Print 41 comment(s) - last by m51.. on Nov 3 at 11:07 PM

You're doing it wrong.
Turbos are on 75% of new cars sold in Europe

You don't have to be a scientist or an automotive engineer to look at the fuel economy that major automakers are squeezing out of their vehicles with normal combustion engines today and wonder if we really need EVs and hybrids. More than one diesel car in Europe is able to provide fuel economy as good or better than the hybrids people generally think are so fuel thrifty.
The catch is that we rarely see diesel engines in the US inside a car, that will be changing, but the diesel car isn't common today for American drivers. One thing that is becoming very common for fuel efficiency sake is the addition of a turbocharger to allow a smaller displacement engine to produce acceptable power to provide the performance drivers expect.
The turbocharger is something that was often thought of for performance cars like the Grand National Buick in the mid to late 1980's. Today the turbo is used in a number of engines including the very popular EcoBoost line from Ford. Ford's EcoBoost engine inside the F-150 truck is selling very well and has a towing capacity on par with normal engines with larger displacement. The turbocharger is even more widely used in Europe where Reuters reports that 75% of all new cars come with one.
Craig Balis from Honeywell Turbo Technologies told Reuters in an interview, "The turbocharger is a green technology in the sense that it's helping cut emissions and raise fuel economy. It's a critical component to get more fuel efficiency out of the engine."
"Emissions regulations in Europe, the United States and worldwide are a driving force for cleaner, greener vehicles and that's a great landscape for turbocharging," said Balis. "We're confident about the continued evolution of combustion engines and the growing role turbocharging has."
Reuters reports that a diesel engine that has a turbocharger can get 40% more mileage than one without a turbo and a gas engine can go 20% further per liter of fuel than one without a turbo. With the impressive economy that normal engines with turbochargers achieve there are many that wonder if we even need EVs and hybrids.
Pierre Gaudillat, policy officer at the Transport and Environment lobby group in Brussels, was asked if we need EVs from a CO2 point of view. He said, "That's a valid question. The answer is: maybe not. Turbos are a no-brainer for cutting CO2 because the efficiency gains are really quite significant. In the near term, we don't really need and can't count on electric vehicles to deliver the CO2 savings. Maybe not until about 2030 or 2050."

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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