I don't think for a moment that the Ryger's HCCI is like those being discussed here, Ryger has found a way of controlling this HCCI after blowdown becomes not enough time in a normal twostroke. I think spark ignition until this happens, then spark plug/system is just along for the ride.
All of this requires a high pressure transfer system to still push fuel air up into the combustion chamber, at elevated cylinder pressures.
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