Many findings suggest that the particulate emission from GDI engine is less but smaller in size, causing further entrainment to the human lung if exposed.
GDI engines release about 1,000 times more particles than traditional petrol engines and 10 times more than new diesel engines. It is because direct injection results in uneven burning of fuel due to uneven mixing of fuel and air. The second reason is that GDI engines operate with a higher pressure in cylinders than old style engines.
I am guessing,
Stratified mode always generates PM/PN, like in Diesel engine, we have charge stratification but PM size is high, because of higher compression ratio of diesel engine ranging from 15-23 minimising spray penetration, hence fuel is relatively less scattered compared to GDI, compression ratio 12, so nucleation chances in Diesel are higher, GDI are leaner comparatively since they are spark initiated, compared to Diesel, hence PM size due lack of oxygen.
Relatively small scatter area, less oxygen produces produces bigger PM.
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