CT2-1: Application of a Reduced Elementary Reaction Scheme to Three-dimensional Numerical Simulation of Knocking Phenomenon in a Spark Ignition Engine Fueled by LPG-DME Mixture(CT: Combustion, Thermal and Fluid Science,General Session Papers)

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In this study, the authors tried to understand the knocking phenomenon in a spark ignition engine fueled by LPG-DME mixture. The authors' original 3-D CFD code "GTT" linked to the CHEMKIN-II subroutines, called "GTT-CHEM", was used for not only understanding this knocking phenomenon but also estimating the knock intensity, which is usually measured by the completely different way on the test bed, from the CFD results. Then, a several different shapes of piston cavity were examined by both CFD and actual engine tests. As to the 3-D chemical kinetics calculation technique, for largely saving the computational time with little deterioration of accuracy, the authors constructed a reduced elementary reaction scheme for LPG-DME mixture by combining and reducing the GRI-Mech's scheme for LPG (mostly propane) and the Curran's scheme for DME. This reaction scheme was employed in the GTT-CHEM code, into which a modified version of the Kong's turbulent combustion model based on elementary reactions was incorporated. The GTT-CHEM code with the original reduced elementary reaction scheme was able to reproduce the knocking phenomenon reasonably well in the LPG-DME mixture fueled spark ignition engine. Finally, after actual engine experiments about different piston cavities, it has been found that a knocking intensity estimation index derived from HCHO behavior in CFD results is a good prophetic index to expand the knocking limit.