Fuel Processing Technology 223 (2021) 106999

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Fuel Processing Technology

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Research article

The influence of hydrogen addition on the combustion characteristics of a

common-rail CI engine fueled with waste cooking oil biodiesel/
diesel blends
Mehmet Akcay a, *, Ilker Turgut Yilmaz b, Ahmet Feyzioglu b
a
Mus Alparslan University, Faculty of Engineering and Architecture, Department of Mechanical Engineering, Mus, Turkey
b
Marmara University, Faculty of Technology, Department of Mechanical Engineering, Istanbul, Turkey

A R T I C L E I N F O A B S T R A C T

Keywords: In this study, the effect of hydrogen assisted intake air on combustion characteristics of a diesel fuel-waste
Common rail CI engine cooking oil biodiesel (WCOB) blend fueled CI engine has been extensively studied. While the diesel and B25
Waste cooking oil biodiesel (75% diesel fuel+25% WCOB) fuels used as the main fuel were sprayed directly into the cylinder, the hydrogen,
Hydrogen enrichment
the secondary fuel was mixed with the intake air at 10, 20, 30 and 40 lpm flow rates and taken into the cylinder.
Combustion characteristics
The maximum in-cylinder pressure (CP) values decreased with B25 fuel compared to diesel fuel. But
Heat release
B25‑hydrogen dual-fuel mode operation exhibited higher maxium CP and RoPR value according to diesel fuel. It
was seen that hydrogen has a more significant effect on premixed pilot fuel combustion phase compared to the
diffusion combustion phase. It was observed that the combustion duration (CD) of neat B25 fuel lower than that
of diesel fuel, generally. In case of B25‑hydrogen dual-fuel mode operation, CD increased depending on
increasing hydrogen addition rate. It was seen that hydrogen enrichment has no adverse effect on ringing in­
tensity (RI).

1. Introduction vegetable oils [8].

Biodiesel wich can be obtained from vegetable, animal and waste
Nowadays, fossil fuels are used as the main energy source in internal oils, has many important advantages compared to fossil based fuels,
combustion engines (ICE). These fuels cause pollutant emissions such as such as non-explosive, low sulfur content, low aromatic content, envi­
carbon monoxide, nitric oxide, hydrocarbon and smoke emission as well ronmentally friendly and renewable [9,10]. However, some properties
as greenhouse gas (GHG) emissions that cause global warming such as of biodiesel such as low calorific value, low cetane number, high vis­
CO2 [1]. The greenhouse gases increase the temperature of our planet cosity and density cause some negativity in CI engine performance and
and cause climate change [2]. In addition to the fossil fuel resources emissions [11]. In generally, it is stated that lower engine power and
cause climate change, negativities such as increasing costs have forced higher NOx emissions are obtained with the use of biodiesel. [12]. The
researchers to seek for alternative fuels. It has been seen that, the studies studies are carried out on the use of biodiesel in dual-fuel mode with a
of alternative fuels for compression ignition (CI) engines were concen­ second fuel in order to increase its combustion performance [13].
trated on biodiesel [3], CNG [4], hydrogen [5], alcohols [6], LPG [7], Hydrogen is a long-term renewable, recyclable and non-polluting

Abbreviations: B25, 25% waste cooking oil biodiesel and 75% diesel; B100, 100% waste cooking oil biodiesel and 0% diesel; CD, combustion duration, ◦ CA; CI,
compression ignition; CP, In-cylinder pressure, bar; CPmax, maximum in-cylinder pressure, bar; CHRmax, maximum cumulative heat release, J; COHR, center of heat
release, ◦ CA; DI, direct ignition; Diesel, 0% waste cooking oil biodiesel and 100% diesel; EOC, end of combustion, ◦ CA; FLP, Fuel line pressure, bar; HRRmax(pilot),
maximum heat release rate (in pilot injection stage), J/◦ CA; HRRmax(main), maximum heat release rate (in main enjection stage), J/◦ CA; H10, 10 lpm hydrogen flow
rate, L/min; H20, 20 lpm hydrogen flow rate, L/min; H30, 30 lpm hydrogen flow rate, L/min; H40, 40 lpm hydrogen flow rate, L/min; HES, hydrogen energy share,
%; ID, ignition delay, ◦ CA; lpm, liter per minute, L/min; RI, Ringing intensity, MW/m2; RoPRmax (pilot), maximum rate of pressure rise (in pilot injection stage), MPa/
◦
CA; RoPRmax (main), maximum rate of pressure rise (in main injection stage), MPa/◦ CA; SOC, start of combustion, ◦ CA; TDC, top dead center; WCO, waste cooking oil;
WCOB, waste cooking oil biodiesel.
* Corresponding author.
E-mail address: m.akcay@alparslan.edu.tr (M. Akcay).

https://doi.org/10.1016/j.fuproc.2021.106999
Received 27 May 2021; Received in revised form 18 August 2021; Accepted 19 August 2021
Available online 28 August 2021
0378-3820/© 2021 Elsevier B.V. All rights reserved.
M. Akcay et al. Fuel Processing Technology 223 (2021) 106999

