The point of this proposition is to find a more applicable paradigm for engine position that accounts for variations as discussed.gruntguru wrote: ↑07 Dec 2022, 00:58Musing here. V or V% is a commonly used normaliser in thermodynamic analysis of heat engines and probably does everything you want. As I mentioned earlier V% is the same as Stroke% if you ignore clearance volume.
Unfortunately, none of these (including CA or CA%) allows direct comparison (between two engines) of combustion events like MBT, MFB and location of PCP. One reason is cyclic variation of crankshaft angular velocity. This is different for different engine configurations eg I4 engines suffer extreme speed variation due to inertia torque (all pistons are stopped simultaneously transferring all their momentum to the crankshaft) whereas a 90* V Twin has zero inertia torque. Of course combustion events also contribute to cyclic speed variation - decreasing with cylinder count and relative flywheel mass. Getting back to the point - two engines may have PCP occurring at the same location measured in CA or V% but quite different time period ATDC due to one engine being an I4 and the other a V8.
Whilst V% is very relevant it is a product of position, B/S, L/R etc etc not the primary parameter/s.
This is getting warmer though and thank you for this musing.
Cycle variations are not part of this primary parameter, at this stage consider a single cylinder engine and not cyclical variations , just the one event of say, 720 degrees of rotation.
The crankshaft config is a later factor to be, if needed, adjusted for along with others as previuosly mentioned. This aspect shows why the transfer of information from single cylinder test rigs to the full multi cylinder operation is often fraught with problems.But let us not digress.