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TRANSCRIPT
Mr. Kotaro Kojima 9 Development of On-‐Board Water-‐in-‐Diesel Emulsion (WiDE) Fuel System Utilizing Ultrasonic Cavitation to Realize Ultra Low-‐Emission Diesel Engines Environmental Technology Commercialization Plan Elevator Pitch: The novel on-‐board emulsion technology overcomes the barriers hindering the marketing of low-‐emission fuels and opens the door for the target customers, diesel engine manufacturers to produce an engine that can meet stringent emission regulations while anticipating a reliable influx of revenue. This system revolutionizes diesel engine architecture by using ultrasonic cavitation for sub-‐second fuel/water emulsification near the fuel injectors. Subsequent combustion results in unsurpassed emission reduction.
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Executive Summary Nitrogen oxides (NOx) and particulate matter (PM) from diesel engines have generated much public concern, damaging the atmosphere and threatening human health. Water-‐emulsified fuel is a promising alternative fuel capable of simultaneously reducing these emissions while maintaining the combustion efficiency. However, water contents in the fuel have a tendency to coalesce if the fuel is not agitated periodically. This ingredient separation curtails engine performance, therefore triggering counter effects. Combined with excessive costs of production and transportation, emulsion instability obstructs widespread usage of water-‐emulsified fuel. An on-‐board water-‐in-‐diesel emulsion system was developed as a solution to this issue. Designed for engine implementation, the technology utilizes ultrasonic cavitation to instantly emulsify water with diesel fuel near the injectors, allowing for subsequent low-‐emission combustion. This approach is economical as it removes the concerns of emulsion instability as well as the need for mass production at chemical plants and transportation. A proof-‐of-‐concept study was conducted to characterize the system with water-‐emulsified fuels, diesel, and biodiesel. Optical diagnostics were applied in combustion experiments to evaluate PM emission levels. Flame-‐color segmentation analysis on acquired flame images gave strong evidence that water-‐emulsified fuels emit significantly less PM than conventional diesel fuels. Fuel spray visualized through a laser-‐scattering technique revealed the homogeneous and atomized spray patterns of the water-‐emulsified fuels. The innovation can not only overcome the barriers hindering the commercialization of emulsion fuels but also solve one of most serious air-‐pollution challenges worldwide through reductions of NOx and PM. Problem Summary and Proposed Solution Diesel engines emit hazardous pollutants, particularly NOx and PM, which not only damage our environment, but also threaten human health (Nadeem et al., 2006). Due to increasingly stringent emission standards implemented by the various agencies worldwide, many hardware-‐based technologies are being developed to minimize these exhaust gas emissions. After-‐treatment devices such as selective catalytic reduction (SCR) and NOx absorber catalysts (NAC) are able to reduce the formation of NOx considerably. Diesel oxidation catalysts (DOCs) and diesel particulate filters (DPFs) are also devices commonly utilized for the reduction of PM. However, there is often a trade-‐off relationship since the techniques that are used to reduce NOx, lead to an increase in PM and black smoke and vice versa (Basha, & Anand, 2011). In addition, they tend to increase the fuel consumption of the engine (Subramanian, & Ramesh, 2001). Thus, it is challenging to simultaneously reduce both NOx and PM while maintaining the engine performance. In recent decades, water-‐emulsified fuel has emerged as a promising alternative fuel with capability to reduce PM and NOx emissions simultaneously while at the same time enhancing the combustion efficiency. (Basha, & Anand, 2011; Subramanian, & Ramesh, 2001). In spite of its advantages, a major concern of water-‐emulsified fuel is its stability. The constituent parts of water-‐emulsified fuel have a tendency to separate over time. Where the emulsion composition has altered due to ingredient separation, the engine performance and emissions is significantly diminished. Additionally, if water-‐emulsified fuel were stored in fuel dispensers at gas stations like traditional fuels, the emulsion would destabilize; and if pumped into a diesel engine and combusted, the exposed water would damage engine components. Lastly, the manufacturing of water-‐emulsified fuel at dedicated factories with specialized equipment, the transportation of the aforementioned fuel to desired locations, and the infrastructure of fuel pumps and dispensers would incur large expenses. Hence, there is a pressing need for an innovation overcoming the barriers to the commercialization of water-‐emulsified fuel, while maintaining the superior low-‐emission and combustion efficiency characteristics of the water-‐emulsified fuel. In an attempt to present a solution to this issue, a novel on-‐board water-‐in-‐diesel emulsion (WiDE) fuel system was designed and a proof-‐of-‐concept prototype was constructed. The technology utilizes ultrasonic cavitation to emulsify fuel and water directly before the injectors, so that the resulting fuel can be injected immediately into the engine, essentially removing the concerns of emulsion instability while realizing the benefit of low-‐emission combustion promised by the water-‐emulsified fuel. This technology is economically advantageous as it eliminates costly emulsion manufacturing plants, expenses for transportation, and the infrastructure of fuel dispensers. Summarize the STEM Concepts and Principles Underlying the Overall Plan Fascination with tiny oxygen bubbles emerging from a platinum catalyst in a hydrogen peroxide contact lens solution led the author to research about the phenomenon of ultrasonic cavitation and the uses of cavitation in engineering. A curiosity-‐driven experiment to see if an ultrasonic jewelry cleaner could help vegetable oil mix with
