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Analyzing Stability in Water-in-Diesel Fuel EmulsionHarshal Patila, Ashish Gadhavea, Swapnil Manea & Jyotsna Waghmareb

a Institute of Chemical Technology, Mumbai, Maharashtra, Indiab Dept. Oils, Oleochemicals & Surfactant Technology, Institute of Chemical Technology,Mumbai, Maharashtra, IndiaAccepted author version posted online: 07 Oct 2014.

To cite this article: Harshal Patil, Ashish Gadhave, Swapnil Mane & Jyotsna Waghmare (2014): Analyzing Stability in Water-in-Diesel Fuel Emulsion, Journal of Dispersion Science and Technology, DOI: 10.1080/01932691.2014.962039

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1

Analyzing Stability in Water-in-Diesel Fuel Emulsion

Harshal Patil1, Ashish Gadhave

1, Swapnil Mane

1, Jyotsna Waghmare

2

1Institute of Chemical Technology, Mumbai, Maharashtra,. India,

2Dept. Oils,

Oleochemicals & Surfactant Technology, Institute of Chemical Technology, Mumbai,

Maharashtra, India

Email: jyotsna.waghmare@gmail.com

Received 1 September 2014; accepted 2 September 2014.

Abstract

The diesel engine exhaust gas consists of many hazardous components which need to be

reduced. Incorporation of water in fuel restricts the emission of such toxic gases and

helps to reduce pollution. The aim of this research work is to develop water-in-diesel fuel

emulsion having maximum stability. Initially, the most suitable surfactant/blend of

surfactants has been investigated which gives maximum stability to W/D emulsion. It is

found that blend of SPAN 80/TWEEN 80 gives effective result. The W/D emulsion was

prepared by high speed mixing homogenizer and adding a small amount of water into

diesel containing blend of SPAN 80/TWEEN 80. The results show that 10% W/D

emulsion having 5% surfactant concentration gives most desirable emulsion stability.

Beyond 10% water concentration, the properties of W/D emulsion get lowered.

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KEYWORDS: Water-in-diesel emulsion, Stability, Surfactant, Mixing, Viscosity.

1. INTRODUCTION

The diesel engine has more than a hundred years of history. It is considered as one of the

most important players in modern technology due to high thermal efficiency and fuel

economy. Nowadays, almost all ships, heavy trucks and many automobiles are driven on

diesel engines. In small vehicle areas too, like cars, buses etc., diesel engines stand as a

strong competitor with petrol engines. Diesel engines are performing a significant role in

power plants, hospitals, marine, land etc., too. However, harmful emissions through

diesel engines have been regarded a major concern considering the health and the

environment. These emissions include unburned hydrocarbon (HC), carbon monoxide

(CO), nitrogen oxides (NOx) and particulate matter (PM) [1]

. Much lower or “near zero”

levels of pollutants are emitted from modern diesel engines equipped with emission after-

treatment devices such as NOx reduction catalysts and particulate filters. But there are

other sources that could contribute to pollutant emission from internal combustion

engines. Though they are usually in small concentrations, they could sometimes be of

high toxicity. These additional emissions include metals and other compounds from

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engines wear or compounds emitting from emission control catalysts (via catalyst

attrition or volatilization of solid compounds at high exhaust temperatures). Furthermore,

there is a possibility of formation of new species which are normally not present in

engine exhaust, but could be facilitated by catalysts. Diesel particulate filters have been

reported as a source of emission of highly toxic dioxins and furans. A possibility of new

emissions must be considered whenever additives are introduced into the fuel.

