2 stroke thread (with occasional F1 relevance!)

[Tommy Cookers]

fwiw my guess would be that thousands of DKW motorcycles got there first
DKW cars also

[johnny comelately]

The world's first looper?

https://oldmachinepress.com/articles/page/23/

Scroll about 1/4 way down.

What a fantastic story, something for everyone.
Halo effect (maybe) from being trapped underwater upside down in mud.
Thin section wings for invigorating laminar flow discussions

[johnny comelately]

@ Pinger, recent 2T developments in (highly constrained rules-wise) Kart racing have included (AFAIK)
exhaust port-nozzle-pipe research into both liquid cooling ( to reduce temp of the returning fuel-air charge),
& 'sonic' nozzle design shapes - to obviate 'shock-choke' - gas-flow issues at high rpm..

High speed inlet hysterisis is a fairly mysterious area, but of huge significance
, do you have any information?

[J.A.W.]

Check this thread-site, Johnny, look for recent posts from member 'Wobbly' & others.. or try a 'search'.

https://www.kiwibiker.co.nz/forums/show ... gine-tuner

[johnny comelately]

@ Pinger, recent 2T developments in (highly constrained rules-wise) Kart racing have included (AFAIK)
exhaust port-nozzle-pipe research into both liquid cooling ( to reduce temp of the returning fuel-air charge),
& 'sonic' nozzle design shapes - to obviate 'shock-choke' - gas-flow issues at high rpm..

Cooling the 'stored' charge is pretty cunning. Highlights an inherent problem with branch manifolds which is that the piston at or around TDC gets a positive pulse (which it has no use for) which can only add heat to its skirt. The pulse will be of lower pressure than with a full fat expansion chamber and will impact only the skirt - not the rings. A minor problem given the lower state of tune, but any unnecessary heat flow to a piston is unwelcome.

Re 'adjustability' of tuned pipes to rpm. Power valves do a good job there as well as their primary task of masking the port. The change in timing neatly re-synchs the pipes to the rpm. High maintenance though by what I can ascertain, requiring regular cleaning of carbon if they are not to stick.

VE (or ME) and effective gas exchange during transition and over the rev range is one of the keys (highly sensitive to throttling), the other being combustion (where they have an inherent advantage over the 4T).
All these methods above have been fantastic at improving the charged two stroke

[johnny comelately]

Check this thread-site, Johnny, look for recent posts from member 'Wobbly' & others.. or try a 'search'.

https://www.kiwibiker.co.nz/forums/show ... gine-tuner

Thanks for that. If only they would have used methanol

[J.A.W.]

Kart racing engine parameters are ~ rules constrained as F1 currently is..
..but methanol based fuel - is still used in several other competition classes..

[63l8qrrfy6]

@ Pinger, recent 2T developments in (highly constrained rules-wise) Kart racing have included (AFAIK)
exhaust port-nozzle-pipe research into both liquid cooling ( to reduce temp of the returning fuel-air charge),
& 'sonic' nozzle design shapes - to obviate 'shock-choke' - gas-flow issues at high rpm..

Cooling the 'stored' charge is pretty cunning. Highlights an inherent problem with branch manifolds which is that the piston at or around TDC gets a positive pulse (which it has no use for) which can only add heat to its skirt. The pulse will be of lower pressure than with a full fat expansion chamber and will impact only the skirt - not the rings. A minor problem given the lower state of tune, but any unnecessary heat flow to a piston is unwelcome.

Re 'adjustability' of tuned pipes to rpm. Power valves do a good job there as well as their primary task of masking the port. The change in timing neatly re-synchs the pipes to the rpm. High maintenance though by what I can ascertain, requiring regular cleaning of carbon if they are not to stick.

VE (or ME) and effective gas exchange during transition and over the rev range is one of the keys (highly sensitive to throttling), the other being combustion (where they have an inherent advantage over the 4T).
All these methods above have been fantastic at improving the charged two stroke

What's the inherent combustion advantage over 4T ?

[J.A.W.]

Apart from firing - twice as often?
Most 2Ts have no poppet valves to compromise the combustion chamber shape/cause heat control issues.

[johnny comelately]

Apart from firing - twice as often?
Most 2Ts have no poppet valves to compromise the combustion chamber shape/cause heat control issues.

Yes precisely, and you can spend your time on boundary layer management amongst other things

[johnny comelately]

No reason some technical sophistication cannot be added to the exhaust to gain a wider power-spread
for road machines..

A internal cone, able to be moved fore & aft - within the fat part of the pipe - in tune with rpm change,
(controlled as exhaust 'power valves' & the like have been - for the past few decades)..

http://www.rpdinc.com/10435-thickbox/plastic-funnel.jpg

we did have that where the distance between the two cones was varied via a rack and pinion system according to rpm, eventually banned

Further, it was a mach 4 and flogged the factory bikes (late 70's). Rev activated stepper motor. And the bloke that got it banned (sore loser) is mentioned elsewhere in the forum.

[63l8qrrfy6]

Apart from firing - twice as often?
Most 2Ts have no poppet valves to compromise the combustion chamber shape/cause heat control issues.

I read that as 2T combustion being somehow superior to 4T on a 'per powerstroke' basis.
I would argue that the lack of poppet valves in a 2T does not make up for the poor charge motion.

[63l8qrrfy6]

Apart from firing - twice as often?
Most 2Ts have no poppet valves to compromise the combustion chamber shape/cause heat control issues.

Yes precisely, and you can spend your time on boundary layer management amongst other things

You what ?

[J.A.W.]

Most 2Ts have no poppet valves to compromise the combustion chamber shape/cause heat control issues.

I would argue that the lack of poppet valves in a 2T does not make up for the poor charge motion.

"You what?"

Do by all means, present your reasoning..

[manolis]

Hello all.

Are the best engines in the world the giant two stroke marine engines?

With the cheapest fuel (the residual of the distillation) they achieve more than 50% BTE (BSFC less than 160gr/kWh).

Typical compression ratio: only 12:1.

And they have a big exhaust poppet valve on the cylinder head.




Adding an intake-transfer poppet valve on the piston crown, the lubrication problem of the 2-strokes has been solved (portless cylinder liner, 4-stroke lubrication):



Thanks
Manolis Pattakos