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water through cavitation gave insight on cavitation-‐induced emulsion. Further research on the subject introduced the author to the concept of water-‐emulsified fuel and made him aware about its impeded commercialization. The following three STEM concepts were used together to develop the current technology. Ultrasonic cavitation is a unique condition in liquid media induced by ultrasound. Intense sonic pressure waves from ultrasonic transducers can cause the rapid formation of micron-‐sized bubbles or “voids.” The implosive collapse of these bubbles generates intense local heat and high pressures (up to 5,000 K and 1,000 atm) and liquid jet streams (Suslick, 1990). These extreme conditions can result in effective mixing of immiscible liquids, creating an emulsified liquid commonly known as emulsion (Figure 1). An emulsion is a mixture of two or more immiscible liquids formed through mechanical agitation, with one of the liquids dispersed as small droplets in the other. Emulsions have found numerous and various applications in paint, food, cosmetics, and pharmaceutical industries (Nadeem et al. 2006). In recent years, emulsions of water and diesel fuel, also known as water-‐emulsified, have received much attention in alternative fuel sectors. Spray combustion is a complex principle of physical chemistry. It involves fluid dynamics, chemical reactions, and molecular transport (Warnatz et al. 1996). When fuel is injected through an orifice into a combustion environment, it breaks up into various sizes of droplets before heat vaporizes it. Efficiency of subsequent combustion heavily depends on the extent of mixing of fuel vapor and air. The turbulent nature of spray combustion makes it difficult to measure and model the phenomenon in detail. Commercialization Assessment of the Overall Plan Problem, pain point or market opportunity: Long-‐term epidemiologic studies have reported an increased risk of cardiopulmonary mortality, lung cancer mortality, and respiratory mortality associated with increasing exposures to primary pollutants in the diesel engine exhaust. Despite the urgent need for low-‐emission diesel combustion, an effective method to minimize diesel engine emissions has yet to be developed. Although devices like SCR, NAC, DOCs, and DPFs have notable pollutant mitigation efficiencies, none of these can minimize both NOx and PM while concurrently maintaining the engine performance. As a promising method to meet this predicament, water-‐emulsified fuel has emerged as an alternative fuel capable of reducing both NOx and PM while preserving combustion efficiency. However, emulsion instability and excessive production/distribution costs prevent its commercialization. Thus, there is a pressing need for a breakthrough technology able to eliminate the emulsion instability and high production/distribution costs in order to introduce water-‐emulsified fuel into the market.
Proposed solution: The proposed solution is to generate water-‐emulsified fuel on-‐board diesel engines. The key to the success of this scheme is an engineering design that permits an ultrasonic transducer and a mixing control valve to effectively create cavitation for making water-‐emulsified fuel in real-‐time fashion. By integrating this on-‐board WiDE fuel technology into diesel engines, water-‐emulsified fuel would be formed during engine operation near the injector pump and consumed immediately for combustion. This approach essentially removes the concerns of emulsion instability in the fuel tank or fuel dispensers as well as the needs of mass production at chemical plants and transportation; thus, the true economical benefit of the water-‐emulsified fuel will be realized. For this reason, the proposed solution is not only patentable but also superior to the current state-‐of-‐the-‐art. While three patents (Coleman, & Sibley, 1997; Cottell, 2011; Hendren, 2003) describe the idea of an on-‐board fuel system, they fall short to claim the use of ultrasonic cavitation to mix water and fuel within the engine. These patents also do not claim an economical solution of using a dual-‐purpose water mixture for the emulsion, which saves an additional water reservoir and water pump. Furthermore, the systems described in these patents do not find yet another constituent of the novel technology that uses a mixing control valve, eliminating the necessity for a pair of flow sensors (for water and fuel). Target customers and intended users: Initially, the on-‐board WiDE fuel system would be licensed to diesel engine manufacturers for implementation into existing and new diesel engines. These diesel engine manufacturers are expected to be widely international, ranging from American corporations Caterpillar Inc. and Cummins Inc. to
Figure 1. Cavitation-induced emulsion. (Left) Separated fuel and water. (Right) Emulsified fuel with <1 sec. exposure to cavitation. Photo by author.
