BMW is using a 635d model, d for diesel, to demonstrate that electronic noise cancellation can be used instead of heavier materials to decrease the noise created by the compression ignition engine.
At the same time, engineers claim that they can tune the sounds that remain to give them a more pleasing character.
While active noise cancellation is not a new technology, Japanese makers have it in production, the urgent need to reduce the weight of fuel guzzling automobiles to meet increasingly stringent economy and CO2 emission regulations is bringing a new urgency to the search for more applications of existing techniques.
BMW claims that the sporty performance characteristics of its diesel engines and their high torque, especially when starting up and accelerating are contradicted by the “acoustic sensation” of diesel vehicles.
In a diesel, harsh ignition impulses during combustion are responsible for their characteristic noises — commonly called clatter or knocking. Already, makers of diesel cars are using various passive deadening techniques to isolate the sound from passengers, and sometimes outsiders. The problem is that heavier materials, starting with the engine block and cylinder head provide better attenuation. As makers reduce weight, they often add it back with insulation or sprayed on materials.