Experimental Study of Hydrogen Addition on Waste Cooking Oil
Biodiesel-Diesel-Butanol Fuel Blends in a DI Diesel Engine
Selçuk Sarıkoç1 &Sebahattin Ünalan2&İlker Örs3 Published online: 2 May 2019
# Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
In this study, the effects of hydrogen addition on diesel-biodiesel-butanol fuel blends were investigated in terms of engine performance, combustion, and emission characteristics under different engine operating conditions. The experiments were performed with eight different fuel blends at a constant engine speed of 2000 rpm, which is the maximum torque value of all test fuels. The four operating conditions were at 25%, 50%, 75%, and 100% engine loads. Hydrogen was delivered to diesel-biodiesel-butanol fuel blends through the intake manifold with different rates of fuel mass consumption. The experiment results were compared with euro diesel and absence of hydrogen addition for all test fuels. The experimental results have revealed that at 2000 rpm engine speed, the brake torque, in-cylinder pressure, and exhaust gas temperature increased with the addition of hydrogen. Nevertheless, the brake-specific fuel consumption, carbon monoxide (CO), carbon dioxide (CO2), hydrocarbon
(HC), nitrogen oxides (NOx), and smoke opacity emissions decreased under various engine conditions. The heat release rate
was generally shown to be decreased with higher engine loads and increased with lower engine load conditions, while a rise in thermal efficiency was observed. Therefore, the addition of hydrogen in a diesel engine usually exhibited fewer emissions, improved the combustion process, and increased the brake torques of the engine by comparison to the absence of hydrogen addition.
Keywords Hydrogen addition . Diesel-biodiesel-butanol fuel blends . Engine performance . Combustion characteristics . Exhaust emissions
Nomenclature
ABDC After bottom dead center
EVO Exhaust valve open
ATDC After top dead center
HC Hydrocarbon
be Effective brake-specific fuel
consumption (g/kWh) HRRmax Maximum heat release rate
Be Effective fuel consumption (g/h)
ID Ignition delay
BBDC Before bottom dead center
IT Injection time
BP Brake power (kW)
IVC Intake valve closed
BSFC Brake-specific fuel consumption
IVO Intake valve open
BTDC Before top dead center
LHV Lower heating value
B20 20% biodiesel plus 80%
euro diesel (volumetric)
Me Effective engine torque (Nm)
B20But5 20% biodiesel plus 75% euro diesel plus 5% butanol (volumetric)
n Engine speed (rpm)
B20But5 + H2 20% biodiesel plus 75% euro
diesel plus 5% butanol (volumetric) + hydrogen
NaOH Sodium hydroxide
B20But10 20% biodiesel plus 70% euro diesel plus 10% butanol (volumetric)
NO Nitrogen monoxide
* Selçuk Sarıkoç
1
Energy Division, Department of Mechanical Engineering, Bayburt University, 69000 Bayburt, Turkey
2
Energy Division, Department of Mechanical Engineering, Erciyes University, 38039 Kayseri, Turkey
3 Cihanbeyli Vocational School, Department of Motor Vehicles and
B20But10 + H2 20% biodiesel plus 70% euro
diesel plus 10% butanol (volumetric) + hydrogen
NOx Nitrogen oxides
BTE Brake thermal efficiency
P Cylinder pressure (bar)
CD Combustion duration
Pe Effective brake power (kW)
CFPP Cold filter plugging point
PM Particulate matter
CI Compression ignition
ppm Parts per million
CN Cetane number
rpm Revolution per minute
CO Carbon monoxide
Qnet Heat value (J)
CO2 Carbon dioxide
SOC Start of combustion
CPmax Maximum cylinder pressure
TDC Top dead center
D Diesel
THC Total hydrocarbons
DI Direct injection
Tex Exhaust gas temperature
D100 100% euro diesel
WCOME Waste cooking oil methyl ester D100 + H2 100% euro diesel+hydrogen
V Cylinder volume (m3)
EGT Exhaust gas temperature
θ Represents crank angle (oCA)
EOC End of combustion
γ Specific heat the ratio
EVC Exhaust valve closed
Introduction
Fast depletion of fossil-based fuels and dramatically increased environmental problems have revealed the importance of al-ternative, clean, and renewable energy resources. Vehicular pollution has constituted approximately 30% of the world’s greenhouse gases. Furthermore, urban NOxemissions, which
are responsible for acid rain, smog, and ground level ozone layers, due to diesel engines, cause almost 50% of NOx
emis-sions. Therefore, reducing PM and NOxemissions are
impor-tant solutions for diesel engine environmental pollution. For this purpose, hydrogen has emerged as a promising clean and renewable alternative energy source in this century [1,2].
The diesel engine combustion and emission characteristics could be improved with some of the fuel blends such as diesel-biodiesel, diesel-natural gas, diesel-hydrogen, and diesel-alco-hols. Usually, biodiesel and alcohols are used by many re-searchers to decrease exhaust emissions because they consist
more oxygen and less sulfur and carbon content compared to euro diesel. Ethanol, methanol, and butanol are the most used alcohols in internal combustion engines. Butanol has more advantages than ethanol and methanol for operation in diesel engines. Some of the important advantages are a higher cetane number and energy content, better miscibility in diesel fuel, less corrosiveness, lower vapor pressure, and more similarity with petrol-based fuels compared to ethanol and methanol. Therefore, butanol is a more convenient fuel additive for die-sel engines [3–6].
