Experimental Investigation for the Effect of Cavity Geometry on the Flame Propagation and Auto-Ignition in RCM

In this experiment, we investigated the auto-ignition and flame propagation behavior by using flat piston and cavity pistons which has different geometries, depth, and width of the cavity. In this study, flame behavior inside the cavity is visualized with the ion-probes, which is embedded every 3mm radially from the center of the piston. We also used the pressure sensor in the combustion chamber and high-speed camera through the quartz window near the cylinder wall. Flame appearance obtained with high-speed camera shows that the flame propagation of the cavity piston is faster than that of flat piston. This is considered because of the outward induced flow in the squish area. That is, the flame propagation inside the wide cavity area pushes the unburned gas outwardly and induced the outward flow in the squish area. This induced flow promotes the flame propagation. As a result, unburned gas is consumed rapidly, and thus, it is also found that the intensity of Knocking is reduced by using cavity piston compared with flat piston. The combined analysis using the ion-probe and pressure data indicates that in the cavity piston auto-ignition occurred in the cavity area immediately after auto-ignition in the squish area and the knocking.