Nozzle Flow Versus Pressure/Viscosity

Status
Not open for further replies.
Joined
Dec 12, 2002
Messages
43,886
Location
'Stralia
Been some debate around what drives nozzle flow for things like chain sprays and piston cooling jets...came across the following curves, so thought it might be fun to spend a lazy Saturday morning with Bernoulli and my new chart, along with some very good HTHS versus Oil Pressure data to see where it went.

Here's the correction curve for nozzles with viscosity, at constant pressure...calculate your flow using the appropriate equations, and apply the corrector...clearly viscosity changes the rate of flow through the nozzles...pick the 41 psi line, and you can clearly see that a 10cst oil flows 20% less than the theoretical, versus a 20cst flowing 40% less than a fluid with now viscosity effect...so at a constant 41psi, a 10cst oil would flow 33% more massflow than a 20cst oil (0.8/0.6).

viscosity-correction-factor.gif


However, next line up (172psi), clearly the lines are WAY closer together...both flow a lot more than the 41psi line, and the difference between them is 0.9/0.8, or 12.5%.

Which brings into topic another correction curve, this one isoviscosity lines versus pressure.

viscosity-correction-factor-v.gif


Can see clearly that at the range of oil pressures that are suitable for engine operation (say 50 to 100psi), there's literally no difference (there IS, but it's tiny) between the 5 and 10cst lines. There's no 20cst line, and given the exponential spacing, I'll decree that in the range 50-100psi, the correction is 0.95, nearly nothing but it's there.

So we've got the two curves, flow correction at constant pressure, and flow correction at constant viscosity.

But we KNOW that pressure in an engine changes with viscosity, and we have at hand some very comprehensive and handy data produced by CATERHAM, demonstrating that there is a strong correlation between HTHS and operating oil pressure...it's good research.

So I used those figures, and the corrections to get a theoretical spray volume for a 1.5mm orifice. the "95C correction" is to correct for density at the stated 95C test temperature

nozzle%20flow.jpg


And tried the same model for if there was a 10psi poppet valve in the circuit which some do...

Nozzle%20Flow%20Poppet.jpg


Given that the KV DOES influence flow by the tiniest bit, I'm still fixated on using the lowest KV100 for the HTHS.

Take for example M1 racing 0W50, with a 3.8 HTHS and 17.2 KV100, would develop the oil pressure (motive for squirter volume) of Redline 10W30, but have the flow correction of 17.2 cst, same as the M1 15W50...would have less piston cooling than the 15W50, AND the 10W30...
 
Looking at your tables, which include the difference in oil pressure, it seems higher KV doesn't negatively impact the cooling effect of the squirters, or lower kv doesn't either but you could of course run out of oil pressure if you go too low (but you'd have to go low in HTHS aswell)

I agree. sufficient hths + low KV.

The question really is, what is sufficient HTHS... so far I'm sticking to 3.5 cP in a fresh oil as I'd rather have more viscosity than needed, than less. A3B4 0w30 in my case.
 
Exactly, the premise of my post was (again) that things like piston cooling nozzles are pressure/density controlled, and viscosity has a much smaller part to play.

Some posit that a reduction in viscosity results in more flow (yes, true in the minor part), however when that provides a lower supply pressure, then viscosity can't make back up the difference.

High Shear Viscosity clearly affects the oil gallery pressure...and lower gallery pressure clearly affects piston cooling.
 
Interesting charts and tables.

I wish I had the instrumentation and the rig to determine how many Joules of Thermal energy would be transferred (carried off) at different flows vs viscosity. It would be an interesting experiment.
 
I recall a slide in a hydraulic model presentation - just to show impacts on residual pressure sensitivity - where inside diameter had the greatest impact and viscosity was at the bottom of a long list ...
To name a few: I.D. >> flow rate >> length >> density >> viscosity ...

Nozzles required enough pressure drop at the nozzle - so you must design such that too much pump pressure is not consumed elsewhere such to have desired impact (QxVnoz) to get that function done (cool, clean, lube, etc)
 
Originally Posted By: 4WD
Nozzles required enough pressure drop at the nozzle - so you must design such that too much pump pressure is not consumed elsewhere such to have desired impact (QxVnoz) to get that function done (cool, clean, lube, etc)


That's why if you look at (say) piston cooling nozzles, they are a larger diameter, bar the last few mm that are at design diameter...keeps the pressure differential at the nozzle, not lost in the feed tube.
 
Your (Shannow's) paper is from the same group as the two I linked. It always worries me when most of the work on a topic is coming from the same lab.
 
Status
Not open for further replies.
Back
Top