Many experiments have been conducted on the usage of butanol and biodiesel in CI diesel engines. The engine perfor-mance, combustion, and emission characteristics have been investigated by many researchers and substantial progress has been obtained from experimental results. The addition of alcohol to the fuel has increased the brake-specific fuel con-sumption, while causing a reduction in the brake thermal ef-ficiency. The ignition delay period is prolonged by increasing the alcohol rate in the fuel blend. The exhaust emissions ob-served with the addition of alcohol cause no significant in-crease in nitrogen oxides (NOx) emissions, whereas there is a decrease in carbon monoxide (CO) and smoke emissions [6]. Increasing the ratio of n-butanol in fuel blends has affect-ed the BSFC, BTE, and EGT. N-butanol leads to an increasing of BSFC and BTE, while causing a reduction in the values of EGT. Moreover, the experimental results revealed that carbon monoxide, nitrogen oxides, and smoke opacity emissions de-creased, whereas HC emissions increased with the increasing ratio of n-butanol in the fuel blend [4]. The value of HC, CO, NO, and smoke opacity emissions have been reduced, while the values of CO2emissions are increased compared to euro
diesel with the addition of n-butanol in the fuel blend [7]. In addition to these, biodiesel also has a noticeable effect on exhaust emissions. It is observed that the value of CO and smoke emissions decreases with the usage of mustard oil biodiesel-diesel fuel blends with respect to euro diesel. Nevertheless, the values of NOxemissions have been
in-creased by the use of this oil in biodiesel in fuel blends [8]. Hydrogen is a promising fuel due to some important prop-erties such as high flame velocity, higher calorific value, dif-fusivity, high ignition temperature, and ultra-low emissions [6]. The hydrogen auto ignition temperature (858 K) is higher than euro diesel (530 K) so hydrogen ignite is more difficult in the compression process. Thus, hydrogen could be used by spark ignition engines more conveniently as an alternative fuel [9,10]. However, the addition of hydrogen has been investi-gated by most researchers in terms of diesel engine perfor-mance, combustion, and exhaust emission characteristics [10–14]. Some experiments have been performed, by the au-thors, with diesel engines, which use hydrogen as an additive. Different hydrogen addition techniques and various fuel blends have been investigated and evaluated by many re-searchers in terms of engine performance, combustion, and
emission characteristics. Saravanan and Nagarajan [15], stud-ied hydrogen-diesel dual-fuel engine injection techniques. Fuel injected from 5-mm and 100-mm distance in front of the intake valve, which were defined as port and manifold injection techniques, respectively. The port and manifold in-jection techniques have not been found to have a remarkable difference in performance. Yilmaz and Gumus [10], delivered at 20 lpm (H20) and 40 lpm (H40) hydrogen flow rate into inlet manifolds under 50 Nm, 75 Nm, and 100 Nm engine loads at 1750 rpm. The hydrogen had a favorable effect on brake-specific energy consumption and BTE, so both in-creased at low engine loads. Hydrogen addition has shown a reduction of HC and CO2emissions. However, EGT, HRR,
and cylinder pressure have demonstrated an increase with hy-drogen addition at all engine operating conditions. The hydro-gen flow rate of 20 lpm has reduced NOxemissions, while an
increase has been observed in the case of a 40-lpm hydrogen flow rate. Karagöz et. al. [11] have experimentally researched the engine performance, combustion, and emission character-istics of diesel engines, which were fueled by hydrogen and euro diesel, as a dual fuel. The energy-based rate of 0%, 22%, and 53% hydrogen addition effects were examined at 1100 rpm constant speed. With respect to experimental results, there was a positive effect on CO emissions, reduction of the smoke value, and BTE, while increasing the value of the BSFC, maximum cylinder gas pressure, peak heat release rate, THC emissions, and NOxemissions, were with increased
per-centages of hydrogen.
Some important unregulated emissions such as formalde-hyde (HCHO), acetaldeformalde-hyde (CH3CHO), alkenes (ethylene
(C2H4), propylene (C3H6), 1,3-butadiene (C4H6), arenes
(ben-zene (C6H6)), toluene (C7H8), xylene (C8H10)), and
particu-late emissions have been considered in respect to effects of hydrogen addition at various engine operation conditions. Although the value of formaldehyde increased with H30 ad-dition, hydrogen addition has shown remarkably exhibited reductions in acetaldehyde (CH3CHO), the olefins (C2H4,
C3H6, and C4H6), and the aromatic hydrocarbon (C6H6,
C7H8, and C8H10) emissions. Furthermore, particle size and
the number of concentrations have decreased with hydrogen addition at all engine operating conditions [16,17]. However, Jhan et al. [18] obtained a reduction in the amount of formal-dehyde with 0.6% and 1.2% of hydrogen addition by increas-ing the amount of percentage engine load. The amount of acetaldehyde emissions was decreased by the increase of en-gine loads. The values of CO and CO2emissions were
de-creased by the addition of low-level hydrogen, whereas THC increased at higher engine loads. Additionally, the amount of NOx emissions was reduced at a low engine load, while it was increased at a high load condition with the addition of hydro-gen. The obtained results are that carbonyl emissions and for-mation of ozone layers were decreased by the addition of hydrogen in a heavy duty diesel engine [19].
Hydrogen-natural gas mixtures have been reviewed by Akansu et. al. [20] for internal combustion engines. They con-cluded that the general trend of HC, CO, and CO2emissions
have shown a reduction with increased hydrogen addition, while NOxemissions usually increase. Dimitriou et. al. [21]
investigated the combustion and emission characteristics of hydrogen and the diesel fuel engine. Formation of soot, car-bon, and NOxemissions were observed at a reduction with
low engine load operating conditions, while NOxemissions
increased with medium load conditions.
Decreasing of engine performance and increasing of NOx
emission are a significant disadvantage for use in diesel engine of biodiesel as fuel. Besides, biodiesel has negatively cold flow properties such as high viscosity, low pour point, and CFPP. The butanol was added in diesel fuel-biodiesel blend for minimizing of these disadvantages. Thus, both decreased exhaust emission and improved cold flow properties of the fuel. But, butanol decreased, significantly, engine perfor-mance values. Therefore, in this study, for the improvement of performance parameters, air absorbed by the engine was enriched with hydrogen, which optimized according to engine performance, combustion, and emission characteristics. Besides, hydrogen addition effected positively both exhaust emissions and combustion parameters.
Experimental Setup
The biodiesel was obtained by a transesterification reaction in single-step using waste cooking oil, methanol (25%v/v oil), and 1% m/m oil of NaOH (alkaline catalyst). Further informa-tion about the biodiesel producinforma-tion process and condiinforma-tions were followed according to the author’s previous study [7]. The physicochemical properties of main fuels and some fuel properties of test fuels have been shown in Tables1and2.
In this study, hydrogen was added by means of the intake manifold, directly to the injection diesel engine, which was fueled with waste cooking oil biodiesel fuel blends with euro diesel (it is in Euro-6c norm) and butanol. The tests were performed in order to investigate their various ratios of fuel blend effects on engine performance, combustion, and exhaust emissions. For this purpose, the experiments were carried out with the experimental setup, devices, and procedures as expressed below:
The engine was coupled to a Net Fren-NF150 hydraulic dynamometer for loading to measure the engine speed range, which was 0–6500 rpm, and the torque range, which was 0– 450 Nm. The torque values of the hydraulic dynamometer were measured with a CAS brand SBA 200 L model load cell that is capable of measuring a range of 0–200 kg with 1-g precision. Detailed technical properties of the test engine are given in Table3.
The fuel consumption of each test was determined by using a digital high-precision balance machine and watch, which is known as a gravimetric method. The fuel consumption values were measured with a Dikomsan JS-BH digital balance ma-chine, which has a capacity of 0–6 kg and the precision of 0.1 g load. The exhaust emissions were measured with a mOByDic-5000 4 gas analyzer and smoke meter, which were used for reading values of CO, CO2, HC, NOx, and smoke
opacity emissions.
