Residual water mixture (RWM) is a fuel of an "oil- in-water" emulsion with a water content of about 30% ( by weight) to the final residual oils such as asphalt and pitch after distilling crude oils. The fuel shows two orders of magnitude lower viscosity, than the neat residual oils because of water content included in the emulsion, so it can be used in a pump to supply fuel to a burner. In this article, the atomization characteristics of the sprays of a twin-fluid atomizer and, in particular, NOx emission characteristics in the flue gases in a small furnace, are discussed for asphalt/water (As/W) emulsions, one of the RWM fuels, in combustion experiments. It is concluded that As/W fuels can be expected to be used as substitute fuels for C heavy oil because of improved combustive quality of residual oils and nearly equivalent NOx emissions to C heavy oil. The result is based on dispersed flames induced by the secondary atomization due to the microexplosion effect of the fuel droplets.