For the technically inclined there is more information in the following VW self study guide:-
http://www.volkspage.net/technik/ssp/ssp/SSP_336.pdf
A few points stand out.
The extra fuel is *not* injected during the exhaust stroke; it occurs during the power stroke, about 35 degrees after TDC.
During stop start driving, while on the overrun, fuel is injected 35 degrees after TDC but there is no injection at the normal time. The fuel vapourises and no power is generated but the fuel is burnt in the filter. My guess is that this is what can cause oil dilution.
There is a sensor measuring the pressure difference across the filter. A clogged filter will give rise to a larger pressure difference than an unclogged one. By this means the carbon load can be estimated.
http://www.volkspage.net/technik/ssp/ssp/SSP_336.pdf
A few points stand out.
The extra fuel is *not* injected during the exhaust stroke; it occurs during the power stroke, about 35 degrees after TDC.
During stop start driving, while on the overrun, fuel is injected 35 degrees after TDC but there is no injection at the normal time. The fuel vapourises and no power is generated but the fuel is burnt in the filter. My guess is that this is what can cause oil dilution.
There is a sensor measuring the pressure difference across the filter. A clogged filter will give rise to a larger pressure difference than an unclogged one. By this means the carbon load can be estimated.