AMONG the difficulties usually associated with measurement of combustion-chamber volume by liquid methods are amount of time required, contamination of combustion-chamber deposits, and inaccuracies arising from entrapped air.
Use of a gaseous fluid such as air as the measuring medium eliminates most of the objectionable features of volume measurement with liquids. Techniques utilizing air for volume measurement fall into two basic classifications: dynamic or sonic methods, and static or pneumatic systems.
Cylinder leakage and acoustic damping by engine deposits affect the accuracy of volume measurements based on dynamic properties of combustion-chamber volume, hence small volumes occupied by combustion-chamber carbon deposits must be measured separately by static or pneumatic means.