I was thinking about this a bit more in the bath...
Today, almost all gasoline will contain additives to prevent inlet valve deposits (IVDs). It's been a very long time since I played around with gasoline additives but generally speaking, the main constituent is a polymeric detergent. Chemically speaking, these are not too dissimilar to the polymeric ashless dispersants you have in engine oil. The entire point of these additives is that they are non-volatile. On an MPI engine, when the gasoline is injected into air, the bulk of the gasoline is evaporated but the polymer is not. Minute droplets of polymer have momentum and physically 'hit' the back of the inlet valve to impart a degree of 'physical' cleaning. At the same time active nitogen sites on the polymer backbone do a bit of 'chemical' cleaning.
Now these polymers are very thick and viscous and to make them usable, they are usually diluted in a 'carrier oil'. As often as not, this would be a heavy Group I 500SN base oil. This functions like a poor man's detergent. It's essentially non-volatile so, like the polymeric detergent, will do some physical scouring of the valve surface (but won't do any chemical cleaning).
Now while this is all fine and dandy in an MPI engine, I do wonder if in a TGDI engine, these very additives might be contributing in a big way to LSPI. In a GDI engine, fuel is invariably sprayed DOWNWARDS. Now the bulk of the gasoline will evaporate but anything that doesn't evaporate will have momentum and carry on it's downward path until it hits something like the top of the piston or the side of the cylinder. It doesn't take a whole lot of imagination to see how this mix of very heavy fuel/polymeric detergent/heavy base oil might accumulate in the top ring land space.
So to all of you guys who think the answer to LSPI us using top-tier gas, then you might want to reconsider, as it might be that that's causing the problem!
Today, almost all gasoline will contain additives to prevent inlet valve deposits (IVDs). It's been a very long time since I played around with gasoline additives but generally speaking, the main constituent is a polymeric detergent. Chemically speaking, these are not too dissimilar to the polymeric ashless dispersants you have in engine oil. The entire point of these additives is that they are non-volatile. On an MPI engine, when the gasoline is injected into air, the bulk of the gasoline is evaporated but the polymer is not. Minute droplets of polymer have momentum and physically 'hit' the back of the inlet valve to impart a degree of 'physical' cleaning. At the same time active nitogen sites on the polymer backbone do a bit of 'chemical' cleaning.
Now these polymers are very thick and viscous and to make them usable, they are usually diluted in a 'carrier oil'. As often as not, this would be a heavy Group I 500SN base oil. This functions like a poor man's detergent. It's essentially non-volatile so, like the polymeric detergent, will do some physical scouring of the valve surface (but won't do any chemical cleaning).
Now while this is all fine and dandy in an MPI engine, I do wonder if in a TGDI engine, these very additives might be contributing in a big way to LSPI. In a GDI engine, fuel is invariably sprayed DOWNWARDS. Now the bulk of the gasoline will evaporate but anything that doesn't evaporate will have momentum and carry on it's downward path until it hits something like the top of the piston or the side of the cylinder. It doesn't take a whole lot of imagination to see how this mix of very heavy fuel/polymeric detergent/heavy base oil might accumulate in the top ring land space.
So to all of you guys who think the answer to LSPI us using top-tier gas, then you might want to reconsider, as it might be that that's causing the problem!