Combined effect of water emulsion and ZnO nanoparticle on emissions pattern of soybean biodiesel fuelled diesel engine

Journal Pre-proof Combined effect of water emulsion and ZnO nanoparticle on emissions pattern of soybean biodiesel fuelled diesel engine

Suresh Vellaiyan, C.M. Anand Partheeban PII:

S0960-1481(19)31592-7

DOI:

https://doi.org/10.1016/j.renene.2019.10.101

Reference:

RENE 12470

To appear in:

Renewable Energy

Received Date:

06 February 2018

Accepted Date:

18 October 2019

Please cite this article as: Suresh Vellaiyan, C.M. Anand Partheeban, Combined effect of water emulsion and ZnO nanoparticle on emissions pattern of soybean biodiesel fuelled diesel engine, Renewable Energy (2019), https://doi.org/10.1016/j.renene.2019.10.101

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.

Journal Pre-proof

Combined effect of water emulsion and ZnO nanoparticle on emissions pattern of soybean biodiesel fuelled diesel engine Suresh Vellaiyan a*, C.M. Anand Partheeban b a Department

of Mechanical Engineering, Haramaya Institute of Technology, Haramaya University, Ethiopia.

b Department

of Mechanical Engineering, United Institute of Technology, Coimbatore, India

* Corresponding

Author; Suresh Vellaiyan, Department of Mechanical Engineering, Haramaya

Institute of Technology, Haramaya University, Ethiopia. Tel: +251 0905487286. e-mail: [email protected]

Journal Pre-proof

Combined effect of water emulsion and ZnO nanoparticle on emissions pattern of soybean biodiesel fuelled diesel engine Abstract The present study investigates the effect of water emulsion and ZnO nanoparticle on the emissions pattern of a diesel engine running with SB. Test fuels were prepared based on the different percentage of water and mass fractions of nanoparticle, and the emission characteristics were compared with SB. The physicochemical properties were measured based on EN14214 standards, and the characteristics of nano-fuels were examined using SEM, EDS and UV-visible absorption spectrum. Experiments were carried out in a computerized, single-cylinder, fourstroke diesel engine with an eddy current dynamometer. The experimental results reveal that SB20W emulsion fuel promotes a drop of 41.4% and 28.3% in NOx and smoke emissions at BP of 2.56kW compared to SB, respectively. SB10W emulsion fuel promotes an improvement of 40% and 33.3% in HC and CO emissions compared to SB at 2.56kW BP, respectively. An inclusion of ZnO nanoparticle in SB20W emulsion fuel significantly reduces the NOx, HC, CO and smoke emissions irrespective of load conditions, and an increase in the mass fraction of nanoparticle further reduces the emissions level. At 2.56kW BP, SB20W100ZnO emulsion fuel reduces the NOx, HC, CO and smoke emissions by 7.1%, 40%, 33.3% and 15.1% compared to SB20W emulsion fuel, respectively.

Key words: Diesel engine; soybean biodiesel; emulsified biodiesel; ZnO nanoparticle; surface characteristics; emission characteristics.

1

Journal Pre-proof

Acronyms BP

:

Brake power

ppm

: Parts per million

CO

:

Carbon monoxide

SB

: Soybean biodiesel

CO2

:

Carbon dioxide

SB10W

: SB + 10% water

EDS

:

Energy dispersive spectrum

SB20W

: SB + 20% water

HC

:

Hydrocarbon

SB20W50ZnO

: S210W+50ppm ZnO

nm

:

Nano-meter

SB20W100ZnO

: SB10W+100ppmZnO

NOx

:

Oxides of Nitrogen

SEM

: Scanning electron microscopy

PM

Particulate matter

1. Introduction In the present century, consumption of fossil fuels is drastically increased throughout the world due to an industrialization, which will leads to an oil crisis within three decades. Apart from that, diesel fuel is commonly exercised in transportation, power generation, industry and agricultural sectors due to its better fuel economy and remarkable performance in the diesel engine compared to gasoline fuel [1, 2]. However, the emissions released by the diesel engine exhaust, especially the high amount of NOx and PM emissions are not only affect the environment but also the human health [3]. Hence, these two critical issues direct the automotive manufacturers and engine researchers to develop the alternative sources for diesel fuel and emission control techniques for existing and future generation diesel engines. In order to meet the fossil fuel demand, the biodiesel produced from vegetable oils has received much attention, as it is renewable, non-toxic and biodegradable. The biodiesel can be

