Shock storing conrod arm mod

[Ecky]

Originally Posted by Logic

Yes, but I think you're missing the point here:

Lets say you have the head off an engine and have turned one of the pistons to exactly TDC.
Pushing down on the piston (by hand) has exactly zero effect on rotating the cankshaft as there is zero 'horizontal' component to the applied force.
The ONLY way you'll get the piston to move down is by loosening the main crankshaft bearings.

Now take the cylinder/s off too and turn the piston and conrod 90 degrees.
Now pushing on them applies a force that is at 90 degrees to the crankshaft where your push applies maximum torque to it.

Another way of looking at it:
With the cylinder/s on: Turn the crank till the same piston is 1/3rd to halfway down.
Now your push on the piston easily turns the crank.

That is the issue the OP was trying to ameliorate:
Ideally he/we wants TDC to be when the crank's at 90 degrees to the conrod...
Linear piston generator anyone!?

I might be missing the point, but I'm speaking based in large part on personal experience with tuning.

A typical balanced (non offset) engine, at light load and moderate RPM (let's say, 3000+) will have its ignition event happen as much as 40-60° before TDC, because combustion takes time to complete. Ignition starts and the flame front spreads and cylinder pressure starts increasing, all before the piston reaches TDC. A relatively large amount of energy is lost simply due to combustion trying to spin the engine backwards for a significant portion of the stroke.

A good rule of thumb is that you can extract the most energy out of combustion (in a traditionally balanced engine) if you try to get peak pressure to happen sometime around 15-20 degrees past TDC. If you can speed up combustion, you don't need to start combustion as early.

Even large offset crank engines still start ignition prior to TDC during some parts of their map, particularly at high RPM and low load.

Faster combustion has the additional benefit of increasing the "push" while cylinder pressures are already high and the piston is still at a favorable angle during its stroke. Slow combustion still has otherwise usable energy being released after the piston has already left it behind.

[Logic]

Originally Posted by Ecky

I might be missing the point, but I'm speaking based in large part on personal experience with tuning.

A typical balanced (non offset) engine, at light load and moderate RPM (let's say, 3000+) will have its ignition event happen as much as 40-60° before TDC, because combustion takes time to complete. Ignition starts and the flame front spreads and cylinder pressure starts increasing, all before the piston reaches TDC. A relatively large amount of energy is lost simply due to combustion trying to spin the engine backwards for a significant portion of the stroke.

A good rule of thumb is that you can extract the most energy out of combustion (in a traditionally balanced engine) if you try to get peak pressure to happen sometime around 15-20 degrees past TDC. If you can speed up combustion, you don't need to start combustion as early.

Even large offset crank engines still start ignition prior to TDC during some parts of their map, particularly at high RPM and low load.

Faster combustion has the additional benefit of increasing the "push" while cylinder pressures are already high and the piston is still at a favorable angle during its stroke. Slow combustion still has otherwise usable energy being released after the piston has already left it behind.

Yep, thx Ecky I'm perfectly aware of all that.
(Hence my 'search' for some easy free Hydrogen from a normal engine. Copper plating of the combustion chamber for eg. which pgfpro will try!)

You might want to look at pgfpro's posts on precombustion chambers and high compression, lean burn.
He's running unbelievable #s!
Well... F1 believes him as they are (now?) doing the same thing, thx to fuel restrictions.
Let's hope the tech trickles down, but I expect ...er... Big 'Management' will 'throw a spanner in the works'.


Also consider the NON ISSUE all this is with a Linear Generator...

https://www.youtube.com/watch?v=gdTDcODrxFo

This is the ideal (series hybrid) engine IMHO and the designers of such are not seeing the wood for trees by NOT running the generator (4-Stroke) as a Linear Motor for all but the power stroke...