18d and 20d engines are now more efficient and burn less fuel than before.
BMW is reportedly giving its 2.0-liter, four-cylinder diesel engine another turbocharger in its weaker variants. We are talking about the engine with internal code B47, which is now renamed to B47TU1.
While in most of the cases a second turbocharger means more power, the case with the 18d and 20d versions is quite different. Both the units remain generating the same power, 150 horsepower (110 kilowatts) and 190 hp (140 kW) respectively, but are now more efficient than before and consume less fuel. Also, both now meet the Euro 6c emissions standard and are ready for the new WLTP and the RDE test cycles.
We don’t have exact numbers for most of the models that use the 2.0-liter diesel, but the CO2 emissions are said to fall by four to five percent on average, mainly thanks to improved thermodynamics. Also, reworked are the shapes and surfaces of cylinder liners and pistons, while the injection pressure has been increased. Similar measures also apply to the three-cylinder B37 engine, which now becomes the B37TU1.
As a side effect of the second turbocharger, the motors should feel stronger and more responsive than before. BMW is using two quite different turbos in this layout, one small exhaust gas turbocharger with variable geometry, used in the lower rpm range, and one big turbo with fixed geometry for the higher load range.
Another positive effect from the revision is the reduced level of engine noise. Depending on the engine load and the driving condition, the engine is now “several decibels” quieter than before, according to our friends at BMW Blog.
The most powerful version of BMW’s four-cylinder diesel, the 231-hp (172-kW) 25d variant, already uses two turbochargers and is expected to receive similar mechanical improvements soon, which will make it more efficient and, probably, increase its power output.
Source: BMW Blog