2

Journal Pre-proof

replaced in existing diesel engines without any engine modification and additional cost [4, 5]. In addition to that, the biodiesel has better physicochemical properties compared to conventional diesel fuel, such as enhanced cetane number, absence of aromatics and sulphur, and high oxygen content [6]. This high oxygen concentration in biodiesel leads to complete combustion, which may results in reduced level of harmful emissions such as sulphur oxides, PM and CO. At the same time, the higher combustion temperature associated with biodiesel leads to high level of NOx emission that indicates the negative impact of biodiesel fuelled diesel engine [6-8]. Out of several vegetable oil based biodiesels, SB is attracted many researchers since it is more abundant in developing and developed countries, and having high oil derivation rate compared to other biodiesels. Apart from that, the physicochemical properties of transesterified SB directly meet the EN 14214 standards [7, 8]. A plenty of valuable researches have been conducted using SB and their blends with conventional diesel fuel. The combustion characteristics show that SB and its blends significantly reduce the ignition delay period and the premixed combustion peak. This may be due to the higher cetane number of SB and its blends [8, 9]. The performance characteristics show that SB and its blend with conventional diesel lead to a marginal drop in brake torque, and a significant increase in brake specific fuel consumption. This may be due to lower heating value of SB compared to conventional diesel fuel [9, 10]. As far as the emissions characteristics are concerned, all the reports conclude that SB and its blends with conventional diesel fuel promote a significant drop in HC, CO, PM and smoke emissions. This could be the positive attributes of SB and its blends such as improved combustion efficiency, high oxygen concentration and uniform air-fuel mixing. However, the NOx emission associated with SB and its blends with diesel fuel is higher than ordinary diesel fuel. This may be due to the enrichment of oxygen in

3

Journal Pre-proof

biodiesel that can promotes high local combustion temperature and results in high magnitude of NOx formation [9, 11, 12]. In order to reduce the NOx emission from the diesel engine exhaust, several attempts have been made by the researchers that can be generally classified as a pre-processing and postprocessing emission control techniques. Out of these, water emulsion with diesel engine fuel, the pre-processing technique is mostly preferred by many researchers as the simultaneous reduction of NOx and PM emissions can be attained without any engine retrofitting [13-15]. The water emulsified diesel fuel reduces the peak flame temperature during the combustion process due to the high latent heat absorption of water particles and results in lower NOx emission [13]. The better air-fuel mixing and enhanced atomization associated with emulsion fuel combustion also promote a lower level of HC, CO and PM emissions [14]. In addition to that, engine performance also improved for emulsified fuel compared to conventional diesel fuel due to the microexplosion and secondary atomization associated with emulsion fuel [14, 16]. In water emulsified diesel fuel engine, an increase in the water concentration above the particular limit leads to emit more amount of HC and CO emissions due to the loner ignition delay period associated with water emulsified fuel [17]. Several attempts have been made to shorten the ignition delay period of water emulsified diesel fuel engine by including metal-based nanoadditives such as cerium oxide, alumina, carbon nanotubes and zinc oxide [6, 18-20]. The presence of nanoparticle in base fuel promotes enhancement in thermal conductivity and surface area-to-volume ratio. These properties promote a better air-fuel mixing and an improved chemical reaction that results in complete combustion [6, 20]. Out of several nanoadditives, ZnO nanoparticle is preferred in the present study owing to its positive thermal properties compared to other nanoparticles. In addition to that, eco-friendly, non-hazardous synthesis route, and

4

Journal Pre-proof

enhanced wear and friction characteristics of ZnO nanoparticle are directed to choose the ZnO nanoparticle as a suitable additive for the present study [17, 20]. Karthikeyan et al. [21] conducted the emission characteristics of the diesel engine fueled with canola oil methyl ester with ZnO nanoadditive. The report concludes that ZnO nanoadditive inclusion reduces the NOx, CO and HC emissions by 18.7%, 14% and 50% compared to plain canola oil, respectively. Vellaiyan and Amirthagadeswaran [20] investigated the emission characteristics of the diesel engine fueled with water emulsified diesel fuel and ZnO nanoadditive. The experimental findings indicate that the ZnO nanoparticle inclusion with emulsion fuel reduces the NOx, CO and HC emissions by 32.5%, 25% and 9.9%, respectively. The same authors also pointed out that the mass faction of 100ppm ZnO nanoparticle in the water emulsified diesel fuel is the optimum condition to promote better combustion, performance and emissions level [22]. The use of SB blends with diesel fuel and water emulsion with diesel are the active fields of inquiry in the past two decades as the engine manufacturers have to meet the fuel demand and stringent pollution regulations. As far as the author’s knowledge is concerned, no efforts have been attempted to study the surface and optical properties of ZnO emulsified SB, and the combined effect of water and ZnO nanoparticle inclusion on the emissions pattern of SB fuelled diesel engine. Hence, the present study attempted to investigate the surface, optical properties of ZnO nanofuel, and the emissions characteristics of water emulsified SB (SB10W and SB20W) and ZnO nanoparticle incorporated SB emulsions (SB20W50ZnO and SB20W100ZnO). The experimental results are used for a comparison with pure SB.

5

Journal Pre-proof

2. Materials and Methods 2.1. Materials In this work, SB was prepared from crude soybean oil (Agro biotech, India), which was used as continuous phase of the emulsion. Sulphuric acid, methanol and potassium hydroxide (Gogia Chemical Industries Pvt. Ltd, India) were used for transesterification process. Sorbitan monolaurate with hydrophilic-lipophilic balance 8.6 (Estelle Chemicals Pvt. Ltd, India), a nonionic surfactant that can burn with no soot and free of sulphur [7] was used as the surfactant. Double distilled water was used as the dispersed phase of the emulsion. ZnO nanoparticle (Sigma-Aldrich, India) was used as an additive and di-methyl ether was used as a solvent. 2.2. Soybean biodiesel preparation

Pure soybean

Esterification

crude oil

process

Removal of unwanted mixture of methanol & water followed by acid value test

\,i]

