influence BSFC.22
The density of biodiesel is much higher than neat diesel
fuel. So, the amount of biodiesel injection into the com-
bustion chamber when equated with diesel fuel for the
same power production is more.23
As illustrated in
Figure 7, it can be realized that the BSFC of all the
fuels used in the test declines when the engine load rises
throughout the load spectrum.24,25
Figure 6. The brake thermal efficiency versus engine load for
different test fuels.
Figure 5. Changes in in-cylinder pressure with crank angle.
Figure 7. The changes in brake specific fuel consumption
versus engine load for all tested blends.
6 International J of Engine Research 00(0)

7. It was observed that the BSFC of both K20 and J20
is, correspondingly, around 25% and 21% higher than
that of neat diesel fuel, primarily because of the higher
fuel consumption related to the volumetric efficiency of
a constant rate of fuel injection along with the higher
density and viscosity of biodiesel blends.26
However, NPs added blends of K20GNP50 and
J20GNP50 have lower BSFCs than their corresponding
K20 and J20 blends. They exhibited on average 15.00%
and 16.48% reduction of BSFC than K20 and J20,
respectively. Such decrement could be attributed mainly
to their relatively higher heating value and the higher
value of the cetane index. Further increase of the con-
centration of NPs to the blends (K20GNP100 and
J20GNP100) have exhibited the highest BSFC among
all the test fuel blends with NPs. This impact is mainly
because the higher kinematic viscosity of biodiesels
might source poorer atomization of the fuel, henceforth
poorer mixing with air, resulting in higher BSFC.27
Neat diesel fuel has the maximum heating value, the
lowest viscosity, and density from all the test fuels.
JB20 mixture has the uppermost viscosity and density
from all the test fuel samples.
Exhaust gas temperature. The difference of exhaust gas
temperature (EGT) under different load conditions for
various mixtures of biodiesel with and without adding
GPN is compared with diesel in Figure 8. It can be
detected that the EGT in the case of J20 and K20 were
recorded as 392 and 387°C, respectively, at full-load
conditions, which is much lesser than neat diesel fuel.
The maximum reduction in EGT is observed to be
about 6.60%–8.11% as compared to diesel operation.
Such reduction could be credited to the lesser heat-
ing value and larger viscosity of biodiesel which primes
to a reduction in the maximum cycle temperature in
the combustion chamber, which is reflected in the cylin-
der pressure versus crank angle diagram. NPs added
blends of J20GNP50 and K20GNP50, showed higher
exhaust gas temperature than J20 and K20 blends.
They showed on average 3.54% and 3.34% increment
of exhaust gas temperature than their respective base
blends. In the case of nanoparticles added blends of
J20GNP50 and K20GNP50, average exhaust gas tem-
perature values were measured as 408 and 400°C with
an increase of 3.85% and 3.25%, respectively, at full-
load. This change in the exhaust gas temperature is
attributed to the higher calorific value, and an increase
in the cetane number brings higher local ultimate tem-
perature, resulting in higher EGT. Further addition of
GNP100 in J20 and K20 has shown a significant reduc-
tion of EGT compared to J20GNP50 and K20GNP50,
respectively.
Engine emission characteristics
Carbon monoxide emission. In general, CO can be formed
either over a highly lean mixture or a vibrant mixture.
In the highly lean mixture, flame propagation is com-
plicated; fuel pyrolysis with incomplete oxidation out-
comes in CO formation. On the other hand, insufficient
air mixed with fuel primes to inadequate combustion in
an unreasonably rich mixture produces CO emissions.28
The variation of CO emissions with the load for the
base diesel fuel and the blends of jatropha and Karanja
biodiesels with and without GPN is shown in Figure 9.
In diesel fuel at full-load conditions, CO release was
recorded as 2.29%, whereas for blends of J20 and K20
oil biodiesel, the CO releases were recorded as 2.08%
and 2.16% at full-load conditions, respectively. The
average CO discharges for blends of J20 and K20 were
reduced by 9.17% and 5.85%, correspondingly com-
pared to neat diesel fuel.
The reduction in CO discharge can be ascribed to
the better oxygen content and improved cetane index of
biodiesels compared to neat diesel operations. The CO
emissions for J20GNP50 and K20GNP50 were
recorded as 1.92% and 2.18%, respectively, at the full-
load conditions. The addition of the GNP50 blends has
Figure 8. The changes in exhaust gas temperature for all
tested blends.
