Homogeneous charge compression ignition (HCCI) combustion is a spontaneous multi-site auto-ignition of a lean premixed fuel-air mixture, which has high heat release rate, short combustion duration and no evidence of flame propagation. In HCCI engines, there is no direct control method for the time of autoignition. Auto-ignition timing should be controlled in order to make heat release process take place at the appropriate time in the engine cycle. Heat release analysis is a diagnostic tool which aids engine experimenters. It facilitates the endeavors being conducted in obtaining a control method by investigating heat release rate and also cumulative heat release. This study can be divided into two parts. First, traditional first law heat release model which is widely used in engine combustion analysis was presented and the applicability of this model in HCCI engines was investigated. Second, a new heat release model based on the first law of thermodynamics accompanying with a temperature solver was developed and assessed. The model was applied in four test conditions with different operating conditions and a variety of fuel compositions, including i-octane, n-heptane, pure NG, and at last, a dual fueled case of NG and n-heptane. Results of this work indicate that utilizing the modified first law heat release model together with a solver for temperature correction will guarantee obtaining a well-behaved and accurate apparent heat release trend and magnitude in HCCI combustion engines. (C) 2010 Elsevier Ltd. All rights reserved.