Originally Posted By: G-MAN
Originally Posted By: RI_RS4
Similar problems occured with the introduction of DI in diesel engines. It was solved with fuel lubricity enhancement and modifications to oil formulations.
Huh? I don't buy that at all.
I don't support you - I actually agree with RI_RS4.
Originally Posted By: G-MAN
First, "direct" injection has always been the way fuel is delivered in a diesel (with or without a pre-chamber).
Sorry, but that is just not correct. On a diesel engine, when the injector outlet is sited in the main combustion chamber, then this is known as "Direct Injection". However, when the injector outlet tip is sited in a remote chamber (or pre-chamber as you incorrectly state), then this is known as "Indirect Injection".
Originally Posted By: G-MAN
Second, unlike with a gas DI engine, on a diesel, the injectors fire BTDC at the end of the compression stroke, so virtually none of the cylinder wall is exposed to the spray.
Not completely true. On modern diesels with common rail, electronically controlled diesel injection and piezo injectors, the injectors can pulse-"fire" upto around five times per cycle on each cylinder - and this can be before or after TDC.
Originally Posted By: G-MAN
On a gas DI engine, the injectors fire ATDC on the intake stroke, so the potential for cylinder wash-down is great.
Not at all true. On all Volkswagen Group FSI engines (along with their forced induction derivatives such as TFSI and TSI), the injection process follows the same priciples as common rail/piezo diesels. Sadly you show little understanding of the combustion process in internal combustion engines - and specifically the FSI engines, whereby the main pulse of injector operation will be just before the spark timing (always before TDC), with the FSI engine also using a specific post-spark injection to improve emmissions and prevent overheating of the combustion chamber.
Originally Posted By: G-MAN
Also, on a diesel, combustion propagates outward from the injector, so that also lessens the potential for cylinder wall wash-down vs a gas DI engine.
Again, not completely correct. On both petrol and diesel engines, under "correct" combustion, the combustion process will always start from, and propogate outwards from the source of ignition. So on a spark engine (petrol), this will be from the spark plug, and for a compression ignition engine (diesel), this will be the outlet tip of the injector.
The real issue regarding fuel dilution on FSI engines - which is NOT a common problem in Europe, is simply down to the fact that North American (US, Canada & Mexico) variants of FSI engines do NOT utilise the "stratified" or lean-burn mode of fuel injection. It is this element of over-fueling which seems to be the root cause of fuel dilution issues in North American FSI engines.