2 stroke thread (with occasional F1 relevance!)

[riff_raff]

Not all r-r, since..
-an N/aspirated 2T should/would readily beat an N/A 4T mill of equal cc..
& the same goes for forced induction too.. ..its a physical matter of work done/thermodynamics..

A N/A 2T? Just how could such an engine be made to work? Even the loop scav 2T engines used on dirt bikes and chainsaws rely on crankcase pumping for scavenging. Which means they are not truly "normally aspirated".

[J.A.W.]

A N/A 2T? Just how could such an engine be made to work? Even the loop scav 2T engines used on dirt bikes and chainsaws rely on crankcase pumping for scavenging. Which means they are not truly "normally aspirated".

Seems you as poorly informed about this r-r.. ..as you were about 2T suitability for high-speed desert work..
( Did you read the KX 500 article/data Uniflow cited/linked?)

The air/fuel mixture in such a 2T machine is transferred from under the piston to above, by piston thrust,
- but at no time is it any form of "supercharge" above atmospheric pressure - in the accepted sense..

[uniflow]

A N/A 2T? Just how could such an engine be made to work? Even the loop scav 2T engines used on dirt bikes and chainsaws rely on crankcase pumping for scavenging. Which means they are not truly "normally aspirated".

Seems you as poorly informed about this r-r.. ..as you were about 2T suitability for high-speed desert work..
( Did you read the KX 500 article/data Uniflow cited/linked?)

The air/fuel mixture in such a 2T machine is transferred from under the piston to above, by piston thrust,
- but at no time is it any form of "supercharge" above atmospheric pressure - in the accepted sense..

The air fuel entering the carb takes four strokes to excit the exhaust as burnt gas. Crank case is just a transfer means, no supercharge although years ago DKW used extra crank case pumping pistons that did create supercharge. The twostroke exhaust tuned pipe is responsible for most of the gas transfer work done, now with the 24 / 7 reed system ( on the pipe, the reed block is open full time, just an inlet hole with the one way valves disabled / removed out of the way) you can see the crank case as a pump is worthless. The crank case is still needed for low speed opperation off the tuned pipe.

[J.A.W.]

Indeed - U..
& just as envisioned by W. Kaaden, an effective method of harnessing harmonic pulse-jet power to a shaft..

[manolis]

Hello Uniflow.

You write:
“The twostroke exhaust tuned pipe is responsible for most of the gas transfer work done, now with the 24 / 7 reed system ( on the pipe, the reed block is open full time, just an inlet hole with the one way valves disabled / removed out of the way) you can see the crank case as a pump is worthless.”

Consider the case wherein the following Harmonic PatTwo:



has tuned exhaust pipe and runs at high revs, with the control-valve (at the middle) wide-open.

During the scavenging of the top cylinder, the inlet port (or hole) of the lower cylinder is open.


You also write:
“The crank case is still needed for low speed opperation off the tuned pipe.”

During the “low speed operation off the tuned pipe”, the Miller-like cycle gets into play.

Thanks
Manolis Pattakos

[J.A.W.]

Manolis, I'd be interested to see your design shown stat above in metal, here is a slotted piston in current 2T use..

http://www.snowmobile.com/products/fuel ... -1775.html

[Richard]

But for sporty/competition/fun machines for discretionary sale to private users,
as opposed to purely business-use purposes..
..other parameters are perhaps also too valuable/important to be ignored.. ( or we'd only have Diesel/CI mills?)

My point was that comparing 4 stroke and 2 stoke engines with the same displacement doesn't make sense. If we're comparing performance then we should consider the optimum configuration for each.

Obviously the optimum for a series with defined volume is going to be different for a series that relies on fuel or air flow restrictions.

[J.A.W.]

It made "sense" to directly compare them for decades, as it still does in showrooms today R.. so why not?

(Although, outboard boat engines are traditionally category listed by horsepower units).

However it is a matter of thermodynamic fact that 2Ts do more work per turn of the shaft,
'spool up' quicker & provide a more lively response..
2T construction principles also mean they are less expensive, lighter, more compact,& more powerful..

This applies to atmo & forced induction engines, plus the higher peak pressures in the 4T ( discussed elsewhere)
mean a yet heavier, even more expensively built mill, especially when durability is required per current F1 reg's..

Obvious answer.. Ban them..

[gruntguru]

I don't think 2T would have much if any advantage in the current formula. The best reason for banning them is road-relevance (lack of).

Road cars generally have not embraced 2T:
1. Traditionally due to oil burning, HC emissions, uneven idle and cruise etc.
2. Modern 2T tech has fixed all the above problems but not the issues of excess air, NOx and reduction catalyst incompatibility.

Funnily, the lean-burn nature of current F1 makes the engines less road relevant for the same reason!

[J.A.W.]

I don't think 2T would have much if any advantage in the current formula. The best reason for banning them is road-relevance (lack of).

