The fuel properties of three-phase emulsions as an alternative fuel for diesel engines

Diesel engines are employed as the major propulsion power for in-land and marine transportation vehicles primarily because of their rigid structure, low breakdown rate, high thermal efficiency and high fuel economy. It is expected that diesel engines will be widely used in the foreseeable future. However, the pollutants emitted from diesel engines (in particular nitrogen oxides and particulate matter) are detrimental to the health of living beings and ecological environment have been recognized as the major air pollution source in metropolitan areas and have thus attracted much research interest. Although diesel oil emulsion has been considered as a possible approach to reduce diesel engine pollutants, previous relevant applications were restricted to two-phase emulsions. Three-phase emulsions such as oil-in-water-in-oil briefly denoted as O/W/O emulsions and water-in-oil-in-water, denoted as W/O/W, have not been used as an alternative fuel for any combustion equipment. Studies on the properties of three-phase emulsion as fuel have not been found in the literatures. The emulsification properties of an O/W/O three-phase diesel fuel emulsion were investigated in this experimental study. The results show that the mean drop size of the O/W/O emulsion was reduced significantly with increasing homogenizing machine revolution speed. An increase in inner phase proportion of the O/W/O emulsion resulted in increasing the emulsion viscosity. The viscosity of O/W/O emulsion is greater than that for water-in-oil (denoted briefly as W/O emulsion) for the same water content. More stable emulsion turbidity appeared for three-phase O/W/O diesel emulsions added with emulsifier with HLB values ranging from 6 to 8. In addition, three-phase O/W/O emulsions with greater water content will form a larger number of liquid droplets, leading to a faster formation rate and greater emulsion turbidity at the beginning but a faster descending rate of emulsion turbidity afterwards. The potential for using O/W/O emulsions as an alternative fuel for diesel engines was also evaluated.     

Regimes of Multiple Emulsions of W1/O/W2 and O1/W/O2 Type in the Continuous Couette‐Taylor Flow Contactor

The flow regimes of multiple emulsions in the continuous Couette‐Taylor flow (CTF) contactor and characterization of the dispersion state are reported. The proposed method of multiple emulsion preparation is a one‐step procedure on the contrary to the classical two‐step procedure. The effect of operating parameters in the CTF contactor on multiple emulsion appearance, structure (drop size and packing), and rheological behavior is discussed. The key factors affecting multiple emulsion preparation in the CTF apparatus were the phases ratio, the rotational flow, and an annular gap width. The influence of an axial flow was more significant in the range of small rotational rates. The operating conditions were optimized to find the best characteristic multiple emulsions (largest interfacial area). The paper presents the same exemplary data of using W₁/O/W₂ emulsions as emulsion liquid membranes (ELMs) in the extraction process and O₁/W/O₂ for control active agent (drug) release.     

Preparation of water-in-oil and ethanol-in-oil emulsions by membrane emulsification

In this work, water-in-oil emulsions (W/O) and ethanol-in-oil emulsions (E/O) emulsions were prepared successfully by membrane emulsification. The emulsifiers selected were PGPR and MO-750 for the W/O and E/O emulsions, respectively. For W/O emulsions prepared with an oil pre-filled membrane, the dispersed flux was lower and the droplet size sharper than that obtained with a water pre-filled membrane. On the contrary, for E/O emulsions prepared with the membrane pre-filled with oil, the dispersed phase (ethanol) rapidly pushed out the oil from the membrane pores. Therefore, the pre-treatment of the membrane had almost no effect on the dispersed phase flux and on the droplet size. The droplet size distribution of the E/O emulsion was close to that obtained with a classical homogenizer. The dispersed phase fluxes were high and no fouling was observed for our experimental conditions (1.6 l emulsion, 10 wt% ethanol). These results confirm that membrane emulsification could be an interesting alternative for the preparation of E/O emulsions for the purpose of biodiesel fuels, considering the scale-up ability of membranes and their potentiality for industrial processes.     

