How does the BMW 50d tri-turbo diesel engine work?

If the twin-turbo systems are an assembly known as sequential or parallel, the rather technical side of BMW's tri-turbo should be noted, which slightly combines the two technologies. Please note, if you have no idea about turbochargers, I invite you to take a look here.

How does this three turbo engine work?

First of all, it should be noted that this supercharging system consists of two small turbines (1 and 3 in the diagram) with variable geometry, as well as a large standard turbocharger (2 in the diagram). Each of the latter activates certain speeds, and then they are detected consistently in high modes (well, if you can call it high speeds, because diesels never go very high ...).

At low revs, below 1500 rpm, the first turbo (one of the two small variable geometry ones) is requested by the exhaust (fresh air coming in from outside still passes through the big turbo). Even if it does not yet work in this speed range). Then, starting at 1500 rpm, the big one kicks in too, because the exhaust flows are now enough to spice it up. Keep in mind that the three turbines are not activated together from the very beginning of the mode, because in this case breathing is not important enough for the work of the three compressors. Finally, at 2500 rpm, the third can finally start working thanks to the opening of the damper (called the bypass), which then allows exhaust gas to be supplied to this turbocharger (because I remind you that is the energy that allows you to drive the engine). turbo is the "wind" produced by exhaust gases).

From an architectural point of view, we can think of turbines 1 and 2 as being in series with respect to each other, while turbines 1 and 3 (two small ones) are in parallel.

At the start, the exhaust gas flow is moderate, so the small turbine takes over the first stage of boost.

Already at 1500 rpm, the engine develops a torque of 650 Nm!

The engine develops 740 Nm (!) from 2000 to 3000 rpm, incredible compared to the (“only”) 381 hp produced.

Here's an official BMW animation explaining how it works:

Animation with BMW triple turbo diesel engine - M550d xDrive

Reliability?

Reviews of this very little-known engine may be sparse. One thing, though, is that a naturally aspirated engine will potentially always be more reliable than a turbocharged engine, especially when there are three of them!

BMW Sheets

All comments and reactions

Dernier comment posted:

Fiphi77 (Date: 2018, 08:25:09)

Great "gas plant" …… in France for 80 km / h on the road!

Il I. 1 reaction (s) to this comment:

• Administrator SITE ADMINISTRATOR (2018-08-25 10:10:08): A bit true, but let's face it everywhere. Worst of all is the USA, where it is impossible to drive even 110th by car.

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