Figure 9. Carbon monoxide versus the engine load for all
tested blends.
Bidir et al. 7

8. further decreased the CO releases than J20 and K20
blends by about 16.16% and 4.80%, respectively. The
further reduction in CO emission is because incorporat-
ing the GPN in the biodiesel mixtures expands the heat-
ing value and density of the fuel and can thus reduce
the CO emissions. However, a slight increase in CO
level is noticed with the samples which higher NPs com-
pared to their respective J20GNP50 and K20GNP50.
This slight variation in CO level may be attributed to
the more GPN in the biodiesel blends increases the
number of carbon molecules in the fuel and reduces the
carbon to hydrogen ratio. Because of this, it resulted in
incomplete combustion and, which further increases the
CO emission in the engine exhaust.
Hydrocarbon emission. There are two core causes of HC
discharge in the diverse combustion atmosphere of
CIDE that is, locally over-lean and over-rich fuel-air
combinations. The HC emission from the engine for
blends of jatropha and karanja biodiesel fuels versus
engine load is shown in Figure 10.
HC discharges were recorded as 33 ppm for diesel
fuel at full-load condition, whereas for J20 and K20,
HC emissions were 31 and 29 ppm, respectively. The
UHC discharges of biodiesel blends with additives are
lesser as compared with the neat diesel operation. The
reduction is because the blend strength varies from rich
to lean and UHC releases reduce as the load on the
engine rises. Biodiesel comprises a better amount of
oxygen molecules, which aids in combustion and gives
excellent burning of the fuel blend in the combustion
cylinder.29
From the figure, there is a substantial drop
of HC releases noticed for blends of jatropha biodiesel
with GNP compared to J20 and K20 biodiesel fuels.
An average of 24.24% and 19.70% UHC discharge
decrease were detected using J20GNP50 and
K20GNP50 blends biodiesel, respectively. The reduc-
tion in the HC level in the engine exhaust maybe
because the GNP accelerates the reaction rates of the
mixture throughout the combustion chamber hence
reduce the carbon HC in the exhaust. A tendency like
that of CO emission can be observed the highest HC
level for graphene added blends of J20GNP100 and
K20GNP100 biodiesel as contrasted to all blend’s of
biodiesel fuel. Its higher density and viscosity may
result in poorly atomization and spray formation of the
fuel drops, which caused partial combustion and more
significant UHC release.30
Nitric oxides emission. Figure 11 displays the oxides of
nitrogen (NOx) level out of the exhaust emission of
blends of jatropha and Karanja biodiesel fuels and die-
sel operation against various loads. As discussed in the
introduction part, the production of oxides of nitrogen
in engine cylinder depends on properties of fuel blends,
mixture strength, are stoichiometry, and combustion
rate.
At full-load conditions, the concentration of NOx is
found to be maximum in the case of J2GNP50 and
K20GNP50 operation when compared to all other bio-
diesel blends, whereas, for blends of J20, K20, NOx
emissions were 328 and 319 ppm, respectively and on
average between 4.46% and 1.48% slightly more than
that of diesel fuel. In this investigation, J20GNP50 and
K20GNP50 produced 18.60% and 10.97% higher NOx
releases than neat diesel operations. The cause for
higher NOx may be due to the addition of 50 mg/L gra-
phene nanoparticles in the biodiesel/diesel blend
increasing the calorific value, cetane index, and mass
density of the fuel. Higher heating value, higher density
of inserted fuel units, and lower viscosity of the fuel aid
the combustion process and give the phenomenon of
determined combustion that has short ignition delay
because of high cetane number. Subsequently, for
J20GNP100 and K20GNP100, NOx emissions were
Figure 10. The variation of hydrocarbon emissions with engine
load for all tested blends.
Figure 11. Nitrogen oxides emission versus the engine load
for all tested blends.
8 International J of Engine Research 00(0)

9. recorded as 338 and 331 ppm at full-load conditions,
respectively.
Nevertheless, NOx release reductions considerably
with a rise in the proportion of GNP100 compared to
J20GNP50 and K20GNP50. Because, more quantity of
graphene nanoparticles added in the blends gives rise
to poor fuel injection from the nozzle due to heteroge-
neous mixture, which leads to sluggish in the combus-
tion.30
In addition, more quantity of graphene
nanoparticles added in the blend’s mixture is available
inside the cylinder as a heterogeneous charge. Hence, a
more liquid fraction of fuel pockets gives poor combus-
tion and can thus dramatically reduce NOx emissions.
