3 January 2008

BMW is introducing two “Advanced Diesel with BluePerformance” models at the 2008 North American International Auto Show (NAIAS) in Detroit. The Tier 2 Bin 5 compliant X5 xDrive35d and the 335d to be unveiled at the show later this month will be available on sale in all 50 states in late 2008.

Both vehicles are powered by a 3.0 liter inline-six engine with Variable Twin Turbo Technology, rated at 265 hp (198 kW) and 425 lb-ft of torque. A urea-SCR catalyst is used to reduce NOx emissions. The same engine was introduced in Europe in 2006. The European version has a higher rating of 286 hp and 428 lb-ft of torque, and is not fitted with the SCR catalyst as EU NOx emission standards are more relaxed than the Tier 2 requirements.

In the twin turbo technology, a small turbocharger is utilized at low engine speeds. Thanks to its low inertia, this turbocharger can develop boost without delay. As engine speed increases, the second, larger turbocharger is engaged, developing maximum torque of 425 lb-ft at just 1,750 rpm. Interaction of the two turbochargers is controlled by the engine control unit. Other technical highlights, presented for the first time in 2007, include an aluminum crankcase and third-generation piezo common-rail fuel injection system.

The BMW 335d accelerates from 0-62 mph in 6.2 s, and offers a fuel economy of 23/33 mpg (city/highway). For comparison, the gasoline fueled 335i with manual transmission has a fuel economy of 17/26 mpg (city/highway).

The BMW X5 xDrive35d will accelerate from 0-62 mph in 7.2 s. It has a fuel economy of 19/25 mpg (city/highway, provisional data), compared to 15/21 mpg in the gasoline fueled X5 3.0si.

Exhaust gas aftertreatment system in the “Advanced Diesel with BluePerformance” technology incorporates an oxidation catalyst and a diesel particulate filter—both housed in one unit in a close-coupled location—and an SCR catalyst with urea (AdBlue) injection. Cold-start NOx emissions, which could be a problem with the SCR catalyst positioned away from the exhaust manifold, are controlled through a rapid engine warm-up strategy.

The urea solution is stored in two tanks: a heated, 1.6 gallon “active” tank, and a 4.5 gallon “passive” tank. This arrangement allows to minimize the energy used for heating of urea solution in cold weather operation (SCR-urea solutions freeze at -11°C), and provides more flexibility in incorporating the tanks onto the vehicle. The urea solution from the active tank is delivered to the exhaust system through a heated piping system and injected upstream of the SCR catalyst using a dosing valve. Consistent distribution within the exhaust gas stream is ensured by a static mixer. The operation of the SCR system is controlled by the engine management computer. A NOx sensor downstream of the SCR catalyst provides feedback on the concentration of NOx in the exhaust emissions. This feedback could be used for the OBD, as well as for some of the control functions, but no details on the control strategy were revealed.

The average driving range provided with the supply capacity of the two urea tanks is sufficient to have the urea solution replenished only when the driver needs to change the engine oil.

Source: BMW