Formation of

Heating the crude oil up

methyl ester and

to 60°C with KOH &

glycerol

Methanol

Separation of

Drying and washing

Transesterification process

Pure soybean biodiesel

methyl ester

Fig.1. Flow diagram of SB preparation from crude soybean oil

6

Journal Pre-proof

A two-stage acid and alkyl based transesterification process was followed in the present study to convert the crude soybean oil into SB. The flow diagram of SB preparation from crude soybean oil is depicted in Fig.1. Initially, the higher acid value of crude oil was treated with an esterification process to reduce the acid value less than one. During the esterification process, the crude soybean oil was heated up to 60⁰C, mixed with a measured quantity of sulphuric acid (1%) and methanol (20:1 oil molar ratio), and stirred constantly for about an hour. The resulting solution was involved in a transesterification process. During this process, the solution was once again heated to 60⁰C, stirred with potassium hydroxide and methanol solution (8:1 oil molar ratio), and allowed for sedimentation. The separated glycerol was removed from the container and residue methyl ester was washed and dried continuously. The derived pure methyl ester of SB can be directly used in the diesel engine as the biodiesel. 2.3. Emulsion fuel preparation and stability measurement The predetermined mass fraction of ZnO nanoparticle (50 ppm and 100 ppm) was dispersed in SB using UP 400S ultrasonic processor (200-400V; 50/60Hz and amplitude of 20100%). The photographic view of ultrasonic processor is shown in Fig.2. The mechanical homogenizer was used to disperse the water particles in nanoparticle incorporated SB. The experimental setup of emulsion fuel preparation is shown in Fig. 3. During the process, the desired quantity of double distilled water (10% and 20%) was added drop-by-drop continuously to nanoparticle mixed SB during the high-speed of mechanical agitation (5000 rpm). In the same way, the surfactant (1% total volume) also added with SB to reduce the surface tension between the SB and water. The entire mixture was allowed to stir constantly for about 30 minutes. The resulting solution was replaced to Ultrasonic sonication bath to homogenize the mixture. The photographic view of Ultrasonic sonication bath is shown in Fig. 4.

7

Journal Pre-proof

Fig.2. Photographic view of Ultrasonic Processor

8

Journal Pre-proof

Fig.3. Photographic view of emulsion fuel preparation setup

9

Journal Pre-proof

Fig.4. Photographic view of Ultrasonic sonication bath

Fig.5. Schematic layout of emulsion fuel stability measurement setup In order to measure the stability of water emulsified biodiesel, laser beam assisted photonic circuit was developed in the present study and the schematic layout is represented in

10

Journal Pre-proof

Fig.5. The laser beam from the source was allowed to penetrate the emulsion surface and was focused on the photo resistor circuit. The photo resistor circuit was connected to a multi-meter, which shows the uniform indication during the stable condition. The separation of water and biodiesel in the emulsion fuel brings the high-density water at the bottom of container, and biodiesel is above the water surface. At this condition, the multi-meter display an uneven readings due to the density variation. 2.4. Characterization of ZnO nanoparticle in emulsion fuel The ZnO nanoparticle incorporated emulsion fuel is dried and keeps in the powder form to analyze the surface characterize of ZnO nanoparticle, as it is difficult in the liquid form. Scanning electron microscopy image and energy dispersive spectrum of the sample were obtained by JSM-6390LV and OXFORD XMX N, respectively. To confirm the dispersion of nanoparticle in the prepared fuel, 5ml of sample fuel was mixed with 20ml of di-methyl ether. The resulting solution was placed in UV- visible absorption spectrometer and the optical properties were examined. The di-methyl ether was used as the solvent to convert the milky emulsion fuel into clear form. Based on the absorbance wavelength, the dispersed particle size was calculated as follows [20]: ―0.3049 + 𝑟𝑎𝑑𝑖𝑢𝑠 (𝑛𝑚) =

―26.23012 +

10240.72 𝜆𝑝 (𝑛𝑚)

2483.2 ―6.3829 + 𝜆𝑝 (𝑛𝑚)

where λp is peak absorbance wavelength in nm.

11

(1)

Journal Pre-proof

2.5. Engine testing setup and test procedure A computerized, single cylinder, four strokes, variable compression ratio and natural aspirated diesel engine was used as the test engine in this study. There was no modification in the injection system and it was maintained at 23⁰ before top dead centre. AVL five-gas analyzer was used to record the emissions parameter during the experiments. AVL smoke meter was used to measure the smoke opacity. The detailed specifications of the test engine and gas analyzer are listed in Table 1. Initially, the engine was allowed to run for 15 minutes to obtain steady state exhaust temperature and speed. Once the steady state was obtained the emissions parameter were recorded. The schematic layout of engine experimental setup is shown in Fig. 6. Experiments were conducted at different engine load conditions say no load, 25%, 50%, 75% and peak load, and the corresponding BP were calculated as 0kW, 0.85kW, 1.71kW, 2.56kW and 3.42kW, respectively. At each loading condition, experiments were repeated 10 times and the average value was taken into account. The overall uncertainty of experimental results are calculated as 1% using the following equation: 𝑂𝑣𝑒𝑟𝑎𝑙𝑙 𝑢𝑛𝑐𝑒𝑟𝑡𝑎𝑖𝑛𝑖𝑡𝑦 = 𝑢𝑛𝑐𝑒𝑟𝑡𝑎𝑖𝑛𝑖𝑡𝑦 𝑜𝑓 (𝑊 + 𝑁 + 𝐵𝑃 + 𝐶𝑂 + 𝐻𝐶 + 𝐶𝑂22 + 𝑁𝑂2𝑥 + 𝑠𝑚𝑜𝑘𝑒2) (2) 2

