(2-22) Numerical Analysis of the Interaction between Thermo-Fluid Dynamics and Auto-Ignition Reaction in Spark Ignition Engines((SI-7)S. I. Engine Combustion 7-Modeling)

Abstract

The interaction between thermo-fluid dynamics and auto-ignition reaction was analyzed by the CFD simulation integrating the low temperature oxidation reaction. In the first analysis, a compression auto-ignition of a premixed mixture in a rapid compression machine was solved in a laminar axisymmetric field. The computed results show that the temperature field becomes non-uniform at the end of compression, being higher in the outer region and lower in the central region ana near wan regions, This is due to the vortex induced in the piston-liner corner and wall heat transfer. It is shown that the auto-ignition initiates different places depending on whether local temperatures are outside or inside the negative temperature coefficient regime of the low temperature oxidation reaction. In the second, the auto-ignition in an s. i. engine was analyzed in a three dimensional turbulent field by solving the spatially filtered transport equations instead of the Reynolds averaged ones in consideration of the strong non-linearity to temperature in the reaction terms in the fluctuating temperature field. The computed results for a disk-shaped combustion chamber with a central spark plug show that temperature fluctuations appear during compression due to random variations in the wall heat transfer which were generated by the random motion flow, though a uniform temperature field was assumed as the initial condition. Figure 1 shows the computed pressure compared with the experimental results. The calculation terminated at the auto-ignition initiation, which was assumed as the time when any local temperature of the unburned mixture reached 1100 K. The predicted time of the first local auto-ignition appearance is seen to be 1.1 deg. BTDC, which falls in the range of the cycle variation in experimental results. The computed temperature fields of the unburned mixture at this time are shown in Figure 2. The figure demonstrates that the auto-ignition sites appear sporadically as seen in the high-speed photographs presented in the literature.