2 stroke thread (with occasional F1 relevance!)

[manolis]

Hello all.

Manolis wrote:
“If it was to run at higher revs (say 10,000rpm for 400hp/lit) then only a rotary exhaust valve could do the job.”


An issue with the exhaust poppet valves in the 2-strokes is the energy consumed during the opening, when the pressure inside the cylinder is still high (worse in case of supercharging, turbocharging).

The moment the cam lobe presses the exhaust valve to open, the gas pressure in the cylinder (say, 10 bar (?)) presses the valve “upwards”.

With an exhaust valve of 40mm diameter, the force the cam lobe has to overcome equals to the inertia force required to accelerate the valve assembly, plus the valve spring force, plus the gas pressure force (125Kp / 275lb).

The big part of the energy spent for the opening of the exhaust valve is non recoverable. Etc.


By comparison, a rotary valve has not such issues to deal with.



Thanks
Manolis Pattakos

[Tommy Cookers]

news to me .....
http://quasiturbine.promci.qc.ca/ETheor ... Piston.htm
http://quasiturbine.promci.qc.ca/ETypeCombustion.htm
http://quasiturbine.promci.qc.ca/ETheor ... ematic.htm

[manolis]

PatATE: Asymmetric Transfer and Exhaust in two-stroke engines


Hello all.

Here is an unconventional two-stroke (the PatATE) in comparison to a conventional two-stroke:



The main difference is that the exhaust port is now a "hybrid" port (the 4): at the end of the expansion the valve 7 connects the hubrid port with the exhaust passageway 5, and the exhaust starts the conventional way.

Later the valve 7 opens the transfer passageway 6 and seals the exhaust passageway 5; the exhaust continues through auxiliary (and "lower") exhaust ports 8; the transfer uses the conventional (symmetrical) transfer port 9 and the hybrid port 4.

Later the piston closes the conventional transfer port 9 and the auxiliary exhaust ports 8.

In the conventional two-stroke the exhaust remains open for several degrees (while the transfer is closed). In the PatATE the transfer continous (while the exhaust is closed). Regarding the operation of the engine, it looks like a significant difference.

Here are some more drawings / graphs:












For more: http://www.pattakon.com/pattakonPatATE.htm

Thanks
Manolis Pattakos

[Pinger]

Manolis, you are aware that from 10CAD ABDC the flow in a transfer port reverses and mixture in the cylinder is drawn back into the carnkcase? Very quickly you arrive at the conclusion that the same could be achieved with no loss of torque by merely restricting the delivery ratio - the primary variable in charge loss to the exhaust port. Unless of course Blair is wrong and I'm an idiot for believing him.

[Tommy Cookers]

not exactly on thread but imo a worthwhile read
http://www.pprune.org/tech-log/409778-w ... ble-2.html

[J.A.W.]

Hi Manolis, your new 2T design, as accepted for patent - does look interesting..

..have you done meaningful 'in metal' - tests with it, yet?

I'd be curious to know how the dynamic heat aspects of the exhaust port/'nozzle' functional ( re: 'blowdown/reversion')
flows are affected by that 'trap-door' valve, per EGT/R (inc' - 'deto/cook-off' potential via 'wet' transfer, so - DI?) - or not..

[manolis]

Hello Pinger.

The flow is not necessary to reverse.

For instance, by using a rotary valve for the control of the communication of the hybrid port(s) with the transfer and the exhaust passageways, say like:







during the “overlap” (or scavenging) the exhaust continues at the one side of the hybrid port while the transfer is happening at the other side of the hybrid port (like having separates ports on the cylinder liner).

There are two hybrid ports arranged anti-diametrically on the cylinder liner.

The timing plot reminds “4-stroke” timing plots:



In the specific case, but not necessarily, the rotary valve rotates at crankshaft speed:







More at http://www.pattakon.com/pattakonPatATE.htm

Thanks
Manolis Pattakos

[manolis]

Hello J.A.W.

For the PatATE there is nothing in metal yet.

An interesting thing with the rotary valve PatATE is that the rotary valve (which reminds the "flat-head" PatRoVa rotary valve on the cylinder head of a 2-stroke a few pages ago) operates at low pressures and needs not tight sealing.

Thanks
Manolis Pattakos

[Pinger]

The flow is not necessary to reverse.

Agreed. But it will.

[uniflow]

Pinger, yes this flap would just be a liability. But if it were to work as a transfer only as transfer takes place then back to an exhaust port as the reverses exhaust pressure wave returns then it might be useful. I would like to see the mechanism that would suck no power and yet be able to work at that kind of speed, with no dwell, only open and closed. A cam would be far to slow. I have a cylinder along these lines already.
I have considered all kinds of systems regarding twostroke porting. Most of my stuff I try out in the real hardware first.

[manolis]

The flow is not necessary to reverse.

Agreed. But it will.

Hello Pinger.

Take a look at the hybrid port on this animation,:



Take the case the piston is at the BDC:
The one side of the hybrid port serves the exhaust, the other side (i.e. along the periphery of the cylinder) of the hybrid port serves the transfer.

Similarly for all crankshaft angles during the "overlap" or scavenging.

The flow is not reversing.

Thanks
Manolis Pattakos

[manolis]

Hello all.

Take another look at the animations of the last post; now the rotary valve controls the intake, too.

Thanks
Manolis Pattakos

[Pinger]

When I look I see too much friction.
Three layers of viscous oil film friction. Which is two too many. IMO...

[gruntguru]

A lot of the mating surfaces shown in the animation could be removed, relieved or run with large clearances.

[Pinger]

A lot of the mating surfaces shown in the animation could be removed, relieved or run with large clearances.

Fair point.