In this study, a fuel-water rapid internal mixing injector capable of reducing emissions from combustion furnaces operating under high load conditions was developed. Employing this injector allows the injection of a fresh emulsified fuel mixture without requiring surfactants or additional processing equipment. The aim of the present study was to investigate the emulsification, atomization, and emission performance of the injector when using soybean oil as a model high-viscosity fuel from a renewable source. Successful emulsification was observed in the mixing chamber over a wide range of water content ratios up to 0.5, under which a water-in-oil emulsion was discharged from the injector. As the water content ratio was increased, the Sauter mean diameter of the droplets in the spray increased. This is a result of the decrease in the mass flow ratio of atomizing gas to liquid and the increase in the viscosity of the fuel emulsion. Although the emulsification of the base fuel resulted in the discharge of large droplets, the results showed that the nitrogen oxide and particulate matter emissions from a combustion furnace incorporating the injector were found to be reduced simultaneously following the introduction of water even under a high combustion load.

In this study, a fuel-water rapid internal mixing injector capable of reducing emissions from combustion furnaces operating under high load conditions was developed. Employing this injector allows the injection of a fresh emulsified fuel mixture without requiring surfactants or additional processing equipment. The aim of the present study was to investigate the emulsification, atomization, and emission performance of the injector when using soybean oil as a model high-viscosity fuel from a renewable source. Successful emulsification was observed in the mixing chamber over a wide range of water content ratios up to 0.5, under which a water-in-oil emulsion was discharged from the injector. As the water content ratio was increased, the Sauter mean diameter of the droplets in the spray increased. This is a result of the decrease in the mass flow ratio of atomizing gas to liquid and the increase in the viscosity of the fuel emulsion. Although the emulsification of the base fuel resulted in the discharge of large droplets, the results showed that the nitrogen oxide and particulate matter emissions from a combustion furnace incorporating the injector were found to be reduced simultaneously following the introduction of water even under a high combustion load. Highlightso No surfactant is required in the fuel-water rapid internal mixing injector.o Successful emulsification was observed in the mixing chamber.o The NOx and soot emissions were reduced simultaneously.

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The fuel-water internally rapid mixing type of injector has been developed to reduce NOx and soot emissions from combustion furnaces operating under high-load conditions. The injector allows spray injection of water emulsified fuel originating from base fuel and water without any surfactants. The aim of present study is to elucidate the mechanism of emulsification occurring in the injector and the atomization characteristics of the injector. We measured the sizes of fuel droplets discharged from the injector by means of a high-speed shadowgraph method combined with image processing. Soybean oil was used as the base fuel. The flow patterns of the fuel and water in a transparent mixing chamber of the injector were also visualized. In addition, we investigated the inner structure of the large droplets sampled by an immersion droplet sampling method. The base fuel, water and air are separately introduced into the injector. In the mixing chamber of the injector, fuel and water are blown by swirling air, and then impinge on the inner wall of the chamber. The base fuel is emulsified through the mixing of fuel with water resulting from the impingement. The emulsified fuel moves to injection holes along the inner wall, and is finally discharged through the injection holes with atomizing air. The probability profiles of droplet size exhibit that the existence probabilities of coarse droplets with diameters greater than approximately 35 mm are increased when the fuel is emulsified. Although the emulsification deteriorates the atomization capability of the injector, the secondary atomization including the micro-explosion occurring in combustion furnaces would form fine droplets, and thus reducing the soot emission from the furnaces. The microscope observations revealed that the emulsified fuel filling in a large droplet sampled corresponds to W/O type.