In-cylinder pressure measurement and engine speed system components were composed of an amplifier, data acquisition card, encoder, signal conditioner, cylinder pressure sensor, and filter elements. The in-cylinder pressure was measured with a Kistler brand 6052C model piezoelectric pressure sen-sor. All of the tests were performed for at least 100 cycles, of which the average value was taken of the cylinder pressure data for calculating the heat release rate that is derived from the first law of thermodynamics. In order to convert the correct filtering property of the in-cylinder pressure signal, a Kistler brand 5018A amplifier, which was compatible with the pres-sure sensor, was used to convert the voltage of the generating pressure sensor. An Atek brand ARC S 50 model encoder was used to measure the changing of the cylinder pressure accord-ing to each crank angle position. The crank angle signals were
measured by the encoder at each of the 1°CA resolutions. All data for analysis of the combustion process was collected by a National instruments brand, NI USB 62010 model data acqui-sition card. The combustion was analyzed by using Febris software, which is based on the Labview code.
The experiments were conducted at a constant engine speed, which was the maximum torque value of the test fuels. The dynamometer load was varied in steps of full, three-quar-ter, half, and a quarter in all the experiments. The experiments were performed with the addition of hydrogen in diesel-biodiesel-butanol fuel blends. The intake manifold was mod-ified for the addition of hydrogen in this experiment. The hydrogen flow rate was measured by a digital flow meter, an Alicat Scientific brand. A sensitive ball valve system that could be manually controlled in accordance with the hydrogen flow meter to deliver hydrogen into the intake manifold was used. The airflow rate value was determined by using a Lutron brand AM-4204HA model anemometer to ensure that the air flow was laminar before the intake manifold. Hydrogen was delivered from a high-pressure hydrogen cylinder that was about at 250 bar by means of a hydrogen pressure regulator to reduce it to 2–3 bar for use in the hydrogen flow meter. The hydrogen passed through a flame trap which was used for security and placed between the hydrogen pressure regulator
Table 1 Physicochemical
properties of main fuels Property Euro diesel
WCOME Butanol Hydrogen ASTM D6751 Density at 20 °C (g/cm3) 0.8295 0.8756 0.8114 0.08376* –
Kinematic viscosity at 40 °C (mm2/s)
2.3255 4.6513 2.5467 Unmeasured 1.9–6.0 Cetane index 47.15 49.43 < 15* Unmeasured 47 min Flash point (°C) 69.5 172.5 35 Very low 130 min Lower heating value (MJ/kg) 42.65 36.49 33.1 120* – Latent heat of vaporization
(kJ/kg)
≈ 250* Similar with diesel fuel
585* ≈ 450* – Oxidation stability (h) ≈ 14 7.079 < 1 Unmeasured 3 h min Cloud point (°C) − 7 12 <− 25 Unmeasured Report Pour point (°C) − 26 10 <− 25 Unmeasured Report Cold Filter Plugging Point (°C) − 25 5 <− 25 Unmeasured Report Acid Value (mg NaOH/g oil) N/D 0.127 N/D N/D ≤ 0.5 max Iodine value (g I/100 g) N/D 72.045 N/D N/D – Saponification number N/D 205.46 N/D N/D – *Determined by the manufacturer
Table 2 Some fuel properties of
test fuels Property Unit Euro diesel B20 B20But5 B20But10
Density g/cm3at 20 °C 0.8295 0.8463 0.8425 0.8394
Kinematic viscosity mm2/s at 40 °C 2.3255 2.7938 2.7638 2.6229
Cetane index (°C) 47.15 47.95 46.03 44.72
LHV MJ/kg 42.65 40.79 40.69 39.96
and the intake manifold to prevent flashback. The environ-mental reference system was defined asT0= 303.15 K and
P0= 90 kPa. A schematic diagram of the experimental engine
setup system is illustrated in Fig.1. The engine test setup system and all the equipments are described as follows:
The presented numbers were indicated respectively: 1. hy-draulic dynamometer, 2. test engine, 3. hydrogen cylinder, 4. regulator, 5. hydrogen valve, 6. emission analyzers, 7. fuel tank, 8. weight balance, 9. flame arrestor, 10. hydrogen filter, 11. hydrogen flow meter, 12. sensitive hydrogen valve, 13. air flow meter, 14. air inlet, 15. air intake manifold, 16. air filter, 17. exhaust manifold, 18. cylinder pressure sensor, 19. ampli-fier, 20. load cell, 21. encoder, 22. dynamometer control pan-el, 23. data acquisition card, 24. combustion analyzer, 25. exhaust temperature sensor, 26. radiator, 27. cooling liquid temperature sensor, 28. laminar air flow element.
The experiments were performed with a three cylinder di-rect injection diesel engine fueled with a combination of var-ious ratio diesel-biodiesel-butanol fuel blends at 25%, 50%, 75%, and 100% under engine load operating conditions and at a 2000 rpm (the maximum torque value of the test fuels) constant engine speed. In addition to this, the experiments were performed with different ratios of hydrogen and diesel-biodiesel-butanol fuel blends and the results were compared
with euro diesel for all test fuels. Furthermore, to understand clearly the effects of hydrogen addition in the diesel engine, hydrogen and non-hydrogen fuel blends were compared with each other. Before starting the experiments, the engine was run without load until warmed and it reached steady-state conditions. The following experimental parameters were tak-en after the tak-engine arrived at the steady-state condition: & Engine performance such as brake engine torque, BSFC,
and brake thermal efficiency were measured.
& Combustion process: in-cylinder pressure and heat release rate with respect to crank angle and combustion analysis of test fuels were recorded.