Engine performance and emission characteristics of three-phase diesel emulsions prepared by an ultrasonic emulsification method

The emulsification method is a potential technique for reducing pollutant emissions from combustion equipment primarily due to occurrence of micro-explosion to enhance burning. In this study, an ultrasonic emulsification method was applied to prepare two-phase water-in-oil (W/O) and three-phase oil-in-water-in-oil (O/W/O) emulsions. The engine performance and the pollutant emission characteristics of a diesel engine were measured and analyzed. A rather violent ultrasonic wave may result in the phenomena of cavitations and hot spots, which in turn promotes fast chemical and physical reactions. Various kinds of liquid, which are immiscible with each other, may thus become highly mixed so that an emulsion is formed. This study first used an ultrasonic oscillating bath to produce ultrasonic waves by which two- and three-phase emulsions were prepared. The experimental results show that the emulsions prepared by the ultrasonic vibrating method have much finer and better-distributed droplets. The use of these emulsions as an engine fuel produced lower NO emission, lower soot concentration and lower black smoke opacity, while creating a larger brake specific fuel consumption (bsfc) and a larger CO emission compared with that of an engine using neat diesel fuel. However, the variations in the concentrations of CO₂ and O₂ emissions between the emulsions and neat diesel fuel were not significant. In a comparison with the characteristics of the two-phase W/O emulsion, the three-phase O/W/O emulsion was found to have a larger CO emission, larger soot particles and larger bsfc while producing a lower brake thermal efficiency and a lower black smoke opacity.     

Novel extensional device to efficiently form fine oil-in-water food emulsions

Two immiscible liquids are commonly mixed by mechanically dispersing one into the other to form emulsions. Surfactants or emulsifiers confer stability. Mechanical mixing, in practice, is an energy-intensive shear flow that is ineffective when the ratio of the dispersed-phase viscosity to the continuous-phase viscosity exceeds about four. Extensional flows are not subject to this viscosity ratio limit. This superiority of extensional flow was exploited to fabricate a novel, continuous-flow, cone-shaped device with an extensional strain of eight to make fine soybean oil-in-water emulsions. A spherical insert having a wall clearance of 25 μm was an effective design factor. Starting with ‘coarse’ 50 wt.% oil emulsions, two stretching episodes were needed for size reduction. The temperature rise was negligible, and the results were independent of the emulsifier type employed. Increasing flow rate and stretching episodes, reducing wall clearance, enhancing emulsifier concentration, and multiple passes through the device gave progressively smaller drops; the volume-averaged diameter became less than 2 μm, and the number-averaged diameter reached 0.5 μm, narrowing the size distribution. The emulsions that formed had a high viscosity and were stable. The performance of a scaled-up device was compared with other mixers. At equivalent energy density and 50 wt.% oil, drop sizes were similar for a valve homogenizer but larger for a rotor-stator mixer. At 80 wt.% oil, the rotor stator-mixer again required more energy for the same drop size, but emulsions prepared with the valve homogenizer broke. The findings of this study can help to design industrial-scale energy-efficient extensional-flow dominant devices for the formation of food emulsions.     

PERFORMANCE CHARACTERISTICS OF PIPE BENDS AS METERING DEVICES FOR OIL/WATER MIXTURES

The applicability of pipe bends as metering devices for two-phase oil/water emulsions was investigated. The discharge coefficients were determined for emulsions over a wide range of oil and water concentrations. At low oil concentrations, the emulsions were of oil-in-water (O/W) type. However, at high oil concentrations, the emulsions were of water-in-oil (W/O) type. The inversion point was detected by an in-line conductance cell. A sharp change in the electrical conductance occurred upon inversion of one type of emulsion to another. Three standard long radius elbows with different dimensions and radii of curvature were tested. The results indicate that the single-phase calibration curves (discharge coefficient versus velocity) can be used to predict the flow rate of two-phase oil/water mixtures provided that the mixtures are well-homogenized. There is no observable difference between the discharge coefficients of oil-in-water and water-in-oil emulsions. The measured values of the discharge coefficients for emulsions are reasonably close to the values predicted from the equations proposed in the literature for single-phase fluids.     

