[lucifer1881]

Originally Posted by Sutripta

...What is the torque at the flywheel in case of a genset engine which operates at (I assume) constant speed but varying load? Say we connect the engine to the alternator with a shaft which we instrument. (Transmission dynamometer principle.)...

I have answered this in my earlier post. Quoting the relevant part:

Originally Posted by lucifer1881

...Similarly, if an engine is rated for 240Nm at 2000 rpm it will generate that torque irrespective of whether the transmission is engaged or in neutral. The engine, in case of transmission being in neutral, would be running on almost no load since the force required to generate that torque is very low. If the transmission is engaged and the car is moving forward then the engine will be under load conditions depending on weight of the car, traction of the wheels, etc...

Same principle extends to a generator or any engine for that matter.

Example: You are driving at 100kmph in fifth gear at 2500rpm. You approach a steep incline. Without down-shifting, you continue up the incline and floor the accelerator. You will notice that if the incline is steep enough then the engine rpm reduces and so does your speed. This is because the load on the engine increases. The engine first needs to overcome the additional load due to gravity and then impart the rest of its power to the driven wheels. Consequently, the torque being generated at the flywheel and, by extension, the driven wheels is lower. However, if you down-shift and manage to attain 2500rpm you will achieve 100kmph again. The torque is the same. The engine is simply having to work harder to generate that torque.

Torque is a function of how much usable power the engine produces. Under no load conditions, the engine produces maximum torque. Of course, this maximum torque is not of much use since there is no load on the engine which means it is not doing any useful work.

Originally Posted by DirtyDan

How do you measure torque? Does measurement of torque necessarily involve "load"?

Measuring something and defining it are often two different things, but I would like to know just to satisfy my curiosity. Experts? Quasi-experts? Bruce Lee?

Right you are! Load determines how much torque the engine can generate. Torque does not determine the load on the engine.

Theoretically, one may use a torque measuring device that puts zero load on the engine. Practically, it is not possible. Hence, in real world scenarios the measured torque is less than the maximum torque.

Originally Posted by star_aqua

...For an example of tightening a nut or bolt, initially need less torque and as it gets tighter, would need higher torque. What does a torque wrench do?

Torque wrench ensures that you do not tighten a bolt beyond a specified torque. The torque to tighten a bolt does not increase as the bolt is tightened. The load, and hence the force you need to exert while tightening, increases to achieve that torque.
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To repeat, torque is not force. Torque is a function of force. Torque on the wheels is determined by how much usable power the engine is able to transmit to the wheels. This usable power is determined by the load on the engine.

Phew!

[Samurai]

Originally Posted by lucifer1881

Similarly, if an engine is rated for 240Nm at 2000 rpm it will generate that torque irrespective of whether the transmission is engaged or in neutral.

Originally Posted by lucifer1881

Right you are! Load determines how much torque the engine can generate.

Aren't these statements contradicting each other?

[lucifer1881]

Originally Posted by Samurai

Aren't these statements contradicting each other?

How? Load determines how much rpm the engine can generate. As long as an engine generates a given rpm it will produce the given torque.

Higher loads may mean that the engine is not able to reach the given rpm.

[Samurai]

But you said 240Nm rated engine will produce 240Nm of torque at 2000rpm irrespective of load.

[lucifer1881]

Originally Posted by Samurai

But you said 240Nm rated engine will produce 240Nm of torque at 2000rpm irrespective of load.

Yes, it will. As long as it runs at 2000rpm it will produce 240Nm of torque. Higher loads may prevent it from reaching 2000rpm. But irrespective of load, if it is spinning at 2000rpm then it is producing 240Nm of torque.

Higher loads will make the engine work harder, resulting in poor fuel efficiency and greater wear and tear. But if it achieves 2000rpm then it is generating 240Nm.

[Sutripta]

Originally Posted by DirtyDan

How do you measure torque?

In principle, the same way you measure force!

Originally Posted by star_aqua

Which mean the entire torque or the twisting force from the propeller shaft multiplied by diff ratio would be shifted to one axle which offer full traction.
The one which lost the traction would not share the torque from the other axle, hence would not bear any stress. Am I right?

If the diff is locked, yes.

