What is the exact meaning of "rated engine speed"?

[Jerry/MT]

Re: What is the exact meaning of \"rated engine speed\"?

Except for not making it clear that torque vs RPM assumes a load. Running an engine at any RPM under no load (clutch depressed or in neutral) and you are not developing squat for HP or torque.

Pat

I don't know who resurected this zombie but rated speed is the speed at which the the engine develops it's "rated horsepower". If the manufactuer claims that an engine is rated at 90 hp at 2400 rpm. That's the rated hp at the rated rpm. ndividual engine will often produce more that the retaed hp but this rating will be selected so that the worst engine produced will not be below this number.

Often times there is rating given for max pto hp and that is for the max ppto ower available at the engine rpm that gives 540 rpm OR 1000 rpm at the pto which ever rpm (or both) it is rated for.

Max torque is the peak of the torque curve and is much lower rpm than rated rpm. The torque curve vs rpm is not generally "flat" but it is not as "peaky" as the HP vs rpm curve.

As stated above, running the engine from low idle to high idle can run through these various rated speeds but the engine is not producing max power at rated speed under these conditions. The only loads on the the engine at these conditions are the auxilliary loads ( hydraulic loads, alternators, etc) and they are much smaller than rated loads.

What generally limits max power on a diesel at any rpm is visible smoke (the point at which no more fuel can be burned in the cylinder because the charge has run out of oxygen). It'a usually indicated by a certain allowable Smoke Number. When you see a curve of HP vs rpm your looking at the locus of points where whatever the allowable smoke number is, is occuring under load.

 

[patrick_g]

Re: What is the exact meaning of \"rated engine speed\"?

I don't know who resurected this zombie but rated speed is the speed at which the the engine develops it's "rated horsepower". If the manufactuer claims that an engine is rated at 90 hp at 2400 rpm. That's the rated hp at the rated rpm. ndividual engine will often produce more that the retaed hp but this rating will be selected so that the worst engine produced will not be below this number.

Often times there is rating given for max pto hp and that is for the max ppto ower available at the engine rpm that gives 540 rpm OR 1000 rpm at the pto which ever rpm (or both) it is rated for.

Max torque is the peak of the torque curve and is much lower rpm than rated rpm. The torque curve vs rpm is not generally "flat" but it is not as "peaky" as the HP vs rpm curve.

As stated above, running the engine from low idle to high idle can run through these various rated speeds but the engine is not producing max power at rated speed under these conditions. The only loads on the the engine at these conditions are the auxilliary loads ( hydraulic loads, alternators, etc) and they are much smaller than rated loads.

What generally limits max power on a diesel at any rpm is visible smoke (the point at which no more fuel can be burned in the cylinder because the charge has run out of oxygen). It'a usually indicated by a certain allowable Smoke Number. When you see a curve of HP vs rpm your looking at the locus of points where whatever the allowable smoke number is, is occuring under load.

Let me try just one more time to make something perfectly clear.

If there is no load on a running engine there is very little HP being developed and ditto torque. Running an engine at rated maximum HP speed A N D also loading it to hold it down to that RPM while at full throttle will cause it to develop the rated HP.

If you look at fuel consumption per unit time you will see that running at max HP speed with no load consumes way less fuel than full throttle with load holding RPM down to max HP RPM. So little fuel is consumed in the no load case that it is obvious that it is impossible for the engine to be producing much HP. Ya can't get somethin' for nuttin.

Pat

 

[Jerry/MT]

Re: What is the exact meaning of \"rated engine speed\"?

Let me try just one more time to make something perfectly clear.

If there is no load on a running engine there is very little HP being developed and ditto torque. Running an engine at rated maximum HP speed A N D also loading it to hold it down to that RPM while at full throttle will cause it to develop the rated HP.

If you look at fuel consumption per unit time you will see that running at max HP speed with no load consumes way less fuel than full throttle with load holding RPM down to max HP RPM. So little fuel is consumed in the no load case that it is obvious that it is impossible for the engine to be producing much HP. Ya can't get somethin' for nuttin.

Pat

I clicked on the wrong post to quote.

However "As stated above, running the engine from low idle to high idle can run through these various rated speeds but the engine is not producing max power at rated speed under these conditions. The only loads on the the engine at these conditions are the auxilliary loads ( hydraulic loads, alternators, etc) and they are much smaller than rated loads."

I'm in agreement with your statement as stated above. And your point is?

 

[patrick_g]

Re: What is the exact meaning of \"rated engine speed\"?

I clicked on the wrong post to quote.

However...
I'm in agreement with your statement as stated above. And your point is?

Clarity and unanimity. I agree with you but wanted to repeat it with different wording to break it down so it was not quite as easy to gloss over. It was a very important point you made but the typical quick glance was unlikely to "get it."

What you said is right but not so easy to digest in its compact form, sort of like an algebraic formula as opposed to a verbose narrative. The common error for many people is to think you are making X HP because you are turning Y RPM and it just isn't so. I know you know but did it come across to EVERYONE? I hope it does now.

Pat