ESE's works engine tuner

[rgvbaz]

Attachment 260684

So, I had some free time and I tried to connect your discution on pressure waves with EngMod p.waveforms.
The above waves come from my test engine, at it's peak BMEP rpm.
In Honda RS, Yam TZ250 pre-loaded engines as well as the (~)RSA engine I have in EngMod, at the encircle point, TFR pressure is still above 1.

I added some letters to indicate points -me thought- of importance. Please correct me when I say something wrong in the following:

A: Ex port opens, flow starts there, pressure rises (why?). cylinder pressure starts dropping (still relatively too high). Tfr pressure irrelevant to Ex/Cyl pressure.
B: Ex pressure tops, flow speed tops. Cylinder pressure still dropping, gases exit. Tfr oscillate and starts rising, due to case/inlet pressure action.
C: Big depression in pipe, Ex pressure drops. Cylinder pressure drop dramaticaly, gases still exiting. Tfr open, pressure still rises.
D: Tfr pressure tops, start falling.
Blanks -lots of- follow.
E:
F:
G-K: Tfr pressure below 1. No flow?
K: Returning pulse from pipe arrives @ ex port, pressure starts rising. momentarily after, cylinder pressure starts rising. Tfr pressure rises a little more (flow?) before closing soon.
L: Ex pressure tops, a few degrees before closure. cylinder pressure rises, piston compressing hard. Tfr (closed) oscillation due to case/inlet action.
M: Ex pressure oscillation due to pipe action. cylinder pressure rises, piston truly compressing.
N:

Not much, but I have no head to combine every part's action into more analysis right know.

Hope I had a few right's above..
It would be very interesting to know what happens to TFR pressure and it falls at [C,F]. Also at [G,K] and their impact on flow.
(sorry, I ate a few letters after G - brains are pulverised as I said).

Have you ever read sae paper 2001-01-1853?

Its by Blair I think to sell virtual2T software. It looks at optimising a chainsaw engine using a tuned pipe. There is a good discussion on how to interperate the simulator output in there. Vanniks software can show most of the outputs he uses from the Virtual2T simulator. I found the part about left and right pressure exhaust waves very interesting (the left and right exhaust pressure waves combined give the superposition exhaust pressure; the pressure read by a pressure transduser - they themselves (left and right waves) cannot be measured (well appart from the single shot apperatus at QUB))

The exhaust pressure from your engmod screen shot is the superposition pressure. If you use Post2T you can look at the individual left and right waves and their influence on flow.

Dave.

[kiwifruit]

Far out, who knew bucket racing was so serious!

[richban]

Far out, who knew bucket racing was so serious!

Tis the pinnacle buddy.

[jasonu]

Far out, who knew bucket racing was so serious!

You're havin' a laugh right?

http://www.youtube.com/watch?v=1SK3y1a8TYs

[kiwifruit]

I like a laugh

[husaberg]

I like a laugh

Hence your er..."Love" of your bike in your avatar
The bike doesn't look so amused.Possibly because by the looks of it, your really only a 2 stroke guy ..

[Kickaha]

Far out, who knew bucket racing was so serious!

It is the "Premier class" just look at the numbers on the track at Taupo compared to the poofters on Superbikes

[kiwifruit]

Yeah, it certainly is an exciting class! I look forward to taking part more.

[bucketracer]

There's been a bit of discussion about crankcase volume and compression. My view, as explained to me by Wobbly, is that the crankcase is just somewhere to store fuel and air before the transfers open and it is sucked out.

Nowadays an engine needs a large crankcase volume (the Aprilia RSA125's is 675 cc at TDC),

So its true, on a well developed race engine, the crankcase is less a pump than a place to store fuel and air before the transfers open and it is sucked out.

[husaberg]

So its true, on a well developed race engine, the crankcase is less a pump than a place to store fuel and air before the transfers open and it is sucked out.

I just read my origional post that Frits responded to and i see it had a rather crude spelling mistake that may have confused as it would not have translated so well to Dutch the French word "reservoir" pardon my engerishThis is a neat word to describe what bucket is saying above.

Does that make more sense Frits.
The bit i was quoting from Robinson was referring to when a engine was tuned to a higher rev range than it was original to maintain the original pumping efficiency you reduce the volume by an amount specified (inversely proportional to the square root of the original crankcase volume) to match the new higher rev range.
assuming say you don't want to modify the angles and shapes of the transfers or if you have say downsized or upsized an engine?

however Robinson does a couple of chapters later say

"bearing in mind at higher revs there is less time for the scavenge process to take place,
The choices are"

1)high stream velocity

:High crankcase compression
:Narrow port windows
:Late timing (Long blow down period)

2)Low(er) stream velocity

:earlier timing,larger ports
: Direction(s) of streams become critical.

So i guess he had a ball in both courts as it were. but the 2nd option is the modern approach?or slightly different again?

[bucketracer]

...before the local fools start replying ....

how about this. Do you know of any material (preferably not web based) that can accurately quote the VE of a performance two stroke?

I maintain that a performance two stroke IS MOST CERTAINLY NOT "SUPERCHARGED".

A 2-Stroke is not supercharged by its expansion chamber?



From an EngMod2T simulation run. Does a "Delivery Ratio" (VE) > 1 indicate supercharging?

[Frits Overmars]

I just read my origional post that Frits responded to and i see it had a rather crude spelling mistake that may have confused as it would not have translated so well to Dutch....Does that make more sense Frits?

It already made (some) sense the first time; as a former technical editor I am used to reading what people try to write instead of what they are actually writing.
And I do not translate anything to and from Dutch; In my mind I stick with the language that is being used.

The bit i was quoting from Robinson was referring to when a engine was tuned to a higher rev range than it was original to maintain the original pumping efficiency you reduce the volume by an amount specified (inversely proportional to the square root of the original crankcase volume) to match the new higher rev range.

Crankcase pumping only serves to start the engine; once it is running in the power band you can forget all about pumping efficiency.

...high stream velocity >>> Narrow port windows

Why don't we then close the port windows completely? That should give us infinite stream velocity, right? Yeah, right.... If you want velocity, you need a pressure differential. But we do not want velocity per sé; we want mass transportation (no, I'm not talking about public transport) so that means ample time.areas.

[wobbly]

Supercharging by definition is a method to increase the efficiency of an engine by using an external device that creates a higher delivery ratio,than that able to be achieved by the swept volume alone.
This can use energy within the Exhaust gas flow as is done by a Turbocharger.
It can use crank power to drive a pump, that creates more power at the crank than it consumes - a Supercharger.
Or - you can use sonic wave action in a divergent/convergent pipe,that uses that energy to evacuate and then refill the cylinder to a higher level than the swept volume alone could achieve - a Sonic Supercharger.
Next is Chemical Supercharging - where the fuel contains excess oxygen than that contained in the swept volume of air.

[speedpro]

Yeah, right....

You have Tui billboards over there?

[dinamik2t]

Thanks for pointing out the paper Dave (rgvbaz) - and Wob and Frits for the replies. I like papers -sae or others- but in my opinion knowledge acquired from such papers isn't cost efficient; at least for a student like myself. There are so many stuff I would like to read and multiplied by 23$ is a lot of money!
I am not saying researchers (hopefully part of the money goes to them) don't worth it, but unless you 're into it professionally (or be a banker's nephew) it's hard to spend all that $$.

I would prefer a more .. libraric system; get permission to study a paper eg for one hour for 2$. If you find it that usefull buy it now or another time.