fuel [14]. As a result of the combustion of hydrogen with oxygen, water The effect of hydrogen-enriched natural gas on performance, com­
is formed. It contributes positively to air quality since toxic products bustion and emissions in a single-cylinder, 4-stroke, air-cooled, direct
such as hydrocarbons and carbon monoxide are not formed [12,15,16]. injection CI engine fuelled with eucalyptus biodiesel was investigated by
In addition, hydrogen has many advantages compared to fosil fuels such Tarabet et al. [36]. They stated that hydrogen-enriched natural gas was
as high flame propagation rate, high diffusion rate, short flame extinc­ an effective method to reduce CO, unburned HC and smoke emissions by
tion distance, low ignition energy and wide flammability limit [16–20]. improving the combustion process at high loads. There was an increase
The addition of low amounts of hydrogen to CI engines provides a in HRR and maximum CP with hydrogen enrichment compared to pure
more homogeneous air/fuel mixture thanks to its high diffusion rate NG. Korakianitis et al. [37], studied the use of hydrogen as dual-fuel in a
[21] and provides faster completion of the combustion thanks to its high single-cylinder, 4-stroke, air-cooled CI engine fueled with rapeseed
flame speed [22]. Also, due to the higher flame speed, less heat transfer methyl ester (RME) and water-rapeseed methyl ester (RME) emulsions.
occurs to the environment. The flame quenching zone of hydrogen is 3 Hydrogen operation has generally been found to provide the best ther­
times less than that of normal hydrocarbon fuels. Thus, the flame gets mal efficiency compared to normal CI engine operation. Higher
closer to the wall and provides complete combustion of the fuel [23]. maximum CP values were obtained with hydrogen dual-fuel operation
Due to the high autoignition temperature of hydrogen (858 K) it cannot compared to normal CI engine operation. Santhosh and Kumar [38],
be used directly in the CI engine without a spark plug or glow plug. This investigated the effects of hydrogen and 1-Hexanol on the combustion,
makes hydrogen unsuitable as the sole fuel for CI engines. [24]. On the performance and emissions of 2-cylinder, 4-stroke, Common Rail Direct
other hand, hydrogen can be used in dual-fuel mode with diesel fuel in a Injection (CRDI) CI engine. Hydrogen enrichment at 80% engine load
CI engine [14]. exhibited 6.77% higher cylinder pressure and 1.50% lower heat release
There are many studies in the literature on the use of hydrogen in rate compared to pure diesel. Again, with the hydrogen enrichment
dual-fuel mode in CI engines [25–29]. However, there are limited compared to pure diesel thermal efficiency increased while NOx and HC
studies on the use of hydrogen with biodiesel + diesel fuel blends in emissions decreased.
dual-fuel mode. Some of these studies are briefly summarized below: Kanth et al. [39], examined the effect of hydrogen enrichment (10
Chiriac and Apostolescu [30] were examined the effects of hydrogen and 13 lpm), performance, combustion and emission characteristics of a
enrichment on the emissions of a 50 kW, four-cylinder, four-stroke, single cylinder, 4-strokes, water cooled CI engine fuelled with honge
direct injection CI engine fuelled with B20 (%20 biodiesel+%80 diesel) biodiesel blend (diesel 80% and biodiesel 20% by vol.) and diesel fuel.
fuel. The addition of hydrogen into the intake air of the CI engine fuelled Compared to diesel fuel, BTE increased (2.2%) and fuel consumption
with B20 led to increase in NOx emissions and decrease in smoke and CO decreased (6%) with hydrogen enrichment made to the honge biodiesel
emissions. Aldhaidhawi et al. [31] investigated the effect of different blend. In addition, lower CO and HC emissions and higher NO emissions
amounts of energy content (between 0% and 5%) of B20 (80% diesel and were achieved with the hydrogen enriched honge biodiesel blend.
20% rapeseed methyl ester blends, by vol.) fuel on engine performance, Higher heat release and maximum CP values were achieved by hydrogen
emissions and combustion properties. In the study, a 50 kW four- enrichment, while a decrease in combustion duration occurred. Kanth
cylinder, four-stroke, direct injection CI engine was used. It was and Debbarma [40] investigated the effect of hydrogen enrichment (7
observed that hydrogen enrichment did not have a significant effect on lpm) on the performance and emissions of a single-cylinder, 4-stroke,
ignition delay at all tests. On the other hand, the NOx emissions were naturally aspired, DI diesel engine fuelled with diesel and two
increased while the CO emissions, smoke and total unburned hydro­ different biodiesel (rice bran biodiesel and Karanja biodiesel). BTE
carbon (THC) emissions decreased with hydrogen enrichment. increased while SFC decreased with the hydrogen enrichment. While CO
Rocha et al. [15] investigated the effect of the hydrogen addition into and HC emissions decreased in the presence of hydrogen, NOx emissions
the inlet air of CI engine fuelled with B7 (7% biodiesel+83% diesel) fuel increased. Hydrogen enrichment resulted in higher maximum cylinder
on the engine performance. In this study, a diesel generator with a single pressure and rate of heat release. It has been stated that hydrogen re­
cylinder, four-stroke, air-cooled and direct injection diesel engine was duces the CD. Jeyaseelan et al. [41] investigated the effects of hydrogen
used. Hydrogen was sent to the intake manifold up to 10% of the total addition to biodiesel-diesel (B20) and hydrogenated biodiesel-diesel
fuel mass. With the addition of hydrogen, an increase occurred in the (HB20) fuels on engine performance, combustion and emission charac­
maximum pressure and heat release rate (HRR). Tuccar and Uludamar teristics. The hydrogen addition was kept constant as the energy share of
[32] investigated the effect of hydrogen enriched pomegranate seed oil 10%. In the experiments a CRDI engine with four-stroke, twin cylinder,
biodiesel (POB) on engine performance and emissions. Hydrogen was was used. In the case of working with both fuels (B20 and HB20), peak
injected with 5 lpm flow rate into the intake air. Four-stroke, four-cyl­ CP and HRR values increased with hydrogen enrichment. It was
inder Mitsubishi Canter 4D31 CI engine was used in the study. It was observed that the crank angle, which obtained the peak CP and HRR
found that hydrogen addition led an improvement in both engine per­ values with the addition of hydrogen, approached the TDC.
formance and exhaust emissions. Uludamar [33] investigated the effect It was seen in the literature that; limited research has been done on
of hydrogen and hydroxy gas addition on the engine performance and the use of hydrogen as a secondary fuel in a CI engine fuelled with diesel-
emissions in a 4-stroke 4-cylinder CI engine fuelled with a mixture of biodiesel fuel blend. Also, no similar study was found related with the
microalgae biodiesel and low sulfur diesel fuel. With the hydrogen and effect of hydrogen enrichment on the combustion characteristics of a
hydroxy gas addition engine torque, power and CO2 emission improved. commercial CI engine, fuelled with B25 (25% waste cooking oil bio­
Serin and Yıldızhan [34] investigated the effect of hydrogen diesel +75% diesel, by volume) fuel.
enrichment on engine performance and emissions of a 4-cylinder CI B25 is an alternative blend that represents a good balance of cost,
engine fuelled with a mixture of diesel fuel and tea seed oil biodiesel emissions (especially NOx, CO2, and smoke), cold-weather performance,
blends (B10 and B20). Hydrogen enrichment reduced the CO and CO2 materials compatibility. Generally, B25 can be used in diesel engines
emissions for all test fuels. On the other hand, an increase in NOx without modifications. B25 has a similar lower heating value with diesel
emissions occurred. Khandal et al. [35] researched the effect of the fuel. It can be said that B25 fueled diesel engine's fuel consumption,
operating in dual-fuel mode with hydrogen, fuel injection timing (IT) power, and torque parameters are nearly the same compared to diesel
and exhaust gas recirculation (EGR) on the performance, emission and fuel fueled diesel engine. 4 l B25 fuel consists of 1 l B100 and 3 l diesel
combustion characteristics of a single cylinder, four stroke, water fuel. B25 lowers the dependency on diesel fuel. Increasing biodiesel rate
cooled, direct injection CI engine fuelled with honge biodiesel (BHO) decreases the diesel fuel rate. On the other hand, B100 contains less
and cottonseed biodiesel (BCO) fuels. With the application of dual-fuel energy on a volumetric/mass basis than diesel fuel. Therefore, the
mode with hydrogen, while maximum HRR and maximum in-cylinder higher the percentage of biodiesel the lower the energy content. High-
pressure (CPmax) increased, BTE decreased. level biodiesel blends can plug up the filter in cold temperatures.

2
M. Akcay et al. Fuel Processing Technology 223 (2021) 106999

B100 may increase nitrogen oxide emissions. Table 1

Test engine is a commercial engine in accordance with Euro 3 stan­ Specifications of the test engine.
dards. It has a turbocharger and Common-Rail fuel system with double- Type In-line, turbocharged
injection. Therefore, in this study, the effect of hydrogen addition on
Cylinder volume 1461 cm3
the combustion characteristics of a CI engine fuelled with B25 fuel, which Bore 76 mm
unmodified, four-stroke, four-cylinder, water-cooled, turbocharged, Stroke 80.5 mm
Common-Rail fuel injection system, was investigated experimentally. Number of cylinders 4
Diesel + WCOB blend was used as ignition source and main fuel. In the Number of valves 8
Compression ratio 18.25:1
study, the experiments were carried out at different engine loads (40 Nm, Maximum power (4000 rpm) 48 kW (65 hP)
60 Nm and 80 Nm) and at a constant engine speed (1750 rpm). Hydrogen Maximum torque (1750 rpm) 160 Nm
enrichments were 10, 20, 30 and 40 lpm flow rates, by volumetrically and Fuel injection Common-Rail
were named as H10, H20, H30 and H40, respectively. Max fuel injection pressure 1400 bar

2. Materials and methods

the sample number [44].

