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The Tech Behind the Garrett Turbochargers That Keep BMW B57 Diesel Engines Alive

The Bavarian carmaker and the forced induction experts at Garrett are looking to prolong the life of diesel engines by electrifying them and developing new technologies that increase efficiency and power while lowering emissions. One such innovation is the two-stage VNT (variable nozzle turbine) turbochargers used in the latest iterations of BMW’s 3.0-liter B57 inline-six diesel engines.
BMW B57 Engine 10 photos
BMW X5 XDrive 40dBMW X5 XDrive 40dBMW X6 XDrive 40dBMW X6 XDrive 40dBMW 7-Series 740d xDriveBMW 7-Series 740d xDriveBMW 7-Series 740d xDriveBMW B57 Diesel EngineGarrett's Innovative Two-Stage VNT Turbocharger
In the U.S., diesel engines have become less and less popular in recent years, especially after the highly publicized Dieselgate scandal that began in 2015. However, in other parts of the world, such as Europe, these powerplants still enjoy a high degree of popularity. Despite stricter regulations, manufacturers momentarily keep them alive with the use of electrification and by developing more efficient components.

BMW is one of the carmakers that sells plenty of diesel-powered models in Europe. To meet demand and comply with the latest Euro 6d emission standards, they have completely revamped their most popular diesel, the 3.0-liter B57 six-cylinder.

It is now assisted by a mild hybrid system which includes a 48-volt starter generator. It provides 11 hp (8 kW) of additional power, but more importantly, it optimizes the engine’s load range and reduces consumption.

To increase efficiency even further, their partners at Garrett have developed a new generation of two-stage variable nozzle/geometry turbochargers that enable the powerplant to achieve better fuel consumption and performance figures. They manage this feat by adding several technical innovations to the conventional two-stage turbo system.

One of these innovations involves using seven ports on the integrated exhaust manifold. Six of them are fitted to the exhaust, and one is placed on the exhaust gas recirculation (EGR). Combined, these ports help enhance the control of intake and exhaust pressure variations, improving both the high and lower pressures of the VNT turbos.

Another new addition is an electronically actuated turbine bypass valve that works in conjunction with the two VNT actuators to increase engine responsiveness, especially when transitioning from single-stage to two-stage operation. According to Garrett, throttle response and torque delivery are smoother and more powerful when compared to single turbo or conventional two-stage turbo systems.

The manufacturer also states that the addition of the latest VNT technology on the high-pressure turbine improves boost control at low rpms. Furthermore, the transition to the second low-pressure stage now occurs at higher engine speeds (2,250 rpm), which helps the second stage focus on higher-efficiency operating ranges.

The turbochargers also employ a water-cooled compressor which enables higher rate EGR capability, reducing harmful gas production before the exhaust passes through the after treatment devices.

Introduced as a standard feature on BMW diesel models way back in 2012, the two-stage NOx exhaust gas treatment system has also been extensively improved. It now features an oxidation catalyst converter and a special selective catalytic reduction (SCR) coating on the particulate filter. For optimum reduction of nitrogen oxide emissions, a second dosage unit has been integrated at the system's outlet.

Using these technologies, the B57 3.0-liter aided by the 48V hybrid system can produce 340 hp and 516 lb-ft (700 Nm) of torque on models like the 7-Series 740d xDrive, X5 XDrive 40d, or X6 XDrive 40d.

This engine was introduced in Europe last year and became fully compliant with the European Union’s stringent 6d emissions standards, which came into effect earlier this year.


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