2

2

2

2

The detailed list of uncertainty percentage of various measured and calculated parameters is listed in Table 2. Table 1 Specifications of test engine and emission analyzer (a) Engine specifications Parameter

Specification

Engine type

4-stroke, single cylinder, natural aspirated, variable compression ratio diesel engine

Bore × Stroke (mm)

87.5 × 110 12

Journal Pre-proof

Displacement volume (cc)

661.45

Max. power

3.5 kW at 1500 rpm

CR range

12-18

Dynamometer

Eddy current dynamometer (max. load of 7.5 kW) (b) Gas analyzer specifications

Measured quality

Measuring range

Resolution

HC

0 to 20000 ppm vol

≤ 2000: 1 ppm vol, > 2000: 10 ppm vol

CO

0 to 10% vol

0.01% vol

NOx

0 to 5000 ppm vol

1 ppm vol

CO2

0 to 20% vol

0.1% vol

O2

0 to 22% vol

0.01% vol

Table 2 List of uncertainty of various measured and calculated quantities Quantities

Accuracy

Uncertainty (%)

±10rpm

±0.1

±50grams

±0.2

CO emission

±0.01%

±0.1

HC emission

±10ppm

±0.2

NOx emission

±10ppm

±0.2

CO2 emission

±0.01%

±0.1

Smoke meter

±1

±0.1

Brake power

-

±0.85

Engine speed (N) Dynamometer load cell (W)

13

Journal Pre-proof

Fig.6. Schematic layout of engine test setup 3. Results and discussion 3.1. Physicochemical properties of test fuels The physicochemical properties of prepared SB, emulsified SBs and ZnO included emulsified SBs were measured in accordance with EN 14214 standards [23]. The measured properties are listed in Table 3. From the measured value, it is observed that the heating value of SB10W emulsified biodiesel is 8.4% less than pure SB due to latent heat absorption of water particles and an increase in the water concentration further reduces the heating value. However, the enriched oxygen associated with SB can play a vital role during the combustion process to compensate the lower heating value [24]. A marginal increase in heating value is recorded with ZnO nanoparticle inclusion in emulsion fuel due to its better thermal property. The density of water emulsified SB is higher than SB due to its molecular structure. The SB20W emulsified biodiesel density is approximately 2.5% higher than base diesel. An inclusion of ZnO nanoparticle in emulsified fuel further marginally increases the density due to its molecular weight. 14

Journal Pre-proof

Table 3 Properties of SB and emulsion fuels

Fuels

Lower

Density

Viscosity

Flash

Cetane

Stability

calorific

at15⁰ C

at 40˚C

point

index

period

value

(kg/m3)

(mm2/s)

˚C

(hrs)

(MJ/kg) SB

37.9

871.2

3.72

129

55.8

-

SB10W

34.7

884.4

4.58

140

53.4

104

SB20W

31.3

894.4

4.92

152

51.2

90

SB20W50ZnO

31.7

894.9

4.95

154

53.1

78

SB20W100ZnO

32

895.5

4.98

157

54.9

72

EN14214 limits

-

800-900

3.5-5

min 120

min 51

-

The viscosity of SB10W emulsified SB is 23.1% higher than base SB, whereas SB20W emulsified SB exhibits 32.2% higher viscosity value compared to SB. The high viscosity of fuel will directly affects the atomization process during the combustion. The poor atomization may leads to high engine deposit resulting in increases the wear [25]. An addition of nanoparticle further increases the viscosity of emulsion fuels marginally due to its molecular structure. However, the micro-explosion behavior associated with emulsion fuel can improves the combustion behavior and reduces the negative impact due to high viscosity [13, 14]. The flash point of SB emulsion is increased with increase in water concentration. The heat absorption of nanoparticle in emulsion fuel further increases the flash point. Though the flash point value does not affect the combustion process directly, the high value shows the safety aspects such as storage and transportation [16]. The high cetane index promotes better combustion efficiency and engine performance [8, 9]. The cetane index of emulsified SB is lower than pure SB. However, the ZnO included emulsion fuel promotes high cetane index due to its longer chain length and degree of instauration [17]. The increase in water concentration and mass fraction of 15

Journal Pre-proof

ZnO nanoparticle lead to drop in the emulsion stability. However, the emulsified biodiesels and ZnO incorporated emulsified biodiesels show the sufficient stability period due to the presence of surfactant and high speed of mechanical agitation. Overall, it is noted that the nanoparticle addition in ppm level did not cause any significant changes in density, viscosity and calorific value, but better improvement was achieved for flash point and cetane index.