& Exhaust emission characteristics in terms of exhaust gas temperature, CO, CO2, HC, NOx, and smoke opacity were
noted
These readings were repeated for 25%, 50%, 75%, and 100% engine loads for each test fuel at 2000 rpm engine speed. Then hydrogen was passed from the hydrogen flow meter, which adjusted the flow of hydrogen in increments of 1 to 15% with a regular interval of 0.5% as the mass rate of liquid fuel consumption. The hydrogen injection ratio was optimized based on when the engine was properly running. According to the hydrogen flow rate optimization tests, less flow rate (< 9%) was shown as no visible effect on the engine performance and combustion at 25%, 50%, and 75% engine loads. However, the effects started when the hydrogen flow rate was up to 3% at 100% engine load. A high hydrogen flow rate, up to 12%, had negative effects on the running of the engine, which caused blasts in the intake manifold or stopped the engine. Therefore, the experiments were not able to con-tinue beyond the addition of 12% of hydrogen due to blasting and knocking. As a result of hydrogen optimization, the opti-mized hydrogen flow rates where the engine properly per-formed were with 9%, 10%, 11%, and 10.5% hydrogen flow
Fig. 1 The engine experimental test setup system
Table 3 Technical specifications of the Lombardini diesel engine Specifications Units Properties
Model LDW 1003
Engine type Four stroke, direct injection (DI) Number of cylinders 3
Cylinder volume cm3 1028 Bore–stroke mm–mm 75–77.6 Compression ratio 22.8:1 Maximum engine power kW (Hp) 19.5 (26.5)
rate in terms of the mass ratio of fuel consumption for D100, B20, B20But5, and B20But10 fuel blends, respectively, at 25%, 50%, and 75% engine loads. However, hydrogen flow rates were decreased to 5%, 4.5%, 4%, and 3% for D100, B20, B20But5, and B20But10 fuel blends at full load engine oper-ating conditions, respectively. After these proportions of hy-drogen were added to the fuel, the blends were given the names D100 + H2, B20 + H2, B20But5 + H2, and B20But10
+ H2, respectively.
In this study, industrial hydrogen gas, comprised of 99.99% high-purity hydrogen and diesel was used as euro diesel. The amount of hydrogen addition was determined by the hydrogen mass intake rate (S). Tarabet et. al. [14] have defined a similar expression known as the mass participation rate. The hydro-gen mass intake rate could be calculated with intake hydrohydro-gen mass divided by the sum of intake hydrogen mass and the mass flow of fuel consumption rate in the diesel engine. The hydrogen mass intake rate of the test fuels is given in Table4. The heat release rate could be calculated by using the first law of thermodynamics that was the conservation of energy in the combustion duration net heat release converted into me-chanical work, depending on the crank angle as follows: dQnet dθ ¼ γ γ−1P dV dθ þ 1 γ−1V dP dθ; ðJ=deg CAÞ ð1Þ
In this equation, dQnet(J) represents the energy transfer
value of heat passing through the cylinder wall and the com-bustion chamber wall at the end of comcom-bustion,γ is the spe-cific heat ratio,θ (oCA) is the crank angle, V (m3) is the cylinder volume, and P (bar) is the cylinder pressure [7].
In this study, experiments were performed in triplicate to ensure test results and the arithmetic mean values were used for calculating the engine performance, the process of com-bustion, exhaust emissions, and uncertainty parameters.
The root mean square method, or propagation of uncertainty method, was developed by Kline and McClintock to prove the certainty of experiments. This method is one of the more pre-cise methods for calculating uncertainty of an experimental system. The uncertainties of the experimental systems could
be computed, whether the uncertainties of systems have been in acceptable limits of uncertainty, as follows in this expression:
wR¼ ∂x∂R 1 w1 2 þ ∂R ∂x2 w2 2 þ … þ ∂R ∂xnwn 2 " #1 2 ð2Þ x1, x2,x3,..., xnare the independent variables related to R
func-tion. Each of these independent variables have uncertainties such as w1,w2,...,wndefined. wR refers to root mean square
values of total R functions which all affect the uncertainty of the test system [7,22].
Results and Discussion
In this study, a comparison of the engine performance, com-bustion, and emission characteristics of hydrogen addition on various diesel-biodiesel-butanol fuel blends at different engine loads were investigated. Furthermore, this experimental study researched the effects of hydrogen addition on each test fuel in terms of engine performance, combustion, and emission char-acteristics of the DI diesel engine as compared to neat euro diesel and without hydrogen addition.
The experiments were done in triplicate to confirm that the results were repeatable in the test. The experiment uncertainty of the total system has been calculated at 0.9636%. This can be considered as an acceptable level in the reliability of the test system. The accuracy of the measurement equipment and un-certainty of calculating quantity such as brake torque, brake power, BSFC, thermal efficiency, HRR, emissions, and total system uncertainty is given in Table5.
Engine Performance Characteristics
Brake Engine Torque
The engine was run with incremental engine speeds, ranging from 1000 to 3600 rpm with a regular interval of 100 rpm due
Table 4 The hydrogen mass
intake rate of the test fuels Test fuels Engine load (%)
The hydrogen mass intake rate (%)
Test fuels Engine load (%) The hydrogen mass intake rate (%) D100 + H2 25 9% B20But5 + H2 25 11.5% 50 9% 50 11% 75 9% 75 11% 100 5% 100 4% B20 + H2 25 10% B20But10 + H2 25 11% 50 10% 50 10.5% 75 10% 75 10.5% 100 4.5% 100 3%
to the determination of the maximum brake engine torque value of all test fuels. The maximum brake torque value was obtained with full open throttle and under 100% engine load at 2000 rpm engine speed. After this determination, all experi-ments were conducted at 2000 rpm in different engine opera-tion condiopera-tions. Variaopera-tion of the brake engine torque values with respect to the engine speed are given in Fig.2 and Table6.
Both biodiesel and butanol decreased brake engine torque compared to diesel fuel. The most important reason, in this case, is both fuel have lower LHV compared to diesel fuel. The other reason of decrease torque is the poorer atomization due to higher density and viscosity of biodiesel [23]. High density and viscosity lead to bad injection characteristics. The droplet diameter of injected biodiesel blends higher than diesel fuel. This case affects combustion negatively. Besides, cetane number is decreased with addition of butanol. Therefore, torque values decreased due to increase ignition delay and occur poor combustion [24].
The use of hydrogen showed a positive effect on the brake engine torque values. The enrichment with hydrogen gas of air entering the engine for all test fuels showed an increasing trend of brake engine torque values. Because, hydrogen has high LHV (approximately 120 MJ/kg). Higher LHVand faster
flame speed of hydrogen increased engine torque values. Besides, torque was improved due to enhanced combustion with both hydrogen and extra oxygen molecules within bio-diesel and butanol [25].
