Combustion equipment (e.g., diesel engines, power boilers) emits significant amounts of hazardous gasses, such as Nitrous Oxides (NOx), hydrocarbons (HC), carbon monoxide (CO), carbon dioxide (CO2) as well as particulate matter (PM) and black smoke. Due to the widespread use of this equipment, the resulting damage to human health and the environment is tremendous. Adding 5 – 25% of water to the base fuel, such as diesel or kerosene, in the form of a very fine emulsion (nanoemulsion) significantly reduces these harmful emissions.
Environmental Benefits
In terms of environmental benefits, water-in-diesel emulsion is one of the most attractive petroleum-based alternative fuels. It can be used in unmodified diesel engines, and has been shown to reduce the NOx emission by up to 35% because water reduces the local adiabatic flame temperature. In addition, PM is reduced by up to 60% and black smoke commonly associated with the use of straight diesel is dramatically reduced because the emulsion fuel burns much more completely.Economic Benefits
There is also an immediate economic benefit to using emulsion fuels. The addition of finely dispersed water reduces fuel consumption by improving its atomization and burning efficiency. Since water has a much lower boiling temperature than the fuel, it is vaporized much more readily upon heating. At the “superheat limit temperature” of about 270 C, micro-explosions of the fine water droplets occur throughout the emulsified fuel. This enhances atomization and leads to better mixing of fuel and air in the engine. The presence of a large low-tension water-oil interface improves the atomization further. Therefore, although water replaces part of the fuel, the loss in energy content is mostly compensated by the increase in the remaining fuel’s combustion efficiency. The net result is a significant fuel cost reduction, which commonly exceeds any emulsion manufacture expenses.
Achieving Stability
The main challenge faced by emulsion fuel manufacturers is how to achieve long-term stability of the final product while minimizing the costs of production. While stable microemulsion-based fuels have been introduced to the market before, they had limited commercial success because they required prohibitively high surfactant ( surface-active agents used to stabilize emulsions) concentrations. Nanoemulsion-based fuels, on the other hand, are much more promising, as their stability comes with much lower surfactant content requirements. Since strong shear forces are necessary for the production of stable nanoemulsions, special equipment, such as a high-pressure homogenizer or a high-intensity ultrasonic processor, must be used. While this results in additional production costs, these are commonly outweighed by cost benefits due to the reduction in surfactant content.
Ultrasonic Production
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Laboratory, bench and industrial-scale ultrasonic processors are available for the production of emulsion fuels with exceptional stability. Once the fuel formulation is finalized and the procedure is optimized in the laboratory, the process can be directly transferred to the production scale, where the quality of the final product is maintained while the productivity is increased by a predictable "scale-up factor". Watch this video for more information.
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