INTAKE FLOW 4

[thundair]

Does any one know the advantages of tumbling at the valve for an intake charge?

I and others I know were all looking for vertical and horizontal swirl.

Cheers

 

[iolair]

Depending on the inlet port/manifold geometry the decending piston can generate kinetic flow energy within the port to produce a vertical twin counter rotating vortices of various intensity within the operating cylinder. The vortices help mix the air/fuel molecules more completely....a process that continues after the intake valve closes and they also help in filling the cylinder by delaying port/cylinder pressure equalization after the piston rounds BDC....the old ram effect. Obviously this all works best in a narrow operating range.....but if you could magically alter port geometry at each data point over a broad operating range.....this would be all good.

 

[thundair]

iolair

Sounds familar to F1 technology

I was able to have a brief contact with one of the engineers on the Gen lV Chevrolet engine and after looking at my high port design with converging walls, I thought he would be impressed. Not so.. His comment was that it was old technology and the new was to tumble the mixture into the chamber. I am stuck

 

[globi5]

Actually tumbling air when it enters the combustion chamber is old technology too.
Saurer patented and produced this 1937 already and increased power by 15% compared to their previous diesel engines. The intake valve had a vane such that it would give the air entering the combustion chamber an extra twist.
Go on

http://www.uspto.gov

and search for: Patent No. 2,205,493

 

[iolair]

I got my stuff from Ricardo, cira 1919 or so. : )

 

[Marquis]

In my experience there are two distinct types of motion within the cylinder, tumble and axial swirl and it's possible to have a combination of both.
Tumble will tend to decay into smaller eddies that lose momentum as the piston approaches TDC. It will also be most apparent at the "wrong times" during the 720 degree cycle: some engines it occurs strongly around peak valve lift and in others (where valve shrouding has been made deliberatetly to create tumble) it occurs at low inlet valve lifts.
Swirl can be imparted to the inlet charge with staggered inlet cam profiles (on a combsution chamber with twin intake valves) or by valve deactivation or perhaps with port de activation. It doesn't decay as much when the piston reaches TDC and there will be plenty of motion within the cylinder when the ignition point is likely to occur.

Increased cylinder motion WILL improve combustion burn rate. However this will have minimial impact on fuel economy and performance directly (if anything it detracts from full load peformance- but more on that later). the increased motion can be MADE to work for you in terms of part load fuel economy by being able to withstand more EGR (retaining a more stable combustion with more dilution with an inert gas such as EGR). Similar story for lean bun at part load without going so readily into misfire.

There is also a benefit to having more charge motion in during catalysts warm up- on spark ignition engines- where by alot more ignition retard can be dialed in without combustion stability decaying as much. This is invaluable when you're trying to get your car through emissions.

Detriment is that tumble or swirl illicited solely by the intake ports WILL have a negative effect on full load performance- whereby momentum is being used up in the charge motion within the cylinder- rather than getting the air in. (i.e your port flow coefficients ill be adversely effected) .A varaible device of some sort would be helpful and indeed many have been patented.

 

[NickE]

The current generation of subaru H-4 has TGV's (Tumble generator valve) in the intake runners directly off the head. This is approximately half of a butterfly valve, there are drive units and position sensors also. They only are active (IE: perpendicular to the flow) when at cold start, and immediately move to full open when the pedal is touched.



Nick
I love materials science!

 

[thundair]

TO All

Would it be advantages to move the intake short side radius away from the cylinder wall to induce tumble without fighting the eddys coming off the cly wall as the piston comes up to TDC?


Marquis

Thanks for all the info

Could you help the project with


"Swirl can be imparted to the inlet charge with staggered inlet cam profiles"

Pardon my brain blanks but how do you stagger inlet on a two valve?

"where valve shrouding has been made deliberatetly to create tumble"

What is that configuration that is engineered into the head to cause tumble? side squish,bathtub,hemi?


Regards

 

[mattsooty]

thundair,

It quite feasible in a DOHC engine to grind 2 separate lobes per cylinder on each cam. In this case for the inlet cam 1 of each cylinders valves will have a slightly different MOP...

This system will impart swirl but there are penalties at cold start and warm up idle. Swirl often causes the charge to wander wide of the spark plug. With very large and cold boundary layers this motion can cause partial fire to occur with subsequently high CO/HC emissions and high engine roughness caused by cycle to cycle variation.

MS

 

[Marquis]

Thundair

"where valve shrouding has been made deliberatetly to create tumble"

What is that configuration that is engineered into the head to cause tumble? side squish,bathtub,hemi?"

I've seen it done on Pent roof chambers but I don't see why it can't be done on, say a Hemi. The chamber is "closed" with , say, squish near the intake valve(s) near the bore. This is done so it shrouds the inlet flow -partcicularly at low valve lifts. At low valve lifts this will cause a larger proportion of the air to go over the more open-less shrouded side of the valve.

There will be less tumble as the valve lifts higher and the short side gets less shrouded. This is perhaps not very elegant solution and this WILL impact on outright flow coefficient.

 

[thundair]

I am now working on a 8.2L V12 off shore boat power plant
and the lead on the engine has followed F1 technology as applicable to the project. No pneumatic valves but port design is straight, with no bowl and no short side radius, although it is a converging tract. I cant wait to see it flow as soon as we get the software to do the virtual dynamics.

I feel that the word tumble may be the same as my understanding of vertical swirl

 

[globi5]

thundair,

Here's a link with pictures showing different intake tumble approaches:

http://www.kfztech.de/kfztechnik/motor/brennverfahren.htm

http://www.autozine.org/technical_school/engine/petrol1.htm

It generally appears to be more crucial with diesel and fuel direct injection engines, since fuel droplets have less time to mix.

Honda has been using the staggered inlet valve opening on its vtec-e engines since the early 90's.
But they only use the staggering concept at partial throttle settings. At full throttle both inlet valves open equally to increase airflow.
I remember reading an article about it over 10 years ago, but couldn't find an appropriate link.

http://www.insightcentral.net/encyclopedia/envtece.html

So valve shrouding might not necessarily be appropriate if you want to maximize power output on an off shore gasoline power plant. (Note that VWs FSI uses an extra throttle (tumble flap) to cause a tumble motion only at partial throttle as well.

http://www.audiworld.com/news/01/iaa/fsi/at010030.jpg)

 

[thundair]

Thanks to all I think Ive got it now.
I may revisit some old designs to see wich worked well and where they worked best..

Regards