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Turbos are on 75% of new cars sold in Europe


Source: Reuters

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By m51 on 11/3/2011 11:07:01 PM , Rating: 2
He is correct in that a properly designed turbocharged engine will be thermodynamically more efficient than the NA engine. This stems primarily from critical flow effects out of the exhaust ports that allow the turbocharger to recover additional energy from the exhaust gas stream. This energy is used to increase the intake manifold pressure which directly increases the engine torque. A quick reality check of this is the reduced exhaust temperature downstream of the Turbocharger which is evidence of the energy being recovered from the exhaust gasses and returned to the system.

This is a completely separate issue from the efficiency gains due to Volumetric efficiency, which is also real. Increase Volumetric efficiency reduces pumping losses (also called throttle losses). Pumping losses are the result of the engine pumping it's displacement every 2 revolutions from the low intake manifold pressure up to atmospheric pressure (exhaust manifold pressure). This is just wasted work. The less volume you pump and the smaller the pressure differential from input to output the lower your pumping losses will be. Although it seem non-intuitive, because of the fluid dynamics a properly designed turbocharged engine can actually achieve higher intake manifold pressures than exhaust manifold pressures (upstream of the turbo), which actually helps push the engine around.

Often though most car turbo designs are not designed for maximum efficiency but for maximum power and responsiveness. People buying a turbocharged car are looking for performance, not gas mileage, and the engine is designed accordingly.

A good place to look for Turbocharged engines designed for maximum efficiency are the huge turbo-diesels used in freighters and container ships. These can achieve thermodynamic efficiencies above 50%.


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