Originally Posted by Flettner
Its not hard to get HCCI just hard to make it useful.
Highway Biker
Its not hard to get HCCI just hard to make it useful.
Highway Biker
Thats just too funny you guys. You got me there Frits. The gullible test would not work on my computer. Probably time for an upgrade.My grandfather is in no way involved, Husa. In other words: drop the Mr.
Would you please remove the phone number Husa? You can leave my bank account details. Thank you.
EDIT: Sh*t! That is the number of my swiss account. Please remove immediately!
Forum whore
Re the twin Vs single pipe testing.
The only time I have seen a single pipe beat out the twins is in a very specific application such as a freestyle jetski.
In this setup the single pipe is capable of generating alot more initial Hp below the natural powerband of the engine - and this
is exactly what is needed to do backflips etc from nil water speed.
But in enabling this to work, a huge amount of what would be regarded as normal "top end " is sacrificed.
I did experiment quite extensively with headers that had an interconnecting pipe, and even ended up trying a servo controlled
butterfly flap plate to control the interaction,but finally conceded that if I spent enough time working on the "normal " pipe design
I could get a better final result.
ie not worth the effort in the end.
Re the cutaway piston on the Ex side idea.
This was developed as a cheat in Jetski stock class racing ( yes it won several World titles as the tech guys never found it ) and the cutaway started with around 1/2
the duration of the transfers.
We spent so much time to then re calibrate the pumpers, that the duration was never changed after that.
It needed really severe reverse jetting ( that we had anyway ) but the big increase in top end power was for sure worth the risk of being thrown out of tech.
Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.
Highway Biker
So I think you are saying the exhaust port is open to the crankcase from about 30-35 BTDC to 30-35 ATDC ? With a 2:1 there likely would be a vacuum in the exhaust port at this time because of the 2 cylinders tied together with one pipe. But the AF mixture that gets pulled out of the crankcase into the exhaust port would never be returned to the crankcase (I think), so is it just the extra draw on the crankcase (that is piston plus exhaust) that makes the difference, or is the raw AF going into the exhaust port lighting off and increasing the pipe gas temp, or both, or something else. I guess what I am curious about is what is the theory behind the results.
Hardcore Biker
My bad, I had been blinded by 4-stroke simplicity when I wrote these lines.Scavenging efficiency is about equal to boost pressure on a 4-stroke, but not on a two-stroke. Let me explain:
In the paper on HCCI they achieved HCCI combustion up to 16 bar BMEP on a 4-stroke engine charged to 3bar absolute pressure.
On a naturally aspirated 4-stroke engine, a scavenging efficiency of about 1 is common for most car engines, so that each cylinder burns about the volume it displaces.
Charge that with 1 bar above atmosphere and your engine will now burn about twice the volume it displaces.
Charge it with 2 bar above atmosphere as in the linked paper and - you guessed it - it will burn roughly 3 times the volume it displaces.
So, scavenging efficiency is about equal to absolute boost pressure for the 4-stroke.
As the formula for BMEP is not the same for 4T and 2T engines, this correlates to 8 bar BMEP on a two-stroke - and this is where I should have expressed myself more thoroughly - it correlates to 8 bar BMEP on a two-stroke which is supercharged so much that it reaches a scavenging efficiency of 3. As a good two-stroke engine with an expansion chamber exhaust pipe can reach a scavenging efficiency of 1.5, the results of the paper correlate to 4 bar BMEP on a two-stroke engine with an exhaust pipe.
And from 4 bar to about 16 bar is still a long way to go. And this is why I can not see full load HCCI on the Ryger engine.
Highway Biker
I believe this part is incorrect. Its more or less 16 bar for both, only the 2 stroke would make twice the HP at the same BMEP.
16 bar is incredibly pitiful for 2 atmospheres of boost with regular spark ignition, and HCCI is supposed to be super efficient combustion. It would be hard to even make a regular engine run so bad that it only made 16 bar with 2 atmospheres boost, (like maybe shut the ignition off for 2 out of every 3 times the plug fires). The HCCI engine must have been extraordinarily lean with a lot of exhaust gas taking up precious space too.
