Thanks Chris, not being a chemist I value your input! I just know a little about a lot of things, and get notions that may be off-the mark. But, I think, the principles are there. "Nasty" chemicals are made in the engine. The curious thing about room temperature chemistry versus combustion chamber chemistry, is that in the combustion chamber there is a lot of heat, molecules become ionised, and the pressure is more than 20 times atmospheric in parts, so a lot of odd reactions occur that would not happen at STP. e.g. NOx formation. And what happens in the spark in spark ignition engines? - Possibly Ozone formation etc.? - I really haven't a clue, but your advice will be of interest (to me at least).
I only really know that engine oils contain additives (Such as Zinc compounds) to neutralise all the various acids in the blow-by gases, that when dissolved in oil (with some H2O), form highly corrosive acids that need to be neutralised by the Zinc, etc, additives. And similarly, the move from steel to stainless steel exhausts was in part due to the acidic condensate accumulating in exhaust systems and causing "early life" failures. (Such failures are banned by legislation in the emissions laws - minimum 80,000km lifetime, etc. & "no leaks" clauses.).
Thanks.
K2