Can a motor produce the same HP at different RPM with different Loads

[nukisen]

Thanks Gonzo!
Then I do agree with Submarine Tom!
And also me votes for the simple answer.

NO!

[hwsiii]

Gentlemen I appreciate your time and answers very much. The only reasons y'all are disagreeing so much is My fault. I tried to state the problem clearly, but I didn't accomplish that.



Thank you very much for your efforts in helping me understand.



H

[nukisen]

Oh Thats really okay!
Caused by I think most of us does enjoy discusions!

Good luck hwsiii!

[tunnels]

Originally Posted by hwsiii

My question is can a 292 HP motor produce 280 HP at 5,000 RPM and also produce that same 280 HP at 4,130 RPM.

If that is true then my next question is can it also produce that same HP at 3,519 RPM.

My analysis shows that it can make 280 HP at 5,000 RPM and 4,130 but that it can't produce that 280 HP at 3,519 RPM, and I just want to know if I am correct.

The different loads of course are different Pitch props, a 19" pitch a 23" pitch prop and 27" pitch prop.

I have a little knowledge of props, but absolutely NO knowledge of motors.

Thank you very much for your help,
H

Go find the power and torq curve for that particular motor and look for your self

[Jango]

HP relative to RPM is a Parabolic Curve, so yes, the curve crosses the Same HP only twice. MAX HP is at the top of the curve and occurs only at that point.

[Karl2]

Originally Posted by hwsiii

My question is can a 292 HP motor produce 280 HP at 5,000 RPM and also produce that same 280 HP at 4,130 RPM.

If that is true then my next question is can it also produce that same HP at 3,519 RPM.
H

"...can a 292 HP motor produce 280 HP at 5,000 RPM and also produce that same 280 HP at 4,130 RPM..." The answer is yes.

"...If that is true then my next question is can it also produce that same HP at 3,519 RPM.." Possible but not likely.

If 5,000 rpm is WOT then 4,130 is 82% of WOT. In the diesel world it is common that an engine produces full power 15-20% below WOT. This would be equally possible in a modern gasoline engine.

Two examples:
CAT C9-575 is rated at 2,500 rpm and produces full power from 2,100 rpm.
Volvo D11-670 is rated at 2,370 and produces full power from 2,000 rpm.

All of this only possible on the full load curve. On the prop demand curve there is only one point, one rpm, where the engine will produce max power.

Karl

[jonr]

I've never seen a properly tuned engine where increasing the throttle caused less power. But you are mixing the concepts of rpm and throttle position (which aren't necessarily related). There are engines where running at a higher (but less than max rated) rpm (by decreasing load) will reduce your HP output.

> If 5,000 rpm is WOT then 4,130 is 82% of WOT

For example, I can run 5000 rpm at 25% of WOT and I can run 4130 rpm at 100% of WOT. All depends on how I control load.

[Karl2]

Originally Posted by jonr

I've never seen a properly tuned engine where increasing the throttle caused less power. But you are mixing the concepts of rpm and throttle position (which aren't necessarily related). There are engines where running at a higher (but less than max rated) rpm (by decreasing load) will reduce your HP output.

> If 5,000 rpm is WOT then 4,130 is 82% of WOT

For example, I can run 5000 rpm at 25% of WOT and I can run 4130 rpm at 100% of WOT. All depends on how I control load.

"...I've never seen a properly tuned engine where increasing the throttle caused less power..." This is the actual behavior of every properly tuned diesel engine. At some point just beyond rated rpm the engine manufacturer has designed in a governor curve that reduces power as rpm increases.

In most (All ?) gasoline engines the situation is different. In most cases there is no "function" like this inherent to the design. But there will be an upper rpm limit where power will start to decrease with increasing rpm (Mechanical limitations, air flow limitations, pumping losses, etc. etc).

"...But you are mixing the concepts of rpm and throttle position..."

No mixing of concepts. If you read my previous post: "..All of this only possible on the full load curve.." In other words: 100% throttle position at the rpms I was talking about.

Karl

[jonr]

> In the diesel world it is common that an engine produces full power 15-20% below WOT

Looks like you consider WOT equivalent to max rated rpm - very different than the throttle position that the term comes from. Since diesels don't have actual throttles, I guess one can define it however they want. And they can choose full *rated* power as anything also.

> full power 15-20% below WOT. This would be equally possible in a modern gasoline engine.
No, full power always comes at WOT. Closing the throttle plate only causes more work and less fuel/air.

> then 4,130 is 82% of WOT...In other words: 100% throttle position at the rpms
Ok, you don't consider WOT and 100% throttle position the same thing. I do.

[Karl2]

jonr,


This started with two simple, and good, questions. Like many others I responded specifically to the two questions and added:

“..In the diesel world it is common that an engine produces full power 15-20% below WOT. This would be equally possible in a modern gasoline engine…”
It appears that you have taken issue with the last statement.

“..Looks like you consider WOT equivalent to max rated rpm…”
No, not really, in the context of a marine engine turning a prop I consider WOT to be the max rpm the engine can achieve with the selected prop. This may or may not be rated rpm. If below rated I consider the vessel “over propped”.
This is pretty consistent with how the entire marine industry uses the term WOT

“…very different than the throttle position that the term comes from. Since diesels don't have actual throttles,…”
Of course. What is your point ?? Use some other terminology for a diesel ?
How about TLPTSTECUTATLIOTAMAES (The-Lever-Position-That-Signals-The-Engine-Control-Unit-To-Apply-The-Longest-Injector-On-Time-At-Maximum-Achievable-Engine- Speed)

“..full power 15-20% below WOT. This would be equally possible in a modern gasoline engine.
No, full power always comes at WOT. Closing the throttle plate only causes more work and less fuel/air…”
First, may I suggest you focus on two key words in my original statement: POSSIBLE and MODERN.
Second, since your latest comment to this gives the impression of being factual and scientific when it in fact is an opinion that lacks merit I will amend my original comment to read:
“..This would be equally possible in a modern gasoline engine. As a matter of fact, engines like this are being produced today by the tens of thousands by companies like Harley Davidson, Honda, Suzuki, Ducati, Yamaha, etc.”

Is anybody doing this today on a marine gasoline engine ? I don’t know for sure but I don’t think so.
Would there be any reason for marine engine manufacturer to spend money developing this for a modern marine gasoline engine ? Maybe, maybe not.

“..Ok, you don't consider WOT and 100% throttle position the same thing. I do..”
As before: “…in the context of a marine engine turning a prop I consider WOT to be the max rpm the engine can achieve with the selected prop…”

Karl

[powerabout]

when we say 'full power' are we talking torque or horsepower?