No that isn't what I was saying, I said it turns particles into combustion byproducts. Actually this process does put out less particulates then PI ice engines by a little, with the caveat when everything is in pristine condition when they test them. If there was never an issue with low pressure PI systems, why chose this mess instead? GPF is basically a smokeless burn barrel, just cause you cant see the smoke doesn't mean something is happening.
Well, this is the same architecture as diesels with DOC, plus regenerative DPF, right (sans SCR)?
So the operating guideline is that the regeneration of the DPF is done correctly, such that the burning of the particulates produces less particulates than otherwise would have been without a filter trap. For diesel, they've done everything they know to reduce combustion particulates - ultra high pressure fuel injection to maximize fuel surface area exposed to oxygen, multi-injection electro piezo injectors for more of this, and feedback control injection timing. Also ultra low sulfur diesel fuel (sulfur promotes formation of particulates during combustion).
That's why diesels had to go to a particulate filter trap to get as close to zero particulates as possible, because all the things the industry has done to decrease particulate VOLUME has decreased particulate SIZE that penetrates lung tissue more easily, so their goal now is zero particulates. Ok, brief history of diesel emissions reductions there.
So, as we discussed, Mitsubishi launched GDI single injector in the 90's touting 20% increase in fuel economy from their LAB tests. IRL, it turned out to be only 5% because their rich burn mode (engine under load) used MORE fuel than a port injector because there's less time to volatize the gasoline during the compression stroke than there is for port injection during the intake stroke AND compression stroke. So, it's like running the engine with the choke on in the old carburetor days.
Therefore, for only a +5% improvement in fuel economy, they dumped a whole bunch of unburned pollutants into the exhaust stream and the engine oil. Nice, huh? Instead of balancing fuel economy against exhaust emissions, they worshiped a single performance criteria (mileage), realized what they'd done, and are now trying to bandaid the exhaust pollution with a DPF.
Obviously, the better solution that should have been done in the 1st place was dual injection: direct during lean burn only, and intake port during rich burn only. Or just left it alone as sequential port injection.
The reason diesels can do BOTH rich and lean burn with a single direct injector is the ultra high pressure that diesel fuel can be injected, they're pushing near 40,000 psi today. Gasoline is limited to <60 psi. Why? It's explosive...the flashpoint is -40 degrees (C or F). Diesel Fuel flash point is +125 F. Gasoline CAN NOT be injected at high enough pressure to volatize the fuel to small enough particles to combust cleanly.
<end rant - for now>