Intake Valve Design(Diesel) 2

[CoersDiesel]

First of all I would like to state that I have read and learned a lot off of the threads on this site. There are many, very knowledgable people on here.

As for my question, I would like to know if machining grooves onto the surface, just as the valve area expands off of the stem and exiting at the top side of the seat, would promote swirl into the combustion chamber?

As mentioned in the subject, this is for a Diesel performance application with high boost. With a high fuel rate, I would like to promote better fuel to air mixing prior to ignition.

 

[CoersDiesel]

Here is a picture of a turbo billet compressor wheel that shows a similar groove pattern to that of which I am thinking of.

http://www.grayforge.com/axis/IMG_0759_zoomed.jpg

 

[CCycle]

Three things come to mind.
1. Any grove you could get in there probably would not make much difference.
2. You are removing material in a critical area needed for cooling conduction and strength.
3. Today's diesels are highly optimized. Any change in induction would probably get you off the optimum.

 

[CCycle]

We posted at the same time.
Nice job. You must have added material or made a new valve.
How did you do the machining?

 

[ivymike]

uh, that wasn't the valve.

 

[CoersDiesel]

Thanks for the replies.

Yes I do understand the strength and cooling aspect.

I was just thinking in terms of fluid flow and how to optimize the velocity off of the valve to fill the cylinder.

Yes, modern day diesels are optimized however that gets thrown out the door when you port and polish, lower the compression, significantly increase boost, and turn excessive rpms.

I am just trying to complete my thought process with either an ending or further research.

 

[patprimmer]

How will all the extra metal help. It wil hinder airflow and add weight to he valve.

Swirl at that point is mostly lost inside the cylinder.

Real useful swirl at the time the fuel is burning comes from chamber/piston shape and their interaction, or individual valve timing in a multi point, and port angle to bore axis.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[patprimmer]

The use o a decompression plate that reduces squish orquench area hurts swirl a lot.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[CoersDiesel]

Thanks for all the replies.

I am ending that thought process with a conclusion that primary swirl will be a direct result of piston bowl design while leaving the valve/port design for optimized flow into the cylinder.

 

[IceStationZebra]

Such small ridges would not have much affect especially when you consider that the airflow rushing past any quasi-static part will have turbulence along the part's surface. Then consider that any oil or soot deposits will fill they ridges in. Fuel mixing is a combination of swirl (or lack of it) and injector design. Low swirl engines need more holes, high swirl can get away with fewer holes because the swirl helps distribute the fuel.

I do not necessarily agree with your last statement that primary swirl is solely/mainly the result of the bowl design. Most bowls are symmetrical, which promotes turbulence not swirl. The port shape and relation to the bowl is what promotes swirl. Check the following web site for some interesting reads. They don't tell the whole story but you can glean some good info.

http://www1.eere.energy.gov/vehiclesandfuels/resources/fcvt_reports.html

ISZ

 

[MikeHalloran]

Hello? It's a Diesel.

You can't mix fuel and air prior to ignition ( unless you're "fumigating" with something like alcohol, and that's a whole other set of challenges ).

The Diesel fuel ignites as it's injected, or soon thereafter, when the blankety- blank thing is running anywhere near right.



Mike Halloran
Pembroke Pines, FL, USA

 

[IceStationZebra]

Hello?!? Hello?!?

Just because its a diesel don't mean it's stone age technology.... All of the diesel fuel does not ignite instantly upon injection. (If it did the injectors would melt!) The fuel cloud burns from the outside in, due to a lack of oxygen in the center of the spray. A certain amount of swirl is beneficial in breaking up this cloud.

So yes Virginia, some diesel fuel does mix with air prior to ignition.

ISZ

 

[patprimmer]

ISZ

I think ignition is the point when the fire in the charge is started not the continuing process.

The ridges in the picture were very big and certainly effective. My point is not effectiveness, but desirability at that point. s I said previously, they were a major obstruction to flow and increased valve weight. Also not previously said, they are stress raisers.

Also, my very rushed post about 5 up mixes some terminology up a bit and incorrectly uses swirl and turbulence interchangeably but I think the line of thought can be interpreted.


Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[CoersDiesel]

I appoligize for the misuse of the word "swirl". Obviously swirl is the rotation of air while turbulence is the tumbling of air.

I would like to think that depending on the size and location of the valve in relation to the bore and the port wall(s) in relation to the valve would promote the majority of the swirl although the piston bowl design would also have a role with the incoming air either reflecting off of or skirting through the bowl.

No, diesel fuel does ignite as it leaves the injector tip.
There is a short delay between injection and start of combustion. The cetane(ignition quality) value of the fuel and injection timing control combustion timing.

Yes, in larger engines swirl/turbulence are less important because the momentum and energy of the injected fuel jets are sufficient to achieve adequate fuel distribution and rates of mixing with the air. Smaller engines require more swirl/turbulence with less fuel jet penetration.

Yes, more well formed holes in the injector tip promote better atomization with help with fuel/air mixing. However, when injecting large amounts of fuel it is hard to keep the holes small due to the increasing load on the injection pump because of the restriction which can cause a plunger to stick.

 

[BrianPetersen]

Direct-injection automotive diesel engines have a helical shape to the intake port that induces a bulk swirling action as the air comes in from the manifold and moves down past the throat of the valve.

Surface roughness, whether deliberately (grooves like you are suggesting) or accidentally (by leaving the port surfaces as-cast) introduced, is only capable of producing small-scale turbulence which quickly gets dominated by the bulk flow inside the cylinder. At the end of the compression stroke, when the piston closely approaches the head and squishes a large portion of the total charge into the bowl, that intensifies the swirl and introduces far more bulk small-scale turbulence that will completely dominate whatever's left of the small-scale turbulence that came from the intake stroke. This is why the presence or absence of small-scale turbulence (from roughness) in the intake tract doesn't matter with a diesel. Gasoline engines rely on having some turbulence to keep the fuel suspended and encourage mixing in the intake port. Diesels have no use for that.

Nutshell summary, I don't think what's proposed is going to accomplish anything useful, and it'll probably just act like a bit of flow restriction, which runs counter to getting better performance out of the engine.

 

[CoersDiesel]

Thanks for your input and thats the conclusion I had come to after doing some deeper thinking on the matter. Especially since the fuel is not introduced until very late in the compression stroke, the air characteristics would be dominated by it.

 

[Lou Scannon]

CoersDiesel, in reference to your photo of the billet compressor wheel, the marks are naturally there due to the CNC machining process. What reason do you have they are there for any other reason?

 

[Lou Scannon]

Ummm, I meant to write "what reason do you have to believe ...

 

[CoersDiesel]

That was the closest picture I could think of that would mimick the idea that I was thinking of. I am not really versed on the design elements of compressor wheels, however I could see some benefits from the grooves in the form of adhesion and channeling of the air.

 

[curtis74]

Depending on the type of chamber in the piston, swirling air might help. If you can get the incoming air to swirl enough that it continues all the way through compression until injection it might help slightly.

I know what you're proposing; instead of injecting fuel into stagnant air, inject it into a turbulent stream. Kinda like stirring your coffee before adding the cream. If the air is swirling, the injection of diesel keeps hitting "fresh" air as its injected.

I'm not entirely sure you'll notice a measurable difference. The high compression of diesels along with the modern injection seems to work fine. I think it would have more beneficial results on an IDI engine. I think modern common-rail, high-pressure injection has all but cured that issue, but I'd really like to see the outcome of this. If nothing else, the turbulence should increase the flame front speed which could extend the effective RPM range.