A low‐energy emulsification batch mixer for concentrated oil‐in‐water emulsions

This work shows the formation of a high internal phase ratio oil‐in‐water (O/W) emulsion using a new type of a two‐rod batch mixer. The mixture components have sharply different viscosities [1/3400 for water‐in‐oil (W/O)], similar densities (1/0.974 for W/O), and an O/W ratio of 91% (wt/wt). The simple design of this mixer leads to a low‐energy process (10⁶ < energy density [J m^?3] < 10⁷), characterized by low rotational speed and laminar flow. The droplet size distribution during the emulsification was investigated according to different physical and formulation parameters such as stirring time (few minutes < t < 1 h), rotational speed (60 < Ω < 120 rpm), surfactant type (Triton X‐405 and X‐100), concentration (from 1 to 15.9 wt % in water), and salt addition (30 g/L). We show that all studied parameters allow a precise control of the droplet size distribution and the rheology. The resulting emulsions are unimodal and the mean droplet diameter is between 30 μm and 8 μm. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Formation of O/W emulsions by static mixers for pharmaceutical applications

Oil-in-water (O/W) emulsions produced by static mixers in the laminar flow regime are characterized for their oil drop size spectra. The emulsions are used in the first process step for the production of microspheres for pharmaceutical applications by the emulsion extraction method. However, emulsion generation by static mixers in the laminar flow regime is rarely discussed in the scientific literature. Here we deduce a non-dimensional correlation for predicting the Sauter mean oil drop size as a function of the static mixer operation parameters and the liquid properties. First, the material properties of the organic and water phases are characterized. Second, the oil drop size spectra of the emulsions are measured by laser diffraction. Dimensional analysis is used to describe the relationship between the process parameters of the static mixer and the Sauter mean oil droplet size. Emulsion production experiments using SMX static mixers with two different diameters are carried out with the mixing of the two liquids taking place in the laminar flow regime. We provide results covering a wide range of all process parameters, which were identified influencing the droplet size of the emulsion. The correlation achieved is related to the non-dimensional drop-size based Ohnesorge number of the emulsification process and allows for the prediction of the mean oil droplet size with good accuracy, which is an essential information about the emulsion properties relevant for the pharmaceutical application.     

Breakup of non-newtonian emulsion jets

The breakup of non-Newtonian emulsion jets into drops was experimentally studied by ejecting both O/W and W/O emulsions vertically downward into stagnant air through nozzles. Breakup lengths of non-Newtonian emulsion jets were found to be almost equivalent to those of Newtonian jets. Experimental breakup data establish that the static surface tension of the oil phase can be used as the surface tension of W/O emulsion jets, whereas the dynamic surface tension of aqueous surfactant solutions is used as that of O/W emulsion jets. Diameters of drops formed from non-Newtonian emulsion jets are in good agreement with the prediction from the stability theory previously developed by the authors. When the rheological index in a power law model is appreciably smaller than unity and the Ohnesorge number is significantly large, however, drop sizes are larger than the prediction because of the profile relaxation in jets. The critical velocity of emulsion jets, either O/W or W/O emulsion, is significantly lower than that of homogeneous Newtonian jets.     

A rapid benchtop NMR method for determination of droplet size distributions in food emulsions

The determination of water and oil droplet size distributions in food emulsions by low‐field NMR has the advantage of a simple and non‐perturbing sample preparation. Furthermore, NMR performs very well with respect to precision. The current implementation on most benchtop NMR spectrometers deploys a variation of gradient duration and requires continuous corrections for gradient imbalances, thus making the whole procedure a time‐consuming one. By using variation of gradient strength and further stretching the capability of commercial benchtop NMR spectrometers, both water and oil droplet sizes can be measured in a more rapid manner, typically two to three times faster. The measured droplet size distributions are equivalent to those assessed by the current (slow) method, for both O/W and W/O emulsions. Furthermore, the rapid method shows a good performance with respect to precision. In addition, the method is able to determine droplet sizes in samples with much smaller amounts of dispersed phase.     

