It is empirically known that high temperature hear release (HTHR) combustion is characterized by the heating value of low temperature heat release (LTHR) and much study of LTHR reactions has been done, but the direct effects of fuel chemicals on HTHR were not enough investigated. Nippon Oil and Nissan have researched the hydrocarbon breakdown process since 2002 and found some interesting test results. In this paper the possibility of the improvement of HCCI engine performance was discussed.