Atomization and combustion characteristics of a fuel–water rapid internal mixing injector

In this study, we investigated the atomization characteristics of rapid internal mixing injector (RIM injector) developed in our laboratory. RIM injector successfully emulsifies base fuel without any surfactant just before fuel injection. The diameter of droplet discharged from RIM injector was evaluated based on processing of shadowgraph images. It was found that Sauter mean diameter (SMD) of droplet is determined by the gas to liquid ratio (GLR) and viscosity of emulsified fuel. The increasing GLR decreases SMD value. As water content ratio is increased, the inner structure of droplet changes to W/O type emulsion. The emulsification increases its viscosity, which deteriorates the atomization characteristics. We proposed an empirical formula as functions of GLR and Reynolds number reproducing the deterioration resulting from increasing viscosity. The formula successfully predicts the SMD variation with respect to GLR and water content ratio. Finally, we examined the effect of atomization air ratio on NOx and PM emissions. The quantity of atomization air significantly influences the PM emission because the increasing air improves the mixing of fuel vapor with combustion air.