How can the higher RON mean you use less petrol?
The injectors inject whatever they inject.
The engine goes around and X revs at Y mph and that cant be changed...so how does it use less?
An engine with knock sensors fitted will advance its timing as far as it can without significant knock, advanced timing means it can produce more power.
The octane number indicates the fuels resistance to knock, therefore high octane fuel can run with more ignition advance and produce more power as a result, this can lead to reduced consumption because with the engine producing more power from the fuel you dont need to put your foot down so much and use as much fuel.
On an older car without knock sensors you would need to change the ignition timing to suit the fuel, ignition timing is only part of the story though, a high compression engine will need high octane knock resisting fuel anyway as the high compression will cause low octane fuel to spontaneously ignite (knock)
What shell is offering isnt high octane fuel though, its something different to make the economy improve, I have no idea what.