2.1. Experimental setup and procedure Pn = {(Pn− 1 ) + 2(Pn ) + (Pn+1 ) }/4 (1)
The pressure values of cylinder and fuel line were obtained by
In this study, four cylinder, water cooled, turbocharged, common-
averaging of 200 consecutive pressure data. Again, using the average
rail injection and double injection a CI diesel engine without any mod­
value of 200 consecutive CP, HRR analysis was performed. HRR analysis
ifications was used. No changes were made on the fuel injection timings,
was carried out with a single zone combustion model based on the first
fuel injection pressures and other physical structures of the test engine.
law of thermodynamics. The HRR for each crank angle is determined by
The engine's exhaust gas recirculation system (EGR) was disabled to
Eq. (2) [45].
prevent the impact on test results. A water-cooled eddy-current dyna­
mometer (Cussons, P8602) with a capacity of 150 kW and 8000 rpm was γ 1
dQ = (PdV) + (VdP) (2)
used to control engine speed and measure its load. The detailed char­ γ− 1 γ− 1
acteristics of the test engine are shown in Table 1.
Hydrogen was sent to the intake manifold and taken into the cylinder where, dQ is HRR (J/oCA), γ is the ratio of specific heats (Cp/Cv), P is the
together with the intake air. Because, in the study by Masood et al. [42] CP (Pa), V is the variable cylinder volume (m3).
it was stated that hydrogen induction into the inlet manifold increased All tests within the scope of the study were carried out at a constant
brake thermal efficiency by about 19% compared to hydrogen injection motor speed of 1750 rpm and at different motor loads of 40, 60 and 80
directly into the cylinder. A mixing chamber was used to induct Nm. In the B25 fuel tests, hydrogen was added into the engine's inlet air
hydrogen in to the intake manifold. This mixing chamber placed be­ at 10, 20, 30 and 40 lpm flow rates. The energy shares of hydrogen (HES)
tween turbocharger and intake manifold. The distance between mixing are defined as the ratio of the energy of hydrogen to the total energy of
chamber and intake manifold was enough for forming a homogeneous the fuels sent to the cylinder, and calculated by the Eq. (3).
hydrogen-air mixture. ṁhydrogen LHV hydrogen
The CI engine used in the experimental study was equipped with an HES = (3)
ṁhydrogen LHV hydrogen + ṁfuel LHV fuel
CP sensor, fuel-line pressure sensor, temperature sensor and crank
encoder. The intake air, engine oil, fuel, exhaust, inlet and outlet tem­ where, LHV and ṁ are the lower heating values (MJ/kg) and the mass
peratures of cooling water of the test engine were measured using K type fuel (kg/h), respectively. The energy share ratio of hydrogen to the total
thermocouples. CP value was measured by an Oprant OPTD 32288 GPA energy output was given in Fig. 2.
model air-cooled pressure sensor which was placed in the glow plug The measurement of experimental data contains some errors.
socket of the engine's first cylinder. The fuel injection pressure value was Therefore, it is important to make an analysis of the experimental un­
measured with the Piezo resistive Kistler C6533 A11 sensor placed on certainty to maintain the accuracy of the experiment. Total uncertainties
the fuel line of the engine's first cylinder. A charge amplifier (Kistler are calculated based on the uncertainty of each measurement [46]. The
4067C2000S) was used to amplify the signals from the fuel line pressure accuracy and total uncertainties of the measuring devices performed in
sensor. The crankshaft position was determined by the Kubler-brand the experimental study were calculated by the Eq. (4) according to the
incremental encoder with a resolution of 360 pulses per revolution. Kline and McClintock method [21,47] and presented in Table 2.
The schematic view of the experimental setup is given in the Fig. 1. The [( )2 ( )2 ( )2 ]1/2
experimental setup used in the study was presented in detail in the ∂R ∂R ∂R
WR = w + w +…+ w (4)
reference [43]. ∂x1 1 ∂x2 2 ∂xn n
Before starting the data collection, the test engine cooling water
temperature was allowed to reach 80 ◦ C and was stabilized engine where, WR is the total uncertainity value, R is te given fonction, x1, x2,
running. CP and fuel line pressure data were obtained for each crank­ …,xn is the independent variables, w1, w2, …wn is the uncertainties of
shaft angle and recorded using a data acquisition card (National In­ the independent variables.
struments 6343). Eq. (1) is used to correct for the noise occurring in the In addition, the overall experimental uncertainty was determined
instantaneous pressure data. Pn indicates the pressure data, n indicates using the following Eq. (5);

[
Overall experimental uncertainty = Square root of (uncertainty of fuel consumption)2 + (uncertainty of power)2 + (uncertainty of RoPR)2
+ (uncertainty of CD)2 + (uncertainty of HRR)2 + (uncertainty of RI)2 + (uncertainty of H2 flow)2
2 2 2
(5)
+ (uncertainty of air flow) + (uncertainty of CP sensor) + (uncertainty of FLP sensor)
]
+ (uncertainty of speed)2 + (uncertainty of crank encoder)2

3
M. Akcay et al. Fuel Processing Technology 223 (2021) 106999

Fig. 1. Schematic view of the experimental setup.

B25 Hydrogen
6.63% 5.07% 4.03%
100%
13.27% 10.00% 7.93%
15.23% 11.97%
19.74% 16.15%
Energy Share (%)

20.18%
80% 25.38%
100% 100% 100%
93.37% 94.93% 95.97%
60%
86.73% 90.00% 92.07%
80.26% 84.77% 88.03%
40%
74.62% 79.82% 83.85%

20%

0%

40 Nm 60 Nm 80 Nm

Test Fuels and Engine Loads

Fig. 2. The energy shares of the hydrogen in the B25 fuel.

found as ±2.29%. When similar studies in the literature are examined, it

seen that the amount of total uncertainty calculated as ±1.69% by
[ Venkatesan et al. [48], as ±3.65% by Sidharth and Kumar [49] and as
= Square root of (0.44)2 +(0.45)2 + (0.51)2 +(0.74)2 +(0.74)2 +(1.65)2 ±3.01% by Hossain et al. [50]. In their studies, it has been observed that
+(0.5)2 +(0.5)2 + (0.7)2 +(0.5)2 +(0.06)2 uncertainties regarding emission measurement are high and this in­
]
+(0.05)2 = ±2.39% creases the total uncertainty.

