Mercedes-Benz revealed today the S250 CDI BlueEfficiency, and announced that this is the first 5 litres/100 km car in the luxury segment. Powered by a 2.2-liter four-cylinder CDI engine, the new car delivers an impressive 5.7 liters/100 km (41 mpg) as well as 149g of CO2 emissions. The small four-cylinder diesel engine mated to a 7G-Tronic Plus 7-speed automatic transmission, delivers 204 hp (150 kW) and a maximum torque of 500 Nm. Still, the vehicle can accelerate to 100 km/h (62 mph) in just 8.2 seconds and has a top speed of 240 km/h (150 mph). These performances are a result of two-stage turbocharging, which consists of a small high-pressure (HP) turbocharger and a large low-pressure (LP) turbocharger.
These two are connected in series, and each has a turbine and a compressor driven by this turbine. The HP turbine is located directly at the exhaust manifold and allows the exhaust gas to low through it and then rotates at up to 215,000 revolutions per minute. The HP turbine housing features an integral bypass duct, which can be opened or closed by means of a charge-pressure control flap triggered by a vacuum cell.
"The two compressors are likewise connected in series, and are in addition connected to a bypass duct. The combustion air from the air filter first flows through the low-pressure compressor, where it is compressed as a function of the LP turbine's output. This pre-compressed air then passes into the high-pressure compressor, which is coupled to the HP turbine, where it undergoes further compression. The result is a genuine two-stage turbocharging process." said Mercedes-Benz in the press release.
The advantage of this technology is that it delivers high torque at low engine speeds, while fuel consumption is reduced. Pricing starts at €71,876 ($95,942).