It's an engine from a ~2012 Australian Ford Falcon. The study is titled
Fuel conservation and emission reduction through novel waste heat recovery for internal combustion engines.
I added the annotation for the relief pressure setting. It was taken from this chart provided in the same study showing the relief characteristics at 2,000 rpm. If you look at the oil pressure at 2k rpm from the the previous chart I posted, and compare the pressure at 100°C and 60°C, the oil with ~3 times the viscosity has ~1/3 the flow rate.
If the pump pressure vs engine RPM in Fig 9 (below) is for that engine, then how did they obtain oil pressure data for engine RPM above the relief pressure of 315 kPa (45.7 PSI)? Was that data obtained on an actual running engine with instrumentation? If the pump relief valve was actually starting to open at 45.7 PSI, those oil pressure curves would not be shaped like that above 45.7 PSI line. They would be rolling over very noticeably, but they are essentially remaining near linear. Fig 1 says "typical oil pump flow", so what oil pump is that based on? Any PD pump should not be bypassing any oil until the pressure relief valve starts cracking open. So the pump in Fig 1 obviously has a low relief setting, a lot lower than any engine pump relief pressure specs I've seen.
The bypass design allows the oil pump to produce pressure a lot higher than the nominal relief setting. At higher rpm, maximum pressures can approach twice the relief setting. This seems to be typical for a PD pump pressure relief. Here's a more detailed chart from another study that shows the bypass characteristics at higher engine speeds. The chart on the right is for a conventional oil pump.
The "Focal point 1" zone for the Conventional oil pump clearly shows the pump is in pressure relief. The linear slope down portion of the pressure vs flow rate curves is showing the pump slip (ie, pump efficiency) vs output pressure.
"The bypass design allows the oil pump to produce pressure a lot higher than the nominal relief setting."
This can happen if the flow path for the oil that bypasses the pump when in pressure relief is undersized/restrictive. Even though the PRV opens, the pump output flow can still increase with increased RPM, but there will be a pretty noticable curve inflection (like seen in Fig 10) starting at the point the PRV starts to open. No oil pump will have a perfect pressure control cut-off once the PRV starts opening, but some pumps will control max pressure output better than others.
"At higher rpm, maximum pressures can approach twice the relief setting. This seems to be typical for a PD pump pressure relief."
Not sure how this could happen, because when the releif valve starts operaing, the pump output pressure is going to start rolling over pretty good if the relief valve is designed correctly. Only way I could see this happening is if the PRV was set real low on a high ouput pump, and the PRV was pretty flow restrictive.
That pressure curve looks an awfully lot like the one with the low relief valve setting. Are you sure the relief valve on that engine has an initial opening pressure of 75-80 psi? Is that based on manufacturing spec or physical measurements?
Per Melling, the OEM releif spring on the oil pump is set for 70 PSI - had to dig into my notes to verify. The pump should not be bypassing any oil flow before the PRV starts cracking open (assuming the closed valve isn't leaking). On a side note, if the PRV was leaking slighty, it would be hard to distigish that from pump slip as the pump outpur pressure increased.
Keep in mind that the pump output pressure before the filter is also effected by the filter dP. The oil pressure sensor is located between the filter and main engine feed gallery. The oil filter used is referenced in the title of the Z06 graph, and under those test conditons (200F, 5W-30 oil), the filter dP at high RPM was around 2-3 PSI (per Purolator test data). The LS pump puts out ~6 GPM at 5000 RPM. Not a super high output pump.
If 75-80 psi is just the maximum pressure observed at high rpm with cold oil, then the initial opening pressure would be more like 40-45 psi, if the pressure relief performs similarly to the conventional oil pump in Fig. 10 above. My Subaru has a 102 psi pressure relief, but can easily hit >150 psi measured at the main gallery, which would be >170 psi at the oil pump outlet.