Comparison of fuel properties and emission characteristics of two- and three-phase emulsions prepared by ultrasonically vibrating and mechanically homogenizing emulsification methods

Emulsions have long been considered as an alternative fuel for combustion equipment in order to achieve better fuel economy and pollution reduction. While a mechanical homogenizing method is frequently used to prepare emulsions, the use of an ultrasonic emulsification method to do so is still rather limited, and is mostly applied to two-phase emulsions only. Hence, two-phase W/O and three-phase O/W/O emulsions, prepared by a mechanical homogenizer and an ultrasonic vibrator, respectively, were prepared and used as engine fuel. The emulsion properties, engine performance, and engine emission characteristics between these two emulsification methods were measured and compared. The potential of the ultrasonic emulsification method was also evaluated. The experimental results show that the emulsions prepared by the ultrasonic vibrator appeared to have more favorable emulsification characteristics such as smaller dispersed water droplets that were distributed more uniformly in the continuous oil phase, lower separation rate of water droplets from the continuous phase of diesel fuel and thus a lower separating rate of the dispersed water droplets from the emulsion, larger emulsion stability, and larger emulsion viscosity than the emulsions produced using a mechanical homogenizer. In addition, a larger content of water was emulsified when the emulsion was prepared using the ultrasonic vibrator than the mechanical homogenizer. The emulsions prepared by the ultrasonic vibrator also had a lower fuel consumption rate, lower bsfc, and significantly lower CO emission while at the same time having a larger black smoke opacity. When comparing the two-phase W/O and the three-phase O/W/O emulsions prepared by either the ultrasonic vibrator or the mechanical homogenizer, the two-phase W/O emulsions appeared to have a lower fuel consumption rate, bsfc, CO, and a lower black smoke opacity than the three-phase O/W/O emulsions, regardless of whether they were prepared by ultrasonic vibrator or mechanical homogenizer.     

Influence of Processing on the Physical Stability of Multiple Emulsions Containing a Green Solvent

The influence of the emulsification process on the microstructure and physical stability of model water‐in‐oil‐in‐water (W/O/W) emulsions formulated with a green solvent and a mixture of amphiphilic copolymers as emulsifiers was investigated. Emulsions were prepared by applying a homogenization step with a rotor‐stator device followed by high‐pressure homogenization. Viscous flow tests, transmitted light optical microscopy, globule size distribution (GSD), and multiple light scattering (MLS) measurements were carried out. The GSDs obtained were the result of a recoalescence due to overprocessing and the coalescence of inner droplets with the outer water phase. MLS detected a main destabilization mechanism by creaming. The passing of the emulsion through a high‐pressure homogenizer (HPH) significantly delayed the creaming process.     

Pipeline Flow Behavior of Water‐in‐Oil Emulsions with and without a Polymeric Additive in the Aqueous Phase

New experimental results are presented on the pipeline flow behavior of water‐in‐oil (W/O) emulsions with and without a polymeric additive in the aqueous phase. The emulsions were prepared from three different oils of different viscosities (2.5 mPa s for EDM‐244, 6 mPa s for EDM‐Monarch, and 5.4 mPa s for Shell Pella, at 25 °C). The W/O emulsions prepared from EDM‐244 and EDM‐Monarch oils (without any polymeric additive in the dispersed aqueous phase) exhibited drag reduction behavior in turbulent flow. The turbulent friction factor data of the emulsions fell well below the Blasius equation. The W/O emulsions prepared from EDM‐244 oil exhibited stronger drag reduction as compared with the EDM‐Monarch oil. The W/O emulsions prepared from Shell Pella oil exhibited negligible drag reduction in turbulent flow and their friction factor data followed the Blasius equation. The Shell Pella emulsions were more stable than the EDM‐244 and EDM‐Monarch emulsions. When left unstirred, the EDM‐244 and EDM‐Monarch emulsions quickly coalesced into separate oil and water phases whereas the Shell Pella emulsions took a significantly longer time to phase separate. The Shell Pella oil emulsions were also milkier than the EDM emulsions. The addition of a polymer to the dispersed aqueous phase of the W/O emulsions had a significant effect on the turbulent drag reduction behavior.     

