Naturally aspirated manifold positive pressure

[CapnBoost]

Volumetric efficiency - Wikipedia, the free encyclopedia

I hate wiki with a passion when discussing actual tech. I don't suppose you know of a place online that discusses the method of approaching 120% VE?

Because air is squishy..

Yes, but that doesn't explain how a n/a engine could create 10psi of manifold pressure, even as localized as the valve.

[LeonOfTheDead]

I hate wiki with a passion when discussing actual tech. I don't suppose you know of a place online that discusses the method of approaching 120% VE?.

basically, you need to the design the manifold so that the air speed can be as high as possible, then you have to calibrate the valve timing so that the intake valve opens when the exhaust valve is still opened. in this way the flux of combusted gas going to the exhaust will lead to a general movement of air from the cylinder/manifold to the exhaust line. this period has to be long enough to create this effect but also short enough so that the air from the intake doesn't go in the exhaust directly.
on racing cars that efficiency (120%) isn't really surprising me, but on road cgoing cars, IIRC from my studies, you gain as much as 3-4%.

[Alastor]

I hate wiki with a passion when discussing actual tech. I don't suppose you know of a place online that discusses the method of approaching 120% VE?


Yes, but that doesn't explain how a n/a engine could create 10psi of manifold pressure, even as localized as the valve.

There are a lot of obscure ways to get better performance out of the engine, too bad Hightower was banned because he would probably already have 10 posts in this thread with shit no one has ever heard of.

For the increase in VE there are methods for maximizing the intake charge momentum so that even after the piston reaches BDC fuel is still being driven into the cylinder.

It is basically the same effect as exhaust scavenging except it is for the gases moving into the cylinder. Now that I think about it exhaust scavenging would also drive up the VE. So using these techniques it is probably possible to get a VE well over 100%, but it is probably going to be over a very narrow operating range. I would guess the greater the increase in VE the smaller the operating range.



For creating pressure in the manifold I have read about a technique to use pressure wave resonance to optimization the pressure when the valve opens.

It worked because the intake charge develops momentum as it is pulled into the cylinder. When the intake valve closes the intake charge outside the cylinder has to come to stop against the intake valve, as it comes to a rest the velocity is turned into pressure (momentarily).

If the valve now opens again while this pressure is still high, then this will increase the amount of intake charge that will fit into the cylinder.

But I have also heard that the pressure wave the builds up doesn’t sit next to the valve. Instead the pressure wave bounces off the intake valve and propagates away from the intake valve. However, if the manifold is designed correctly it will bounce back towards the intake valve and timing should be such that the intake valve opens just as the pressure wave reaches the valve again.

[LeonOfTheDead]

For creating pressure in the manifold I have read about a technique to use pressure wave resonance to optimization the pressure when the valve opens.

It worked because the intake charge develops momentum as it is pulled into the cylinder. When the intake valve closes the intake charge outside the cylinder has to come to stop against the intake valve, as it comes to a rest the velocity is turned into pressure (momentarily).

If the valve now opens again while this pressure is still high, then this will increase the amount of intake charge that will fit into the cylinder.

But I have also heard that the pressure wave the builds up doesn’t sit next to the valve. Instead the pressure wave bounces off the intake valve and propagates away from the intake valve. However, if the manifold is designed correctly it will bounce back towards the intake valve and timing should be such that the intake valve opens just as the pressure wave reaches the valve again.

about the last thing of the pressure wave, it doesn't really work in the intake. the better results are seen at the exhaust.

[Matra et Alpine]

As, the problem with the intake is for it to be at all useful the system has to vary the intake to match the engine revs and speed of the fuel/air mix. The ultimate being the massive adjustable trumpets on the Mazda 787B Le Mans racer

[LeonOfTheDead]

As, the problem with the intake is for it to be at all useful the system has to vary the intake to match the engine revs and speed of the fuel/air mix. The ultimate being the massive adjustable trumpets on the Mazda 787B Le Mans racer

IIRC Audi has a double manifold for their turbocharged petrol engines. the shorter one for low revs (so to improve torque), the longer one for higher revs (power), but I could have messed up and perhaps it's the contrary.

