الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
There are a wide variety of alternative fuels in use or at various stages of introduction today. Apart from water-in-fuel emulsions, the term alternative fuels comprises: natural gas, liquefied petroleum gas (LPG), hydrogen, biodiesel, bioethanol, biogas, dimethylether (DME), alcohols such as; methanol and ethanol, vegetable oils and fatty acid methyl esters and blends of these with gasoline or diesel. Nanoemulsion fuel is a special mixture of fuel with water combined with emulsifying and stabilizing additives, using nanotechnology. This technology creates homogeneously dispersed nano-sized water particles (50-200 nm) enclosed within a DROP of oil, which when used in a combustion system creates a water vapor explosion that disperses fuel particles into the superheated steam, thereby generating water-gas reaction. The main aim of the present work is to prepare water-in-diesel fuel nanoemulsion with different water contents via high energy homogenizer. Two types of nonionic surfactants were adopted in these experiments. Each of them was blended with another to form five kinds of mixed surfactant with different HyDROPhilic–Lipophilic Balance (HLB) values used to stabilize water-in-diesel fuel nanoemulsion. Also, study the effects of emulsifier concentrations and water contents on the stability of these nanoemulsions at the optimum HLB. Also, measure the density, kinematic viscosity and rheological properties of the prepared nanoemulsions. Technical grade diesel fuel was used as the continuous emulsion phase and the technical grade emulsifiers used throughout this work are; polyoxyethylene (20) sorbitan monooleate abbreviated “T” (a hyDROPhilic surfactant with HLB = 15) and sorbitan monooleate abbreviated “S” (a lipophilic surfactant with HLB = 4.3). The water used in all experiments was double distilled, deionized and filtered prior to use Nanoemulsions were prepared using a turbine homogenizer (Ultraturrax pro 200, USA) as a high energy emulsification device in two steps: Firstly, a pre-emulsion was prepared by addition of water in different percentages (5, 6, 7, 8 and 9%) gradually by constant rate to a mixture of T and S, so-called TS, and diesel fuel to form five emulsions. The rate of addition was kept approximately constant with constant stirring at 600 rpm. In the second step, the prepared pre-emulsions were stirred at high speed (30,000 rpm) for 5 min. All experiments were run at 30°C. The mean DROPlet size of the prepared nanoemulsions was determined using dynamic light scattering equipment at 30°C. A proper surfactant HLB value is a key factor for the formation of stable emulsions. Two types of nonionic surfactant T and S were evaluated in our preliminary experiments. However, only the combination of T and S had the dramatic effects on the emulsion’s properties. Different ratios of T and S were used to turn the HLB range (from 9.6 to 10.4) of the emulsions. The mixing ratios were adjusted to satisfy the proper HLB values for optimum emulsification conditions. Results show that the mean DROPlet size of water was decreased from 145.4 to 49.55 nm when the surfactant ratio of (T: S wt %) was changed from (49.5: 50.5) to (53.3: 46.7), respectively and gradually increased from 49.55 to 190.1 nm when the surfactant ratio of (T) in the mixed surfactant increased from (53.3: 46.7) to (57: 43), respectively. The minimum DROPlet size (49.55 nm) and the smallest Ostwald ripening were obtained at TSHLB of 10 (optimum TSHLB). Therefore, the emulsifier blend with TSHLB=10 was exhibited a synergetic effect in their effect on the properties of the system and was found to be optimum for the preparation of stable w/o emulsions in this study. The w/o nanoemulsions prepared in this work exhibited a good stability without phase separation for 2 weeks, with a slight increase in the mean DROPlet size with time. The two common probable breakdown processes in these systems are coalescence and/or Ostwald ripening. Ostwald ripening arises from the Summary XVI difference in internal pressure between DROPlets with different sizes. In this mechanism, larger DROPlets grow at the expense of smaller ones due to the molecular diffusion through the continuous phase. A good correlation of r3 and time was obtained with regression coefficients (R2) > 0.99 for all the tested emulsions indicating that the Ostwald ripening was the driving force for the instability. Another objective of this work was to evaluate the influence of emulsifier concentration on the stability of w/o nanoemulsion. Surfactant concentration is very important for a stable w/o emulsion system, since, the emulsifier plays a major role in the formation of nanoemulsions. Concerning the Ostwald ripening rate (ω), it is clear that (ω) decreases with increasing surfactant concentration (from 4.92×10-20 to 2.00×10-27 m3 sec-1) at 5% water content, HLB=10 and 30°C. We also study the effect of water content and oil weight fraction (R) on the stability of w/o nanoemulsion. A good correlation of r3 and time is obtained with regression coefficients (R2) > 0.99 for all emulsions tested in this study. Therefore, the emulsion breakdown could be attributed to Ostwald ripening mechanism. It was obvious that the DROPlet size (nm) increases