Reaction Mechanisms for Natural Gas and Gasoline in Homogeneous Charge Compression Ignition (HCCI) Engine Modeling

Two separate reaction mechanisms were developed to predict the auto-ignition and combustion processes in HCCI engines operated on natural gas and gasoline. Natural gas is considered to be a blend of methane, ethane, propane and n-butane, while gasoline is modeled as a mixture of iso-octane, n-heptane as well as toluene. The mechanisms for natural gas and gasoline are constructed by combining the sub-mechanisms of constituent species reduced by a sensitivity analysis. The specific feature of the mechanisms developed is the retention of low-temperature reaction mechanisms for all constituent species. The mechanisms are restricted in size (67 species and 360 reactions for natural gas, 111 species and 512 reactions for gasoline) to be applicable to detailed-chemistry CFD engine modeling. Nevertheless, validation of the mechanisms showed that ignition delay time data from shock tube experiments could be predicted accurately for the constituent species. Results are presented for the successful application of the mechanisms to the modeling of existing engines: the gasoline mechanism was used to predict the HCCI process in a single-cylinder research engine by means of a 1-D engine cycle simulation code with a multi-zone combustion model. The mechanism for natural gas oxidation was applied to 2-D calculations of HCCI combustion in a heavy-duty engine using the KIVA code