As a result of the analysis, overall experimental uncertainty was

4
M. Akcay et al. Fuel Processing Technology 223 (2021) 106999

Table 2 enrichment on combustion characteristics (indicator diagram, CPs,

Measurement devices and accuracies. HRR, rate of pressure rise (RoPR), cumulative heat release (CHR), center
Measured parameter Measurement device Accuracy of heat release (COHR), CD and ringing intensity (RI) of the turbo­
charged and Common-Rail fuel system CI engine fueled with diesel and
Load, N Load cell ±0.25
Speed, rpm Magnetic pick up type ±1 B25 fuels.
Hydrogen flow rate, L/min New-Flow TMF ±1%
Air flow rate, L/min New-Flow TMF ±1%
Diesel flow rate, g/s Burette-Chronometer ±0.224
Crank angle, ◦ CA Incremental optical encoder ±0.2
Cylinder pressure, bar Oprand 32288GPA ±1%
Fuel line pressure, bar Kistler, 4067 ±0.8% Table 4
Physical and chemical properties of diesel, B25 and B100 fuels and test methods.
Calculated results Uncertainty value (%)
Properties Diesel B25 B100 Method
Fuel consumption, kg/h ±0.44
Engine power, kW ±0.45 Density (kg/m3) at 834.0±0.150 845.0±0.152 879.0±0.158 EN ISO
Rate of pressure rise, bar/◦ ±0.51 15 ◦ C 12185
Combustion duration, ◦ CA ±0.74 Kinematic viscosity 3.427±0.24 3.498±0.25 4.291±0.30 EN ISO
Heat release rate, J/◦ CA ±0.74 (mm2/s) at 40 ◦ C 3104
Ringing intensity, MW/m2 ±1.65 Flash Point (◦ C) 66.0±0.49 87.0±0.64 174.0±1.29 EN ISO
2719
Pour Point (◦ C) − 24.0±1.20 − 20.0±1.00 3.0±0.15 ISO 3016
2.2. Test fuels Cold filter plugging − 20.0±0.20 − 19.0±0.40 − 2.0±0.10 EN 116
point (◦ C)
Cetane number 59.5±0.30 59.8±0.22 60.7±0.24 EN 15195
In this study WCOB was blended with diesel fuel and obtained B25 Lower heating 43.085±0.099 42.407±0.097 37.507±0.086 DIN
(25% WCOB+75% diesel) fuel. The biodiesel used in the study was value, (MJ/kg) 51900–2
obtained from waste cooking oil. The waste cooking oil biodiesel was
supplied from Tarımsal Biyodizel Enerji company. This company has
been established in Izmit in 2014 and produces biodiesel from waste Table 5
vegetable oils. The characteristics of the biodiesel fuel are given in Physical and chemical properties of hydrogen fuel [51].
Table 3 obtained from TBE company. It was observed that the properties
Properties Hydrogen
of WCOB are generally within the limits of EN 14214 standard.
Density, (kg/m3) (1 atm, 20 ◦ C) 0.083764
Diesel, B25 and B100 fuels were analyzed in terms of physical and
Quenching gap in air (cm) 0.064
chemical properties in the Inonu University fuel/petroleum analysis Burning velocity in NTP air (cm/s) 265–325
laboratory accredited according to ISO 17025. Properties of Diesel, B25 Stoichiometric composition in air, vol% 29,53
and B100 fuels are given in the Table 4. In addition, hydrogen's prop­ Flammability limits, (volume % in air) 4–75
erties were shown in Table 5. Auto ignition temperature, (K) 858
Lower heating value, (MJ/kg) 119.93
Minimum energy for ignition in air (mJ) 0.02
3. Results and discussion Flame temperature in air, (K) 2318
Diffusion coefficient in air (cm2/s) 0.61
In this study, it was aimed to determine the effect of the hydrogen

Table 3
Properties of waste cooking oil biodiesel.
Property Unit EN 14214 Limits Waste coking oil biodiesel Measurement Uncertainty Test method

Min. Max.

Density at 15 ◦ C kg/m3 860.0 900.0 879.0 ±0.027 EN ISO 12185

Viscosity at 40 ◦ C mm2/s 3.5 5.0 4.291 ±0.041 EN ISO 3104
Total contamination mg/kg – 24.0 5.0 ±0.301 EN 12662
Oxidation stability at 110 ◦ C hours 6.0 11.0 ±0.427 EN 14112
Flash point ◦
C 120.0 – 174.0 ±1.740 EN ISO 3679
Cold filter plugging point (CFPP) ◦
C – – − 2.0 ±0.100 EN 116
Cetane number – 51.0 – 60.7 – EN 15195
Methanol content % (m/m) – 0.20 0.01 ±0.000 EN 14110
Water content mg/kg – 500.0 130.0 ±3.354 EN ISO 12937
Sulfated ash content % (m/m) – 0.02 0.005 ±0.003 ISO 3987
Sulfur content mg/kg – 10.0 1.1 ±0.0066 EN ISO 20846
Phosphorus content mg/kg – 10.0 0.29 ±0.014 EN 14107
Sodium mg/kg – 5.0 0.00 ±0.026 EN 14538
Potassium mg/kg 0.21 ±0.026 EN 14538
Calcium mg/kg – 5.0 0.00 ±0.000 EN 14538
Magnesium mg/kg 0.16 ±0.011 EN 14538
Iodine value g iodine/100 g – 120.0 115.0 ±1.829 EN 14111
Ester content % (m/m) 96.5 – 96.8 ±2.614 EN 14103
Linolenic acid methyl ester % (m/m) – 12.0 5.1 ±0.341 EN 14103
Acid value mg KOH/g – 0.50 0.30 ±0.026 EN 14104
Polyunsaturated (≥4 double bonds) methyl esters % (m/m) – 1.0 0.07 ±0.000 EN 14103
Copper strip corrosion (3 h at 50 ◦ C) rating class 1 1a – EN ISO 2160
Monoglyceride content % (m/m) – 0.80 0.08 ±0.006 EN 14105
Diglyceride content % (m/m) – 0.20 0.00 ±0.000 EN 14105
Triglyceride content % (m/m) – 0.20 0.00 ±0.000 EN 14105
Free glycerol % (m/m) – 0.02 0.01 ±0.004 EN 14105
Total glycerol % (m/m) – 0.25 0.03 ±0.004 EN 14105

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M. Akcay et al. Fuel Processing Technology 223 (2021) 106999

100 120
90 110
a) 40 Nm b) 60 Nm
85 100
100

In-cylinder pressure (bar)

In-cylinder pressure (bar)
80 90 Diesel
80 Diesel
B25
75 B25 80
80 B25+H10
B25+H10
60 70 70 B25+H20
B25+H20 21 24 27 30 33
21 24 27 30 33 B25+H30
B25+H30 60
B25+H40 B25+H40
40
40

20
20

0 0
20 40 60 80 100 120 20 40 60 80 100 120
3 3
Cylinder volume (cm ) Cylinder volume (cm )
120
120
c) 80 Nm
In-cylinder pressure (bar)

100 105
Diesel
90 B25
80 B25+H10
75 B25+H20
21 24 27 30 33 B25+H30
60 B25+H40

40

20

0
20 40 60 80 100 120
3
Cylinder volume (cm )
Fig. 3. Indicator diagrams for all test fuels and different engine loads (a) 40 Nm, (b) 60 Nm and (c) 80 Nm.

