Analysing stability in water-in-diesel fuel emulsion

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Analyzing Stability in Water-in-Diesel Fuel Emulsion
Harshal Patil
a
, Ashish Gadhave
a
, Swapnil Mane
a
& Jyotsna Waghmare
b
a
Institute of Chemical Technology, Mumbai, Maharashtra, India
b
Dept. Oils, Oleochemicals & Surfactant Technology, Institute of Chemical Technology,
Mumbai, Maharashtra, India
Accepted 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
To link to this article: http://dx.doi.org/10.1080/01932691.2014.962039
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1
Analyzing Stability in Water-in-Diesel Fuel Emulsion
Harshal Patil1
, Ashish Gadhave1
, Swapnil Mane1
, Jyotsna Waghmare2
1
Institute of Chemical Technology, Mumbai, Maharashtra,. India, 2
Dept. 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.
Downloadedby[ASHISHGADHAVE]at07:1805March2015

2
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

3
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

4
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

5
was purchased from Unitop Chemical Pvt. Ltd. Table.1 indicates the physical state,
density (g/mL @ 25o
C), 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 30o
C using De

6
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
.
ln
max
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
10
A
Γ . AN
(2)
Where, NA= Avogadro’s number.
2.2.2.5. Effectiveness ( CMC)

7
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 CMCmicG (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

8
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

9
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 300o
C 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

10
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

11
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

12
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.

13
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

14
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

15
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
1. Majewski W. A. (2012). What are diesel emissions. DieselNet Technology Guide.
Retrieved 22nd
August 2013 from https://www.dieselnet.com/tech/emi_intro.php.
2. Nicholls J. E., El-Messiri I. A. & Newhall H. K. (1969) Inlet Effects of Direct Water
Injection on DI Manifold Water Injection for control of Nitrogen Diesel Engine
Combustion Oxides -Theory and Experiments. SAE Paper 690018.

16
3. Fu W B, Hou LY., Wang L. and Ma F.H. (2002) Fuel Processing. Technology, 79:
107- 119. DOI: 10.1016/S0378-3820(02)00106-6.
4. Adiga K. and Shah D. (1990), Combustion and Flame. 80: 412-415.
5. Law C. K. (1982), Progress in Energy and Combustion Science 8: 171-201. DOI:
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.

17
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

18
Table 2. Technical characteristics of diesel (fuel no. 2)
Physical properties Value
Density at 15oC, (Kg/m3) 845.8
Specific gravity 0.889
Calorific value (kJ/kg) 44,400
API Gravity 40
Kinematic viscosity, at 400C
(cSt)
3.268
Flash point, oC 53
Pour Point oC 2
Boiling point/range, oC 150–300
Water content, wt.% NIL
Cetane number 52
Adiabatic flame temperature (K) 2740.2

19
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

20
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.

21
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
5 TWEEN20 Partly soluble Insoluble
6 TWEEN60 Partly soluble Insoluble
7 TWEEN80 Soluble Insoluble

22
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

23
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

24
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%).

25
Figure 1. Stability of W/D emulsion (in days) at surfactant concentration 1%. (mixing
time= 20 min.; mixing speed= 5000 rpm ).

26

27

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Analysing stability in water-in-diesel fuel emulsion