The production and the features of water-residual fuel emulsion.

Moroianu, Corneliu ; Samoilescu, Gheorghe ; Patrichi, Ilie 等

1. INTRODUCTION

This paper presents a possibility of producing the water-heavy fuel emulsions by means of ultrasounds. The emulsion (Clayton, 1981), is a heterogeneous system consisted of, at least, an immiscible liquid intimately dispersed in another one under the form of some drops with a diameter over 0.1mm. These systems have a minimum stability which can be increased by additives like surface-active agents, finely powdered solid particles, etc. The reference to the particle dimensions of dispersed phase makes a distinction between the emulsify phenomenon and the solubilization one. The emulsions are considered heterogeneous systems which belong to the pseudo-colloid category. In the analysis of emulsions it is necessary to differentiate the emulsion phases. The phase that is under the form of some fine drops is named the disperse phase or the internal phase. The phase that forms the matrix, in which these drops are suspended, is called the continuous phase or the external phase. Also, the internal phase is named the discontinuous phase while the external phase is called the non-disperse phase. Classically, there are two types of emulsions, starting from the known case of water-oil emulsions (Travis, 2007). When the disperse phase is oil, then it is the oil-water emulsion and it is noted with the symbol O/W. When the disperse phase is water, it is the water-oil emulsion noted with the symbol W/O. This paper presents a possibility of producing the water-heavy fuel emulsions by the naval combustion engines.

2. THE ULTRASOUND ACTION IN LIQUID MEDIA

The ultrasonic activation process of the liquids is based on the cavitation phenomenon (Popa & Iscrulescu, 1983). When an acoustic pressure changing from positive values to negative values acts on a liquid, the liquid volume is put to compression and dilatation, at the same time. When a maximum pressure is reached, in the points where the cohesion is weak, a liquid breakage is produced. This breakage is followed by an overpressure in the point where it has occurred, finding the presence of some cavities. In these hollows, the liquid-dissolved gases, under the form of bubbles which blow up after a short time, generate local pressures of tens of bars. As on the surface and inside the bubbles there are contrary electric charges, with the explosion, the lightning discharges are generated. These produce an ionization of surrounding particles and an emission of ultraviolet rays. The cavitation process is influenced by the frequency and the intensity of ultrasounds. The appearance of cavitation in a liquid depends, to a great extent, on the existence of liquid-suspended undissolved gases (Dragan, 1983). The cavitation can be obtained with acoustic pressures lower than 20 [bar] and in this case, the well-differentiated points appear in the liquid, named nuclear centers. These inhomogenities localized in a liquid form the place of cavitation process. If in a liquid there are introduced particles from another liquid which is inmiscible with the first one, the liquid resistance is reduced, being possible that the included gas molecules to separate the liquid from the particles introduced on their surface. The presence of gas seems to play the role of a real catalytic agent of cavitation formation. The cavity bubble is developed up to a certain extent which, at a certain pressure, depends on the developing time and the ultrasound frequency. The time, t, necessary for the development of spherical cavity bubble from the initial radius R0 to R is given by the relation:

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (1)

where:

[rho]--the liquid density [kg/[m.sup.3]]; P--the hydrostatic pressure [daN/[mm.sup.2]]; [tau]--the surface liquid pressure [N/m].

In the following phase, after the relative slow dilatation of the cavity bubble, its sudden compression and its quick destruction are produced. The compression time of the bubble from a radius [R.sub.m] to a radius R can be calculated by the relation:

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (2)

As a result of the cavity bubble destruction, the gas or the existing vapors inside it are adiabatically compressed, the temperature can reach 1000[degrees]C and a shock wave is generated of which intensity increases with the increase of acoustic pressure. The generation of acoustic cavitation in a liquid causes a series of mechanical, acoustical, optical and chemical effects.

3. THE HYDRODYNAMIC WHISTLE FOR LIQUIDS

The generation of high intensity ultrasounds in liquids was performed by means of hydrodynamic whistle for liquids. The hydrodynamic whistle for liquids, Figure 1, is formed of a tapered nozzle (1) provided with a nipple which has in front of it, at a distance of 0,3 - 1 mm, a vibrator segment (2) fixed in one or two nodal points.