Water/fuel emulsion consists of base fuel and water doped with a trace amount of

surfactant. Usually, they show different combustion characteristics. Fuel emulsion offers

a number of potential benefits in combustion processes. This is due to the dilution of gas

and liquid phase reactions and/or secondary atomization caused by the vigorous

evaporation of the interior liquid, called micro-explosion. The participation of water in

the evaporation process is expected to lower the droplet temperature. This results in the

significant reduction in the intensity of the liquid phase pyrolytic reactions which may

lead to the formation of carbonaceous residue [2]

. The reduction in the formation of

carbonaceous residue is more remarkable for low volatile fuels [3]

. Water vapours would

suppress the chemical reaction in the gas phase due to the reduced rate of heat release in

the flame [4]

. Since higher flame temperature is usually a major source of thermal NOx

production, suppress of the chemical reaction is expected to reduce flame temperature

and hence the significant reduction of NOx production [5]

. The enrichment of water

vapour in the fuel-rich region in the vicinity of the droplet surface deep inside the flame

and the simultaneous reduction of the temperature may also result in the reduction of soot

formation. The addition of water would cause the increase in OH- radicals which are very

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effective in the oxidation of the soot precursors. The enhanced oxidation of soot by the

additional OH- radicals might also be one of the significant factors in reducing soot

formation.

The role of surfactant is very crucial in emulsion system. It performs two functions. First,

it increases the interaction between the water and the diesel (two immiscible) systems by

reducing interfacial tension. Second, it helps to stabilize the emulsion system. Stability

behaviour of emulsion system is highly dependent on nature, concentration of surfactant.

Surfactant molecules arrange themselves near interfacial film between water (dispersed

phase) and diesel (continuous phase) to stabilize the water droplets in diesel continuous

phase. High concentration of surfactant prevents the merging of water droplets [6, 7, 8, 9]

.

The objective of the present study is to investigate the surfactant or the blend of

surfactants to give maximum water-in-diesel emulsion stability. The stability of the W/D

emulsion was measured as minimum sedimentation and absence of phase separation. We

also studied the effect of parameters such as water concentration, surfactant

concentration, mixing time and speed on the stability of W/D emulsion. The second

objective was to formulate stable W/D emulsion and to study its physical properties.

2. MATERIALS AND METHODS

2.1. Materials

SPAN series (SPAN-20, SPAN-60, SPAN-80, SPAN-85) emulsifier was procured from

Croda India Pvt. Ltd. TWEEN series (TWEEN-20, TWEEN-60, TWEEN-80) emulsifier

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was purchased from Unitop Chemical Pvt. Ltd. Table.1 indicates the physical state,

density (g/mL @ 25oC), molecular formula, formula weight and HLB values of the

emulsifiers. Diesel was purchased from local petrol pump. The technical characteristics

of diesel fuel are mentioned in Table 2. All the chemicals used were of analytical grade

confirming to the specifications.

2.2. Methods

2.2.1. Preparation Of W/D Emulsion

Emulsions were prepared using a homogenizer emulsification device in two steps.

i) First Step: SPAN & TWEEN series surfactants and mixed surfactants

(SPAN+TWEEN) were mixed into diesel. Then, pre-emulsions were prepared by adding

certain amounts of water into the mixture of surfactant and diesel fuel with constant

stirring at 800 rpm.

ii) Second Step: In the second step, the prepared pre-emulsions were stirred at high

speed (5000 rpm) for 20 min.

All emulsions were prepared at room temperature.

2.2.2. Analysis Of Emulsifier

2.2.2.1. Surface Tension Measurements

Different molar concentrations of Span, Tween, and their blends having HLB of 5, 7, 9

and 11 were used for surface tension measurement. Each emulsifier and its mixture were

dissolved in distilled water and their surface tensions were determined at 30oC using De

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Nouy tensiometer ring “Kruss model Gmbh K100”. The instrument was daily regulated

with distilled water.

2.2.2.2. Critical Micelle Concentration

CMC of Span, Tween and mixture of Span and Tween (ST) was determined by the

method adopted by Rosen [10]

. The interfacial tension concentration isotherms (IFTC)

curves were plotted for the prepared surfactants at different temperatures. The CMC

values were determined from the abrupt change in the slope of the IFTC curves.

2.2.2.3. Surface Excess Concentration (Γmax)

Γmax is a useful measure of the effectiveness of adsorption of surfactant at the liquid/air or

liquid/liquid interface since it is the maximum value to which adsorption can be obtained.

