Join Date: Sep 2006
Thanked 24 Times in 13 Posts
Its a mechanism employed for the 2008 particulate emission requirements. In effect there is a large filter to catch the soot, as it fills up (which is does fairly quickly) the pressure gradient across the filter increases, prompting the system to go into an active regeneration -- which is the process by which the soot is burned down as far as it can into an ash. In order to accomplish this, exhaust temps have to increase significantly. This happens through the injection of unburned diesel fuel into the exhaust system at some point; unfortunately, the big three apparently all use in cylinder dosing -- the injection of unburned diesel fuel into the cylinder after combustion has occurred. The result of this is fuel dilution of the engine oil and, most likely, diminished engine longevity.
This seemingly does not absolutely have to occur in this fashion; a separate injector can be placed downstream and directly inject diesel fuel into the exhaust avoiding the problem of fuel dilution, but for some reason they choose not to utilize this strategy.
The cynic in me believes that the real logic behind this is that it decreases the longevity, decreases the expected life cycle, and increases the maintenance traffic and costs (after typical warranty life, of course)....