I'm not an expert in the field of chemistry, nor do I know what an 'HCCI' is, but I'll venture that this means, ROUGHLY,
The HCCI ignition and combustion processes are mainly caused by the kinetic energy found in gasoline which is extracted by an oxidation process.
I can't state categorically that what I've said is accurate for as I said, this is not my field.
Have I covered my butt sufficiently?
Student or Learner