Γmax can be calculated from Gibbs eq. (1).

1. 

lnmax

RT C (1)

2.2.2.4. Minimum Surface Area Per Molecule (Amin)

Amin is the minimum area per molecule (nm2/molecule) at the oil-water interface. The

average area occupied by each adsorbed molecule is given by Eq. 2.

16

min

max

10A

Γ .  AN (2)

Where, NA= Avogadro’s number.

2.2.2.5. Effectiveness ( CMC)

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The effectiveness of adsorption or surface pressure ( CMC) of the surfactant was also

calculated from the Eq. 3.

CMC o CMC (3)

2.2.2.6. Thermodynamic Parameters Of Micellization

The ability of micellization process depends on thermodynamic parameter (standard free

energy, ∆Gmic). The ∆Gmic was calculated by choosing the following expression Eq. 4.

2.3 RT 1 . log CMC  micG (4)

2.2.2.7. Thermodynamic Parameters Of Adsorption

Many investigators dealt with the thermodynamics of surfactant adsorption at interface.

The thermodynamic parameter values of adsorption ∆Gad were calculated by using Eq. 5.

– 0.623. . ad mic CMC minG G A (5)

2.2.2.8. Solubility Of Emulsifier

Solubility of each emulsifier was checked by adding 1% (by volume) of emulsifier in 10

ml of water and diesel separately at room temperature. The solutions were stirred gently

and kept for 30 min. Then, each solution was checked for solubility of emulsifier in both

water and diesel.

2.2.3. Study Of Consumption Of Mixed Surfactants, Water Content And HLB On

W/D Emulsion Stability

For mixed surfactant solutions of SPAN 80 and TWEEN 80 were prepared having HLB

values of 5, 7, 9, 11. These surfactant solutions were used to make W/D emulsions. These

four mixed surfactant solutions with different concentration (1%, 2%, 5% by volume)

were mixed in diesel. Then, W/D emulsion solutions were prepared by high-speed mixing

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homogenizers with a gradual addition of certain amounts of water. The amount of water

varied from 0% to 40% by volume. All the emulsion solutions were kept at room

temperature and were checked for stability.

2.2.4. Effect Of Mixing Speed And Mixing Time

The effect of mixing speed was determined by using 10% W/D emulsion. The mixture of

SPAN 80 + TWEEN 80 surfactant with HLB= 9 was solubilised in diesel fuel. The

overall surfactant concentration was 1% by volume. The emulsions were then prepared

by adding 5% and 30% water (by volume) into premix (diesel + mixture of surfactants) at

three different mixing speeds; 3000 rpm, 5000 rpm and 8000 rpm for 10 min.

3. RESULTS AND DISCUSSION

3.1. Analysis Of Emulsifiers

The detailed analysis of SPAN, TWEEN series of emulsifiers and mixture of SPAN 80+

TWEEN 80 and SPAN 85 + TWEEN 80 is given in Table 3 and Table 4.

The most important task in preparation of emulsions is the selection of a suitable

surfactant that will satisfactorily emulsify the chosen immiscible components at a given

temperature. It has long been recognized that with a homologous series of surfactants,

there is a range in which the polarity of the molecule is highly influencing. This means

the contributions of the polar hydrophilic head and the nonpolar lipophilic tail should be

optimal for a specific emulsion. Surfactants play a major role in the formation of the

emulsion. Emulsion droplets are normally stabilized by the surfactant molecules. The

