A turbocharger is a device driven by exhaust gases that increases engine power by pumping air into the combustion chambers.

Combustion is limited not by the amount of fuel that can be injected but by the amount of air an engine can gulp in to mix with that fuel. Forcing air into an engine’s intake manifold at higher-than-atmospheric pressure allows more fuel to be burned, which results in higher output. The related supercharger also compresses intake air but is driven by a belt, chain or gears. To oversimplify, the turbocharger employs two encased fans mounted on either end of a common shaft. The engine’s exhaust gases are routed through one fan, called the turbine, which rotates the shaft. This, in turn, spins the opposite fan, called the compressor, which compresses the air entering the engine’s intake manifold.

Turbo and superchargers often work in tandem with an intercooler, which serves to cool the compressed air before it enters the engine. Compressing the air heats it, which makes it less dense and negates some of the positive effect, and may cause pinging or knocking. Intercoolers typically are simple radiators through which the intake air passes to shed some heat, increasing the density before combustion. The “inter” means between, as intercoolers are positioned between the turbo and the intake manifold.

Bmwturbo

BMW turbocharger pictured

Turbochargers have advantages and disadvantages. The main advantage — which propelled their adoption in production vehicles in the past two decades — is that they grant power on demand from otherwise efficient, compact, usually four-cylinder engines. The disadvantages include additional cost, complexity and, in actual use, turbo lag. Turbo lag is the delay in response that occurs when the driver tromps on the accelerator. The turbo takes a second or two (or more) to get up to a speed at which it’s compressing the intake air enough to effect an output increase. Over the years, attempts to lessen turbo lag have come mainly in the form of twin turbo designs. Nowadays, the combination of sophisticated computerized engine-management systems and single, low-mass turbines seems to be making great strides for Saab and Audi, among others.

As for the engineering and cost factors, turbos typically require the use of stronger pistons, connecting rods and crankshafts than the same engine without a turbocharger would need. Turbos generate considerable additional heat and cause the engine itself to run hotter, so heat-resistant valves and a larger cooling-system radiator are common. The turbine may spin at rates above 100,000 rpm, which requires an ample supply of pressurized engine oil, along with a higher-volume oil pump and perhaps an oil cooler. Heat is one of oil’s greatest enemies, so turbocharged vehicles require shorter oil-change intervals — or at least carry a higher likelihood of damage when the schedule isn’t kept.

Information for this was taken from the Cars.com’s glossary, written by Joe Wiesenfelder.

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Answered by Joe Bruzek on April 7, 2009 in Glossary | Permalink

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