3.1. Indicator diagrams complete combustion [1,17,29]. The similary experimental results ob­
tained by Rocha et al. [15], Yilmaz et al. [22] and Parthasarathy et al.
The variation of CP related to cylinder volume for diesel fuel, B25 [58].
fuel and different rates of hydrogen addition at 40, 60 and 80 Nm engine Hydrogen exhibits sudden combustion during the premixed com­
loads are presented in Fig. 3. In Table 6, maximum CP values and lo­ bustion phase due to its high flame rate, in contrast to the diffusion-type
cations of all test fuels are given. The adverse combustion characteristics combustion characteristic of diesel fuel [59]. Accordingly, the com­
such as high maximum CP were not observed in each study state. bustion of hydrogen and pilot fuel becomes the constant volume process.
When comparing maximum CPs' traces of 40, 60 and 80 Nm engine [60]. This situation can be seen more clearly with increasing hydrogen
loads, it is seen that the maximum CP increased with increasing engine addition ratio, especially at 40 and 60 Nm engine loads. Similar results
load, because of the increase in the amount of fuel sprayed on the cyl­ were obtained in the study by [16,24,29].
inder along with the increased engine load [52]. As seen from Fig. 3 and As hydrogen burns faster than B25 fuel, it has been observed that the
Table 6, the maximum CP decreased with B25 fuel comparad to diesel maximum CP location approaches the top dead center (TDC) with
fuel. The decrease was obtained as 4.15%, 1.55% and 1.82% for engine hydrogen addition. Due to the sudden (constant volume) combustion of
loads of 40, 60 and 80 Nm, respectively. Due to the high viscosity of hydrogen, the maximum CP occurs earlier than in single fuel operations.
biodiesel, fuel injection deteriorates and the fuel cannot be atomized Yilmaz et al. [22], Saravanan and Nagarajan [24] and Dimitriou and
enough. Accordingly, incomplete combustion occurs [53]. In addition, Tsujimura [61] obtained similar results in their studies.
the low calorific value of biodiesel fuel is shown as another reason for
the decrease in CP [54,55]. Similar results were obtained by Raman 3.2. Heat release rate (HRR)
[11], Öztürk [56] and Can et al. [57].
The hydrogen addition to the B25 fuel caused an increase in HRR are considered as important parameters for predicting com­
maximum CP values and higher maximum CP values were obtained bustion behavior within the engine cylinder [62]. The variations of
compared to diesel fuel. It has been observed that the effect of hydrogen averaged HRR with the crank angle for all test fuels at different load
addition on maximum CP value at higher engine loads decreases due to conditions are shown in Fig. 4. In addition, In Table. 6, maximum HRR
the decrease in HES ratio with increasing engine load. The average in­ values and locations of all test fuels are given.
crease in maximum CPs with the hydrogen addition to the B25 fuel tests It can be seen that the HRR curves of the all test fuels are similar. The
were obtained as 6.3%, 5.0% and 3.6% respectively, for the engine loads CI engine used in the experimental study has a double injection fuel
of 40, 60 and 80 Nm as compared with the pure B25 fuel tests. Because system (pilot injection and main injection stages). Hence, all HRR curves
hydrogen has higher diffusion coefficient and flame speed compared to exhibited two peaks. The first peak of HRR consists of combustion of a
diesel fuel, it provides a more homogeneous flammable mixture and small amount of fuel injected during the pilot injection stage and

6
M. Akcay et al. Fuel Processing Technology 223 (2021) 106999

Table 6
Combustion characteristics for different engine loads.
Load Properties Unit Diesel B25 B25 + H10 B25 + H20 B25 + H30 B25 + H40

40 Nm CPmax bar 82.29±0.411 78.87±0.394 80.24±0.401 80.05±0.404 84.59±0.423 87.25±0.436

◦
CA 362±0.181 373±0.187 361±0.181 362±0.181 362±0.181 362±0.181
HRRmax(pilot) J/◦ CA 7.88±0.058 5.20±0.038 5.36±0.040 8.16±0.060 7.94±0.059 10.25±0.076
◦
CA 346±0.173 348±0.174 347±0.174 348±0.174 348±0.174 347±0.174
HRRmax(main) J/◦ CA 34.30±0.254 34.33±0.254 30.75±0.228 31.97±0.237 28.06±0.208 26.05±0.193
◦
CA 373±0.187 372±0.186 372±0.186 374±0.187 373±0.187 372±0.186
RoPRmax (pilot) bar/◦ CA 3.03±0.015 2.84±0.014 2.94±0.015 3.18±0.016 3.27±0.017 3.50±0.018
◦
CA 348±0.174 349±0.175 348±0.174 349±0.175 349±0.175 350±0.175
RoPRmax (main) bar/◦ CA 0.12±0.001 0.25±0.001 0.08±0.000 − 0.17±0.001 − 0.35±0.002 –
◦
CA 370±0.185 371±0.186 370±0.185 371±0.186 370±0.185 –
CHRmax J 632.42±4.680 629.98±4.662 607.65±4.497 556.07±4.115 520.74±3.853 508.18±3.761
◦
CA 399±0.200 398±0.199 399±0.200 398±0.199 399±0.200 399±0.200
COHR J 316.21±2.340 314.99±2.331 303.83±2.248 278.04±2.057 260.37±1.927 254.09±1.880
◦
CA 373±0.187 374±0.187 373±0.187 373±0.187 373±0.187 372±0.186
CD ◦
CA 61±0.451 60±0.444 60±0.444 61±0.451 61±0.451 62±0.459
RI MW/m2 3.37±0.056 2.76±0.046 2.85±0.047 3.30±0.055 3.31±0.055 3.70±0.061
60 Nm CPmax bar 93.36±0.467 91.92±0.460 94.90±0.475 96.36±0.482 96.55±0.9483 98.21±0.491
◦
CA 374±0.187 374±0.187 372±0.186 372±0.186 370±0.185 363±0.182
HRRmax(pilot) J/◦ CA 4.73±0.035 5.01±0.037 5.75±0.043 7.65±0.057 7.97±0.059 10.85±0.080
◦
CA 347±0.174 347±0.174 344±0.172 348±0.174 347±0.174 347±0.174
HRRmax(main) J/◦ CA 44.70±0.331 44.71±0.331 39.90±0.295 40.91±0.303 35.12±0.260 33.11±0.245
◦
CA 373±0.187 373±0.187 372±0.186 373±0.187 372±0.186 372±0.186
RoPRmax (pilot) bar/◦ CA 3.19±0.016 2.96±0.015 3.19±0.016 3.37±0.017 3.48±0.018 3.84±0.020
◦
CA 349±0.175 348±0.174 348±0.174 349±0.175 349±0.175 349±0.175
RoPRmax (main) bar/◦ CA 0.96±0.005 1.00±0.005 0.79±0.004 0.52±0.003 0.25±0.001 − 0.18±0.001
◦
CA 370±0.185 370±0.185 368±0.184 369±0.185 367±0.184 367±0.184
CHRmax J 791.02±5.854 803.61±5.947 792.05±5.861 728.43±5.390 682.09±5.047 662.81±4.905
◦
CA 398±0.199 398±0.199 399±0.200 399±0.200 399±0.200 401±0.201
COHR J 395.51±2.927 401.81±2.973 396.03±2.931 364.22±2.695 341.05±2.524 331.41±2.452
◦
CA 373±0.187 373±0.187 372±0.186 372±0.186 372±0.186 372±0.186
CD ◦
CA 62±0.459 62±0.459 64±0.474 64±0.474 65±0.481 65±0.481
RI MW/m2 2.83±0.047 2.71±0.045 2.99±0.049 3.33±0.055 3.51±0.058 4.14±0.068
80 Nm CPmax bar 110.50±0.553 108.5±0.543 111.8±0.559 112.3±0.562 112.5±0.563 112.7±0.564
◦
CA 373±0.187 373±0.187 373±0.187 372±0.186 370±0.185 370±0.185
HRRmax(pilot) J/◦ CA 11.36±0.084 8.86±0.066 9.51±0.070 11.67±0.086 12.68±0.094 12.97±0.096
◦
CA 342±0.171 342±0.171 344±0.172 342±0.171 341±0.171 345±0.173
HRRmax(main) J/◦ CA 51.49±0.381 52.13±0.386 52.90±0.391 48.29±0.357 40.97±0.303 38.72±0.287
◦
CA 371±0.186 371±0.186 371±0.186 372±0.186 369±0.185 371±0.186
RoPRmax (pilot) bar/◦ CA 3.69±0.019 3.41±0.017 3.59±0.018 3.82±0.020 4.04±0.021 4.18±0.022
◦
CA 345±0.173 346±0.173 347±0.174 348±0.174 347±0.174 348±0.174
RoPRmax (main) bar/◦ CA 1.61±0.008 1.71±0.009 1.62±0.008 1.30±0.007 0.96±0.005 0.51±0.003
◦
CA 368±0.184 368±0.184 368±0.184 368±0.184 365±0.183 366±0.183
CHRmax J 905.63±6.702 929.68±6.880 957.63±7.086 925.88±6.852 789.25±5.840 758.05±5.610
◦
CA 399±0.200 398±0.199 399±0.200 399±0.200 400±0.200 402±0.201
COHR J 452.82±3.351 464.84±3.440 478.82±3.543 462.94±3.426 394.63±2.920 379.03±2.805
◦
CA 372±0.186 373±0.187 372±0.186 371±0.186 370±0.185 371±0.186
CD ◦
CA 66±0.488 65±0.481 65±0.481 66±0.488 67±0.496 68 ± 0.503
RI MW/m2 3.57±0.058 3.19±0.052 3.45±0.057 3.86±0.063 4.18±0.068 4.57±0.075

