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.

 

[BrianPetersen]

Curtis, see my post a few above yours; all automotive diesel engines already use intake ports with a strongly helical/spiral shape in order to encourage swirl. This swirl most certainly gets maintained all the way through the compression stroke.

NOT having swirl will absolutely kill the combustion efficiency of a direct-injection engine. But the way to generate swirl is by the bulk shape of the intake ports, not by a wee bit of roughness in the surface.

 

[curtis74]

Brian.. I had read that and agree. My thought was that increasing any existing swirl could help, but I also said, "I'm not entirely sure you'll notice a measurable difference."

We're on the same page, just different words.

 

[tbuelna]

Swirl is intake charge motion about an axis roughly parallel to the bore axis. Tumble is intake charge motion about an axis roughly perpendicular to the bore axis. Squish is the high velocity, turbulent motion resulting from the intake charge being forced out of the rapidly narrowing space between piston crown and cylinder head at TDC and over the combustion chamber bowl ledge.

As others have noted, current engine design practice is to use tangential or helical intake port geometries. In the past, some have attempted to use shrouded intake valves, but these must be prevented from rotating. There are also instances of using a throttle on one port of a four valve engine, in order to increase swirl at lower engine speeds.

The use of intake swirl in an OHV, DI diesel, piston engine is used to compensate for deficiencies in most injector spray nozzles. If the injector nozzle had an infinite number of holes that produced a fuel spray pattern which yielded instantaneous, perfect mixing of fuel and oxygen, then intake charge swirl would not be necessary. Nor would it even be desirable, since the swirling motion increases the rate of heat transfer and thus is somewhat detrimental to thermal efficiency. Modern ultra-high pressure common rail injector systems, utilizing multiple pre-injections, are very good at distributing a very fine spray of fuel throughout the intake charge. Thus the need for intake swirl to promote mixing is much reduced.