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European conglomerates Daimler AG and Volkswagen AG to Japanese companies Isuzu Motors Ltd. and Komastu Ltd. The intended users of the newly assembled diesel engines would be logistics/trucking companies, construction and agricultural machinery companies, and railway locomotive companies.
Competitors: SCR, NAC, DOCs, and DPFs and other emissions control devices are currently used in diesel engines; nevertheless, they do not possess the effectiveness of the novel technology. Lubrizol, Cam Technologie, Clean Fuels Technologies, and Total S.A. market water-‐emulsified fuel blends at a small-‐scale, mainly in Europe. Large-‐scale commerce is stalled, however, due to high production/distribution costs and emulsion instability issues. Berlin-‐based German company Heilscher Ultrasonics suggests an on-‐board WiDE fuel system concept in a primitive way as a potential application of the company’s high-‐intensity ultrasonic transducer (Heilscher Ultrasonics, 2016). Nevertheless, Gunther Benner, a sales manager, confirmed in an email correspondence that Heilscher Ultrasonics does not own any patent on the idea; rather, the company is interested in becoming an ultrasonic transducer supplier to customers’ unique processes (personal communication, February 26, 2016). Customer value proposition & competitive advantage: A system that creates water-‐emulsified fuel on-‐demand at the point of use (i.e., on-‐board WiDE fuel system) is a valuable and beneficial innovation to the target customers because it lowers the cost of their engine. The cost to install the on-‐board WiDE fuel system into a diesel engine is estimated to be $1,450 (assembly labor: $800, manufacturing: $300, parts: $300, electrical control unit upgrade: $50) per unit assuming a batch of 1,000 units production. If an engine manufacturer adds $1,650 per-‐unit profit, a sale price of the engine would be increased by $3,000 per unit (i.e., approximately 10% of an invoice price of a 500 horsepower diesel engine). This price increase is clearly justified considering the fact that the novel technology will replace after-‐treatment systems such as DPFs or SCRs currently used in diesel engines, which cost engine makers more than $15,000 per unit on average (U.S. EPA, 2015). In comparison to emulsion fuel makers, the on-‐board WiDE fuel approach is more feasible and robust because it eliminates the instability concerns associated with pre-‐processed emulsified fuel. This unique business model is not a classic wholesale-‐retail model. The engine manufacturer does not buy a system from an automobile supplier such as Bosch and double the engine price. Principal revenue streams expected: The principal revenues are expected to come from the licensing of the WiDE fuel technology to diesel engine manufacturers. Note that the author does not intend to manufacture or sell diesel engines. The author would receive a yet-‐to-‐be-‐negotiated upfront fee (expected to be around $90,750), plus an annual royalty rate of 0.25% of wholesale volume, or approximately
Table 1. Financial analysis for 5 years (licensing model)
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$82,500 to the author for every 1,000 unit sold. The upfront fee was calculated by taking 1% of the engine company’s profit due to the WiDE fuel system (an estimated 5,500 units sold in 3 years, multiplied by $1,650 per-‐unit profit). The royalty rate was calculated based on a historically accepted term (1%) with a rather large 75% risk discount considering the WiDE system is one component of a whole engine system. The author has begun an application process to seek $25,000 seed funding for prototyping from Great Lakes Innovation & Development Enterprise (GLIDE) through Cleveland-‐based JumpStart entrepreneur network. The author will seek step-‐up funding of up to $65,000 from GLIDE to fund validation in the second year. Principal startup and operating costs expected to be incurred: A four-‐year financial analysis from the company startup is shown in Table 1. Expansion to four years indicates that profit can be made after the first three years intended for prototyping, validation, marketing, and licensing. A provisional patent to protect the technology costs $300. Professor Mounir Ibrahim at the Cleveland State University (CSU) Washkewicz College of Engineering has agreed to fund the provisional patent fee (personal communication, March 21, 2016). Registration as a State of Ohio Limited Liability Corporation (LLC) costs $125. Prototyping in the first year would entail designing a three-‐way solenoid valve and a compact ultrasonic transducer (<50 watt, >20 kHz); and prototyping of the entire on-‐board WiDE fuel system. Initial CAD designs are in progress, thus, an hourly-‐paid design engineer should cost $150/hour, multiplied by 120 hours of labor is $18,000. Additional costs incurred for prototyping would include parts ($4,500) and machining ($6,000). In the second year, emission validation of the prototype will necessitate an emission gas analyzer ($3,500), instrumentation ($5,000). A research facility (20 ft. by 35 ft.) complete with engine hardware will be available for the prototype validation free of charge at Professor Ibrahim’s lab in CSU (personal communication, March 21, 2016). Marketing would incorporate marketing supplies such as brochures and website ($5,500 over two years). Since target customers are international, the author will exhibit the technology at multinational tradeshows POWER-‐GEN Asia (booth cost: $208/sq. ft. × 25 sq. ft. = $5,200) and POWER-‐GEN International (booth cost: $44/sq. ft. × 25 sq. ft. = $1,100). Each tradeshow will also incur costs (airfare, hotel, food, etc.) for a representative of the company to attend. This will allow for unique access to the power generation industry across world, product promotion, and face-‐to-‐face meetings with customers. U.S. patent filing and a patent attorney fees ($18,000) will be incurred for a U.S. patent in the third year. Concurrently, during the third year, a lawyer to draw up a licensing agreement between the author and a diesel engine manufacturer would cost $24,000 ($400/hour × 60 hours). Other costs including salary to the author, office rental/utilities, administrative, insurance, and office equipment are listed in Table 1. Science and Technology Proof of Concept Review and assessment of the scientific literature: A number of studies have been conducted on water-‐emulsified fuel combustion. Tsue et al. utilized a hot duralumin surface to analyze the micro-‐explosion phenomenon of a water-‐in-‐diesel emulsion droplet within a high-‐pressure chamber (Tsue et al. 1996). To analyze the breakup qualities of a secondary atomization of a water-‐in-‐diesel emulsion, Watanabe et al. conducted experiments where a single WiDE droplet was suspended on a quartz fiber (Watanabe et al. 2010). Literature can also be found on the occurrence of micro-‐explosion in emulsion fuel sprays. Watanabe and Okazaki observed the secondary atomization of emulsified fuel spray using a high-‐speed shadow imaging technique, however micro-‐explosion was seldom detected (Watanabe, & Okazaki, 2013). In contrast, Mizutani et al. reported the effective observation of micro-‐explosion in oil-‐in-‐water emulsion spray flames created by a ring pilot burner (Mizutani et al. 2000). Other methods have been used in the study of water-‐emulsified fuel apart from the aforementioned ones. Various kinds of four stroke engines have been employed to evaluate emissions and combustion characteristics of water-‐emulsified fuel. Nadeem et al., for example, fuelled a Ford diesel engine test bed with diesel and emulsified fuels stabilized by conventional and gemini surfactants to study performance and emissions (Nadeem et al. 2006). Discussion of your findings with relevant cited references: In the present research, a water-‐in-‐diesel emulsion was successfully engineered through low-‐power (1.4 W) ultrasonic cavitation in a chamber approximately 0.3 cm3
in volume within <1 sec of residence time. Hendren describes a propeller agitator up to 6000 RPM to create an oil-‐in-‐water emulsion (Hendren, 2003) while Cottell proposed a non-‐vibrating anvil to emulsify water and fuel through cavitation (Cottell, 2011). Coleman and Sibley cite a mixing apparatus upstream of the fuel injectors for creating fuel-‐in-‐water emulsion (Coleman, & Sibley, 1997). According to the author’s flame-‐color segmentation analysis applied to open spray flames of fuel variations, PM