The Effect of Brake-Specific Fuel Consumption
The brake-specific fuel consumption values are given in Fig.3
for different engine operating conditions. BSFC values of B20 are higher approximately 2.84% than D100. BSFC increases generally with biodiesel usage because it has the lower heating value and poorer atomization due to higher density and vis-cosity [26]. Butanol addition increased BSFC further by about 22.41% according to B20. The reason of this increase is more fuel consumption for maximum performance because butanol has a lower thermal value than biodiesel [27]. Especially when fuel consumption of butanol blended fuels is highly at full load running conditions. Because, in this condition, engine needs high power, but butanol is not providing this required energy due to its low LHV. The average values of BSFC were decreased with the addition of hydrogen in the fuel blends due to its high LHV. When test fuels with/without hydrogen are compared, BSFC values of D100, B20, B20But5, and B20But10 fuels decrease by14.9%, 16%, 18.3%, and 17.1% respectively with hydrogen addition. These results are sustain-able with the results of other similar studies in literature [23,
25,28]. Added hydrogen on blended fuels decreased BSFC values’ higher rate compared to diesel fuel. Diesel engines run with much air (high air/fuel ratio) for full burning of sprayed
Table 5 The accuracy of the measurement equipment and uncertainty of the test system
Measurement Accuracy Calculated quantity Uncertainty (%) Hydraulic dynamometer ± 0.03% Brake torque 0.5761 Piezoelectric pressure sensor ± 1% Brake power 0.121 Digital rotary encoder ± 0.01 rpm BSFC 0.751 Cylinder volume ± 1% Thermal efficiency 0.0017 Cylinder pressure ± 1% Total engine performance 0.9612
CO2 ± 3% HRR 0.0071
CO ± 3% Emissions 0.0686
Exhaust gas analyzer HC ± 3% Total system 0.9636
NOx ± 4%
Smoke opacity ± 2%
Fig. 2 Variation of brake engine torque with engine speed
Table 6 The maximum brake engine torque values of test fuels at 2000 rpm
Fuels without Hydrogen Fuels with Hydrogen
D100 57.6 Nm D100 + H2 59.9 Nm
B20 55.3 Nm B20 + H2 59 Nm
B20But5 53.4 Nm B20But5 + H2 58.5 Nm
fuel. Furthermore, the high oxygen content of biodiesel (10.2%) and butanol (21.59%) [7] by weight provided extra burn with hydrogen entering in the cylinder. Therefore, de-crease for BSFC values of blended fuels is more comparable to pure diesel fuel due to hydrogen enrichment. But decrease in BSFC with hydrogen addition at full load running condi-tions is lower compared to other loads because the engine did not allow high hydrogen ratio at the same conditions.
The Effect of Brake Thermal Efficiency
The changing of brake thermal efficiency with engine load for test fuels are given in Fig.4. The oxygen content of B20 was increased with the biodiesel addition (20% by volumetric) in diesel fuel. The increased oxygen in fuel improved combus-tion efficiency [29], and therefore, biodiesel addition in-creased thermal efficiency at an average of approximately 1.7% according to D100. Besides, biodiesel increased thermal efficiency slightly with injection of somewhat more fuel for decreased pomp lacks due to high density and viscosity values [30] of B20 according to D100. The low LHV of butanol caused a decrease of about 16.17% of thermal efficiency
values. On the other hand, worsening of combustion efficien-cy due to the very low cetane number of butanol [31] may be another reason for the drop in thermal efficiency. The hydro-gen addition improved thermal efficiency values for all test fuels due to its high LHV and combustion efficiency. The rise rate of thermal efficiency increased with content of oxygen in fuels. The hydrogen addition increased thermal efficiency values by about an average of 2.31%, 2.33%, 3.67%, and 2.92%, respectively, according to fuels (D100, B20, B20But5, and B20But10) without hydrogen.
The Combustion Characteristics
The variation of the cylinder pressure and heat release rate versus crank angle curves is given in Fig.5for different en-gine operation conditions. For all the test fuels in Table7, all engine combustion characteristics such as ignition delay (ID), combustion duration (CD), maximum cylinder pressure (CP), and maximum heat release rate (HRR) parameters were determined.
According to results of combustion characteristic, CP values increased depending on engine load due to decrease of injected fuel amount at middle and low loads. Maximum CP values are obtained with B20 at all engine operating con-ditions. Some studies in the literature have observed that the biodiesel addition to the diesel fuel may cause a slight de-crease in the maximum CP and maximum HRR values due to lower calorific [32] value and poor atomization [30,33] characteristics of the biodiesel fuel. But numerous studies have shown that biodiesel addition increased generally maxi-mum CP value due to its higher cetane number [27,34] and oxygen content [35, 36]. High cetane number of biodiesel improved control combustion duration and ignition quality. Besides, combustion is accelerated suddenly due to the oxy-gen content of biodiesel, and therefore the maximum CP value of B20 is higher than that of D100. The maximum HRR of B20 is very close to D100. But crank angle obtained of max-imum HRR value with B20 is earlier than that of D100 for started to combustion before D100 due to oxygen contents of biodiesel.
Butanol decreased both maximum CP and maximum HRR values due to its high latent heat of vaporization and low LHV. Both high volatility and low LHV caused decrease of temper-ature in the cylinder [31] and was delayed at start of combus-tion. The effective combustion occurred after TDC too. Thereby, the maximum CP decreased along with the peak the HRR value of butanol-blended fuels.
There was a further increase in the maximum cylinder pres-sure when hydrogen was added to fuel blends. That fast-burning velocity ensures a more homogenous air–fuel blend and the higher diffusivity of hydrogen improved the combus-tion process [10]. Therefore, hydrogen addition increased the
Fig. 3 Variation of BSFC values with engine loads
Fig. 5 Variation of the cylinder pressure and heat release rate versus crank angle curves in different engine operation conditions
Table 7 Engine combustion characteristics of test fuels at different engine loads
ID (°CA) CD (°CA) CPmax (bar) HRRmax (J/°CA) ID (°CA) CD (°CA) CPmax (bar) HRRmax (J/°CA) 25% load 50% load D100 5 64 51.32 21.91 5 46 54.39 26.59 B20 6 35 55.72 23.25 6 41 58.23 25.44 B20But5 5 50 54.86 21.96 5 37 56.44 25.18 B20But10 6 60 52.91 21.28 5 43 55.61 24.2 D100 + H2 6 63 55.56 18.27 4 61 58.6 22.46 B20 + H2 5 41 60.85 25.61 6 42 61.41 26.95 B20But5 + H2 4 67 58.63 23.78 6 40 59.4 23.62 B20But10 + H2 6 59 56.72 18.8 6 36 58.94 26.66 75% load 100% load D100 6 46 56.91 28.3 7 38 59.16 27.54 B20 7 41 60.81 28.42 8 42 62.98 26.77 B20But5 5 37 56.24 26.47 8 52 57.44 23.03 B20But10 6 43 54.49 23.77 6 43 56.11 26.52 D100 + H2 6 61 60.91 19.48 6 66 63.6 17.44 B20 + H2 6 42 62.55 25.9 7 65 67.41 17.52 B20But5 + H2 7 40 58.81 25.45 6 42 61.41 25.01 B20But10 + H2 7 36 57.81 24.51 5 37 60.23 25.64
maximum cylinder pressure due to rapid combustion at a con-stant volume [37]. The maximum HRR values decreased with hydrogen addition. Maximum HRR values of test fuels was decreased by the hydrogen addition because it increased the propagation of the burn flame due to high flame velocity, diffusivity in air, a low cetane number, and the high auto-ignition temperature of hydrogen [10].
