Experimental Investigations of the Top Land Volume

Abstract

With the necessity to a further reduction in fuel consumption or CO₂, the late combustion phase is of high importance throughout the range of operation. Because of the high differences in density between burnt and unburnt zones, a relatively large unburnt mass is concentrated in a relatively small volume near the wall and the top land volume.

To investigate the thermodynamic interactions between the boundary zones of the combustion chamber and the flame front, a state-of-the-art Mercedes-Benz-single-cylinder research engine was equipped with extensive measurement technology. To detect the piston movement and the top land volume, eddy-current distance sensors were applied to the cylinder. The radial pressure distribution in the top land volume is detected with four miniature pressure transducers. As main part, surface thermocouples were applied in two layers around the top land volume with additional surface thermocouples in the boundary zones of the cylinder head as a reference.

Based on a wide range of operating points and a spark timing variation, the temperature distribution in the different top land levels is investigated in comparison with the cylinder head temperatures. Lastly, two different top land volumes, realized by a piston variation, are compared. Thereby, the temperatures in the bigger top land volume indicate a slightly lower compared to the standard geometry. This difference even increases for the lower top land level.