hydrogen. The second peak of HRR consists of combustion of the diesel Hence, lower HRR values are achieved with the hydrogen addition in the
fuel injected in main fuel injection stage. This trend is related to the fuel main injection sections. This situation can be seen in detail in Table 6.
injection system of the test engine and is observed regardless of the When the table is examined, it is seen that the highest HRR values are
presence of hydrogen [28]. obtained with hydrogen addition in the pilot injection stage, while the
When the Fig. 4 is examined, it is seen that a negative HRR value was HRR values are lower in the case of hydrogen added operation in the
obtained before starting the combustion. This is due to the evaporation main injection stage. Only, with the 80 Nm engine load and 10 lpm
of the liquid fuel accumulated during the ignition delay period and the hydrogen addition, slightly higher maximum HRR value obtained in the
heat absorption from the environment. The HRR value becomes positive main injection phase. The maximum HRR values increase with the
when the combustion starts [52,63]. The combustion process is become increasing engine load. With the increased engine load, more B25 fuel is
in three phases. The first is pilot fuel-premixed instantaneous combus­ injected into the combustion chamber, which increases the heat release
tion, the second is hydrogen premixed instantaneous combustion and during the premixed combustion phase [68]. Due to the decrease in the
the third is diffused main fuel‑hydrogen controlled combustion. The amount of B25 fuel with increasing hydrogen addition rate, the second
hydrogen premixed combustion phase occurs earlier due to the higher peak HRR decreases again. Compared with B25 fuel tests, the maximum
burning rate of hydrogen [64,65]. reduction in HRR was obtained as 24.1%, 26.1% and 25.7% respectively
As can be seen from Fig. 4, HRR increased with hydrogen enrichment for 40, 60 and 80 Nm engine loads with 40 lpm hydrogen addition.
before the main injection because of the higher flame speed and
instantaneous combustion of hydrogen [47,66]. It is stated that
3.3. Rate of pressure rise (RoPR)
hydrogen has a more significant effect on premixed combustion phase
compared to diffusion combustion phase, the increasing of the hydrogen
The variation of RoPR with crank angle for various test fuels and 40,
addition rate increases the first HRRs [67]. In this study, most of the
60 and 80 Nm engine load conditions are given in Fig. 5. In additon, the
hydrogen is burned by pilot B25 fuel in the premixed combustion phase.
maximum RoPR values and locations (as ◦ CA after TDC) of the all test

7
M. Akcay et al. Fuel Processing Technology 223 (2021) 106999

40 36
50 48
a) 40 Nm b) 60 Nm
32 40
28 40

Heat release rate (J/ CA)

30 32
Heat release rate (J/ CA)
24
4 2
24

o
20
30 1 365 370 375 380
o

368 372 376 380

0 0
20
Diesel -1
Diesel
-4 B25 20 -2
336 340 344 B25+H10 332 336 340
B25
10 B25+H20 B25+H10
B25+H30 10 B25+H20
B25+H40 B25+H30
B25+H40
0 0

320 340 360 380 400 420 320 340 360 380 400 420
o o
Crank angle ( CA) Crank angle ( CA)

60 56
c) 80 Nm
48
50
Heat release rate (J/ CA)

40

32
40
o

2
364 368 372 376 380
0
30
-2 Diesel
20 330 333 336 B25
B25+H10
B25+H20
10 B25+H30
B25+H40
0

320 340 360 380 400 420

o
Crank angle ( CA)
Fig. 4. Variation of heat release rate (HRR) with ◦ CA for all test fuels at different engine loads (a) 40 Nm, (b) 60 Nm and (c) 80 Nm.

