I thought the 7th injector was for reductant, which is what the AdBlue is too. Drop it on the CAT and let it do its job.
DPF filter is finer than a CAT, so pressure sensors are needed to ensure it doesn't block up.
One day every car (unleaded too) might have particulate (soot) filters. I can't say I'd miss the black smoke pouring from exhausts, as long as they get the technology right - or teach the drivers to let the tech work properly.
DPF filters are significantly different to a catalytic converter.
Filter/Converter - The difference is evident in their name alone.
The DPF is similar to a CAT in that it has a honeycomb substrate type make up, but instead of being straight through, the end of the filter is a dead end and the gas/particulate matter must make two 180deg turns to exit the filter.
So its like an down, back, down and out path for the gas, with the particulates caught at the end of these turns.
Only excessive (above normal) temperature's can light off or burn up the particulate matter that accumulates inside a dpf. And even this burn off cycle has limited options before the dpf must be replaced.
Catalytic converters use a Catalyst, being Rhodium, Platinum, and other types of precious metals to cause a reaction between various gasses in order to convert them into more inert types of gasses before they leave the exhaust system.
Passive systems work by guessing when the filter needs cleaning. It has inputs from other sensors that it can use over a period of time.
This is no different to other open loop or passive type system used in diesel and petrol vehicles.