This is revealed in low exhaust temperature, as shown
in Figure 8. GNP expansion to J20 and K20 fuel mixes
improves the ignition and causes a rise in the cylinder
pressure and temperature, increasing the NOx dis-
charge.31
It is in agreement with various investigations
that portray biodiesel can deliver higher NOx for its
higher oxygen content.32,33
This higher oxygen content
leads to complete burning, higher temperature, and
intensifications in NOx release.34
Smoke opacity. The creation of smoke is principally a
process of altering particles of hydrocarbon fuels into
elements of soot. It is believed that the ‘‘heavy ends’’ of
diesel fuel may pyrolyze to yield the type of smoke that
is observed from the diesel engine. This is believed to be
the path of formation of polycyclic aromatic hydrocar-
bons (benzo-pyrence) found in soot. Figure 12 repre-
sents the smoke emission behavior of the engine run
with various biodiesel fuel blends compared to the con-
ventional diesel operation. It can be seen that the engine
run with and without GPN added biodiesel/diesel
blends exhibits a rise in smoke emission at all loads.
Blends of J20 and K20 offered on average 19.02% and
24.20% reduced smoke opacity than neat diesel fuel. It
could be credited to the advanced SOC of J20 and K20
for higher cetane numbers. Henceforth, the combustion
happening earlier allows an extra period for the oxida-
tion of the soot.35
For blends of J20GNP50 and k20GNP50, smoke
levels were recorded as 4.19 and 4.28 mg/m3,
respec-
tively, at full-load conditions, respectively. The signifi-
cant drop in smoke levels were found to be about
33.42%–38.32% for both graphene nanoparticles
added blended fuels compared to neat diesel operations.
The drop in smoke levels might be because the addition
of NPs increases the carbon to hydrogen ratio, which
helps in the combustion process and enhances the com-
bustion ultimately, reducing the generation of smoke
levels in the engine exhaust. However, an increase in the
quantity of GNP100 in the fuel combinations of J20
and K20 was not favorable for reducing the smoke opa-
city, as illustrated in Figure 12.
Conclusion
The subsequent conclusions are drawn based on the
carried out experimental study.
The blended test fuels of jatropha and Karanja bio-
diesel have higher relative density and lesser calorific
value compared to neat diesel. These blended biodiesel
fuels’ cetane index, flash point, density, and kinematic
viscosity are much higher than neat diesel. The addition
of GNP (50 mg/L) to the J20 and K20 blends displayed
increased calorific value, cetane index, density, and
viscosity.
The peak in-cylinder pressure is highest with diesel,
but the position of peak pressure rises advances with
the addition of 50 mg/L of NPs in J20GPN50 and
K20GNP50 and is accompanied by a better amount of
heat release compared to J20 and K20 blended fuels.
Equivalently, the MGT is recorded higher for D100.
During engine trials, J20 gave better BTE and BSFC
than K20, but both blended biodiesel fuels performed
poorer than conventional diesel. GNP incorporated test
fuels showed increased BTE and reduced BSFC. The
maximum and minimum efficiency recorded from all
blended fuels was from using J20GNP50 and K20,
respectively. The BSFC of J20GNP50 showed a reduc-
tion of 17.39% compared to J20. This decrease in
BSFC is due to the catalytic effect of the GNP addition.
The CO, UHC, and smoke opacity emissions are
found highest with diesel. About 9.17% reduction in
CO, 11.52% reduction in UHC, and 24.21% reduction
in smoke opacity were observed with blended biodiesel
fuels. For the GNP added fuels, a reduction of about
16.16% in CO, 24.24% reduction in UHC, and 38.33%
reduction in smoke opacity was observed. While the
NOx emission was found to increase by about 4.46%
Figure 12. The smoke opacity versus engine load for all tested
blends.
Bidir et al. 9

10. and 18.60% for the biodiesel blended fuel and GNP
added fuel, respectively, compared to D100.
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with
respect to the research, authorship, and/or publication of this
article.
Funding
The author(s) disclosed receipt of the following financial sup-
port for the research, authorship, and/or publication of this
article: The author would like to recognize the MU-HU-
NMBU phase IV NoRAD project for the financial support
through a Ph.D. scholarship grant (EiT-M/Ph.D./007/09),
RTF-DCS fellowship grant (DCS/2019/000287), and DTU
for the technical support during the work presented in this
study.
ORCID iD
Ftwi Y Hagos https://orcid.org/0000-0002-8774-8577
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