The article is pretty superficial and overly general in some of its assertions, but has pretty good discussion on the HCCI and the latest topic in the engine community: RCCI. HCCI has been under development for at least 15 years, and always seems a constant 10 years away from practical production. The problem is engine control, and not being able to predict what the engine load will be 10 combustion cycles into the future, which is kind of a fatal failing in an automobile engine. In order to control the ignition point in an HCCI engine, the temperature of the charge must be known at the point of intake valve closing. This makes it necessary for either the intake manifold temperature or the intake valve closing point be actively controlled on every engine cycle. The former is impossible, while the latter could be possible if a reliable and efficient fully variable valvetrain could be developed.
RCCI is a descendent of HCCI in that compression is used to ignite an homogeneous charge, but the timing of ignition is changed according to the proportion of diesel and gasoline that is injected. Because the technology exists to control the amount of fuel from cycle to cycle, it is more feasible to vary the reactivity of the fuel mix. The major drawback is having two fuel systems in the vehicle, and a minor problem is having to design a combustion chamber with two injectors.
Between the two, my money is on RCCI.
