BorgWarner’s new series turbocharging technology proves internal combustion engines are far from dead in a world of automotive power plant technology.
BorgWarner's R2S turbocharging system consists of two series-connected turbochargers. This setup features a variable turbine geometry (VTG) turbocharger for the high-pressure stage, combined with a larger water-cooled turbocharger optimized for low-pressure exhaust gas recirculation (EGR).
EGR is essential to reduce nitrogen oxide formation in the combustion chamber. It’s particularly tricky in high-performance diesels, whose exhaust is hot and frequently contains particulates and corrosive elements. The low-pressure EGR is captured downstream of the exhaust emission control system and then mixed with the fresh air upstream of the low-pressure stage’s compressor.
BorgWarner uses a special protective coating on the turbocharger compressor wheel to withstand the extreme loads and the corrosive particles.
Controlled by an electric actuator, BorgWarner's VTG turbocharger responds quickly at low engine speeds, resulting in a rapid rise in boost pressure for nearly instant acceleration. As the engine speed increases the turbochargers work together, gradually shifting to the larger, low-pressure turbocharger.
At higher engine speeds, all of the gases flow directly to the larger B03 turbocharger, maintaining smooth power delivery at higher speeds. By combining two series-connected turbochargers of different sizes, BorgWarner's technology provides high boost pressures over the entire engine speed range.
Small Engine, Big Power
The R2S system allows Volkswagen engines to comply with the tough Euro 6 emissions standard, but just as impressive is the power output.
The 2L four-cylinder engine is the most powerful diesel engine in its class, with 240HP (176 kW) and a maximum torque of 369lb.-ft. (500Nm). In tests, it achieved an average fuel economy of 44mpg (5.3 liters/100 km). The diesel engine debuted in the VW Passat.
So why stop there? We know that with balance shafts, it’s possible to create smooth running four-cylinder engines of capacities of up to 3L. The 2L version already produces more horsepower and torque than the common V-8s normally aspirated power plants used to power full-size pickup trucks and the large SUVs of 20 years ago.
From an efficiency and manufacturing cost standpoint, it’s clear that even full-sized cars and light trucks could be powered by four-cylinder turbo diesels with advanced technology.
For years, domestic automaker engineers and marketing people have told me that more cylinders sells more vehicles, but I think the current generation of automotive buyer is much more sophisticated.
Fiat Chrysler for example, is marketing a small displacement diesel in their Ram pickup truck line and it’s proving very popular. With modern lightweight chassis and materials like aluminum used for Ford’s F150, it’s easily possible to create a full-sized pickup or SUV that would perform well with 2L or 3L four-cylinder engines using series turbocharging.
The combination of high power, excellent fuel economy and a growing acceptance of diesel engines from the American car buying public may make series turbocharged small diesel engines the wave of the future.