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emission level of the spray combustion of water-‐emulsified fuel (3% water content) was found to be 40% lower than traditional diesel fuel. Nadeem et al. has reported up to 70% in PM emissions decrease with emulsified fuel containing 15% water content by volume (Nadeem et al. 2006). PuriNOx, Lubrizol’s water/diesel emulsion, has been verified by the California Air Resources Board (ARB) as capable of 63% PM reduction compared to conventional fuels (U.S. EPA, 2002). Barnes et al. investigated the effect of 10% water addition to fuel, reporting a 20% lowering in PM from a city bus engine (Barnes et al. 2000). Statement of a single, clear and compelling (1) testable hypothesis or (2) engineering design: An energy-‐efficient, ultrasonic water-‐emulsified fuel technology will be designed for on-‐board diesel engine implementation and evaluated with a proof-‐of-‐concept combustion experimentation. Inquiry or design-‐based discussion (Experimental Materials and Methods) Dual-‐Purpose Water Mixture: Methyl alcohol (Duda Energy) and a surfactant, Clear EX (Lion Specialty Chemicals) was mixed into the water for emulsion to prevent freezing and corrosion: methyl alcohol for anti-‐freezing and surfactant for corrosion-‐prevention. The Clear EX contains polyoxyethylene (a nonionic surfactant) and amin compounds for corrosion-‐prevention as well as a chelating agent for anti-‐bacterial effect. Long-‐term stability, rustproof, and anti-‐bacterial performance of the surfactant have been reported previously (Kunio et al. 2003). Because the water for emulsion is mixed with surfactant and methyl alcohol, it meets the specifications for windshield washer fluid as an anti-‐freezing and hydrophobic liquid. Thus, the mixture of water, methyl alcohol, and surfactant, called dual-‐purpose water mixture, can function as both windshield washer fluid and water for emulsion. This eliminates the need for the installation of an additional water reservoir and pump in the engine. Note that this dual-‐purpose water mixture would be a separate product with proprietary composition, manufactured and sold by another entity of business. Refilling of the water mixture would come by one-‐gallon containers just as windshield washer fluids sold at gas stations. On-‐Board WiDE Fuel System: The on-‐board WiDE fuel system concept was conceived for diesel engine implementation. Figure 2 illustrates how the technology operates in a standard diesel engine system. A single water reservoir supplies water for both the water-‐emulsified fuel and the windshield washer fluid. It serves dual-‐purposely and eliminates the need of an extra water pump. When the engine is started, the fuel and water are pumped out of their respective reservoirs and converge at the three-‐way solenoid valve (hereafter called “mixing control valve”), which regulates the water-‐to-‐fuel ratio. In the
Figure 3. Biodiesel made by the author. Photo by author.
Figure 2. On-board WiDE fuel system integrated into a diesel engine common rail/fuel injection system. Sketched by author.
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emulsion cavity, the fuel and water are emulsified by ultrasonic cavitation induced by a transducer. Subsequently, the freshly produced water-‐emulsified fuel is fed into the common rail where it is injected into the diesel engine and combusted. The unused fuel is looped back to the emulsion cavity where it is re-‐emulsified with constituent fuel and water.
Proof-‐of-‐Concept Experimentation: A prototype of the emulsification chamber (see Figure 5 inset) was constructed for proof-‐of-‐concept combustion flame and fuel spray experiments on four fuel types: diesel, biodiesel (Figure 3), water-‐emulsified diesel, and water-‐emulsified biodiesel. It was made of a fitting nut welded to a straight ½ inch fitting coupler. Two holes were drilled on either side of the coupler. ⅛ inch tubes were welded into those holes: one for fuel inlet and the other for water inlet. A third tube was welded to the remaining opening to create the emulsified fuel outlet. An ultrasonic transducer was inserted through the fitting nut. It was intruded into the cavity to have direct contact with the liquids for creating instant emulsification as the fuel and water converge. A photograph and a schematic of the experimental apparatus are pictured in Figure 4 and Figure 5, respectively. The open-‐air burner was a suitable format to create an open fuel spray, providing an excellent opportunity for non-‐intrusive optical diagnostics of the combustion flame and fuel spray of the various fuels. Ultrasonic Transducer: Amplitude to Watts Calibration: The ultrasonic transducer used in the prototype had a variable power output of 10 to 750 watts (W). The ultrasonic transducer had a ½ inch piezoelectric tip made with lead zirconate titanate crystals (PZT) material. Although the amplitude control on the ultrasonic transducer could set the ultrasonic vibrations at the probe tip at any desired level between the amplitude of 