Efficient Encapsulation of a Water-Soluble Molecule into Lipid Vesicles Using W/O/W Multiple Emulsions via Solvent Evaporation

We developed a novel method for preparing lipid vesicles with high entrapment efficiency and controlled size using water‐in‐oil‐in‐water (W/O/W) multiple emulsions as vesicle templates. Preparation consists of three steps. First, a water‐in‐oil (W/O) emulsion containing to‐be‐entrapped hydrophilic molecules in the water phase and vesicle‐forming lipids in the oil phase was formulated by sonication. Second, this W/O emulsion was introduced into a microchannel emulsification device to prepare a W/O/W multiple emulsion. In this step, sodium caseinate was used as the external emulsifier. Finally, organic solvent in the oil phase was removed by simple evaporation under ambient conditions to afford lipid vesicles. The diameter of the prepared vesicles reflected the water droplet size of the primary W/O emulsions, indicating that vesicle size could be controlled by the primary W/O emulsification process. Furthermore, high entrapment yields for hydrophilic molecules (exceeding 80 % for calcein) were obtained. The resulting vesicles had a multilamellar vesicular structure, as confirmed by transmission electron microscopy.     

Ansatz zur Beschreibung der zerkleinerungsrelevanten Strömungsverhältnisse beim Emulgieren von W/O‐Emulsionen mit Lochblenden

This paper presents an indirect way to classify the flow during emulsification with orifices and deals with the influence of the flow type on droplet size distribution of the resulting w/o emulsions. Based on the different areas in the slope of the discharge coefficient it was possible to identify different flow conditions. W/O emulsions of two material systems were prepared in the different flow conditions and the droplet size distributions of these emulsions were measured. It was observed that the resulting droplet size distributions of the emulsions strongly depend on the present flow pattern.     

Preparation of W1/O/W2 emulsions and droplet size distribution measurements by pulsed‐field gradient nuclear magnetic resonance (PFG‐NMR) technique

Multiple emulsions of W₁/O/W₂ type are of major interest in life sciences, offering possibilities for the encapsulation of water‐soluble active agents. In food science, they are also applied for fat reduction. The droplet size distributions of the inner and outer emulsions are of main importance as they influence the rheological and sensorial properties, the release kinetics, as well as the structural and microbial stability. However, the determination of the inner and outer droplet size distributions is a major challenge, as conventional measurement techniques cannot be applied. Pulsed‐field gradient nuclear magnetic resonance (PFG‐NMR) is well known as a non‐destructive tool for droplet size determination, especially in simple emulsions. In this work, double emulsions of the W₁/O/W₂ type were prepared with polyglycerol‐polyricinoleate (PGPR) and polyoxyethylen‐20‐sorbitan monolaurate (Tween 20) as emulsifiers by means of rotor‐stator emulsification machines. PFG‐NMR was applied for measurements of the inner phase (W₁) droplet size distribution as well as for the characterization of the O phase. The W₁ values were compared with results from laser light diffraction of simple emulsions (W₁/O type) and were found to be consistent within the experimental errors, if restricted diffusion in the outer water phase (W₂) and additional effects are considered.     

Dynamometer evaluation and engine wear characteristics of palm oil diesel emulsions

Dynamometer engine tests at steady-state conditions and a wear characteristics study were carried out on an indirect-injection diesel engine with palm oil diesel (POD) and its emulsions. The POD fuel was obtained in commercial form, and its emulsions were created by mixing POD fuel to contain 5 and 10% of water by volume. Variations in the engine’s performance characteristics were determined from the results of steady-state tests carried out at fifteen selected torque-speed matrix points of the engine’s performance map. The wear characteristics tests were performed by running the engine at half throttle setting for twenty hours for each fuel system. Then a desk-top comparison study was performed between the base-line fuel system of ordinary diesel (OD), POD, and its emulsions. Promising results have been obtained. Neither the lower cetane number of POD fuel nor its emulsification with water presented obstacles to the operation of the diesel engine during a series of steady-state engine tests and the twenty-hour endurance tests. Engine performance and fuel consumption for POD and its emulsions are comparable with those of OD fuel. Accumulations of wear metal debris in crank-case oil samples were lower with POD and its emulsions than with baseline OD fuel.     