3.2. SEM, EDS and UV- visible absorption spectra analyses

Fig.7. SEM image of ZnO sample The SEM image of ZnO sample in the nanofuel is shown in Fig.7. From the photographical representation, it is noted that the ZnO nanoparticles are marginally agglomerated in the sample fuel, which is commonly observed when the nanofuel is dried into the powder form. The presence of surfactant in nanofuel also leads to high porous nature [26, 27]. The energy dispersive spectrum of the sample is represented in Fig.8. The graphical representation 16

Journal Pre-proof

shows that the sample has a composition of Zn and Oxygen, and the corresponding weight percentage is noted as 88.1 and 9.3. A marginal deflection in the counts is observed at 3.54keV energy due to the presence of surfactant. Fig.9 shows the UV-absorption spectrum of ZnO included water emulsified SB. From the graphical representation, it is noted that the absorbance peak occurs at a wavelength of 255 nm. By using equation (1), the particle size in the emulsion fuel is calculated as 1.02 nm.

Fig.8. Energy dispersive spectrum of ZnO sample

17

Journal Pre-proof

Fig.9. UV- absorption spectrum of ZnO sample 3.3. Nitrogen oxides emission The NOx emission characteristics of SB, water emulsified biodiesels and ZnO incorporated emulsion fuels are represented in Fig. 10 under varying BP conditions. In general, the NOx formation in diesel engine is high due to more oxygen concentration, better equivalence ratio and high combustion temperature compared to gasoline engine [28]. The rich oxygen concentration associated with SB that can offer enhanced oxidation of hydrocarbon molecules can be further increases the NOx emission [8, 9]. From the experimental results, it is observed that an increase in the water concentration in SB reduces the NOx formation in diesel engine. The water particles present in the emulsified SB may absorb the heat during the combustion process that can reduces the combustion flame temperature and resulting in low NOx formation [14, 16]. SB10W emulsified biodiesel promotes 25% lower NOx emission at 75% load condition compared to pure SB, whereas 20% water concentration in SB promotes 41.4% NOx reduction. 18

Journal Pre-proof

The average reduction of NOx emission for emulsified fuel is recorded as 22.1% and 37.5% for SB10W and SB20W emulsified fuels compared to SB, respectively.

NOx, ppm vol

1800 1500 1200 900 600 300 0 0

SB

SB10W

0.85 1.71 Brake power, kW SB20W

SB20W50ZnO

2.56

3.42

SB20W100ZnO

Fig. 10. Variation of NOx emission with respect to engine BP ZnO nanoparticle included emulsified biodiesels further reduces the NOx formation compared to SB and water emulsified biodiesels. This may be due to the enhancement in thermal conductivity, improvement in cetane number and better surface area-volume ratio of ZnO nanoparticle. These possessions can promote lower ignition delay period (less fuel accumulation during the pre-mixed combustion stage) that results in lower peak in-cylinder pressure and heat release rate [21, 22]. The average NOx emission reduction for SB20W50ZnO emulsion fuel is noted as 8.7% compared to SB20W emulsified fuel, whereas SB20W100ZnO emulsion fuel exhibits 12.9%. 3.4. Carbon monoxide emission The high CO formation during the combustion process is a result of lower oxygen availability that is not sufficient to convert CO into CO2 completely. The higher CO emission indicates the incomplete combustion [29]. Fig.11 shows the graphical representation of CO 19

Journal Pre-proof

emission of all test fuels under different BP conditions. From the figure, it is observed that the formation of CO is drastically reduced with increases in engine load from no load condition to 75% engine load condition, and slowly increased at peak load. The lean flame combustion zone at low engine load conditions generates more amount of CO emission. The lack of oxygen inside the jet core, the impinged fuel on the cylinder walls and the end portion of injected fuel at peak load condition lead to formation of more CO emission [16, 30]. The emulsified SBs exhibit high CO emission compared to pure SB at low and medium loads. This may be due to high latent heat absorption of water particles during the combustion process [13, 14]. SB20W emulsified biodiesel exhibits 33.3% higher CO emission at no load condition compared to pure SB, whereas 20% increases is recorded at 25% load condition. However, at higher engine loads, the CO emission is significantly reduced with SB10W emulsion fuel due to better oxidation. At 75% load condition, SB10W emulsified biodiesel exhibits 33.3% lower CO emission compared to SB. Similar to HC emission trend, CO emission also increased for SB20W emulsion fuel at all engine loads due to the high heat sink effect of water-emulsified fuel.

CO, %vol

0.1 0.08 0.06 0.04 0.02 0 0

SB

1

SB10W

2 Brake power, kW

SB20W

SB20W50ZnO

20

3

4

SB20W100ZnO

Journal Pre-proof

Fig.11. Variation of CO emission with respect to engine BP The ZnO nanoparticle included SB20W emulsified fuel shows the better CO emission characters at all engine loads compared to SB20W emulsion fuel. This may be due to the secondary atomization characteristics associated with water-emulsified fuel that can be able to disperse the nanoparticle uniformly during the combustion process and resulting in complete combustion [16, 24]. The catalytic activity of ZnO nanoparticle and its improved combustion characteristics lower the carbon combustion-activation temperature also results in more complete combustion. SB20W100ZnO emulsified biodiesel promotes 33.3% CO emission reduction at 75% load condition compared to SB20W emulsified biodiesel. The average reduction in CO emission is recorded as 21.5% and 33% for SB20W50ZnO and SB20W100ZnO emulsified biodiesel, respectively. In addition to that, it is clearly noted that SB20W100ZnO emulsified biodiesel exhibits lower CO emission compared to all other test fuels under all loading conditions. 3.5. Hydrocarbon emission Fig. 12 represents the variation of unburned hydrocarbon emission of all test fuels under different engine load conditions. From the figure, it is noted that water-emulsified SBs exhibit high HC emission compared to SB at low load conditions. This may be due to the presence of water particles in emulsified fuel that can reduce the combustion temperature and lead to incomplete combustion [17, 22]. At no load condition, SB20W emulsion fuel exhibits 19% higher HC emission compared to pure SB. However, the high in-cylinder and wall temperature at high engine loads accelerate the micro-explosion and results in low magnitude of HC emission. At peak load condition, SB10W emulsion fuel promotes 35.7% lower HC emission compared to pure SB. On the other hand, the high heat sink effect associated with high water concentration