[Matra et Alpine]

The hi-power RX-8 has that. But now it's only optimal at two times

[Knuto]

IIRC Audi has a double manifold for their turbocharged petrol engines. the shorter one for low revs (so to improve torque), the longer one for higher revs (power), but I could have messed up and perhaps it's the contrary.

Its the contrary i think
Since the speed of sound is ~constant you need shorter pipes for higher revs since the time is shorter for the compression wave to return to the valve at higher revs.

When tuning the intake pipes you get peaks and throughs in torque through the rpm range. For example
-peaks: 4000 8000 16000rpm
-throughs: 6000 9000 12000rpm

Then you time the exhaust waves so that you get
-peaks: 6000 9000 12000rpm throughs:
-throughs: 4000 8000 16000rpm

What you end up with is a smooth tourqe curve. 0.3 bar (4.3 psi) gauge pressure for the intake compression wave can be seen IIRC. But in this case 10psi~0.7 bar. This seems high. You can also use the effect of resonating plenum and timing the different cylinders together, but this gives lower pressure differences->lower gains. In a an engine analyzing tool i think i saw VE of 140% on one engine. VE>100% is quite normal i think

Leon, you spoke of overlap scavenging. I think that is less used in a lesser degree in road cars since it quickly gives a rough idle if the overlap becomes big. On racecars the overlap is very large and gives good hp gains, but very rough idle (F1 idles at 4-5000rpm right?)

This was on top of my head so please correct me if im wrong

[LeonOfTheDead]

Its the contrary i think
Since the speed of sound is ~constant you need shorter pipes for higher revs since the time is shorter for the compression wave to return to the valve at higher revs.

When tuning the intake pipes you get peaks and throughs in torque through the rpm range. For example
-peaks: 4000 8000 16000rpm
-throughs: 6000 9000 12000rpm

Then you time the exhaust waves so that you get
-peaks: 6000 9000 12000rpm throughs:
-throughs: 4000 8000 16000rpm

What you end up with is a smooth tourqe curve. 0.3 bar (4.3 psi) gauge pressure for the intake compression wave can be seen IIRC. But in this case 10psi~0.7 bar. This seems high. You can also use the effect of resonating plenum and timing the different cylinders together, but this gives lower pressure differences->lower gains. In a an engine analyzing tool i think i saw VE of 140% on one engine. VE>100% is quite normal i think

Leon, you spoke of overlap scavenging. I think that is less used in a lesser degree in road cars since it quickly gives a rough idle if the overlap becomes big. On racecars the overlap is very large and gives very rough idle, F1 idles at 4-5000rpm right?

This was on top of my head so please correct me if im wrong

(didn't know you were into this kind of technical stuff )

first of all, F1 idles at 7.000 rpm IIRC.
about overlap scavenging (didn't know the english words ), it wasn't very used in road cars, but VVT has helped a lot in this field. obviously, we are considering sports cars and the likes, no Fiat Panda. otherwise, your considerations are all right.

[Knuto]

(didn't know you were into this kind of technical stuff )

first of all, F1 idles at 7.000 rpm IIRC.
about overlap scavenging (didn't know the english words ), it wasn't very used in road cars, but VVT has helped a lot in this field. obviously, we are considering sports cars and the likes, no Fiat Panda. otherwise, your considerations are all right.

Oh yeah thats right

I'm on my 4th year in engineering. Material science. And i love reading about engines when i get the chance. Do you study auto engineering?

EDIT: BTW, im studying for italian exam right now, do you have any online radiostation or italian music to suggest??

[LeonOfTheDead]

Oh yeah thats right

I'm on my 4th year in engineering. Material science. And i love reading about engines when i get the chance. Do you study auto engineering?

EDIT: BTW, im studying for italian exam right now, do you have any online radiostation or italian music to suggest??

yep, but I'm considering leaving Modena for a better place. do you know of any good automotive engineering course? I think its time for the thread I was thinking of since quite some time.