Emission Characteristics
The effect of hydrogen, butanol, and biodiesel addition to euro diesel on exhaust gas temperature, CO, CO2, HC, NOx, and
smoke opacity emissions were investigated at various engine loads. The obtained results were compared to each other and with literature conclusions.
The Effect of Engine Load on Exhaust Gas
Temperature
The test fuel’s exhaust gas temperature (EGT) variables with engine loads are presented in Fig.6. Biodiesel increased EGT values average 14.23% compared to D100 due to improve to combustion efficiency [26] of its oxygen content. Besides, biodiesel-blended fuel caused an increase amount of fuel injected to obtain the needed power output [27]. Butanol ad-dition in biodiesel-blended fuel decreased EGT values by 5.87% compared to B20 due to butanol’s high oxygen content [27] that increased burn speed and its high evaporation heat [24] that draws heat from the environment during combustion. The EGT values for hydrogen enrichment were increased av-erage of 6.76%, 5.26%, 4.78%, and 5.85% for D100, B20, B20But5, and B20But10 respectively. This increase in EGT with hydrogen enrichment is due to the improvement of com-bustion [38], hydrogen’s high temperature at end of burn [39], and its longer combustion duration.
The Effect of Engine Load on CO Emissions
The effect of fuel blends on CO emission was considered at 2000 rpm for various engine operating conditions, as given in Fig.7. B20 decreased CO emission values by an average of 26% according to D100 due to the oxygen content of biodie-sel. The CO emission values were decreased by about 22.7% compared to B20 with the use of butanol which has a richer oxygen content. The oxygen provides high combustion effi-ciency for biodiesel [33] and less CO emission release for butanol which has low contents of C atoms [24]. The value of CO emission reduced by an average of 12.19%, 13.67%, 20.92%, and 13.16% with the use of hydrogen for D100, B20, B20But5, and B20But10 respectively. This can be explained by the fact that the higher flame velocity and non-carbon con-tent of hydrogen enhances complete combustion and de-creases CO emissions [40]. Additionally, the high diffusivity of hydrogen has ensured a more homogeneous air-fuel mix-ture [12]. The chemical structure of hydrogen has not included
Fig. 6 Variation of exhaust gas temperatures with engine loads
Fig. 7 Variation of CO emissions with engine loads
any carbon atoms, so for all loads, there are low CO emissions [41].
The Effect of Engine Load on CO
2Emissions
The changing of CO2emission values with respect to engine
loads are shown in Fig.8. The average values of CO2
emis-sions increased by 5.52% with use of biodiesel-blended fuel compared to D100 due to the oxygen content of B20 because C atoms that can find enough oxygen occurred in CO2instead
of CO. Unlike the biodiesel effect on CO2emissions, the
ad-dition of butanol has shown a reduction by 11.3% in CO2
emissions to increase by the amount in the fuel blend accord-ing to B20. This situation may be explained due to butanol having a lower value of the C/H rate and carbon content com-pared to biodiesel and euro diesel fuel [42]. The addition of hydrogen to fuel blends has decreased the CO2emissions by
about 1.5% for all test fuels without hydrogen due to its im-proved combustion process, and it is a carbon-free fuel com-pared to hydrocarbon fuels [13].
The Effect of Engine Load on HC Emissions
The test fuel’s hydrocarbon (HC) emission variation with the engine loads are given in Fig.9. Although HC emissions decreased by 14.1% with the biodiesel addition compared to diesel fuel due to improving combustion efficiency of biodiesel’s oxygen content [30], it is increased marginally by 31.76% with the butanol addition in biodiesel blended fuel according to B20 due to worsening combustion efficiency of butanol’s very low cetane number [27]. Hydrogen decreased HC emissions by about 6.8% according to D100 and by 8.6% according to B20 at low and mid loads. The reason may be the lack carbon atoms in the chemical structure of the hydrogen gas [43]. Besides, the high combustion energy of hydrogen increased the temperature of burn-end [16], and it provided
full combustion for test fuels. The amount of hydrogen in the intake manifold at full load is very low compared to other loads. Besides, the oxygen required for the full combustion of hydrogen is not supplied due to lower air intake for com-bustion of injected fuel. Therefore, HC emission increased by about 3.86% for all test fuels.
The Effect of Engine Load on NO
xEmissions
The test fuel values of NOxemission variables with engine
loads are presented in Fig.10. NOxemissions are substantially
related to the combustion reaction period, cylinder gas tem-perature, and the amount of existing oxygen [44]. The increase to maximum in cylinder pressure and HRR values with bio-diesel addition have substantially increased average by 10.6% the formation of NOx because high cylinder temperatures im-prove the formation [16]. Butanol has decreased cylinder tem-perature so that a lower combustion temtem-perature can be one of the main reasons of reducing NOx emissions [7]. Thus, NOx
emissions decreased about 14.4% with the butanol addition in
Fig. 9 Variation of HC emissions with engine loads Fig. 11 Variation of smoke opacity values with engine loads Fig. 10 Variation of NOxemissions with engine loads
biodiesel blended fuel compare to B20. Hydrogen decreased NOxemissions of test fuels by about an average of 5.6%,
4.62%, 5.26%, and 2.91% according to D100, B20, B20But5, and B20But10 respectively at low and mid loads. Similar results were also obtained by Ref. [23,38]. This can be explained that oxygen in intake air reacted with H atoms replaced by N atoms. But hydrogen addition increased NOx emissions at full load due to lower H amount and overly high combustion temperature. These rise values are 1.77%, 2.48%, 1.29%, and 1.4% respectively for D100, B20, B20But5, and B20But10. These rise trends were also reported by Bari et al. [28] and Saravan et al. [39].
The Effect of Engine Load on Smoke Opacity
Emissions
The smoke opacity emissions with a variation of engine loads is presented in Fig.11. Smoke opacity values of B20 are lower in average with 31.55% compared to D100 due to oxygen content in the chemical structure of biodiesel. This results were also supported to those reported by Dhar et al. [30]. Butanol contents has higher oxygen than biodiesel. Therefore, it has further reduced smoke opacity values by 24.21% and 41.6% for B20But5 and B20But10 compared to B20. Yesilyurt et al. [24] also obtained similar results. The oxygen in fuels has improved combustion quality and oc-curred cleaner burning. Thus, opacity and the particles amount of exhaust gas are decreased. Smoke opacity values were de-creased by averages of 11.34%, 17%, 17.75%, and 19.26% for D100, B20, B20But5, and B20But10 respectively. While Miyamoto et al. [9] also presented similar results, Bose et al. [43] provided an improvement by use of hydrogen at their study. The effect of hydrogen on smoke opacity has shown a reduction in opacity levels due to hydrogen, including non-carbon atoms [10], high diffusivity, and a more homogenous air-fuel mixture [12]. These effects might be attributed to a reduction of the smoke formation by the addition of hydrogen.