10% to 80%, the amount of power required could not be predetermined. It is the resistance to the movement (vibrations) of the probe that determines how much power (wattage) is delivered into the sample. To determine the actual resistance of diesel fuel/water mixture, the output power was measured over the range of possible amplitudes. This test resulted in a linear relationship between the amplitude applied to the transducer and the output power of ultrasound, which was represented by an empirical equation: Output Power (W) = Amplitude (%) – 10. Ultrasonic Transducer: Joules Measurement for Complete Emulsification: Knowledge of energy requirement for complete emulsification of the diesel fuel and water is crucial for automobile electrical management. For this purpose, an ultrasonic energy test was conducted on a 9 to 1 mixture of fuel and water (500 mL in total). The minimum energy of 68 joules was required for complete emulsification based on visual observation. Since the total mixture volume was 50 mL, this equals to the energy usage of 1.4 joules per 1 mL. By multiplying it with the fuel flow rate of 1 mL/sec of the experimental system, the minimum power requirement of 1.4 W was calculated for complete diesel fuel and water emulsification. While the actual fuel flow rate in actual diesel engines is 10-‐20 times more than the fuel flow rate of the experimental system, the total wattage needed to keep the transducer running is not a burden to diesel engines’ electrical supply. Anti-‐Freezing and Rustproof Performance of Dual-‐Purpose Water Mixture: A lab experiment was conducted to test anti-‐freezing and rustproof performance of the water mixture with methyl alcohol and the surfactant. To test anti-‐freezing performance, methyl alcohol content in water was varied from 5% to 30% with an increment of 5%. The samples were set in an environment with an average temperature of -‐15°F for 10 hours. The mixtures crystallized with methyl alcohol concentrations below 30%. The mixture with methyl alcohol concentration of 30%
Figure 4. Experimental apparatus with prototype emulsification chamber (inset) constructed by author. Photos by author at combustion facility in Warrensville Heights, OH.
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stayed liquid without any sign of crystallization. This agrees with the fact that a typical commercial windshield washer has 30% to 40% methyl alcohol concentration. To test anti-‐corrosion ability, the surfactant content in water was varied from 1% to 10% with an increment of 2% to 3%. A piece of steel (5 grams) was submerged in each of those mixtures for 10 days and was observed for an extent of corrosion. The pieces of steel showed signs of corrosion with a slight discoloration of the water with surfactant concentrations below 7%. The steel in the mixtures with 7% and 10% concentrations of the surfactant did not show any surface corrosion. The results suggest a minimum of 30% methyl alcohol and 7% of surfactant for the rustproof and anti-‐freezing ability. The dual-‐purpose water mixture, therefore, would consist of 63% water, 30% methyl alcohol, and 7% surfactant. If the water were mixed with diesel fuel by a 9 to 1 ratio (90% diesel fuel, 10% dual-‐purpose water mixture) the final water-‐emulsified fuel would consist of 90% diesel, 6% water, 3% methanol, and 1% surfactant. Data Acquisition: Photographic Imaging: Imaging for both combustion flame and fuel spray experiments was carried out using a digital camera (Nikon D7000: 16.2 megapixels, 18-‐105 mm lens). Up to 27 images were recorded for each condition. For the fuel spray investigation, a laser diagnostic technique termed “fuel spray visualizer” was constructed. It consisted of a green laser pointer (5 mW, 532 nm) and a pair of mirrors (see Figure 6). The one of the mirrors, located downstream of the optical path, was attached to a gear motor. When the laser pointer was turned on, the laser beam reflected on the first mirror and the subsequent second mirror. Since the gear motor was energized simultaneously, the second mirror spun continuously and thus rotated the laser beam, which then formed a “laser sheet” with 1 mm thickness. This laser sheet scattered off the fuel droplets and visualized or “highlighted” the spray pattern. The laser sheet was directed toward the area of interest and aligned with the burner axis at a 120° angle for enhanced forward scattering. By synchronizing the camera’s shutter exposure and the laser-‐scanning rate, high-‐quality spray images were obtained.
