Twincharger
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Twincharger refers to a forced induction system used on some piston-type internal combustion engines. It is a combination of an exhaust-driven turbocharger and a drive-train-driven supercharger, each mitigating the weaknesses of the other. Any forced induction system puts more oxygen into the cylinders than would be available without force, allowing more fuel to be burned, producing more power. Engines with relatively small displacement can thus be used for a given power output, these smaller-displacement engines being more fuel-efficient in typical real-world vehicle designs than their normally-aspirated counterparts (those without forced induction) of equivalent power.
The term twincharger is a misnomer, as the two “chargers” of the system are of radically different designs. The advantages of this system over other forced induction systems are, in fact, due to the differences between the two.
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[edit] Technical description
A twincharging system combines a supercharger and turbocharger in a complementary arrangement, with the intent of one component's advantage compensating for the other component's disadvantage.
The most common type of twincharging system is a sequentially organized Roots type supercharger, connected to a medium-large sized turbocharger.[citation needed] The supercharger provides near instant manifold pressure, when the turbocharger is otherwise not at its operating speed. Once the turbocharger has reached operating speed, the supercharger can either continue contributing air to the intake (yielding elevated intake pressures), or it can be bypassed and disconnected from the powertrain (increasing efficiency of the induction system).
[edit] Disadvantages
Disadvantages include the energy cost of driving the supercharger and the turbocharger, the latter restricting the flow of exhaust, and, obviously, the expense, complexity, mass, and volume of the components. The added mass and volume may be directly offset by using a smaller and lighter engine for a given output power, and the expense by the reduction in fuel cost compared to that with an equivalent-output engine without the system.
[edit] Commercial availability
The concept of twincharging was successfully used by Lancia in the 1980s on the Lancia Delta S4 rally car. The idea was also successfully adapted to production road cars by Nissan, in their March Super Turbo [1] compact car, and by the Volkswagen Group, badged as TSI, in their Golf, Touran and Tiguan models [2].
Additionally, multiple companies have produced aftermarket twincharger kits for cars like the Subaru Impreza WRX, Mini Cooper Type S, Skyline GT-R, Toyota MR-2, Pontiac Grand Prix GTP, Chevrolet Monte Carlo (s/c), and Buick Regal GS.
[edit] Alternative systems
[edit] Anti-lag system
Twincharging's biggest benefit over anti-lag systems now in race car applications is its reliability. Anti-lag systems typically work by introducing excess fuel and retarding ignition timing to cause combustion in the exhaust manifold, keeping a turbocharger spinning quickly. The heat from this can wear or damage the exhaust manifold and turbocharger, and the unburnt fuel would destroy a catalytic converter. In addition to precluding the use of a catalytic converter, the unburnt fuel is also itself a serious pollutant, so it is generally not allowed in street vehicles due to the environmental damage it would cause.
[edit] Variable geometry turbocharger
A variable geometry turbocharger provides an improved response at widely varied engine speeds. With variable incidence under electronic control it is possible to have the turbine reach a good operating speed quickly or at lower engine speed without severely diminishing its utility at higher engine speed.
[edit] Nitrous oxide
Nitrous oxide (N2O) is mixed with incoming air, providing more oxygen to burn more fuel for high power when a turbocharger is not spinning quickly. This also causes the turbocharger to quickly accelerate, providing more oxygen for combustion, and the N2O flow is reduced accordingly. The expense of both the system itself and the consumable N2O can be significant.
