What are the primary differences between turbojet and turbofan engines?

The robustness of turbojet engines is characterized by their reliance primarily on jet propulsion to generate thrust. This design involves the combustion of fuel in a compressed air stream, which then expands rapidly through the turbine and exits the engine at high speed, creating thrust through Newton's third law of motion. Turbojets are optimized for high-speed operations and are most efficient at higher altitudes and speeds, predominantly in military aircraft and some types of older commercial jets.

In contrast, turbofan engines, while also utilizing jet propulsion principles, incorporate a fan at the front of the engine that significantly contributes to the overall thrust. This fan accelerates a larger volume of air, which creates additional thrust through bypass flow around the engine core. The combination of bypass air and jet propulsion allows turbofans to operate more efficiently at a wider range of speeds and lower noise levels, making them more suitable for commercial aviation applications.

The reliance on jet propulsion as the primary means of thrust generation specifically highlights the operational characteristics of turbojets, distinguishing them within the broader category of gas turbine engines.