fuels for different engine loads are shown in Table 6. As can be seen from The combustion phase for diesel and pure B25 fuels continues even
Fig. 5, the maximum RoPR value has also increased due to the increase during the power stroke, but results in a lower pressure increase due to
in the amount of fuel taken into the cylinders with the increase in the the piston moving towards the bottom dead center [74]. In the Fig. 5, it
engine load for each fuel. The maximum RoPR decreased with B25 fuel is seen that secondary peak RoPR values are formed in the power stroke
compared with diesel fuel for each engine load at the pilot injection of the cylinder resulting from the main fuel injection. The secondary
phase. The decrease in the first peak of RoPR was obtained as 6.1%, peak RoPR values of diesel and B25 fuels are higher than those of the
7.4% and 7.6% for engine loads of 40, 60 and 80 Nm, respectively. This hydrogen enrichment. In Table 6, maximum RoPR values obtained by
situation can be explained by the longer ID of diesel fuel compared to pilot and main fuel injection and the location (as ◦ CA) of these values are
B25 fuel. The high cetane number and oxygen content of the fuel cause a given.
decrease in the ID [56]. Due to the longer ID, more fuel accumulates in With hydrogen enrichment, the amount of B25 fuel injected into the
the combustion chamber and higher RoPR values are obtained with the cylinders during both the pilot and main injection stages is reduced. The
sudden combustion of a large amount of diesel fuel [69]. Similar results hydrogen taken into the cylinder with intake air is ignited by pilot B25
obtained by Shrivastava et al. [70] and Gumus [71]. fuel and an explosive type combustion occurs in the premixed com­
When the Table 6 is examined, it is seen that in the case of diesel and bustion phase [29]. Therefore, as can be seen from Table 6, the
B25 fuels, there is no significant difference in the locations as crank angle maximum RoPR values obtained at the pilot fuel injection stage become
(max. 1 ◦ CA) where the maximum RoPR values are obtained, so B25 and closer to TDC with the addition of hydrogen [29,75]. In addition,
diesel fuel exhibit similar combustion performance. According to the neat because of the most of the hydrogen is burned after pilot fuel injection
B25, the maximum RoPR value increase with the B25‑hydrogen dual-fuel [22] and the energy released from the hydrogen during the main fuel
mode operation. The maximum increase in the RoPR values are obtained injection phase decreases, the secondary peak RoPR values are lower in
as 23.24%, 29.83% and 22.65% for 40 Nm, 60 Nm and 80 Nm engine B25‑hydrogen dual-fuel tests compared to neat B25 fuel test.
loads with 40 lpm hydrogen addition, respectively. The highest maximum
RoPR value is obtained as 4.19 bar/◦ CA with 80 Nm engine load and 40
lpm hydrogen addtion. This value is lower than 9 bar/◦ CA which is an 3.4. Cumulative heat release (CHR)
indicator for the knock [72]. No problem is encountered in the operation
of the engine. The high flame speed of hydrogen causes constant com­ The CHR, which shows the combustion stages in the cylinder, is
bustion and this increases the maximum RoPR [59,68,73]. Similar results obtained by the sum of the consecutive HRR values [76]. Table 6 shows
are obtained by Yilmaz et al. [22]. the maximum CHR with COHR values and location (as crank angle) of
the all test fuels for different engine loads. COHR is determined from the

8
M. Akcay et al. Fuel Processing Technology 223 (2021) 106999

4
Diesel a) 40 Nm 4 Diesel b) 60 Nm
B25 B25
Rate of pressure rise (bar/ CA) 3

Rate of pressure rise (bar/ CA)

3,6 B25+H10 4,0
B25+H10 3
B25+H20 B25+H20 3,5
3,0

o
o

2 B25+H30 B25+H30 3,0

B25+H40 2,4 2 B25+H40
2,5
1,8 2,0
1 1 340 344 348 352 356
340 344 348 352 356

0 0
300 320 340 360 380 400 420 300 320 340 360 380 400 420
1,0 -1 1,0
-1
0,5 0,5
0,0 -2 0,0
-2 360 366 372 378 360 364 368 372 376
-0,5 -0,5
-3 -1,0
-3 -1,0
o o
Crank angle ( CA) Crank angle ( CA)
5
Diesel c) 80 Nm
4 B25 4,5
Rate of pressure rise (bar/ CA)

B25+H10 4,0
3 B25+H20 3,5
o

B25+H30 3,0
2 B25+H40 2,5
2,0
1 340 344 348 352 356

0
300 320 340 360 380 400 420
-1 2,0
1,5
1,0
-2 0,5
0,0
-3 -0,5 360 364 368 372 376
-1,0
-4 o
Crank angle ( CA)
Fig. 5. Variation of rate of pressure rise (RoPR) with ◦ CA for all test fuels at different engine loads (a) 40 Nm, (b) 60 Nm and (c) 80 Nm.

crank angle corresponding to 50% of the total heat release [56]. As can situation is the weaker atomization and slow combustion of B25 fuel
be seen from Fig. 6, CHR value for each fuel increase with increasing compared to diesel fuel [56,71]. With the addition of hydrogen to B25
engine load. As more fuel is sent into the cylinder with increasing engine fuel, COHR is slightly closer to TDC.
load, more heat release occurs [71].
B25 fuel generally exhibited slightly higher CHR (except 40 Nm) 3.5. Combustion duration (CD)
than diesel fuel. Patel et al. [52], who achieved similar results, explained
this situation by taking larger fuel droplets into the cylinder due to the CD is the most important variable among burning characteristics
insufficient atomization of biodiesel compared to diesel fuel, and [76]. The CD of a fuel is defined as difference of start of combustion and
therefore the combustion starts later. The delay of the start of the end of combustion [6]. In this study, CD is the difference between the
combustion causes an increase in HRR and hence CHR, because of there crank angles at which 5% and 95% of the CHR [78]. The change of CD
is a shorter time for heat transfer to the cylinder walls [77]. for each fuel depending on the engine load is given in Fig. 7.
It was observed from Fig. 6 that dual-fuel operation offers lower For each test fuel, the CD increases due to the increase in the amount
maximum CHR, when compared to pure B25 fuel in generally (except of fuel taken into the cylinder along with the increased engine load [76].
80 Nm). The peak CHR first increased with hydrogen addition and then It was observed that the CD for neat B25 fuel lower than diesel fuel,
decreased again with increasing hydrogen addition rate at the 80 Nm generally. Biodiesel fuel improves combustion thanks to its oxygen
engine load. The maximum reduction in maximum CHR with hydrogen content. Therefore, biodiesel fuel is expected to exhibit a shorter CD
addition to B25 fuel tests was obtained as 19.3%, 17.5% and 18.5% for [79].
40 Nm, 60 Nm and 80 Nm engine loads, respectively with 40 lpm In case of B25‑hydrogen dual-fuel mode operation, CD increased due
hydrogen addition. to increasing hydrogen content. It is estimated that the cause of this
With the combustion of hydrogen-air homogeneous mixtures, the situation is the homogeneous mixture of air and hydrogen spread over
flame reaches the cylinder walls. Therefore, heat transfer increases and the cold cylinder inner surface [22]. If the hydrogen amount in com­
net heat release decreases. The hydrogen energy share at 80 Nm engine bustion chamber is high, then more combustion gases are generated
load is less than hydrogen energy shares at 40 and 60 Nm engine loads after the pilot fuel and hydrogen combustion. These gases diluate the air
(see Fig. 2). Therefore, heat transfer decreased especially for 10 and 20 in the combustion chamber. Because of that an EGR effect is seen. Main
lpm hydrogen additions and CHR increased. The highest CHR was ob­ fuel is injected into hot air and combustion gas mixture. Especially
tained with 10 lpm hydrogen addition at 80 Nm engine load. However, carbon atoms cannot reach the aviable oxgygen easily. Because of that,
with the increase of hydrogen addition ratio, CHR decreased again. not ony CD lenghtens but also smoke emission deteriorates [80].
When Table 6 is examined, it is seen that the COHR is slightly away
from the TDC with B25 fuel compared to diesel fuel. The reason for this

9
M. Akcay et al. Fuel Processing Technology 223 (2021) 106999

700 900
a) 40 Nm b) 60 Nm
Cumulative heat release (J) 600

Cumulative heat release (J)

750 810
640
Diesel 795 Diesel
500 620
B25 B25
600
600 780 B25+H10
B25+H10
400 580 B25+H20 765 B25+H20
392 400 408 B25+H30 450 390 396 402 408 B25+H30
300 B25+H40 B25+H40
100 100
75
300 75
200
50
50
100 150 25
25
0
356 360 364 368 352 356 360 364
0 0
340 350 360 370 380 390 400 410 420 340 350 360 370 380 390 400 410 420
o o
Crank angle ( CA) Crank Angle ( CA)
1000
c) 80 Nm
Cumulative heat release (J)

800 950
925 Diesel
B25
900
600 B25+H10
B25+H20
390 396 402 408
B25+H30
400 100 B25+H40

75

200 50
25
352 356 360
0
340 350 360 370 380 390 400 410 420
o
Crank angle ( CA)
Fig. 6. Variation of cumulative heat release (CHR) with ◦ CA for all test fuels at different engine loads (a) 40 Nm, (b) 60 Nm and (c) 80 Nm.