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adsorbed surfactant causes a lowering in the interfacial tension for an easier

emulsification and stabilizes the droplet against coalescence by steric or electrostatic

repulsion. The interfacial tension is directly related to the amount of surfactant adsorbed

and the nature of the interfacial layer. Generally, the interfacial tension (IFT) depends on

the type of emulsifier used to stabilize the water/diesel fuel emulsion, for example, when

the oil droplet contains a sufficient concentration of the low polarity emulsifier, the IFT

at oil/water interface is high. In contrast, the interfacial tension decreases with high

polarity emulsifier. But, the presence of more than one surfactant molecule at the

interface leads to further decrease in IFT if compared with individual emulsifier. The

interfacial tension properties for SPAN 80, TWEEN 80 and blends of SPAN and

TWEEN (ST) at 300oC are listed in Table 3 & 4. From these obtained data, it is obvious

that the interfacial tension (γ) decreased from 16.83 and 13.62 mNm-1

for SPAN 80 and

TWEEN 80, respectively to 11 mNm-1

for ST. The lowering in γ causes a reduction in the

droplet size. The amount of surfactant needed to produce a smaller droplet size depends

on the concentration of surfactant in the bulk which determines the reduction, as given by

inspection the data listed in Table 4.

It was found that there is a relation between the surface active properties and the

efficiency of emulsifiers used to stabilize W/O emulsion. This means that the maximum

enrichment of the emulsifier molecules on the interface was exhibited with the emulsifier,

which has the smallest Amin. Also, a reversible proportion between Amin and Γmax was

noticed, where with a small Amin, the maximum Γmax occurs. The maximum Γmax was

exhibited with the blend emulsifier (ST) because the maximum synergism happens with

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the mixture components, the result of a good emulsification and emulsion stabilization

result was obtained. The individual demulsifier SPAN 80 exhibited a lower Amin and

higher Γmax among the TWEEN 80 and mixture of SPAN 80 and TWEEN 80 (SPAN 80+

TWEEN 80) emulsifiers. These results of surface active properties for those emulsifiers

consist of emulsion stability for them. Based on this, the use of (SPAN 80+ TWEEN 80)

will strongly adsorb to diesel droplets and, therefore, stabilize against coalescence in

comparing with the use SPAN 80 and TWEEN 80 individually.

The results of the thermodynamic parameters of adsorption are shown in Table 4 for the

same emulsifiers and gave evidence on the relation between the surface active

proportions and the emulsification efficiency. The more ΔGad value indicates that the

emulsifier molecules adsorbed strongly on the interface. Generally, the ΔGad is slightly

greater than ΔGmic which suggests that the molecules prefer to adsorb on the interface

than to make micelles. This means TWEEN 80 got adsorbed on the O/W inter-face and

provided protection against coalescence comparing with SPAN 80. By comparing the

data obtained from interfacial tension properties and thermodynamic parameters, it was

observed that, there is a direct relation between surfactant concentration, IFT (γ) and

droplet size. The droplet radius decreases with the increase the surfactant concentration

and the decrease in interfacial tension (γ) of SPAN+TWEEN (ST) mixture.

The solubility of all the emulsifiers in both water and diesel was checked by adding 5%

of surfactant in 10 ml of water and diesel individually. It was observed that all the

emulsifiers, except TWEEN 80, are partially soluble in water. TWEEN 80 is the only

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emulsifier from all the emulsifiers chosen for study possesses complete solubility in

water media. The same results were not observed when solubility of emulsifiers in diesel

was checked. All the emulsifiers from TWEEN series are completely insoluble in diesel

while all the SPAN emulsifiers (SPAN 20, SPAN 80, SPAN 85), except SPAN 60, are

completely soluble in diesel. SPAN 60 is the only emulsifier from SPAN series not

soluble in diesel. The results are mentioned in Table 5.

The emulsion stability test was done to find out the emulsifier which will give maximum

emulsion stability. It was found that single emulsifier failed to make a stable emulsion

and if it does then the stability is for very short period of time. But the mixed emulsifier

having same concentration as that of single emulsifier forms very stable emulsion. This is

because of the synergism effect occurred in mixed surfactant.

3.2. Effect Of Consumption Of Mixed Surfactants, Water Content And HLB On

W/D Emulsion Stability

Tween 80/Span 80 was used as the mixed surfactant system to make water-in-Diesel

emulsion. The influence of the consumption of these two mixed surfactants on the

stability of water-in-Diesel emulsion was investigated and the results were shown in Fig.

