SkyActiv-X technical research and control system boss Mitsuo Hitomi confirmed that in its ideal guise, the engine's ability to combust petrol through compression ignition will require Regular 91 RON fuel, and any higher octane rating will force the engine to revert to pure spark plug ignition like a conventional engine.
Hitomi-san suggested a partial solution is planned for markets like Europe where 91 RON fuel is scarce or unavailable, which would be supplied with engines using a higher 16:1 compression ratio to enable both compression and spark ignition functions to operate. This spec won't deliver quite the same efficiency gains as the 15:1 compression ratio version delivered to 91 RON-using markets such as Australia, however. For context, international versions of the existing SkyActiv
petrol engine feature world-leading 14:1 compression ratio, while Australian and US models come with a still-impressive 13:1 ratio.