Gas turbine on and off to run it only at high efficiency. The emergence of the continuously variable transmission may also alleviate the responsiveness problem. Turbines have historically been more expensive to produce than piston engines, though this is partly because piston engines have been mass-produced in huge quantities for decades, while small gas turbine engines are rarities; however, turbines are mass-produced in the closely related form of the turbocharger. The turbocharger is basically a compact and simple free shaft radial gas turbine which is driven by the piston engine's exhaust gas. The centripetal turbine wheel drives a centrifugal compressor wheel through
Gas turbine engine compressors more shallow, to accommodate the shallow working line. On their large civil turbofans, Rolls-Royce split the compression system into three: a fan, an intermediate-pressure (IP) compressor and an HP compressor, each unit being driven by its own turbine unit. The RB199 military turbofan also has this arrangement. A free-piston gas generator is a free-piston engine whose exhaust is used to power a gas turbine. It combines the functions of compressor and combustion chamber in one unit. These machines were quite widely used in the period 1930–1960 but then fell out of favour. Gas turbine engine compressors As the name suggests,