My RPM vs OP data was with 5W-30 at 200F (around 11.5 cSt). The oil pump PRV is not set to 40-45 PSI (it would be obvious in the data if it was), so no oil would be bypassing the pump below a pump output pressure of 70 PSI. Sure, if the oil was cold the pump would hit pressure relief at a much lower RPM. Fig 10 doesn't say what oil viscoity was used, and doesn't show any info for changing oil temp/viscosity on the curves, it just showing curves for whatever viscosity they used to generate that data.
It won't be 100% linear, but I don't think it would be highly non-linear as it is in the chart from your Z06 either.
The Z06 graph is not linear for two reasons as the RPM increases: 1) Some slight pump slip, and 2) pump output pressure decrease due to increased journal bearing "self-pumping" and the associated bearing side leakage. The increased bearing self-pumping acts like a scavaging pump on the pump supply, which will decrease the oil pressure supply. Most people are not aware of this phenomina unless they really understand how journal bearing operate. Oil flow through journal bearings is effected by many factors.
Here's basically how the oil pressure vs RPM would look on a running engine, based on different factors. This is a generic model I did (not for my Z06) to simply show what the curves would look like based on different operating conditions. If a pump was supplying flow to a fixed resistance, the curve will look like the red and orange lines. If the pump is supplying oil to a running engine with journal bearings, the curves will look like the green and blue lines. If the pump slip factor is included, it just moves the same curve shape down on the graph - the more pump slip the mover the curve moves down. Pump slip in this model was assumed pretty extreme (goes from 5% slip at 1 GPM to 20% slip at 15 GPM) to see it's effect. IMO, pump slip in a a healthy automotive PD pump isn't going to chage that much as its output pressure increases. A pretty worn out oil pump might have slip that bad. The green and blue lines are essentally the same overall shape as my Z06 graph.
It could be that pressure drop across bearings doesn't rise as quickly with rpm, and if an engine has piston squirters they may only flow at high rpm, but pressure drop across other components can behave in the opposite way, with pressure rising quadratically with flow rate (oil filters as just one example). Oil temperature and viscosity both affect how turbulent the flow is as well, which can make dP-flow curves more or less linear. It's all a bit complicated to model, and maybe some engines do naturally have very different curves, but I still think the simplest explanation is that the pump is in pressure relief.
Yes, it's a bit complicated, and agree that every engine will have it's own specific RPM vs OP characteristics. All engines also have journal bearings, which effect the RPM vs OP curve. The Z06 does not have piston oil squirters, so that's out of the equation. Piston sqirters are essentiall an orifice, and they flow any time the engine is running. Some "fancy" ones have a check valve in them to close off flow below a certain oil pressure level, like 25 PSI so they don't operate at low RPM. The flow vs P curve for oil squirters would basically be like the orange line in the graph above. Anything that basically acts like an orifice will have a flow vs pressure curve in that shape. A pressure fed oiling system basically acts like a "modified" orifice type of restriction, except when it's rotating and the jorunal bearings are self-pumping. When the self-pumping journal bearings are added to the system, it causes the pump supply pressure to roll over like the blue line in the graph above. So the roll-over is a combination of factors, mainly the pump slip + the journal bearing side leakage.
Here are the specs for main gallery pressure at 80°C for my Subaru:
700 rpm: 9.5 psi, or 13.6 psi / 1000 rpm
3,000 rpm: 47 psi, or 15.7 psi / 1000 rpm
The pressure-rpm curve is close enough to a straight line that intersects near zero, at least until above 5,000 rpm when pump slip becomes significant and the flow rate starts to level off. If anything, pressure rises a bit faster than rpm.
As mentioned in other threads discussing the Subaru high volume oil pumps, are the specificatiions for the pump in the service manual based on a pump on bench in a lab, or is it actual data obtained from the pump on the engine? A PD oil pump will not show the same RPM vs output pressure when connected to a fixed output resistance (like in a lab bench test) vs on a running engine because of the journal bearing self-pumping effect.