Forum whore
I think that as the piston on the downstroke approaches BDC, and the diffuser starts to create a depression in the header, then the other piston is
approaching TDC and the cutaway exposes that case to this negative pressure ratio.
This increases the delivery thru the reeds around TDC for that cylinder, creating more bulk flow and carb velocity that continues for longer as that piston drops.
Then as the return wave starts to appear in the header, some of that excess mixture is returned ( or the out flow is at least slowed down ) as the cutaway piston
then closes the port on its downstroke - just as the other piston is then ( as is normal ) closing its port on the upstroke.
Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.
Hardcore Biker
Well that is yes and no I guess. I don't think the two-stroke would be able to draw the same amount of air per cycle than the four-stroke with the same boost level. But it could if you would double the boost. So the proportions regarding the charging remain as they are, I'd say.
To be able to draw the amount of air needed to achieve 16 bar BMEP (2T) with the same (lean) HCCi combustion parameters as in that paper, the Ryger would need to be able to draw 4 times the air per cycle as the RSA! I can not imagine how this can be done with an expansion chamber only.
I agree with you on the numbers of 16 bar being lousy for 2 atm boost. But it may be really good in terms of BSFC. But much more power could be achieved by running richer and with conventional combustion. The same would be valid for the Ryger, there would be no point in running HCCI if your after hp.
Forum whore
Why? Just because it hasn't been done doesn't mean is can't be done. I'm sure there is a way to control it, and I'm going to have a go at it, the more I read the more interested I become. Now where is that old AG 100 engine under the bench, all I need to do is tie the gas set to it, take the plug out and volare
Highway Biker
I think 16 bar limitation on the 4 stroke was based on having X amount of air and exhaust in the cylinder to make it run as desired, so a 2 stroke with that same X amount of air and exhaust in the cylinder should also near 16 bar, but yes it might take more boost to get that X amount of air and exhaust into a 2 stroke. A regular tuned pipe couldn't get that much into the cylinder or we'd all be riding 100+ HP 125 s with regular spark ignition that only turned 13000 rpm.
No matter a naturally aspirated HCCI making 14-16 bar doesnt exist as far as I can tell unless the Ryger has achieved it. It is fathomable that some unique condition exists allowing it at full throttle but then how would it be achieved at other conditions with just mechanical controls and likely non-moving mechanical controls.
Highway Biker
Were you able to determine where best to bring the headers together and what sort of angle the headers would have relative to each other where they meet?
Most people I know seem to think making the headers so that they come together at the least possible distance from the port, without undue bends is best. It seems to make sense, but I have also wondered if maybe not bringing the headers together until almost the large mid section of the pipe might work so that the pipe header and a lot of the diverging section work like individual pipes and the reverse cone reflects the two.
Building it like that you could say why not just build it single pipes because it would be halfway a single pipe anyway but I was thinking for when rules insist 2:1. Maybe build single pipes and connect the stingers but I think that wouldnt fly with the rules.
No8 Wire Extraordinaire
So how did Vegas go?
Don't you look at my accountant.
He's the only one I've got.
Forum whore
They call that cheating.
Scooter boy
Anything not specifically prohibited must be assumed legal until addressed by a rule.This gives a certain advantage to intelligent and innovative race teams. This will often draw whining from those who aren't. There is no "spirit" in rules,as this gives the power of interpretation the ability to decide a contest instead of skill on the part of the racer and team.
Forum whore
Yep damn right, it was cheating like hell - sadly, nowhere in the rules did it say that the piston length must remain stock.
But it was the team that paid me a shit load of cash to win a world title that made the conscious decision to do so - not me.
Its only a cheat if you get caught - if you dont, then some people are comfortable and dont feel guilty every time they look at the trophy.
Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.
There are currently 126 users browsing this thread. (0 members and 126 guests)
Posting Permissions
Reply With Quote
Bookmarks