Conclusions
In this experimental study, the effects of hydrogen addition on ternary (diesel-biodiesel-butanol) fuel blends in a DI diesel engine were investigated. The engine experiments were con-ducted at 2000 rpm engine speed and four different engine loads (25%, 50%, 75%, and 100%).
The conclusions obtained from the experimental results are below:
& The ternary fuels are suitable for use in diesel engine due to their fuel properties such as density, viscosity, cetane index, and LHV which are similar with neat diesel fuel.
Especially that butanol addition improved cold flow properties.
& The engine performance parameters worsening, with the use of biodiesel and butanol, improved owing to hydrogen enrichment. Especially when hydrogen’s high calorific value reduced the BSFC values by up to 18.3% by increas-ing up to 3.67% the BTE for ternary fuels.
& Hydrogen has increased maximum CP and HRR pressure values of oxygen-rich ternary mixtures by an average of 6.65% and 1.71% respectively due to its better combustion energy. Besides, hydrogen generally caused longer CD and IG compared to test fuels without hydrogen. The combus-tion analyses of hydrogen-enrichment ternary fuels are quite similar to that of diesel fuel as shown in Fig.5. & A decline of up to 20.92% for ternary fuels was observed
on the CO emission values with the use hydrogen com-pared to fuels without hydrogen. This reduce obtained 53.3% according to neat diesel fuel. There is a drop up to average of 1.5% of CO2emissions by hydrogen
enrich-ment. This drop observed on all test fuels is owed to the positive effect of hydrogen on the combustion.
& While hydrogen addition decreased HC emissions at low and partial loads, it increased full load according to fuels without hydrogen. Because the amount of injected hydro-gen to the intake manifold at full load is lower compared to other loads. Especially that obtained HC emission values with hydrogen addition to B20But5 fuel are lower with average of 16.11% according to D100 at low and partial loads, although it is higher by 0.8% compared to D100 at full load.
& NOx emissions decreased up to 5.26% with hydrogen addition at low and partial loads according to fuels without hydrogen for ternary fuels. But, it increased slightly due to lower hydrogen ratio and overly exhausted temperature at full load. Especially when NOx emissions of hydrogen-enriched B20But10 ternary fuel are lower with average of 7.23% for all load compared to D100.
& The decreasing smoke opacity values with the use of bio-diesel and butanol were further reduced with hydrogen addition. Hydrogen enrichment provided a considerable reduce as 66.32% on smoke opacity values compared to D100.
As a result, when performance, combustion, and exhaust emission parameters are evaluated, B20But5 H2 fuel as a ter-nary fuel provided optimum working conditions. Besides, it can say that hydrogen addition has eliminated the negative effect of butanol and biodiesel on the engine performance.
Acknowledgments The authors would like to acknowledge Erciyes University and Bayburt University, for the Scientific Research Projects Unit of Erciyes University, Turkey and for the financial support under the grant number FOA-2015-5817 and FBA-2017-7704.
References
1. Javed S, Satyanarayana Murthy YVV, Satyanarayana MRS, Rajeswara Reddy R, Rajagopal K (2016) Effect of a zinc oxide nanoparticle fuel additive on the emission reduction of a hydrogen dual-fuelled engine with jatropha methyl ester biodiesel blends. J Clean Prod 137:490–506
2. Sharma P, Dhar A (2018) Effect of hydrogen supplementation on engine performance and emissions. Int J Hydrog Energy 43(15): 7570–7580
3. Hosseini SM, Ahmadi R (2017) Performance and emissions char-acteristics in the combustion of co-fuel diesel-hydrogen in a heavy duty engine. Appl Energy 205:911–925
4. Doğan O (2011) The influence of n-butanol/diesel fuel blends uti-lization on a small diesel engine performance and emissions. Fuel 90(7):2467–2472
5. Han X, Yang Z, Wang M, Tjong J, Zheng M (2017) Clean com-bustion of n-butanol as a next generation biofuel for diesel engines. Appl Energy 198:347–359
6. Emiroğlu AO, Şen M (2018) Combustion, performance and emis-sion characteristics of various alcohol blends in a single cylinder diesel engine. Fuel 212:34–40
7. Örs I, Sarıkoç S, Atabani AE, Ünalan S, Akansu SO (2018) The effects on performance, combustion and emission characteristics of DICI engine fuelled with TiO 2 nanoparticles addition in diesel/ biodiesel/n-butanol blends. Fuel 234:177–188
8. Uyumaz A (2018) Combustion, performance and emission charac-teristics of a DI diesel engine fueled with mustard oil biodiesel fuel blends at different engine loads. Fuel 212:256–267
9. Miyamoto T, Hasegawa H, Mikami M, Kojima N, Kabashima H, Urata Y (2011) Effect of hydrogen addition to intake gas on com-bustion and exhaust emission characteristics of a diesel engine. Int J Hydrog Energy 36(20):13138–13149
10. Yilmaz IT, Gumus M (2018) Effects of hydrogen addition to the intake air on performance and emissions of common rail diesel engine. Energy 142:1104–1113
11. Karagöz Y, Gülerİ, Sandalcı T, Yüksek L, Dalkılıç AS (2016) Effect of hydrogen enrichment on combustion characteristics, emis-sions and performance of a diesel engine. Int J Hydrog Energy 41(1):656–665
12. Karagöz Y, Sandalcı T, Yüksek L, Dalkılıç AS (2015) Engine per-formance and emission effects of diesel burns enriched by hydrogen on different engine loads. Int J Hydrog Energy 40(20):6702–6713 13. Koten H (2018) Hydrogen effects on the diesel engine performance
and emissions. Int J Hydrog Energy 43(22):10511–10519 14. Tarabet L, Lounici MS, Loubar K, Khiari K, Bouguessa R, Tazerout
M (2018) Hydrogen supplemented natural gas effect on a DI diesel engine operating under dual fuel mode with a biodiesel pilot fuel. Int J Hydrog Energy 43(11):5961–5971
