You know its interesting that higher octane fuel is less volatile than low octane. Low octane fuel basically goes “bang” and is susceptible to flash (pre-ignition) where high octane burns at a very controlled rate. That way, it is possible to produce a sustained rate of expansion to push the pistons down.
So! Tell me. Shell V Power here is loaded with all sorts of other additives here to help keep the internal parts free from gumming and carbon etc. Is the US version of any brand’s top flight fuel loaded in a similar way or is it all about this AKI index?
I can't speak for all products from all brands in the US but, in general, the additive packages (detergents and whatnot) are the same across all of the products from a given company. Chevron advertises "Techron" in their fuel and it's in all grades. Same with BP's "Invigorate".
I checked out Shell's product marketing wank for their V-Power Nitro+ Premium and I'll be damned if I can figure out which products they sell it in. Their regular fuels are "nitrogen enriched" which was a marketing thing that started a decade or two ago when that generation of detergents came out (a bunch of fuel companies came out with nitrogen marketing crap around the same time). Basically, even their low-tier fuels have detergents in them.
Effectively, in the US, the main difference between product grades is octane modifiers and marketing garbage. I think it's telling when they obscure product information with pretty pictures and non-informative information.
Additionally, these detergent packages are mostly to help keep the intake valves clean. Normally, oil vapor, carbon and other schmoo will build up on the valves and impede airflow into the engine. This works because most engines until the last 5-10 years had fuel injected into the intake track. The detergent-laden fuel hits the valves and helps to wash the gunk off. Now most newer engine designs (and modifications of old designs) have fuel injected directly into the combustion chamber, completely bypassing the valves.
So, modern engines blunt the utility of these detergent packages anyway.
Edit: also, there's no relationship between vapor pressure (volatility) and octane rating.