By explode I mean instantaneously combust (or act like diesel). All hydrocarbon fuels will explode if mixed with oxygen and put under enough pressure. The lower the octane, the lower the pressure needed to make it go bang (without a spark).
The spark plug is used to ignite the fuel/air at the correct time.
Just to explain why this is important - Higher octane fuel self 'detonates' at a higher temperature and when it does ignite from the spark it burns more fiercely (so creates more expansion on the burn and so more power or the same power from less fuel).
Engines that are prone to knocking (self detonation) will run better on higher octane. It pushes the temperature at which fuel ignites beyond its self detonation point so the spark itself initiates the fuel burn in a controlled manner through the cylinder.
The fuel temperature is a function of a number of things including the amount of compression (compress any gas and it will heat up) which explains why many high performance engines need higher RON - it isn't necessarily for performance as such but simply to stop self-detonation of the fuel.
My 3.0 is only 10.7:1 which is lower than many, so, from a fuel burn aspect will easily tolerate 95RON.
Better fuel consumption will result from using higher octane fuel, but, it won't be dramatic and is unlikely to recover the much higher cost increase I face at the local garage. Doing 60-100 miles a day (well you have to when the weather is this good) means the additional cost is significantly higher even of some improved fuel consumption results.
98RON fuel or higher tends to come with additional additives to provide cleaning. This is probably where the major fuel players products win out. That however is a marketing ploy not the fuel itself. All fuel is the same as its delivered from the refinery, but then, they each add their own additive mix.
Decent 95RON fuel from a major supplier is likely to be better than that from a supermarket - the fuel is the same but the additives are not.
I think majority of benefit comes from this rather than higher octane itself for daily use. However, if you're standing on it routinely and running the engine harder more often then 98RON where it is optional is likely to be much more noticeable. Super-unleaded is likely to give you a much cleaner engine (with clear benefits) but less benefit in terms of power unless you're in the habit of hoofing it more than most. Consumption improvements may be limited if that's what you're after.
Many subscribe to running one full tank in 4 or 5 of 98RON simply to get the benefits of the additives. That sounds a sensible compromise to me.
