BMW Four-Cylinder Engines Return to US in 2011
WOODCLIFF LAKE, NJ - BMW's four-cylinder engine will return to its U.S. lineup of vehicles for the first time since 1999. The automaker said that U.S.-specific model and timing information will follow at a later date but that the engine will arrive in vehicles in 2011. The new 2.0L engine will combine twin-scroll turbocharging with high-pressure direct-injection and BMW's VALVETRONIC intake control and offer 240 hp and 260 lb.-ft. of torque.
The engine achieves its maximum output of 240 hp at 5,000 rpm, 1,500 rpm lower than in the normally aspirated inline-six. The peak torque of 260 lb.-ft., comes on stream at just 1,250 rpm. The four-cylinder engine features an all-aluminum crankcase, making it lighter and more compact than a six-cylinder engine of equivalent power. The turbocharger is a twin-scroll system. The exhaust streams leaving the two pairs of cylinders are kept completely separate as they flow through the exhaust manifold and the turbocharger, taking a spiral path to the turbine wheel. This configuration results in very low exhaust back pressure at low engine rpm, and allows the energy of the exhaust gas pulses to be optimally managed and translated into powerful rotation of the turbine blades, without a delay in throttle response.
The patented BMW VALVETRONIC system with seamlessly variable intake valve lift control manages combustion air mass inside the engine, resulting in much faster response. Pumping losses are kept to a minimum, making the engine more efficient, according to BMW.
The High Precision Injection direct-injection system also helps to improve efficiency. Centrally positioned between the valves, solenoid injectors with a maximum injection pressure of 200 bar (2,900 psi) precisely control the supply of fuel. The fuel is injected very close to the spark plug, resulting in clean and homogeneous combustion, the company stated.
The cooling effect of the injected fuel also allows for a higher compression ratio than might otherwise be possible. This results in further efficiency improvements, according to the company.