Turbocharging is a particular form of supercharging in which a compressor is driven by an exhaust gas turbine. The concept of supercharging, supplying pressurised air to an engine, dates back to the beginning of the century. By pressurising the air at inlet to the engine the mass flow rate of air increases, and there can be a corresponding increase in the fuel flow rate. This leads to an increase in power output, and usually an improvement in efficiency since mechanical losses in the engine are not solely dependent on power output. Whether or not there is an improvement in efficiency ultimately depends on the efficiency and matching of the turbocharger or supercharger. Turbocharging does not have a significant effect on exhaust emissions.
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