gruntguru wrote: ↑02 Dec 2022, 01:02
johnny comelately wrote: ↑23 Nov 2022, 06:41
The status quo seems to be the use of Crank Angle for various particular engine analysis characteristics.
This fails in comaparative applications because it does not take into consideration the Bore Stroke ratios nor the Rod ratios and their effect on the very parameters that are being measured.
Before someone jumps in and says that some of those measurements are independent it would be prudent to see that a normalised factor that reflects all three parameters as a single encompassing new paradigm would be more indicative.
Not being particularly mathematical, any suggestions as to how this could be achieved?
The starting point would be the conversion of the stroke to a percentage.
Methinks this has been touched on before but I could not find it.
Must admit I also am not sure what you are trying to do. I agree with most of what @Hoff says.
One comment - how does B/S affect things? Two engines with identical displacement and L/R but different B/S will have the same volume - CA relationship.
From a previous post (with the drawing)
"To illustrate the challenge using a standard 266 point 6 cc cylinder.
The difference between an 80mm bore by 53mm stroke
and a 50mm bore by 135.6 stroke
Both at 20 degrees CA
The rod length was 116 mm for both (rightly or wrongly)
Produced piston heights of 2 point 234 and 6 point 43 respectively.
This translates into the different volumes of 11 point 229 cc and 12 point 625 cc respectively."
The long stoke used is for illustrative purposes only, to exagerate the affect. At both 20 degrees CA there is a substantial (as there should be) difference in volume
For example, If you are comparing different fuels in the one engine for say torque and adjust ignition for MBT it is of no consequence.
But if you are comparing different configs, for example, for a partic application using the one fuel (as a reference) , it matters.
Things like the affect on burn patterns or the ability to compare ignition timings etc are all skewed by the differences in stroke if you use CA. Consequently if you are mapping torque impulses it is necessary to standardise the comparators.