Electric supercharger

An electric supercharger is a specific type of supercharger that uses an electrically powered forced-air system that contains an electric motor to pressurize the intake air. By pressurizing the air available to the engine intake system, the air becomes more dense, and is matched with more fuel, producing the increased horsepower to the wheels.^[1]

Electric superchargers vs. belt driven

In general true electric superchargers are built for short duration race use. Applications are currently limited by energy storage. However, where belt driven mechanical superchargers consume some of the power produced by the engine, electronic supercharging systems do not necessarily use much or any otherwise useful engine generated power to operate, in particular at low revolutions (see Supercharging versus turbocharging supercharger), while electric superchargers are decoupled from an engine via a (relatively) oversized energy storage system (e.g. several electric accumulators in series). These results vary based on different, somewhat "raw" boost applications; supplied during low revolution regimes of an engine. The potential of electric supercharging coupled with cutting edge battery, capacitor, and 'waste' energy 'recapture' (such as Toyota's Synergy Drive) technologies appear somewhat promising in terms of net gain.

Power supply for electric superchargers

An electric supercharger, if supplied by series of common stock electric accumulators, runs independent of the engine to which it provides its boost. However, electrical energy consumed is often higher (in the range of 100 A e.g. Power of 10 kW = 12V * 833 A) than what a production-line generator (e.g. alternator) of the engine can supply. Larger alternators are therefore fitted to recharge accumulators (often reconnected from serial to parallel circuit) during the engine run without the boost.

Efficiency

The efficiency of an electric supercharger is curbed by several energy conversion losses (alternator for charging), damp energy while charging the accumulators and the compressor providing boost. The losses are in general higher than direct kinematic linkage of intake air compressor to engine crankshaft. If the alternator implements kinetic energy recovery (KERS), then the battery can be charged on otherwise wasted energy.

Electric assisted turbochargers

Electric assisted turbochargers are turbochargers employing a coaxial electric motor to overcome the time lag of the exhaust gas driven turbine. The electric motor supports the exhaust gas driven turbine at low-end revolutions to compress enough air into engine's intake, while it can be configured as an alternator to extract energy from the exhaust gas driven turbine at high-end revs, which would otherwise need be bypassed via wastegate and eventually replacing the current mechanically driven alternator.^[2] Special consideration need be given to the coaxial electric motor operating in proximity of a hot turbine at very high rotational speed (up to 100000 rpm).

Aftermarket Electric superchargers

Several companies produce low-cost aftermarket "electric superchargers" (essentially a tube with a fan powered by the car's electrical system, connected to the car's air intake) with claims of boosts to engine power output. However, such devices fail to live up to their claimed benefits either by not increasing power input or by actually reducing the output.^[3] This is due to air drawn in by the fan not being compressed as well as any increased air flow not being matched with an increased amount of fuel - a higher air to fuel ratio can hinder an engine's performance through reduced combustion.

References