A novel approach is proposed and investigated to reduce unburned hydrocarbon emissions from a homogeneous charge compression ignition (HCCI) engine by using in-cylinder catalysts. The combustion and emission characteristics of this HCCI engine are numerically simulated in three cases, i.e., the baseline engine with an uncoated piston crown, the engine with a platinum coating oil the top and side surfaces of the piston crown (full coated case) and the engine with a platinum coating only on the side surface of the piston crown (partial coated case). A detailed reaction mechanism of methane oxidation on platinum catalyst is adopted. The results show that the unburned hydrocarbons of the HCCI engine arise primarily from sources near the combustion chamber wall, such as flame quenching at the entrance, of crevice volumes and at the combustion chamber wall, and the adsorption, and desorption of methane into,and from the cylinder wall. The in-cylinder catalyst gives rise to a reduction of exhaust unburned hydrocarbon (UHC) emissions by approximately 15% with the full coating of platinum catalyst on the piston crown, however, with the partial coating, the in-cylinder catalyst can reduce the UHC emissions by approximately 20%. (C) 2007 Published by Elsevier B.V.