Data Analysis Part I: Combustion Flame Images: Respective flame images of biodiesel and water-‐emulsified biodiesels are shown in Figure 7a. PM emissions, commonly known as soot, are carbon micro-‐particles with typical formation between C1 and C3. When PM are heated by combustion, they radiate as blackbody, creating a yellow-‐orange luminous flame. Since there is no other species that is expected to produce such a strong radiation over the range of wavelength, measuring yellow luminescence in flames is a valid scientific method to estimate the PM emission volume conveniently. In contrast, the hue of dark blue to emerald green indicates complete combustion. The blue-‐color flame is
Figure 5. Schematic of the experimental apparatus with instrumentation. Sketched by author.
Figure 6. Fuel spray visualizer with a spinning mirror used for spray analysis constructed by author. Photo by author.
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understood as chemiluminescence from the reactive species in flames (Stamatoglou, 2014). Therefore, the use of flame color is feasible for PM volume analysis. Based on this argument, a computer program was developed in MATLAB language that masked a flame image based on the hue range that was determined for the color separation of interests (Figure 7b). This novel flame-‐color analysis used a hue spectrum that allowed the optimizing of the hue range and separation of the original image into two segments based on the color. For the purpose of PM volume estimations of each fuel variation, the hue range was programmed to isolate the luminous yellow flame (PM representation) from the area encompassing dark blue to emerald green. It is understood that the blue color is chemiluminescence from the reactive species in flames and thus indicates the region where the actual combustion reaction is taking place. The averages of both colors over more than 20 images for each fuel variation were taken. The summation of the yellow pixel-‐intensity was then computed and normalized by the blue pixel-‐intensity sum. This value, hereafter called yellow/blue ratio or Y-‐B ratio, was an optical measure of PM volume, or a PM emission level indicator. The mean pixel (matrix element) value of the averaged flame image was computed by the following equation:
I is the pixel intensity of each matrix element (x, y); X = 3264, Y = 4928 are the number of pixels on each orientation; i is the color type of the image (yellow or blue). Furthermore, the ratio of the mean pixel values of the yellow and blue flames was computed by the following equation:
Φ stands for the Y-‐B ratio. A high Φ indicates the higher PM volume and a low Φ indicates lower PM volume. The use of Y-‐B ratio is effective because it cancelled out the difference in overall intensities among the fuel varieties. Through this data post-‐processing, the PM volume was strictly defined even when the mass flow rate was slightly varied among the different fuel varieties.
Figure 7. (a) Respective flame images of biodiesel and water-emulsified biodiesel. (b) Flame-color segmentation analysis developed by author for PM emission measurements. Photos by author.
(a) (b)
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Data Analysis Part II: Fuel Spray Images: Engine performance in diesel engines depends on many different factors; one of them is fuel spray quality. Fuel spray quality has a decisive impact on combustion in the diesel engine, thus affecting engine starting, efficiency, and emissions. The acquired spray images were analyzed using two image-‐processing techniques: Cutout (intensity threshold) filter and GlowEdges (intensity gradient) filter. The images in Figure 8a are two representative images out of more than 25 laser-‐visualized fuel spray images obtained for each fuel variation. Image intensity histograms for the biodiesel and the water-‐emulsified biodiesel are also shown. Two images with the similar histograms were chosen in order to conduct a non-‐biased analysis. The intensity threshold filter generated six individual images with increasing intensities out of one original spray image (see Figure 8b). According to the Mie scattering theory, the initial fuel spray near the orifice of the burner has higher scattering intensity because the fuel spray is much denser and droplets are larger near the orifice. In contrast, as the droplets travel farther away from the orifice, the droplets break up and create much smaller droplets (Le Gal et al. 1999). Because the smaller droplets do not scatter the laser sheet as much as the larger droplets, the scattering intensity decreases. This means that the level of image pixel intensity represents the spray formation development over the spreading angle of the spray (number 1 being the most intense scattering and number 6 being the least intense scattering). The water-‐emulsified fuel seemed to show steadier spray pattern, which should contribute positively to combustion performance and thus lower PM emission levels. Figure 9 illustrates the representative intensity gradient filtered images of biodiesel fuel spray and the water-‐emulsified fuel spray. These images are seen as enhanced edges where the pixel intensity gradients are higher than a certain threshold. This filter technique is especially useful to visualize individual droplets or clusters along
Figure 8. (a) Respective laser-visualized fuel spray images. (b) Intensity threshold filtered fuel spray images indicating spray formation development. Photos by author.
(a) (b)
Figure 9. Intensity gradient filtered fuel spray images. Photos by author.
