Gasoline HCCI Modeling: Computer Program Combining Detailed Chemistry and Gas Exchange Processes
Paper i proceeding, 2001
A skeletal reaction mechanism (101 species, 479 reactions) for a range of aliphatic hydrocarbons was constructed for application to computational fluid dynamics (CFD) Gasoline Homogeneous Charge Compression Ignition (HCCI) engine modeling. The mechanism is able to predict shock tube ignition delays and premixed flame propagation velocities for the following components: hydrogen (H2), methane (CH4), acetylene (C2H2), propane (C3H8), n-heptane (C7H16) and iso-octane (C8H18).
The mechanism is integrated with a simulation code combining both modeling of detailed chemistry and gas exchange processes. This simulation tool was constructed by connecting the SENKIN code of the CHEMKIN library to the AVL BOOSTTM engine cycle simulation code. Using a complete engine cycle simulation code instead of a code that only considers the combustion process has a major advantage. The initial conditions at the intake valve closure (IVC) have no longer to be set. Typical initial conditions for a single-zone model are the average temperature of the mixture in the cylinder, the cylinder pressure and the species concentrations. When the engine cycle simulation code is used, the initial conditions consist of geometrical data for engine components and pressures and temperatures at different locations in the model scheme representing engine components connected by pipe elements. As gas exchange processes are included in the engine cycle simulation, the program will calculate the conditions at the IVC.
The simulation program is used for parametric studies of the combustion process in the single-cylinder HCCI test engine at Chalmers University of Technology. Furthermore, provision for a link to future multidimensional CFD engine modeling is made. The model was matched to different test cases based on experimental data in order to obtain a tool giving accurate predictions for the different combinations of speed, load, excess air/fuel ratio and valve timings that are characteristic for the HCCI engine operation.