The correct answer is B) less excess air. Compared to a return flow oil burner system, an internally mixed steam atomizer requires less excess air because the atomization process is achieved through the use of steam rather than air. In an internally mixed steam atomizer, the steam and fuel oil are mixed internally, creating a finely atomized spray that can be ignited with a lower amount of excess air compared to an air-atomized system. The steam provides the necessary turbulence and velocity for effective atomization, reducing the need for excess air to facilitate the combustion process. The other options are incorrect because they do not accurately describe the key differences between a return flow oil burner system and an internally mixed steam atomizer. The steam atomizer does not require greater turbulence, higher air velocity, or higher fuel oil viscosity compared to the return flow system.