Interfacial Crystallization of Diacylglycerols Rich in Medium‐ and Long‐Chain Fatty Acids in Water‐in‐Oil Emulsions

The effects of diacylglycerols rich in medium‐ and long‐chain fatty acids (MLCD) on the crystallization of hydrogenated palm oil (HPO) and formation of 10% water‐in‐oil (W/O) emulsion are studied, and compared with the common surfactants monostearoylglycerol (MSG) and polyglycerol polyricinoleate (PGPR). Polarized light microscopy reveals that emulsions made with MLCD form crystals around dispersed water droplets and promotes HPO crystallization at the oil‐water interface. Similar behavior is also observed in MSG‐stabilized emulsions, but is absent from emulsions made with PGPR. The large deformation yield value of the test W/O emulsion is increased four‐fold versus those stabilized via PGPR due to interfacial crystallization of HPO. However, there are no large differences in droplet size, solid fat content (SFC), thermal behavior or polymorphism to account for these substantial changes, implying that the spatial distribution of the HPO crystals within the crystal network is the driving factor responsible for the observed textural differences. MLCD‐covered water droplets act as active fillers and interact with surrounding fat crystals to enhance the rigidity of emulsion. This study provides new insights regarding the use of MLCD in W/O emulsions as template for interfacial crystallization and the possibility of tailoring their large deformation behavior. Practical Applications: MLCD is applied in preparing W/O emulsion. It is found that MLCD forms unique interfacial Pickering crystals around water droplets, which promote the surface‐inactive HPO nucleation at the oil‐water interface. Thus MLCD‐covered water droplets act as active fillers and interact with surrounding fat crystals, which can greatly enhance the rigidity of emulsion. This observation would provide a theoretical reference and practical basis for the application of the MLCD with appreciable nutritional properties in lipid‐rich products such as whipped cream, shortenings margarine, butter and ice cream, so as to substitute hydrogenated oil. MLCD‐stabilized emulsions can also be explored for the development of novel confectionery products, lipsticks, or controlled release matrices.     

玉米油W1/O/W2型多重乳状液稳定性的研究

高脂食品严重危害着人类健康,这引起人们对低脂食品的的不断追求,因此脂肪替代品的开发越来越受到人们重视。本试验以玉米油和生物高聚物为主要原料通过两步乳化法制备W1/O/W2多重乳状液作为脂肪替代品(FS),以离心稳定性为衡量标准,用显微镜直接观察,探讨了初复乳乳化工艺、各相相对体积比对玉米油W1/O/W2型多重乳状液体系稳定性的影响。结果表明:1.影响玉米油多重乳状液稳定性的主要因素有:复乳的乳化工艺,内水相与油相体积之比等。2.两步乳化工艺中第二步乳化工艺对复乳稳定性影响较大,其规律是随着乳化强度的提高,粒径减小,稳定性呈上升趋势,适宜的乳化条件为7200 r.min.1,13 min,而第一步乳化工艺对复乳稳定性几乎没有影响。3.内水相与油相、初乳与外水相均是影响复乳稳定性的主要因素,前者主要是依靠改变初乳黏度来影响复乳稳定性,后者主要是乳滴间范德华力与电排斥力共同作用的结果,适宜的体积比分别为1:4和1:1。     

Drop breakage in a single-pass through vortex-based cavitation device: Experiments and modeling

Liquid–liquid emulsions are used in many sectors such as personal care, home care, and food products. There is an increasing need for developing compact and modular devices for producing emulsions with desired droplet size distribution (DSD). In this work, we have experimentally and computationally investigated an application of vortex-based hydrodynamic cavitation (HC) device for producing emulsions. The focus is on understanding drop breakage occurring in a single-pass through the considered HC device. The experiments were performed for generating oil-in-water emulsion containing 1%–20% rapeseed oil. The effect of pressure drop across the HC device in the range of 50–250 kPa on drop breakage was examined. DSD of emulsions produced through a single pass was measured using the focussed beam reflectance measurements. Comprehensive computational fluid dynamics (CFD) model based on the Eulerian approach was developed to simulate multiphase cavitating flow. Using the simulated flow, population balance model (PBM) with appropriate breakage kernels was solved to simulate droplet breakage in a vortex-based HC device. The device showed an excellent drop breakage efficiency (nearly 1% which is much higher than other commercial devices such as rotor–stators or sonolators) and was able to reduce mean drop size from 66 to ~15 μm in a single pass. The CFD and PBM models were able to simulate DSD. The presented models and results will be useful for researchers and engineers interested in developing compact devices for producing emulsions of desired DSD.