The Better Alternative to the Folly of CA in the Comparative Analysis of IC engines.

[johnny comelately]

Musing 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.

The point of this proposition is to find a more applicable paradigm for engine position that accounts for variations as discussed.
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.

[johnny comelately]

I feel it is reasonable to insert this here. It has been a bit of a hard flog to get traction.
It is mentioned purely to be instructive if needed, nothing else.

"Julien Avezou: The art of engineering your thoughts"
https://www.youtube.com/watch?v=S9VlmQxtt5M

"As engineers we tend to lean towards rational thinking. However, as humans, we are all subject to emotions that create biases in our thought patterns. Inspired by the ‘via negativa’ approach coined by the Greeks and Romans, we know with certainty what destroys success or happiness. Negative knowledge - what not to do - is more potent than positive knowledge - what to do.

In this talk, Julien focuses on a few of the main thought biases he feel are relevant for engineers: Planning Fallacy, Decision Fatigue, the Fallacy of the Single Cause and Illusion of Attention"

"The Single Cause Fallacy is a logical fallacy in which someone believes that there can only be one cause for an event. This is also known as the reduction fallacy, as well as complex cause or casual oversimplification."

Disclaimer: I am certainly not an engineer, as you may have noticed

[johnny comelately]

A (mathematical) reply from a professor to my search for verification:

"there is a functional relation f() between “percentage of stroke” (POS) and “crank angle” (CA) such that POS = f(CA). If we restrict the domain and co-domain such that where CA is in set [0,720) degrees and POS in set [0,400) percentage then f() is a nonlinear and invertible. "

I know this is simply proving the relationship which is incontrovertible but at least it is a start.

[gruntguru]

It is obvious that POS and CA are related and that the relationship depends only on L/R. Which is better?

For thermodynamics and combustion, POS is clearly superior, both for analysis and for comparing different engines.

For analysing and comparing rotating systems (eg torque variation, inertia torque, torsional vibrations etc), CA is a superior reference frame.

[johnny comelately]

It is obvious that POS and CA are related and that the relationship depends only on L/R. Which is better?

For thermodynamics and combustion, POS is clearly superior, both for analysis and for comparing different engines.

For analysing and comparing rotating systems (eg torque variation, inertia torque, torsional vibrations etc), CA is a superior reference frame.

You realise you have crossed over to the dark side using the term POS