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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.

Mercedes-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.
more here

I'll look for a better pic


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I can't see for sure from teh pic but it looks like a parallel setup, not a serial setup,, where one flows into the other. The old supra tt had this setup and some people modded it so that the bypass would let you keep flow to the small turbo even after the larger turbo spooled. It gave you a little more power but hat's a high revving 3.0 liter gas engine, not a 2.0 liter diesel so I don't know if it will also work on this.

I think it's a serial AND parallel setup. look at this

The basic development goals for future combustion engines for automobile and commercial vehicle applications make more refined charging systems necessary. The design of such a charging system leads to conflicting goals in terms of the rated output of the engine on one hand and the transient response and the range of maximum torque on the other hand. You need a relatively large exhaust turbocharger to attain the nominal output point. The desire for a very high boost pressure even at low engine speeds means, however, that the turbine and the compressor need to be made much smaller. A combination of the two would be ideal.

To resolve this conflict, BorgWarner Turbo Systems has developed regulated 2-stage turbocharging. It meets the demands of an optimal design and allows for the continuously variable adaptation of the turbine and compressor sides of the system for each engine operating point.

With this newly developed charging system, BorgWarner Turbo Systems offers the engine manufacturer an additional extremely high-performing charging system for future engine generations that fulfills the highest requirements in terms of power, fuel consumption and emissions.

The regulated 2-stage turbocharger consists of two turbochargers of different sizes connected in series that utilize bypass regulation. The exhaust mass flow coming from the cylinder flows into the exhaust manifold first. Here it is possible to expand the entire exhaust mass flow using the high pressure turbine (HP) or to redirect some of the mass flow through a bypass to the low pressure turbine (LP). The entire exhaust mass flow is then utilized again by the low pressure turbine (LP).

The entire fresh air flow is first compressed by the low pressure stage. In the high pressure stage, it is compressed further and then the charging air is cooled. Due to the precompression process, the relatively small HP compressor can reach a high pressure level so that it can force the required amount of air to flow through the system.

At low engine speeds, i.e. when the exhaust mass flow rate is low, the bypass remains completely closed and the entire exhaust mass flow is expanded by the HP turbine. This results in a very quick and high boost pressure rise. As the engine speed increases, the job of expansion is continuously shifted to the LP turbine by increasing the cross-sectional area of the bypass accordingly.

Regulated two-stage turbocharging therefore allows for continuous adaptation on the turbine and compressor sides to the actual requirements of the operating engine.

The system can be regulated via pneumatic actuators that control the bypass valve in the same manner as when used in mass-produced turbochargers with swing valves. This makes it possible to model a compact charging system (when detailed knowledge of the complex system response is available) that fulfills the highest torque, response and power requirements while utilizing proven components

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I'll bet that you could fit a CRD jetta engine under a later model. Swap over the ECU and probably most of the wiring harness would fit. Since its the same body, I'll bet that the motor mounts are all the same. The sequential mercedes twin turbo? I highly doubt it would swap in.
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