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I know that some trucks have used this but it's new to light diesels. TDIs have all used a small single turbo, the mercedes will start to use a twin turbo system in which one small turbo provides low end power, then a bypass valve switches exhaust flow to a larger turbo to give better top end power.
I guess they didn't want to use VNT or this gives better top end power.
http://www.dieselforecast.com/ArticleDetails.php?articleID=476
I'll look for a better pic
I guess they didn't want to use VNT or this gives better top end power.
more hereMercedes-Benz is revamping its four cylinder diesel engine lineup with all the latest technology to help improve performance while reducing fuel consumption. The range includes three engines all displacing 2143cc with outputs ranging from 136hp to 204hp and up to 369lb-ft of torque.
For the first time the Mercedes diesel fours will incorporate two-stage turbocharging to help improve both responsiveness and ultimate power output. The two turbos are different sizes connected in series. The first smaller turbo has low inertia allowing it to spin up quickly at low engine speeds.
As the engine speeds up and exhaust gas flow increases, a bypass valve redirects some of the flow to the second larger turbo. The larger turbo takes longer to spool up but provides boost at higher engine speeds. The result is quick response to driver demands at all speeds and a maximum output that now almost matches the 214hp of the larger heavier 3.0L V-6 diesel.
While the power output of the top of the range engine now matches that of German rival BMW's 123d, fuel consumption has been reduced across the board. The most powerful engine has gone from 168hp to 204hp while the fuel consumption (when installed in the C-Class sedan) has gone from 39.9mpg to 43.6mpg as measured by the EU combined cycle. The mid-level 170hp variant now achieves 46.1mpg.
The improved performance and efficiency comes in part as a result of upgrading the fuel system with the latest common-rail and piezo-electric injection technology. The new fourth generation common-rail system increases the pressure head from 23,200psi to 29,000psi. The increased pressure helps to improve the atomization of the fuel as it flows through the injectors. The more homogeneous mixing of air and fuel in the combustion chamber provides more complete burning for increased power out of less fuel.
The job of actually allowing the fuel into the combustion chambers is realized by new piezo-electric injectors. The older engines use solenoid injectors that move the injector needle with an electro-magnetic coil. A stack of piezo crystals that expand when electrically charged are now used to move the needle. The piezo crystals react more precisely and consistently than the solenoids which results in fuel flow closer to the optimum quantity.
Mercedes has optimized the shape of the combustion chamber and reduced the compression ratio to 16.2:1 (down from 17.5:1). The lower compression ratio reduces the combustion pressure and temperature helping to cut production of NOx.
The engine designers at Mercedes have reduced the mass of many internal components of the engines and increased the strength. The lower reciprocating mass reduces the noise and vibration of the engine providing a more pleasant driving experience.
Efficiency is also improved by reducing parasitic losses caused by ancillary systems. On traditional engines the oil and water pumps are mechanically driven at a speed proportional to crankshaft speed. The output pressures are a direct function of drive speed regardless of the actual demand for oil or coolant pressure. Mercedes has devised a mechanism to electrically manage the flow from these pumps and limit the output to what is actually needed reducing the load on the engine.
When the new diesels debut in the C-Class this fall they will be compliant with EURO V emissions standards. The engines are designed to be compatible with BlueTec after-treatment systems to meet US Tier 2 Bin 5 standards and future EURO VI standards. The engines can be installed longitudinally (as in the C-Class) or transversely and are also designed to be paired up with hybrid systems such as the one demonstrated in the Vision GLK hybrid concept that was shown at last month's Geneva Motor Show.
http://www.dieselforecast.com/ArticleDetails.php?articleID=476
I'll look for a better pic

