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Turbofan
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<p>A turbofan or fanjet is a type of <a href="/facts/Airbreathing_jet_engine/LmtmX4RW">airbreathing jet engine</a> that is widely used in <a href="/facts/Aircraft_engine/XJo2Bd2e">aircraft propulsion</a>. The word "turbofan" is a combination of references to the preceding generation engine technology of the <a href="/facts/Turbojet/8FMD6dNg">turbojet</a> and the additional fan stage. It consists of a <a href="/facts/Gas_turbine_engine/JJJNwXrG">gas turbine engine</a> which achieves <a href="/facts/Mechanical_energy/gI4oMzoY">mechanical energy</a> from combustion, and a <a href="/facts/Ducted_fan/3MMyUhDc">ducted fan</a> that uses the mechanical energy from the gas turbine to force air rearwards. Thus, whereas all the air taken in by a <a href="/facts/Turbojet/8FMD6dNg">turbojet</a> passes through the <a href="/facts/Combustion_chamber/FNqjDrN8">combustion chamber</a> and turbines, in a turbofan some of that air bypasses these components. A turbofan thus can be thought of as a turbojet being used to drive a ducted fan, with both of these contributing to the <a href="/facts/Thrust/EM04CqV7">thrust</a>. </p><p>The ratio of the mass-flow of air bypassing the engine core to the mass-flow of air passing through the core is referred to as the <a href="/facts/Bypass_ratio/rpsDPRHL">bypass ratio</a>. The engine produces thrust through a combination of these two portions working together. Engines that use more <a href="/facts/Propelling_nozzle/GDstAvRx">jet thrust</a> relative to fan thrust are known as <i>low-bypass turbofans</i>; conversely those that have considerably more fan thrust than jet thrust are known as <i>high-bypass</i>. Most commercial aviation jet engines in use are of the high-bypass type, and most modern <a href="/facts/Fighter_aircraft/NuIvaGJg">fighter</a> engines are low-bypass. <a href="/facts/Afterburner/aDeuyqp3">Afterburners</a> are used on low-bypass turbofan engines with bypass and core mixing before the afterburner. </p><p>Modern turbofans have either a large single-stage fan or a smaller fan with several stages. An early configuration combined a low-pressure turbine and fan in a single rear-mounted unit. </p>