21

Journal Pre-proof

increases the HC emission [17]. SB20W emulsion fuel exhibits 44.4% higher HC emission when compared to SB10W emulsion fuel at peak load condition.

HC, ppm vol

30 20 10 0 0

SB

1

SB10W

2 Brake power, kW SB20W

SB20W50ZnO

3

4

SB20W100ZnO

Fig.12. Variation of HC emission with respect to engine BP The inclusion of ZnO nanoparticle in SB20W emulsified biodiesel reduces the HC emission at all loading conditions. An increase in mass fraction of ZnO nanoparticle is directly proportional to drop in HC emission. This could be the positive effect of ZnO nanoparticle during the combustion process such as lower ignition delay period and better explosion characteristics. In addition to that, the ZnO nanoparticle can be act as a catalyst during the combustion process and promotes complete combustion [21]. At 75% load condition, SB20W50ZnO emulsified fuel exhibits 20% lower HC emission when compared to SB20W emulsified fuel, whereas at full load condition it exhibits 15.4%. SB20W100ZnO promotes 40% HC emission reduction at 75% load condition and the average reduction in HC emission is recorded as 28.8% compared to SB20W emulsified biodiesel.

22

Journal Pre-proof

3.6. Carbon dioxide emission

CO2, %vol

12 9 6 3 0 0

SB

SB10W

0.85 1.71 Brake power, kW SB20W

2.56

SB20W50ZnO

3.42

SB20W100ZnO

Fig.13. Variation of CO2 emission with respect to engine BP The high CO2 formation during the combustion process indicates the efficient combustion of the fuel that can promotes complete oxidation of CO into CO2 [31]. The CO2 emission of all test fuels under varying BP conditions is depicted in Fig.13. It is noted that CO2 emission has increased with increase in load for all test fuels due to increases in fuel consumption [32-34]. The water emulsified SB exhibits lower CO2 at low loads compared to SB due to latent heat absorption of water particles that can be resulting in poor combustion. However, the CO2 emission of SB10W emulsion fuel is increased at higher engine loads. This character indicates that SB10W emulsion fuel promotes efficient combustion at high load conditions due to the micro-explosion phenomena. At the same time, SB20W emulsion fuel lower CO2 emission under all loading conditions compared to SB10W emulsion fuel. From the graphical representation, it is noted that the ZnO nanoparticle included SB20W emulsified biodiesel endorses the higher CO2 emission, and an increases in the mass fraction of

23

Journal Pre-proof

nanoparticle is directly proportional to increases in CO2 emission. This could be the positive effects of ZnO nanoparticle in water emulsified biodiesel, such as complete combustion, shorter combustion duration and better explosion [17, 20]. Out of all sample fuels, SB20W100ZnO emulsified biodiesel has revealed higher level of CO2 at 75% and peak load conditions. 3.7. Smoke opacity The smoke opacity of test fuels under varying BP conditions is indicated in Fig.14. An incomplete combustion of hydrocarbon, and the partial reaction of carbon atom presents in the fuel are the main sources of smoke formation [31]. From the graphical representation of experimental results, it is noted that the water emulsified SB significantly reduces the smoke opacity compared to SB. The emulsified fuel has rich oxygen and OH concentrations compared to SB that promotes efficient combustion and results in lower smoke formation [13, 15]. In addition to that, the micro-explosion phenomena associated with water-emulsified biodiesel can offer enhanced air-fuel mixing and improve the combustion efficiency. SB20W emulsified biodiesel offers 28.3% lower smoke opacity compared to pure SB at 75% engine load condition. An increase in water concentration with SB further reduces the smoke formation. An average reduction of 27.5% in smoke opacity is recorded with SB20W emulsified biodiesel at all loading conditions.

24

Smoke opacity, %

Journal Pre-proof

15 12 9 6 3 0 0

SB

1

SB10W

2 Brake power, kW SB20W

SB20W50ZnO

3

4

SB20W100ZnO

Fig.14. Variation of smoke opacity with respect to load An inclusion of ZnO nanoparticle further reduces the smoke opacity at all loading conditions. This could be due to the lower explosion delay associated with nanoparticle included emulsion fuel resulting in a reduced amount of fuel accumulation inside the combustion chamber [10, 19]. SB20W100ZnO emulsified biodiesel exhibits better smoke opacity under all loading conditions compared to all other test fuels. An average reduction in smoke opacity is recorded as 16.1% for SB20W100ZnO emulsified biodiesel compared to SB20W emulsified biodiesel, whereas 39% drop in smoke opacity is recorded compared to pure SB. 4. Conclusion Emulsion fuels with different concentrations of water (10% and 20%) and mass fraction of ZnO nanoparticle (50ppm and 100ppm in SB20W) in SB were synthesized, and the physicochemical properties and surface characteristics were measured. The emissions pattern of test fuels was investigated under varying BP conditions, and the results compared with pure SB. Based on the experimental results, the following conclusions can be drawn from this study:

25

Journal Pre-proof



The biodiesel produced from soybean crude oil, its water blends and ZnO nanoparticle included emulsified biodiesels can be directly used in existing diesel engine as the measured fuel properties are at par with EN 14214 standards.