1, 2 and 3. Generally, the stabilization time increased as the consumption of mixed

surfactants increased. It is cleared from figure 1, 2 and 3 that the stabilization time was

the highest for mixed surfactant systems having HLB value of 9. The most stable water-

in-Diesel emulsion of single surfactant system (SPAN or TWEEN) could only be stored

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for 20 days. Interestingly, the stabilization time of the emulsions using mixed Span

80/Tween 80 emulsifier went up to 25 or 30 days.

Figure 1, 2 and 3 show that as the percentage of water in W/D increases, the stability

decreases. At 5% water-in-diesel emulsion, the maximum stability was achieved for all

concentrations of mixed surfactants. The emulsion stability reached the lowest value

beyond 25% water concentration and remained almost stagnant beyond that point. The

W/D emulsion remained stable only for 1 day and then the water got separated.

The surfactant plays a very complicated but important role in emulsion stability.

Effectiveness of the surfactant is determined by transportation of surfactant molecules to

W/D interface and get absorbed to form a surface layer. Figure 1, 2 and 3 depict the

effect of surfactant concentration on stability of W/D emulsion. The emulsion stability

found to be increased with increase in the surfactant concentration from 1% to 5%. The

maximum stability observed at 5% W/D emulsion with 5% surfactant concentration. The

emulsion was stable for 30 days without any water separation. But 10% W/D emulsion at

5% surfactant concentration gave almost same result as that of 5% W/D emulsion which

saves 5% of fuel. Therefore, even though 5% W/D emulsion gives highest stability, we

recommend 10% W/D emulsion at 5% surfactant concentration.

3.3. Effect Of Mixing Speed And Mixing Time

Shearing action whose shearing strength would directly influence the water droplet size

in the emulsion is the necessary condition to disperse water phase into the oil phase.

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Table 6 shows the stability profile for 5% and 30% W/D emulsions for different mixing

speed.

As can be concluded from Table 5, the stability increased considerably from 8 hrs to 14

hrs and from 2 hrs to 5 hrs for 5% and 30% W/D emulsions respectively by increasing

the mixing speed from 3000 rpm to 5000 rpm. But further increase in speed from 5000

rpm to 8000 rpm did not make much difference in emulsion stability. There was only 1 hr

increase in the stability for 3000 extra rpm. Therefore, beyond 5000 rpm, there would be

a waste of energy. So, 5000 rpm is the effective mixing speed to make W/D emulsion.

A rational stirring provides the shear to elongate the droplet before breaking. Increasing

the mixing energy is the most obvious way to reduce the droplet size. The influence of

mixing time on the stability of W/D emulsion was investigated. The mixed surfactant

concentration in the emulsion was maintained at 1% by volume. 5% and 30% W/D

emulsions were prepared in a homogenizer with 5000 rpm stirring and at different time

intervals ranging from 5 to 30 min. The results are shown in Table 7. As the mixing time

increased from 5 to 30 min, the stability of the emulsion increased significantly.

However, stabilization time remained almost stagnant beyond 20 min of mixing time.

Therefore, 20 min is found to be the most effective mixing time to make W/D emulsion.

3.4. Effect Of Water Content And Mixing Speed On The Emulsion Activity

The effects of water content and mixing speed on volumetric distribution of various

layers were studied by varying water concentration and stirring speed. The emulsions

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were prepared by varying water concentration and mixing speed of homogenizer. Mixed

surfactant of SPAN 80 and TWEEN 80 of HLB=9 was used. The surfactant concentration

was kept constant (1%) for all emulsion solutions. The water concentrations used were

10% and 30%. Three different mixing speeds (3000 rpm, 5000 rpm and 8000 rpm) were

used for both water concentrations. Once emulsions were made, they were centrifuged at

2000 rpm for 5 min and then checked for sedimentation layer.