with increasing the water content (5, 6, 7, 8 and 9 wt %), i.e. it was 49.55, 66.80, 78.88, 91.63, 104.40 nm, respectively after 360 h. The Ostwald ripening rate (ω) increases with increasing the water contents (from 2.0 to 10.0 × 10-27 m3sec-1) at 10% of mixed surfactant concentration and TSHLB=10. Therefore, increasing of the water percentage in the emulsion could reduce the stability of the produced nanoemulsion. Results show that the mean DROPlet size was increased from 49.5 to 104.4 nm with the decrease in R. The interfacial tension and thermodynamic properties of the used emulsifier were measured. Generally, the interfacial tension depends on the types of emulsifier used to stabilize the water/oil nanoemulsion. But, the presence of more than one surfactant molecule at the interface leads to the decrease in the interfacial tension comparing with the individual emulsifier. The surface properties of the surfactants individually and the mixed surfactant, including the critical micelle concentration (cmc), the values of interfacial tension at the cmc (γcmc), the maximum surface pressure (πcmc), the maximum surface excess concentration at surface saturation “effectiveness”, (Γmax) and the minimum surface area per surfactant molecule (Amin) were measured and illustrated. from the obtained data, it is obvious that the interfacial tension (γcmc) was decreased from 7.5 and 5.5 mNm-1 for T and S, respectively to 3.8 mNm-1for TS. Regarding the structure and hyDROPhobicity of S (HLB = 4.3) and T (HLB = 15), T is more hyDROPhilic than S, and γcmc, it was clear that S (γcmc = 5.5 mNm-1) was adsorbed firstly and strongly on w/o interface comparing with T (γcmc = 7.5 mNm-1), which take more time to attain the w/o interface. Accordingly, the lowering of γcmc (3.8 mNm-1) of TS was due to the best synergistic effect between S and T which causes a reduction in the DROPlet size. The relatively small increase in the surface pressure at saturation emulsifier concentrations suggests that T (π = 16.5 mN m−1) and S (π = 18.5 mN m−1) should be more strongly adsorbed to the surface of water emulsion DROPlets. S has the highest value of (Γmax), (1.96 x 10-10 mol/cm2) and T has the lowest value (0.82 x 10-10 mol/cm2), while the mixed surfactant TS has value of (0.94 x 10-10 mol/cm2). On the other hand, T exhibited the highest value of (Amin) (2.02 nm2/molecule) and S has the lowest value of (Amin) (0.85 nm2/molecule), whereas TS has middle value between both (Amin) (1.77 nm2/molecule). This may be regarded to the structure and hyDROPhobicity of T and S emulsifiers. As can be seen, the Gibbs free energy of adsorption ΔGads, also varies strongly with the variation of HLB value of the used emulsifiers. In general, the ΔGads increases with the increase of the emulsifier’s HLB. from the obtained data of ΔGmic, it can be concluded that the micellization process is spontaneous because ΔGmic < 0. Generally, the ΔGads is lower than ΔGmic values. This indicates that, these surfactants favor adsorption more than micellization. Although, the TS has a lower interfacial tension (3.8 mN/m) comparing with S (5.5 mN/m) and T (7.5 mN/m), ΔGads of the surfactants in our work was ranking (according to the more negativity of ΔGads)as follows; -17.42, -18.39 and -20.59 KJ/mol for S, TS and T, respectively. This means that the surfactant (S) is strongly adsorbed on the interface followed by surfactant (T). In respect of the nanoemulsion rheology, it was found that the flow behavior and the rheological behavior of the nanoemulsion systems at all test temperatures and all water contents showed a Newtonian character at all test shear rates (20-90 s-1). The viscosity of the nanoemulsion systems is greater than that of water or diesel fuel per se. With the increase of temperature from 10 to 50°C, the viscosity of the nanoemulsion systems decreases gradually. The logarithmic viscosity and the inversion of absolute temperature data fitted well Arrhenius equation that is applied for Newtonian fluids with correlation coefficients close to unity. The mean water DROPlet size has a significant effect on viscosity of the nanoemulsion system in such a way that with the increase of the water volume fraction in the nanoemulsion system, the mean water DROPlet size increases which lead consecutively to an increase of viscosity of the nanoemulsion. On the other hand, a decrease of viscosity is observed with the increase of time of storage of the emulsion up to 2 weeks for all water loadings. Also, we study the effect of temperature on the density and kinematic viscosity of the stable water-in-diesel fuel nanoemulsions. The kinematic viscosity of the diesel fuel and the prepared nanoemulsions decreases nonlinearly with increasing temperature from 10 to 70°C. The accuracy evaluation of the measured viscosities of the diesel fuel and the prepared nanoemulsions was done by correlation, and the best correlation was obtained by using polynomial regression. The results indicate that the diesel fuel and the prepared nanoemulsions demonstrate temperature-dependent behavior and their densities decreases linearly with the increase in temperatures. The accuracy of the density data was further evaluated by correlation, and the best correlation was obtained using a linear equation.