Which engine type has a single stream of airflow?

The turbojet engine is characterized by its single stream of airflow. In a turbojet, air enters the engine, passes through the compressor where it is compressed, and then enters the combustion chamber where fuel is added and ignited. The high-pressure gases produced then expand rapidly through the turbine and exit the nozzle, creating thrust. This continuous, streamlined path of air through the engine distinguishes the turbojet from other types, which may involve more complex airflow patterns or multiple streams.

In contrast, an open cycle turbine and a closed cycle turbine refer to systems that may recirculate some of the working fluid, which doesn't apply to the straightforward and direct airflow of a turbojet. The turboprop engine, while also utilizing airflow, combines a turbine with propeller mechanics, leveraging a different mechanism that involves a dual stream—one through a turbofan setup and another that drives the propeller, thus not fitting the definition of a single stream of airflow.