The data in Table 8 shows the changes in the emulsion activity with varying in water

content and mixing speed. It was observed that the sedimentation layer decreased from

11% to 6% and 47% to 30% for 10% and 30% W/D emulsions, respectively with mixing

speed of homogenizer ranging from 3000 rpm to 8000 rpm. It can be concluded from data

that higher speed reduces the W/D emulsion droplet diameter and as the droplet size

decreases, emulsion loses its tendency to coagulate and emulsion becomes more stable.

Thus, decrease in the height of the sediment layer was observed. In addition, water

content also affects the sedimentation. It was observed that sedimentation layer increased

with increase in water content. This suggests that larger the dispersed phase in an

emulsion, higher would be the tendency to form sedimentation.

4. CONCLUSION

The study on the stability of W/D emulsion can be concluded as follows:

i) Blend of SPAN 80/TWEEN 80 is able to form most stable W/D emulsion among all

the other single and mixed (SPAN and TWEEN) surfactant systems. This proves once

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again that mixture of low HLB surfactant and high HLB surfactant gives better emulsion

stability.

ii) The blend of surfactant with HLB of 9 is the most desirable for W/D emulsion. In

other words, surfactant having HLB of 9 is most significant to make fuel emulsion.

iii) Surfactant concentration has very positive effect on emulsion stability. Stabilization

time of W/D emulsion increases with an increase in the consumption of surfactant. Blend

of SPAN 80/TWEEN 80 at 5% concentration forms most stable W/D emulsion.

iv) Increase in water content in W/D emulsion decreases the emulsion stability. W/D

emulsion achieves better stability for 5% and 10% water content, but it lowers drastically

beyond 25% water content and then remains stagnant.

v) Mixing speed and mixing time also enhance the emulsion stability significantly up to

a certain limit beyond which it remains same. Therefore, increasing the mixing speed and

mixing time beyond effective limit leads to wastage of energy and increasing the fuel

cost. In this research, most stable W/D emulsion was formulated at 5000 rpm for 20 min

in the presence of a blend of surfactant (SPAN 80/TWEEN 80).

REFERENCES

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August 2013 from https://www.dieselnet.com/tech/emi_intro.php.

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Injection on DI Manifold Water Injection for control of Nitrogen Diesel Engine

Combustion Oxides -Theory and Experiments. SAE Paper 690018.

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3. Fu W B, Hou LY., Wang L. and Ma F.H. (2002) Fuel Processing. Technology, 79:

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4. Adiga K. and Shah D. (1990), Combustion and Flame. 80: 412-415.

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10.1016/0360-1285(82)90011-9.

6. Canevari, G. (1987), In: Proceeding of Oil Spill Conference. American Petroleum

Institute, Washington, DC, 293–296.

7. Christopher, C. (1993), Formation and Breaking of Water-in-Oil Emulsions.

Washington, DC: Marine Spill Response Corporation.

8. Eley, D., Hey, M., Symonds, J. and Willison, J. (1976), Journal of Colloid and

Interface Science 54: 462–466.

9. Fingas, M., Fieldhouse, B. and Mullin, J. (1995), In: Proceeding of Oil Spill

Conference. American Petroleum Institute, Washington, DC, 829–830.

10. Rosen, M. J. and Kunjappu, J. T. (2012), Micelle Formation by Surfactants, in

Surfactants and Interfacial Phenomena, Fourth Edition, John Wiley & Sons, Inc.,

Hoboken, NJ, USA. DOI: 10.1002/9781118228920.ch3.

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Table 1. Physical properties of surfactants.

No. Surfactant Physical

State

Density(g/mL

at 25°C)

Molecular

Formula

Formula

Weight

HLB

1 SPAN- 20 liquid 1.032 C18H34O6 346.46 8.6

2 SPAN- 60 solid ---- C24H46O6 430.62 4.7

3 SPAN- 80 liquid 0.994 C24H44O6 428 4.3

4 SPAN- 85 liquid 0.94 C60H108O8 957.49 1.8

5 TWEEN-20 liquid 1.095 C18H34O6 346.45 16.7

6 TWEEN-60 liquid 1.044 C64H126O26 1311 14.9

7 TWEEN-80 liquid 1.08 C24H44O6 1309.63 15

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Table 2. Technical characteristics of diesel (fuel no. 2)

Physical properties Value

Density at 15oC, (Kg/m

3)

845.8

Specific gravity 0.889

Calorific value (kJ/kg) 44,400

API Gravity 40

Kinematic viscosity, at 400

C

(cSt)

3.268

Flash point, oC

53

Pour Point o

C 2

Boiling point/range, oC

150–300

Water content, wt.% NIL

Cetane number 52

Adiabatic flame temperature (K) 2740.2

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Table 3. Analysis of the emulsifiers.

