What defines an open cycle gas turbine engine?

An open cycle gas turbine engine is characterized by the fact that all the working fluid – the air that is drawn in, compressed, heated, expanded, and then expelled – passes through the engine only once during each operating cycle. In this type of system, fresh air is continually drawn into the engine, and after going through the combustion process, it is expelled to the atmosphere. This one-time passage of air distinguishes open cycle systems from closed cycle gas turbines, where the working fluid is recirculated and reused.

Understanding this concept helps to clarify the nature of open cycle gas turbines and their operational efficiency. They are often favored for their simplicity and because they do not require systems for fluid recirculation, making them easier to maintain and operate in many applications.

The other options do not accurately represent the characteristics of an open cycle gas turbine. The working fluid's recirculation pertains to a closed cycle engine, and cooling air recirculation is also not a feature of an open system. Thus, the defining aspect of the open cycle is that the working fluid passes through the engine only once.