  the bypass ratio (bpr) of a turbofan engine is the ratio between the mass flow rate of air drawn through the fan disk that bypasses the engine core (un-combusted air) to the mass flow rate passing through the engine core that is involved in combustion to produce mechanical energy. for example, a 10:1 bypass ratio implies that 10&nbsp;kg of air passes around the combustion chamber through the ducted fan for every 1&nbsp;kg of air passing through the combustion chamber. the ducted fan, rather than combustion gases expanding in a nozzle, produces the vast majority of the thrust in high-bypass designs. a high bypass ratio provides a lower thrust specific fuel consumption (grams/sec fuel per unit of thrust in kn using si units) for reasons explained below, especially at zero velocity (at takeoff) and at the cruise speed of most commercial jet aircraft; however, the lower exhaust velocities of high-bypass designs also figure strongly in lower noise output, which is a decided advantage over earlier low or zero bypass designs. high bypass designs are by far the dominant type for all commercial passenger aircraft and both civilian and military jet transports. military combat aircraft usually use engines with low bypass ratios to compromise between fuel economy and the requirements of combat: high power-to-weight ratios, supersonic performance, and the ability to use afterburners, all of which are more compatible with low bypass engines. a good example of the differences between a pure jet engine and a low-bypass turbofan may be seen in the spey turbofan used in the f-4 phantom. ==principles== the stoichiometry of the mende entah in a gas turbine engine is limited to a fairly narrow range and tends to a "leaner" fuel mixture to limit the maximum temperatures in the engine. in a pure (zero-bypass) jet engine, all the air taken in is involved in combustion; high temperature and high pressure exhaust gas accelerating by expansion through a propelling nozzle produces all thrust because the compressor stage consumes all the mechanical energy produced by the turbine. in a bypassed design, conversely, the gas turbine component (or engine core) produces a large net positive power output because the turbine produces far more power than the compressor consumes, and this excess power drives a ducted fan that rearward ac
Engineering_ratios Jet_engines