superDorifto wrote:LOL engineer speak...so the delta P is really driven by the fact the the air to water coolers are so damn efficient? I'll be honest, I can't remember anything from my thermo classes other than power cycle calculations for silly things like ideal power plants and turbines. And I've searched for topics and discussions in other forums about charge cooler design and plenum design but have come up empty.
They are efficient because they shed heat faster due to the proximity of water to the exchanger surface and the thermal capacitance of water itself, and because of that efficiency they are physically smaller which takes less time to fill, etc.
superDorifto wrote:My main concern is keeping the flow through the core as laminar as possible, and not creating a series of plenums that drive pressure variations across the cylinders.
Laminar doesn't exist in all those bends, through the compressor, etc. The flow is massively turbulent and will eddy at every bend. The diffusion angle of the cooler itself is going to cause separation. From a micro level the flow is constantly being pulled and reflected due to helmholtz resonance and the general elasticity of the air. The idea is to minimize loss, gain density, and see what happens.
As it is the charge exiting the screws is well above .3 Mach, it hits the wall at the far corner of the blower, changes direction, fills the plenum under the plate...fills the space in the runners, and waits patiently for a valve to open. I am adding 2 additional plenums, and potentially diverting/recombining the charge as it exits the cooler.
The air is compressed due to the diffusion of the velocity, so yes, it will achieve well over Mach at one given point. Turbochargers spin up around 150 - 300K RPM and the velocity vector is incredibly high. That's why they have the A/R scroll housing to diffuse the velocity into pressure. A roots blower relies a bit more on it's shear size and brute force to cram air into the engine, and that's why they are less efficient apart from using direct engine power to turn a gearbox or drive screw.
I'm hoping the having 1/2 and 3/4 grouped together either with seperate plenums, or with baffling will minimize any pressure variations because of the alternating intake events. I'm thinking that each "side" of the plenum will have enough time to stabalize to a consistent charge to each cyl.
When BMW engineers have told me that they simply can only guess at the fluid dynamics within an airbox I assume that means we have no possible chance in hell of really gauging what is going to work apart from trial and error. The OEM manifold on the engine is specified to deliver a VE boost at a particular RPM window, and in the case of extremely high revving engines, they can have two moments of increased VE due to 2nd and 3rd level harmonics.
I would run a single plenum unless you are going to run management that allows you to trim individual cylinders. It's more simplistic and quite honestly you're going to have to link near firing cylinders on the floor of the plenum to really seek a benefit from resonance tuning. Look at the airbox and horn designs on F1 engines, they will often share two cylinders to allow the wake to spill over into the neighboring cylinder and promote a higher chance of a high pressure or moderate pressure moment prior to the valve opening.
Plot significant lift moment as a function of a specific RPM for all 4-cyls with crank degrees expressed on the X-axis. It'll expose where you need to theoretically shift the runner length and plenum volume, but theoretical is just theoretical, it still involves alot of testing and theory rework.
superDorifto wrote:I would hate to have 2 cylinders run rich, and 2 constantly running lean.
I don't think you are going to have that problem.
As far as a velocity gain, the only place to even think about puting a venturi or a restriction would be after the cooler its self. accelerating the charge through the cooler would lower the efficiency of the cooler. either way this thing eats up 8-9 inches of runner length along the spline of each runner. That venturi would be right before the fuel injector....
I'd just avoid all of that and stick with simplicity. Control what you can realistically and simplistically control.