40
a) 40 Nm b) 60 Nm c) 80 Nm
35
Combustion Duratiom ( CA)
o

30

25

20

15

10
el

B2 10

B2 20

B2 30

40

el

B2 30

40

el

B2 10

B2 20

B2 30

40
B2 25

5
1

2
B2

B2
ies

ies

ies
H

H
B
5+

5+

5+

5+

5+

5+

5+

5+

5+

5+

5+

5+
D

D
B2

B2

B2

B2

Test Fuels
Fig. 7. Variation of combustion duration (CD) with hydrogen addition for different engine loads (a) 40 Nm, (b) 60 Nm and (c) 80 Nm.

3.6. Ringing intensity (RI) [ ]2

0, 05.(dP/dt)max √̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅
RI = . γ.R.Tmax (6)
The ringing intensity (RI) relates with the acoustic energy that 2γ.Pmax
caused from resonating pressure. Using with this formula tendency to
produce acoustic oscillations can be determined [81]. RI can be calcu­ where (dP/dt)max is the peak RoPR (kPa/ms), γ is the ratio of specific
lated by the Eq. (6) given below [82]. heats, Pmax is the maximum of in-cylinder pressure (Pa), R is the ideal

10
M. Akcay et al. Fuel Processing Technology 223 (2021) 106999

6
a) 40 Nm b) 60 Nm c) 80 Nm

Ringing intensity (MW/m )

Threshold Level

2
5

0 0

B2 20

B2 30

B2 20
el

el

B2 10

40

el

B2 10

B2 30

40
5

B2 25

5
H1

3
H4
B2

B2
es

es

ies
H
H

H
B
Di

Di
5+

5+

5+

5+

5+

5+

5+

5+

5+

5+

5+

5+
D
B2

B2

B2

B2

B2
Test Fuels
Fig. 8. Variation of ringing intensity (RI) with hydrogen addition for different engine loads (a) 40 Nm, (b) 60 Nm and (c) 80 Nm.

gas constant (J/kgK), and Tmax is the maximum of in-cylinder temper­ tests compared with diesel fuel tests for each engine load. With the
ature (K). hydrogen addition, the maximum RoPR value increased. The highest
The change of RI for each fuel depending on the engine load is given maximum RoPR value was obtained as 4.19 bar/◦ CA with 80 Nm
in Fig. 8. As can be seen from Fig. 8, neat B25 fuel exhibited a lower RI engine load and 40 lpm hydrogen addition.
value than diesel fuel. RI generally increased due to the increasing load • B25 fuel generally exhibited slightly higher CHR (except 40 Nm)
and hydrogen addition ratio. The EURO VI limits for RI below 5 MW/m2 than diesel fuel. In case of B25‑hydrogen dual-fuel mode operation,
[83]. Because of that it can be said that hydrogen enrichment has no the lower maximum CHR is obtained, when compared to pure B25
negative effect on RI. fuel in generally (except 80 Nm). With hydrogen enrichment, it was
observed that the maximum CHR location generally moved away
4. Conclusions from TDC slightly and COHR location generally approached TDC.
• For each test fuel, it was observed that the CD increased due to the
In this study, the effect of hydrogen addition to the intake air of a increase in the amount of fuel taken into the cylinder with increasing
four-stroke, four-cylinder, water-cooled, turbocharged, Common-Rail engine load. It was observed that the CD for neat B25 fuel lower than
fuel injection system, double-injection CI engine fuelled with B25- diesel fuel, generally. In case of B25‑hydrogen dual-fuel mode
diesel fuel blends on the combustion characteristics was experimen­ operation, CD increased based on the increasing hydrogen content.
tally investigated. The results obtained in the study are listed below; • Due to the increased engine load and hydrogen addition rate, the RI
has increased slightly overall. It was observed that hydrogen
• When the indicator diagrams for all test fuels were examined, it was enrichment had no adverse effect on RI.
observed that instantaneous combustion occurred with hydrogen
enrichment and the combustion process took place in a partially Finally, it is concluded that WCOB-diesel blend (B25) can be used
constant volume. successfully in Common Rail DI engines with hydrogen assisted intake
• B25 fuel tests exhibited lower maximum CPs values compared to air. It has been observed that B25‑hydrogen dual-fuel operation exhibits
neat diesel fuel tests. The maximum CP values increased with similar combustion performance to diesel and B25 fuels and causes
hydrogen enrichment. The higher maximum CP value was obtained slightly higher maximum CP and RoPR values. In the future research, the
with 40 lpm hydrogen encrichment compared to diesel fuel tests. effect of hydrogen enrichment on the combustion characteristics of the
• Similar to conventional double injection (pilot injection and main common rail DI engine working with neat WCOB and WCOB-diesel
injection) diesel fuel combustion, all HRR curves exhibited two blends in different ratios can be examined. In addition, the effect on
maximums. In general, B25 fuel tests exhibited slightly higher HRR engine parts such as cylinders, pistons, rings and valves etc. can be
than diesel fuel tests. During the pilot injection phase, the maximum examined in case of long-term dual-fuel operation.
HRR values increased with the hydrogen addition. However, the
opposite HRR trends were seen at the main injection phase. Declaration of Competing Interest
• Similar to conventional double injection (pilot injection and main
injection) diesel fuel combustion, all HRR curves exhibited two None.
maximums. In general, B25 fuel tests exhibited slightly higher HRR
than diesel fuel tests. During the pilot injection phase, the maximum Acknowledgments
HRR values increased with the hydrogen addition to the B25 fuel.
However, maximum HRR values were reduced with the hydrogen This study was supported by Marmara University Scientific Research
addition at the main injection stage. Projects Unit with the project number FEN-K-110618-0334. The authors
• A higher maximum RoPR value was obtained in the pilot injection wish to express their thanks for the financial support of Marmara Uni­
phase compared to the main injection phase. For the pilot injection versity Scientific Research Projects Unit.
phase, the maximum RoPR decreased with B25 fuel test compared
with diesel fuel test for each engine load. However, in the main in­
jection phase, higher maximum RoPR values obtained with B25 fuel

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M. Akcay et al. Fuel Processing Technology 223 (2021) 106999

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