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the outer spray boundaries as well as the injection cone angles. Fuel spray quality can be defined as the degree of atomization and uniformity of the droplet size distribution. This filter defined the atomization and the uniformity of the particular fuel variation. As seen in the Figure 9, the water-‐emulsified biodiesel spray has a smaller injection cone angle while having more uniform, atomized pattern than the biodiesel. The biodiesel has rather uneven spray formation with some larger droplet clusters. Large gaps with no droplets are also observed. Lower viscosity due to the water contents in the fuel and changes in surface tension might have helped water-‐emulsified biodiesel to exhibit more evenly distributed spray formation with smaller droplets. The more evenly distributed small droplets of the water-‐emulsified biodiesel should positively affect engine starting and engine performance. Results and Discussion Figure 10 presents the results of Y-‐B ratio (Φ) analysis on several combinations of the water-‐emulsified fuels against the control properties of the diesel and biodiesel fuels. Notice that each bar graph has a specific shutter speed (1/200, 1/800, or 1/8,000 sec) depending on the experimental condition. Graph A shows a promising trend, indicating PM emission from the biodiesel combustion can be reduced by up to 40% with 3% water content. This observation is also true according to Graph B, which shows an even more dramatic reduction of 50%. Graph A indicates biodiesel combustion generally produces higher amount of PM than regular diesel combustion unless water/fuel emulsion is practiced. This is significant finding because the data suggests that water-‐emulsion is a necessary technology for biodiesel to become truly environmentally friendly in applications to diesel engines. Graph C indicates 35% lowering of PM emissions from diesel combustion through water-‐emulsification. This PM emission reduction primarily owes to a distinct phenomenon of water-‐emulsified fuel combustion called micro-‐explosion (U.S. EPA, 2002). When an emulsion fuel is heated, the water droplets within the fuel are vaporized first because water is more volatile. This vaporization causes the explosion of the whole droplet, violently shattering the fuel droplet into very fine particles. Consequently, an enhancement in the fuel/air mixing process results in improved burning efficiency and thus suppresses the formation of PM. In addition, NOx emissions from the water-‐emulsified fuel are likely reduced as well due to the lower peak flame temperature. The reduction of the temperature is due to the high latent heat from the evaporation of water in the emulsion that absorbs the heat during the combustion.
Conclusion Emulsified fuel is a prime alternative fuel for both transport and stationary diesel engines. The increasing interest to this type of fuel is driven by its benefits of simultaneous reduction of both NOx and PM in addition to its impact on combustion efficiency. Despite its attractiveness, water-‐emulsified fuel has not been widely used due to its instability and production costs. The present paper describes an effort to develop a technology to overcome these obstacles impeding the commercialization of water-‐emulsified fuel. The low-‐emission capability of the technology has been confirmed through a proof-‐of-‐concept study incorporating combustion experiments, optical diagnostics, and unique image-‐processing techniques. The prototyping stage shows strong potential and feasibility
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1 2 3 4
Series1 0.8713 0.9874 0.81 0.6036
D BD
BD,3%W BD,2%W
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Shu]er speed: 1/8,000
Graph A
Graph B
Graph C
Figure 10. Comparison of PM (soot) emissions from various fuel types. D: diesel; BD: biodiesel; W: water volume percentage (water-emulsified fuel). Graphs created by author.
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for the continued development of a robust and reliable on-‐board WiDE fuel system that will, when implemented, make a significant impact on global emissions from the public health and environmental points of view. Implications for Future Research, Design, and Analysis A numerical combustion model should be developed to optimize the water content in the emulsion for each engine operating condition (idle or low/high load). Endurance testing of the mixing control valve and the ultrasonic transducer is necessary before prototyping of the WiDE fuel system for engine implementation. The water-‐emulsified fuel will be tested in various types of commercial diesel engines. Instrumentation data regarding engine performance (horsepower, fuel economy) should be collected to optimize engine parameters such as injection timing, injection pressure, compression ratio, and exhaust gas recirculation (EGR) controls. Acknowledgements Dr. Frank Sun, a mechanical engineer at Sun Valley Technology (OH), provided a facility for experiments. Mr. Jun Kojima answered technical questions about combustion and helped with MATLAB programming. References Cited Barnes, A., Duncan, D., Marshall, J., Psaila, A., Chadderton, J., & Eastlake, A. (2000). Evaluation of water-‐blend fuels
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