No. Emulsifiers SurfaceTe

nsion (mN.

m-1

)

IFT

(mN. m-1

)

Γmax

(x1011

mol/cm2)

Amin(Å2) CMC(mol

dm-3)

1 SPAN20 23 5 2.24 75 1.86

2 SPAN60 24 7 1.6 100 1.35

3 SPAN80 27 16.32 2.03 81.71 1.82

4 SPAN85 32 2.8 2.16 90.21 1.53

5 TWEEN20 38 7.5 2.3 50.65 1.93

6 TWEEN60 33 10.5 2.65 69.72 2.33

7 TWEEN80 39 13.62 1.91 86.89 3.92

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Table 4. Analysis of the mixed emulsifier.

No.

Mix Surfactant ST IFT Γmax Amin ΠCMC CMC ∆Gad ∆Gmic Flashpoint

1 SPAN 80: TWEEN 80 33 10.85 3.44 48.16 61.15 4.75 -18.96 -17.18 113

2 SPAN 85: TWEEN 80 37 9 3.5 47.28 63 4.9 -47.38 -428.1 119

ST- Surface tension (mN/m); IFT- Interfacial Tension (mN/m); Γmax- surface excess

concentration; Amin- minimum surface area per molecule; ΠCMC- Effectiveness; CMC-

Critical Micelle Concentration; ∆Gad- Thermodynamic parameter of adsorption; ∆Gmic-

Thermodynamic parameter of micellation.

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Table 5. Solubility of the emulsifiers. (Emulsifiers concentration 5% in both the media.)

No. Emulsifiers Water media Diesel media

1 SPAN20 Partly soluble Soluble

2 SPAN60 Partly soluble Insoluble

3 SPAN80 Partly soluble Soluble

4 SPAN85 Partly soluble Soluble

5 TWEEN20 Partly soluble Insoluble

6 TWEEN60 Partly soluble Insoluble

7 TWEEN80 Soluble Insoluble

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Table 6. Effect of mixing speed on emulsion stability (in hours)

Water (%) Mixing Speed (in rpm)

3000 5000 8000

5 8 hours 14 hours 15 hours

30 2 hours 5 hours 6 hours

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Table 7. Effect of mixing time of emulsion stability (hours)

Mixing Time (min.)

Water in

emulsion (%)

5 min 10 min 15 min 20 min 25 min 30 min

5 10 hours 14 hours 16 hours 19 hours 20 hours 20 hours

30 2 hours 5 hours 8 hours 10 hours 10 hours 10 hours

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Table 8. Effects of water content and mixing speed on the volumetric distribution of

various layers of the W/D emulsions.

% Water/Mixing speed(rpm)

10/3000 10/5000 10/8000 30/3000 30/5000 30/8000

Sediment form

(%)

11 8 6 47 38 30

Emulsion form

(%)

89 92 94 53 62 70

(Surfactant used= SPAN 80+TWEEN 80 (HLB 9) = 1%).

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Figure 1. Stability of W/D emulsion (in days) at surfactant concentration 1%. (mixing

time= 20 min.; mixing speed= 5000 rpm ).

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Figure 2. Stability of W/D emulsion (in days) at surfactant concentration 3%. (mixing

time= 20 min.; mixing speed= 5000 rpm ).

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Figure 3. Stability of W/D emulsion (in days) at surfactant concentration 5%. (mixing

time= 20 min.; mixing speed= 5000 rpm ).

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