Road cars generally have not embraced 2T:
1. Traditionally due to oil burning, HC emissions, uneven idle and cruise etc.
2. Modern 2T tech has fixed all the above problems but not the issues of excess air, NOx and reduction catalyst incompatibility.

Funnily, the lean-burn nature of current F1 makes the engines less road relevant for the same reason!

You'd need to give it a bit more thought then G-G..

The primary reason 2Ts are banned in F1 is the fundamental thermodynamic advantage of X2 BMEP..

Of course there is very little cross-compatibility between road vehicle emissions reg's & F1 anyhow..
The political decision to focus on 3-way cats ( & 2Ts are naturally better on NOx ) was not via valid
efficiency-based reasoning & cruels true road vehicle lean burn performance, as you know..

[wuzak]

I don't think 2T would have much if any advantage in the current formula. The best reason for banning them is road-relevance (lack of).

Road cars generally have not embraced 2T:
1. Traditionally due to oil burning, HC emissions, uneven idle and cruise etc.
2. Modern 2T tech has fixed all the above problems but not the issues of excess air, NOx and reduction catalyst incompatibility.

Funnily, the lean-burn nature of current F1 makes the engines less road relevant for the same reason!

You'd need to give it a bit more thought then G-G..

The primary reason 2Ts are banned in F1 is the fundamental thermodynamic advantage of X2 BMEP..

Of course there is very little cross-compatibility between road vehicle emissions reg's & F1 anyhow..
The political decision to focus on 3-way cats ( & 2Ts are naturally better on NOx ) was not via valid
efficiency-based reasoning & cruels true road vehicle lean burn performance, as you know..

2 x BMEP for 2 x fuel usage.

[wuzak]

As to why a 2T would not necessarily be such an advantage under the current rules is that:

• The maximum capacity is set (can be no more than 1,600cc)
• The minimum capacity is set (can be no less than 1,590cc)
• The fuel flow is restricted (100kg/hr maximum) and thus the amount of air that can be pumped is restricted
• Minimum dimensions for mounting faces to the tub and gearbox are set.
• Minimum weight and CoG limitations
  [*}Only poppet valve engines are permitted (you could make a 2 stroke with poppet valves) - the engine must have 2 inlet and 2 exhaust valves.

[/list]

Thus, while the maximum operating speed of a current F1 engine is ~12-13,000rpm, we could expect that the 2T would be no more than 6-7,000rpm operating condition, where the fuel flow is much less (59.5-68.5kg/hr).

So, in short, the normal 2 stroke advantages of lower weight and compactness are gone. A lower capacity to allow the 2 x BMEP "advantage" and maintain the rpm to a level where the full fuel flow allowance can be accessed is not permitted, nor can the configuration be changed to a 3 cylinder.

The 2 stroke would be as much, if not more, constrained by the rules than current 4 strokes.

[manolis]

Hello J.A.W.

You write:
“Manolis, I'd be interested to see your design shown stat above in metal “

The kinematic mechanism of the PatTwo harmonic is used in the PatRoVa 4-stroke Rotary Valve prototype (youtube video at https://www.youtube.com/watch?v=6Q-EGdeS0ws )



(more about the PatRoVa at http://www.pattakon.com/pattakonPatRoVa.htm )

A functional prototype is the normal way to proceed.

Yet, it is more challenging the theoretical “evaluation” / analysis of the “24 / 7 breathing” of the above “tuned exhaust at high revs” PatTwo Harmonic (that needs neither reed valves, nor rotary / drum valves).

For instance:
With the control-valve wide open,
the “crankcase-volume” appears as infinite (and the “primary compression ratio” as 1).
With the control-valve closed, the “crankcase volume” can be smaller than in any conventional 2-stroke.

Thanks
Manolis Pattakos

[manolis]

Hello Gruntguru.

You write:
“Road cars generally have not embraced 2T:
1. Traditionally due to oil burning, HC emissions, uneven idle and cruise etc.
2. Modern 2T tech has fixed all the above problems but not the issues of excess air, NOx and reduction catalyst incompatibility.”

The excess air (lean burn) the Diesels operate normally, makes them ideal for two-stroke road applications.

If the lubricant oil is removed from the combustion chamber, a 2-stroke Diesel has several reasons to be more green and fuel-efficient than a 4-stroke Diesel.

It seems that the high specific-lube-consumption (and the problems it causes) in combination with the poor scuffing resistance are the main issues before the 2-stroke Diesels to dominate in cars, in trucks and even in motorcycles.

Regarding the specific-lube-consumption and the scuffing resistance, the PatPortLess 2-stroke engine:



(more at http://www.pattakon.com/pattakonPatPortLess.htm )

and of the PatMar 2-stroke engine:



(more at http://www.pattakon.com/pattakonPatMar.htm )

are better than those of the best 4-strokes.

Thanks
Manolis Pattakos

[wuzak]

Interestingly France, teh country with the highest percentage of Diesel cars, has started to change rules and tax arrangements to discourage the use of Diesels in cars.

I can only assume it is to do with particulates?