Detailed Simulation of Liquid DME Homogenization and Combustion Behaviors in HCCI Engines 2008-01-1705
The homogenization of fuel, air, and recycled burnt gases prior to ignition as well as detailed intake, spray, combustion and pollution formation processes of Homogeneous charge compression ignition (HCCI) engine with liquid Dimethyl ether (LDME) fuel are studied by coupling multi-dimensional computational fluid dynamic KIVA-3Vr2 code with detailed chemical kinetics. An extended hydrocarbon oxidation reaction mechanism including 81 species and 362 elementary reactions used for (HCCI) engine fueled with (LDME) fuel was constructed and studded at different engine conditions by using CHEMKIN software and then a validating reduced mechanism that can be used in a modeling strategy of 3D-CFD/chemistry coupling for engine simulation is introduced to meet the requirements of execution time acceptable to simulate the whole engine physicochemical process including intake, spray, compression and combustion process. The CHEMKIN and improved KIVA-3Vr2/chemistry model results were validated using the experimental data from HCCI engine with intake (LDME) fuel injection. Then, the CFD/chemistry model has been employed to simulate the intake, spray, combustion, and pollution formation process of LDME direct injection with split injection strategy. The models account for intake air flow structure, LDME spray atomization, droplet evaporation and gas phase chemistry in complex multi-dimensional geometries. Simulation results indicate that, under all conditions, the methyl radical plays a very important role in DME pyrolysis and oxidation. In addition, the formaldehyde sub-mechanism is a very important subset of the overall DME mechanism. The external mixture formation of (LDME) is considered as a good way to achieving in-cylinder mixture homogeneity. But the experimental results show that there is some difficulty to inject (LDME) inside the intake manifold because the cavitations inspection inside the injector especially at higher load conditions.