Turbofans

A turbofan is a type of jet engine that generates most of its thrust from a large-diameter fan at the inlet, using a combination of bypass air and core exhaust to power the aircraft. By routing a large portion of incoming air around the engine core, turbofans achieve higher propulsive efficiency and lower noise than traditional turbojets.

In operation, air enters the engine and is split into two streams. A portion passes through the engine core, where it is compressed, combusted, and expanded through turbines that drive the compressors. The remaining air bypasses the core and flows through a separate duct, accelerated by the fan. The thrust is produced mainly by the momentum change of the bypass air, with additional thrust from the core exhaust. Higher bypass ratios increase efficiency and reduce exhaust velocity, leading to quieter operation and lower specific fuel consumption.

Key components include the inlet, fan, low- and high-pressure compressors, combustor, turbines, and the nozzle. The bypass duct surrounds the core, providing the separate path for bypass air. In many modern designs, the fan is connected to the low-pressure spool. Some engines employ a geared turbofan, which uses a reduction gear between the fan and the core to allow each to run at its optimum speed, improving overall efficiency.

Turbofans dominate modern commercial aviation due to their combination of fuel efficiency, reduced noise, and lower emissions compared to turbojet engines. They come in various configurations, with high-bypass designs common for airliners and lower-bypass or military variants optimized for different performance requirements.