15. Saravanan N, Nagarajan G (2009) An insight on hydrogen fuel injection techniques with SCR system for NOX reduction in a hydrogen–diesel dual fuel engine. Int J Hydrog Energy 34(21): 9019–9032
16. Zhou JH, Cheung CS, Leung CW (2014) Combustion, perfor-mance, regulated and unregulated emissions of a diesel engine with hydrogen addition. Appl Energy 126:1–12
17. Zhou JH, Cheung CS, Zhao WZ, Leung CW (2016) Diesel– hydrogen dual-fuel combustion and its impact on unregulated gas-eous emissions and particulate emissions under different engine loads and engine speeds. Energy 94:110–123
18. Jhang S-R, Chen K-S, Lin S-L, Lin Y-C, Amesho KTT, Chen C-B (2018) Evaluation of the reduction in carbonyl emissions and ozone formation potential from the exhaust of a heavy-duty diesel engine by hydrogen-diesel dual fuel combustion. Appl Therm Eng 132: 586–594
19. Jhang S-R, Chen K-S, Lin S-L, Lin Y-C, Cheng WL (2016) Reducing pollutant emissions from a heavy-duty diesel engine by using hydrogen additions. Fuel 172:89–95
20. Akansu S (2004) Internal combustion engines fueled by natural gas? Hydrogen mixtures. Int J Hydrog Energy 29(14):1527–1539 21. Dimitriou P, Kumar M, Tsujimura T, Suzuki Y (2018) Combustion
and emission characteristics of a hydrogen-diesel dual-fuel engine. Int J Hydrog Energy 43(29):13605–13617
22. Holman JP (2012) In: Holman JP (ed) Experimental methods for engineers, 8th edn. McGraw-Hill: Raghothaman Srinivasan 23. Serin H, Yıldızhan Ş (2018) Hydrogen addition to tea seed oil
biodiesel: performance and emission characteristics. Int J Hydrog Energy 43(38):18020–18027
24. Yesilyurt MK, Eryilmaz T, Arslan M (2018) A comparative analysis of the engine performance, exhaust emissions and combustion be-haviors of a compression ignition engine fuelled with biodiesel/ diesel/1-butanol (C4 alcohol) and biodiesel/diesel/n-pentanol (C5 alcohol) fuel blends. Energy 165:1332–1351
25. Uludamar E (2018) Effect of hydroxy and hydrogen gas addition on diesel engine fuelled with microalgae biodiesel. Int J Hydrog Energy 43(38):18028–18036
26. Yıldızhan Ş, Uludamar E, Çalık A, Dede G, Özcanlı M (2017) Fuel properties, performance and emission characterization of waste cooking oil (WCO) in a variable compression ratio (VCR) diesel engine. Eur Mech Sci 1(2):56–62
27. Killol A, Reddy N, Paruvada S, Murugan S (2019) Experimental studies of a diesel engine run on biodiesel n-butanol blends. Renew Energy 135:687–700
28. Bari S, Mohammad Esmaeil M (2010) Effect of H2/O2 addition in increasing the thermal efficiency of a diesel engine. Fuel 89(2):378– 383
29. Canakci M, Hosoz M (2006) Energy and exergy analyses of a diesel engine fuelled with various biodiesels. Energy Sources Part B: Econ Plann Policy 1(4):379–394
30. Dhar A, Kevin R, Agarwal AK (2012) Production of biodiesel from high-FFA neem oil and its performance, emission and combustion characterization in a single cylinder DICI engine. Fuel Process Technol 97:118–129
31. Huang H, Liu Q, Teng W, Pan M, Liu C, Wang Q (2018) Improvement of combustion performance and emissions in diesel engines by fueling n-butanol/diesel/PODE3–4 mixtures. Appl Energy 227:38–48
32. Can Ö (2014) Combustion characteristics, performance and exhaust emissions of a diesel engine fueled with a waste cooking oil bio-diesel mixture. Energy Convers Manag 87:676–686
33. Özener O, Yüksek L, Ergenç AT, Özkan M (2014) Effects of soy-bean biodiesel on a DI diesel engine performance, emission and combustion characteristics. Fuel 115:875–883
34. Alptekin E, Canakci M, Ozsezen AN, Turkcan A, Sanli H (2015) Using waste animal fat based biodiesels–bioethanol–diesel fuel blends in a DI diesel engine. Fuel 157:245–254
35. Can Ö, Öztürk E, Solmaz H, Aksoy F, Çinar C, Yücesu HS (2016) Combined effects of soybean biodiesel fuel addition and EGR ap-plication on the combustion and exhaust emissions in a diesel en-gine. Appl Therm Eng 95:115–124
36. Chang Y-C, Lee W-J, Wu TS, Wu C-Y, Chen S-J (2014) Use of water containing acetone–butanol–ethanol for NO x -PM (nitrogen oxide-particulate matter) trade-off in the diesel engine fueled with biodiesel. Energy 64:678–687
37. Saravanan N, Nagarajan G, Sanjay G, Dhanasekaran C, Kalaiselvan KM (2008) Combustion analysis on a DI diesel engine with hydrogen in dual fuel mode. Fuel 87(17–18):3591–3599 38. Köse H, Ciniviz M (2013) An experimental investigation of effect
on diesel engine performance and exhaust emissions of addition at dual fuel mode of hydrogen. Fuel Process Technol 114:26–34
39. Saravanan N, Nagarajan G (2010) Performance and emission stud-ies on port injection of hydrogen with varied flow rates with dstud-iesel as an ignition source. Appl Energy 87(7):2218–2229
40. An H, Yang WM, Maghbouli A, Li J, Chou SK, Chua KJ (2013) A numerical study on a hydrogen assisted diesel engine. Int J Hydrog Energy 38(6):2919–2928
41. Parthasarathy M, Isaac JoshuaRamesh Lalvani J, Dhinesh B, Annamalai K (2016) Effect of hydrogen on ethanol-biodiesel blend on performance and emission characteristics of a direct injection diesel engine. Ecotoxicol Environ Saf 134(Pt 2):433–439 42. Sukjit E, Herreros JM, Dearn KD, Tsolakis A, Theinnoi K (2013)
Effect of hydrogen on butanol–biodiesel blends in compression ignition engines. Int J Hydrog Energy 38(3):1624–1635
43. Bose PK, Maji D (2009) An experimental investigation on engine performance and emissions of a single cylinder diesel engine using hydrogen as inducted fuel and diesel as injected fuel with exhaust gas recirculation. Int J Hydrog Energy 34(11):4847–4854 44. Barrios CC, Domínguez-Sáez A, Hormigo D (2017) Influence of
hydrogen addition on combustion characteristics and particle num-ber and size distribution emissions of a TDI diesel engine. Fuel 199: 162–168
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