An increase in water concentration in SB reduces the NOx and smoke emissions. SB20W emulsified biodiesel promotes an average reduction of 37.5% in NOx emission and 27.5% in smoke emission compared to SB.



At high load conditions, 10% water emulsified biodiesel exhibits lower magnitude of HC and CO formations compared to pure SB, whereas at low load conditions significant increases are recorded. At BP of 2.56kW, SB10W emulsion fuel exhibits a drop of 40% and 33.3% in terms of HC and CO emissions, respectively.



SB20W emulsion fuel increases the HC and CO emissions compared to SB10W at all loading conditions. The average increases in HC and CO emissions are noted as 33.9% and 40.7% for SB20W emulsion fuel compared to SB10W emulsion fuel, respectively.



An inclusion of ZnO nanoparticle in SB20W emulsified biodiesel significantly reduces the HC, CO and smoke emissions at all loading conditions. 100ZnOSB20W emulsified biodiesel exhibits lower HC and CO emissions compared to all test fuels irrespective of load conditions.



Emulsion fuels exhibit a lower magnitude of CO2 emission at low engine loads, whereas this trend is reversed at high engine loads due to efficient combustion. The ZnO nanoparticle inclusion in SB20W emulsion fuel further increases the CO2 emission marginally. Overall, it can be concluded that inclusion of water and ZnO nanoparticle have the

potential to promote greener emissions in SB fuelled diesel engine. However, in order to detain

26

Journal Pre-proof

the nanoparticle emissions from the diesel engine to the atmosphere, a suitable exhaust gas aftertreatment system has to be developed and its suitability can be studied as a further work in this domain. References [1] British Petroleum, British Petroleum Statistical Review of World energy, 2016 [2] Damanik N, Ong HC, Tong CW, Mahlia TMI, Silitonga AS. A review on the engine performance and exhaust emission characteristics of diesel engines fueled with biodiesel blends. Environmental Science and Pollution Research 2018;25(16):15307-15325. [3] Vellaiyan S, Amirthagadeswaran KS. Influence of water-in-diesel emulsion fuel and compression ratio on combustion, performance and emission characteristics of diesel engine. Journal of Sustainable Energy Engineering 2016;3(3):238-253. [4] Venkata Ramanan M, Yuvarajan D. Emission analysis on the influence of magnetite nanofluid on methyl ester in diesel engine. Atmospheric Pollution Research 2016;7(3): 477–481. [5] Devarajan Y, Munusamy DB, Mahalingam A. Performance, combustion and emission analysis on the effect of ferrofluid on neat biodiesel. Process Safety and Environmental Protection 2017;111:283-291. [6] Vellaiyan S. Enhancement in combustion, performance, and emission characteristics of a diesel engine fueled with diesel, biodiesel, and its blends by using nanoadditive. Environmental Science and Pollution Research 2019:26(10):269561-269573. [7] Vellaiyan S, Partheeban CMA. Emission analysis of diesel engine fueled with soybean biodiesel and its water blends. Energy Sources, Part A: Recovery, Utilization, and Environmental Effects 2018;40(16):1956-1965.

27

Journal Pre-proof

[8] Canakci M. Combustion characteristics of a turbocharged DI compression ignition engine fueled with petroleum diesel fuels and biodiesel. Bioresource Technology 2007;98:1167– 1175. [9] Can O, Ozturk E, Solmaz H, Aksoy F, Cinar C, Serdar Yucesu H. Combined effects of soybean biodiesel fuel addition and EGR application on the combustion and exhaust emissions in a diesel engine. Applied Thermal Engineering 2016;95:115-124. [10]

Shaafi, T., Velraj, R., 2015. Influence of alumina nanoparticles, ethanol and

isopropanol blend as additive with diesel-soybean biodiesel blend fuel: Combustion, engine performance and emissions. Renewable Energy, 80, 655-663. [11]

Hira A, Das D. Performance and emission evaluation of diesel engine fuelled with

biodiesel produced from high free fatty acid crude soyabean oil. Biofuels. 2016;7(4):413421. [12]

Moradi, G.R., Dehghani, S., Khosravian, F., Arjmandzadeh, A., 2013. The

optimized operational conditions for biodiesel production from soybean oil and application of artificial neural networks for estimation of the biodiesel yield. Renewable Energy, 50, 915-920. [13]

Vellaiyan S, Amirthagadeswaran KS. Formulation of stable water-in-diesel

emulsion fuel and investigation of its properties. Energy Sources, Part A: Recovery, Utilization, and Environmental Effects 2016; 38(17):2575-2581. [14]

Ithnin AM, Ahmad MA, Abu Bakar MA, Rajoo S, Yahya WJ. Combustion

performance and emission analysis of diesel engine fuelled with water-in-diesel emulsion fuel made from low-grade diesel fuel. Energy Conversion and Management2015;90:375382.

