This work presents the results of the experimental study on engine speed and cyclic dispersion in a homogeneous charge compression ignition (HCCI) engine. An engine TD43 is used to carry out the research. The combustion parameters are deduced from heat release rate which obtained from the first principle of thermodynamics during a cycle. The experimental results show that the duration of low temperature reaction plays an important role on HCCI combustion, particularly at higher engine speeds. Furthermore, cyclic dispersion in an HCCI engine presents, under certain operates conditions, a periodic behavior corresponding to 2 or 3 cycles of the engine. It is concluded that the residual gas of a cycle modifies the three properties (temperature, dilution and composition) of gas in-cylinder at the following cycle. Therefore, gas residual directly affects the course of combustion in an HCCI engine. The knowledge of the duration of the different phases of combustion, as well as conditions in which the periodical appearance of misfire cycles occurs, is useful for the definition of regulation strategies. (C) 2010 Elsevier Ltd. All rights reserved.