[FIGURE 1 OMITTED]

4. THE EXPERIMENTAL RESEARCHES

In the experimental researches we have determined the fundamental characteristics of water/fuel emulsion (Moroianu, 2001). For stating the quality and durability (endurance) of emulsions produced by the ultrasound generator we shall present the properties of such emulsion in comparison with the non-emulsified fuel. The characteristics of emulsified and non-emulsified fuels are shown in Table 1 for a naval RMC 15 fuel.

5. CONCLUSIONS

The water/fuel emulsion has been stored for a long time, 45 days for a naval RMC 15 fuel. The determinations performed after 45 days have showed that it has a good stability in time without the danger of separating the two liquid components. At the same time, we performed tests related to the behavior of water/fuel emulsion stored in heat-proof vessels at different temperatures (50, 60, 80[degrees]C) for 60 and 150 days. The analysis of dimensions of water drops contained in fuel and that of its percentage distribution showed changes of quality, namely, an increase of average diameter of water drops and a reduction of proportion of water drops with a diameter smaller than 4.8 ([micro]m); though, these indicators are kept at high values. The test results are presented in Table 2 (for 3 months) and Table 3 (for 4 months). It can be found that the quality indicators of water/fuel emulsion (the average diameter of water drops and the proportion of water drops with a diameter smaller than 4.8 ([micro]m) in RMC 10 fuel) vary with the storage temperature, respectively, with the emulsion viscosity and from this point of view it is recommended that for a long storage the temperature should be below 50[degrees]C. Taking into account the naval use of this emulsion, it can be chosen an average time of storage up to 15-20 days as the consumption value at different cargo ships is relatively low and the production possibilities of emulsion are sure because the changes of preparation fuel plant for boilers are minimum. During the experiments it was observed the behavior of water/fuel emulsion under transport conditions and on the circuits of fuel supply plant of boilers. It has been found that the preparation, pre-heating and transport operations along the pipes didn't influence the quality of emulsion.

6. REFERENCES

Clayton, R.,(1981). The Theory of Emulsion and Their Tehnical Treatment, J.A.Churcill Ltd., London

Dragan, O., (1983). Ultrasunetele de mari energii (The high power ultrasounds), Ed. Academiei, Bucharest

Moroianu, C. (2001). Arderea combustibililor lichizi in sistemele de propulsie navale (The liquid fuel burning in the naval propulsion systems), Editura Academiei Navale "Mircea cel Batran" ISBN 973-8303-04-4, Constanta

Popa, B.; Iscrulescu, V. (1983). Procese de ardere in camp sonor (The combustion process in sound field), Ed.Academiei, Bucharest

Travis P.M., (2007), The Theory of Emulsion and Emulsification, ISSN 003-021X, Springer Berlin/Heidelberg

Tab. 1. The characteristics of emulsified and non-emulsified
fuels for a naval RMC 15 fuel

Fuel characteristics Non-emulsified Water/fuel
 fuel emulsion

Lower thermal
power 38650 [+ or -] 845 36920 [+ or -] 845
(kJ/kg).

Water content 0-1 7,5-10,5
(%).

Sulphur content 2,5-3,5 2,2-3,3
(%).

Conradson coke 12-20 11,5-19
content (%).

Density 960-980 960-985
(kg/[m.sup.3]).

Viscosity at 14-26 14-25,5
80[degrees]C
([degrees]E).

Average diameter -- 3-4,4
of water drops
([micro]m)

Proportion of 80-90,6
water drops with a
diameter smaller
than 4.8 ([micro]m).

Viscosity at 2,5-3 3,2-5,8
injection nozzles
([degrees]E).

Tab. 2 The test results in storage for 3 months

Water/fuel Initial Storage for 3 months
emulsion state
characteristics

Temperature -- 50/20,8 60/43,3 80/13,9
([degrees]C)/
Viscosity
([degrees]E)

Average 3,1 3,5 3,8 3,9
diameter of
water drops
([micro]m)

Proportion of 93,7 88,2 82,6 81,2
water drops
with a diameter
smaller than
4.8 ([micro]m)

Tab. 3. The test results in storage for 4 months

Water/fuel Initial Storage for 4 months
emulsion state
characteristics

Temperature -- 50/20,4 60/41,3 80/14
([degrees]C)/
Viscosity ([degrees]E)

Average
diameter of 3,6 3,8 3,9 4,1
water drops
([micro]m)

Proportion of
water drops
with a diameter 87,1 84,2 82,5 80,2
smaller than
4.8 ([micro]m)