28

Journal Pre-proof

[15]

Qi DH, Chen H, Matthews RD, Bian Y. Combustion and emission characteristics

of ethanol–biodiesel–water micro-emulsions used in a direct injection compression ignition engine. Fuel 2010;89:958-964. [16]

Ithnin, A.M., Noge, H., Abdul Kadir, H., Jazair, W., 2014. An overview of

utilizing water-in-diesel emulsion fuel in diesel engine and its potential research study. Journal of Energy Institute, 87, 273-288. [17]

Vellaiyan S, Subbiah A, Chockalingam P. Multi-response optimization to

improve the performance and emissions level of a diesel engine fueled with ZnO incorporated water emulsified soybean biodiesel/diesel fuel blends. Fuel 2019; 237:10131020. [18]

Mehta RN, Chakraborty M, Parikh PA. Nanofuels: combustion, engine

performance and emissions. Fuel 2014;120:91-97. [19]

Selavan VAM, Anand RB. Effect of cerium oxide nanoparticles and carbon

nanotubes as fuel-born additives in Diestrol blends on the performance, combustion and emission characteristics of a variable compression ratio engine. Fuel 2014;130:160-167. [20]

Vellaiyan S, Amirthagadeswaran KS. Zinc oxide incorporated water-in-diesel

emulsion fuel – Formulation, particle size measurement and emission characteristics assessment. Petroleum Science and Technology 2016;34(2):114-122. [21]

Karthikeyan S, Elango A, Prathima A. Diesel engine performance and emission

analysis using canola oil methyl ester with nano sized zinc oxide particles. Indian Journal of Engineering Material Science 2014;21(2):83-87.

29

Journal Pre-proof

[22]

Vellaiyan S, Amirthagadeswaran KS, Dinesh Babu S. Taguchi-grey relational

based multi-response optimization of diesel engine operating parameters running with water-in-diesel emulsion fuel. International Journal of Technology 2018;9(1):68-77. [23]

Anonymous, European Biodiesel Standard DIN EN 14214, Beuth-Verlag, Berlin,

2003. [24]

Vellaiyan S, Subbiah A, Chockalingam P. Multi-response optimization to obtain

better performance and emissions level in a diesel engine fueled with water-biodiesel emulsion fuel and nanoadditive. Environmental Science and Pollution Research 2019;26(5):4833-4841. [25]

Das M, Sarkar M, Datta A, Santra AK. An experimental study on the combustion,

performance and emission characteristics of a diesel engine fueled with diesel-castor oil biodiesel blends. Renewable Energy 2018;119:174-184. [26]

Hongyun J, Ning W, Liang X, Shuen H. Synthesis and conductivity of cerium

oxide nanoparticle. Material Letter 2010;64(11):1254-1256. [27]

Annamalai M, Dinesh B, Nanthagopal K, Sivaramakrishnan P, Isaac Joshua

Ramesh Lalvani, Parthasarathy M, Annamalai K. An assessment of performance, combustion and emission behavior of a diesel engine powered by ceria nanoparticle blended emulsified biodiesel. Energy Conversion and Management 2016;123:372-380. [28]

Hoseini SS, Najafi G, Ghobadian B, Mamat R, Ebadi MT, Talal Yusaf. Novel

environmentally friendly fuel: The effects of nanographene oxide additives on the performance and emission characteristics of diesel engines fueled with Aianthus altissima biodiesel. Renewable Energy 2018;125:283-294.

30

Journal Pre-proof

[29]

Pandian AK, Ramakrishnan RBB, Devarajan Y. Emission analysis on the effect

of nanopartciles on neat biodiesel in unmodified diesel engine. Environmental science and pollution research 2017;24(29):23273-23278. [30]

De Vita A. Multi-cylinder DI diesel engine tests with unstabilized emulsion of

water and ethanol in diesel fuel. SAE paper 1989;890450. [31]

Ozener O, Yuksek L, Ergenc AP, Ozkan M. Effects of soybean biodiesel on a DI

diesel engine performance, emission and combustion characteristics. Fuel 2014;115:875883. [32]

Vellaiyan S. Enhancement in combustion, performance, and emission

characteristics of a biodiesel-fueled diesel engine by using water emulsion and nanoadditive. Renewable Energy 2020:145:2108-2120. [33]

Vellaiyan S. Effect of cerium oxide nanoadditive on the working characteristics of

water emulsified biodiesel fueled diesel engine; An experimental study. Thermal Science DOI: 10.2298/TSI190112305V. [34]

Devarajan Y, Munuswamy DB, Mahalingam A. Influence of nano-additive on

performance and emission characteristics of a diesel engine running on neat neem oil biodiesel. Environmental Science and Pollution Research 2018;25(26):26167-26172.

31

Journal Pre-proof

Declaration of Interest Statement The authors declare that they have no competing financial interests.

Journal Pre-proof

Research Highlights  Emulsified SB with different concentration of water and nanoparticle are prepared.  Physicochemical properties, surface and optical characteristics are analyzed.  SB10W emulsion fuel exhibits lower HC and CO emissions compared to SB20W.  SB20W emulsion fuel shows lower NOx and smoke emissions.  100ZnO in SB20W emulsion fuel reduces all the emissions level.