Actually, I don't listen to the radio , and I can't even suggest a good Italian car site (because they all suck, like "we are the best because we have Ferrari, Lamborghini..." and the usual mindless stuff). perhaps you can have a look at Quattroruote as a car site it sucks, but it's better than nothing.

[Knuto]

yep, but I'm considering leaving Modena for a better place. do you know of any good automotive engineering course? I think its time for the thread I was thinking of since quite some time.

Actually, I don't listen to the radio , and I can't even suggest a good Italian car site (because they all suck, like "we are the best because we have Ferrari, Lamborghini..." and the usual mindless stuff). perhaps you can have a look at Quattroruote as a car site it sucks, but it's better than nothing.

I havnt really attended any auto courses, only self-study when i get the time. Go ahead with your thread man, it would be very nice to get some more info on the typical auto study. At my uni theres no automotive engineering, but there are some courses on diesel propulsion systems and ICE, but they are really only introductions (PV diagrams, different components, dynamics etc), and mostly towards large ship diesels.

lol. I guess they butchered the R8 then... I read some italian magazines while working in Croatia this summer. Didn't seem so bad judging by the pics, but I didn't understand much. Any music to recommend then? Tried to get a hold of the movie "Un bellissimo novembre" (33 Stradale), but proved a little difficult.

Thanks for the link btw

[LeonOfTheDead]

I havnt really attended any auto courses, only self-study when i get the time. Go ahead with your thread man, it would be very nice to get some more info on the typical auto study. At my uni theres no automotive engineering, but there are some courses on diesel propulsion systems and ICE, but they are really only introductions (PV diagrams, different components, dynamics etc), and mostly towards large ship diesels.

lol. I guess they butchered the R8 then... I read some italian magazines while working in Croatia this summer. Didn't seem so bad judging by the pics, but I didn't understand much. Any music to recommend then? Tried to get a hold of the movie "Un bellissimo novembre" (33 Stradale), but proved a little difficult.

Thanks for the link btw

believe me that magazine is rubbish.
btw, music...I don't listen to Italian music either, too girly and it all sounds the same. for as regards movies, I could recommend "Io non ho paura" and "Mediterraneo" by Gabriele Salvatores, or the recent "Gomorra" by Matteo Garrone. The problem is that movies (and music too) contain a lot of "slang", that's to say "dialetti", different languages developed behind Italian in each part of Italy. and when I say part, I mean very small area. the "dialetto" that is spoken at my place is slightly different in the near town, at 20 km...

[Knuto]

believe me that magazine is rubbish.
btw, music...I don't listen to Italian music either, too girly and it all sounds the same. for as regards movies, I could recommend "Io non ho paura" and "Mediterraneo" by Gabriele Salvatores, or the recent "Gomorra" by Matteo Garrone. The problem is that movies (and music too) contain a lot of "slang", that's to say "dialetti", different languages developed behind Italian in each part of Italy. and when I say part, I mean very small area. the "dialetto" that is spoken at my place is slightly different in the near town, at 20 km...

Good, thanks. I think i know what you mean. It frequently occurs that norwegians don't understand my dialetto, even 20 km away. I'll check out the movies. I watched Ronin with dubbing the other day, didn't work that great for me, will be better with the real deal.

So what courses have you had so far in terms of automotive subjects?

[LeonOfTheDead]

Good, thanks. I think i know what you mean. It frequently occurs that norwegians don't understand my dialetto, even 20 km away. I'll check out the movies. I watched Ronin with dubbing the other day, didn't work that great for me, will be better with the real deal.

So what courses have you had so far in terms of automotive subjects?

up to know a very few: one about internal combustion engines, diesel engines, common-rail system, turbo/supercharging, direct injection, and emissions. in another one there were some calculation about forces acting on the various part of the engine, tensions, max loads of singular components, and some more about connecting rods and pistons.
in another we studied a lot about cam systems, including the design of a cam (f***ing damn difficult) without the help of a computer, just math.
something about ECU too, but I will do that course in spring.
not much up to know, the main stuff is going to be in the second part of the degree (university is split in two part: first and second degree, 3+2 years, if you are a genius without any kind of interest or social life).

EDIT: a good recent movie is also "Il Divo" by Paolo Sorrentino