COMBUSTION roughness associated with lateral flywheel vibration can be controlled more effectively by adding a suitable damping system to the flywheel than by altering combustion-chamber shape. The authors reach this conclusion because their quantitative study shows that the degree of shock excitation is dependent on different pressure characteristics at different engine speeds.
At 1000 rpm, low rates and accelerations of pressure rise, obtainable by proper combustion-chamber design, will reduce combustion roughness.
However, at 3500 rpm, it is maximum pressure - which is not dependent on combustion-chamber design - that governs vibration intensity. If vibration is to be diminished by a reduction in maximum pressure, either the spark must be retarded or the volumetric efficiency decreased.
Maximum kinetic energy proved to be the most suitable criterion of disturbance over the entire range of engine speeds.