Originally Posted by lucifer1881

I have answered this in my earlier post. Quoting the relevant part:

Same principle extends to a generator or any engine for that matter.

Now I'm totally confused! So simple (yes/ no) answer please (on expected observations. We will get into the whys and whereofs later).

If the genset engine is connected to the alternator by means of a shaft which is instrumented to measure the torque it is transmitting, what torque values will I see. If I've understood your argument it means that as long as the engine rpm is constant, so is the torque. So the torque reading I get from my instruments should essentially remain the same irrespective of the load on the alternator as long as the engine rpm remains the same?

Regards
Sutripta

[lucifer1881]

Originally Posted by Sutripta

...So the torque reading I get from my instruments should essentially remain the same irrespective of the load on the alternator as long as the engine rpm remains the same?...

Yes. A resounding Yes!

[Sutripta]

OK!
Torque constant. RPM constant. So power (generated by engine, transmitted through shaft) constant?

Regards
Sutripta

[star_aqua]

Originally Posted by lucifer1881

Yes, it will. As long as it runs at 2000rpm it will produce 240Nm of torque. Higher loads may prevent it from reaching 2000rpm. But irrespective of load, if it is spinning at 2000rpm then it is producing 240Nm of torque.

Higher loads will make the engine work harder, resulting in poor fuel efficiency and greater wear and tear. But if it achieves 2000rpm then it is generating 240Nm.

What engine are you talking about?

[Samurai]

He means any automobile engine. Since Thar CRDe engine appears very close to that number, let's consider that.

Thar CRDe engine specification says 247 Nm @1800-2000 RPM. Does it produce 247Nm at 1800-2000 rpm, irrespective of load?

[lucifer1881]

Originally Posted by Sutripta

OK!
Torque constant. RPM constant. So power (generated by engine, transmitted through shaft) constant?

Regards
Sutripta

Power at flywheel is constant. Power generated by engine is more than power at flywheel. Some power goes into countering the load the engine has to overcome. This load is more if the car is laden, for instance, and less if the car is unladen. Hence effective power of the engine is the power generated by the engine - power needed to overcome the load on the engine.

This effective power or power at the flywheel is constant for a given rpm.

[star_aqua]

Originally Posted by Samurai

He means any automobile engine. Since Thar CRDe engine appears very close to that number, let's consider that.

Thar CRDe engine specification says 247 Nm @1800-2000 RPM. Does it produce 247Nm at 1800-2000 rpm, irrespective of load?

No, it doesn't always produce 247Nm at 1800rpm. It is max torque that can be produced by that engine. It is like "upto 50%" discount sale offer advertised in Malls. We always read it as flat 50% discount.

[Samurai]

Originally Posted by star_aqua

No, it doesn't always produce 247Nm at 1800rpm. It is max torque that can be produced by that engine.

Thanks, this is what I believe. However, unlike you I am not a qualified professional in this area.

Can you please provide some technical web resources on the same to convince people who disagree with you on this?

[Sutripta]

Originally Posted by lucifer1881

This effective power or power at the flywheel is constant for a given rpm.

Lets start with the alternator running at its rated (electrical) output. The engine produces power at the flywheel, the shaft carries that power to the alternator, the alternator absorbs that power, generating most into electricity, wasting some. This is a stable steady state.

Now let the alternator be disconnected from its electrical load. This too is a stable steady state. As per previous discussions, the engine is still producing the same power. But now the alternator will draw negligible power from the shaft/ engine. Where is the rest of the power going?

Regards
Sutripta

[1100D]

Originally Posted by lucifer1881

Yes, it will. As long as it runs at 2000rpm it will produce 240Nm of torque. Higher loads may prevent it from reaching 2000rpm. But irrespective of load, if it is spinning at 2000rpm then it is producing 240Nm of torque.

Higher loads will make the engine work harder, resulting in poor fuel efficiency and greater wear and tear. But if it achieves 2000rpm then it is generating 240Nm.

Wrong, absolutely, wrong. At any given RPM the torque produced by the engine is a function of many parameters like throttle position. If Thar has a "Maximum" torque of 240Nm at a certain rpm, thats the maximum. Otherwise, you would get the same constant acceleration for the same load at a certain rpm in any specific gear, without any chance to modulate it.

How much torque the engine produces (apart from the other parameters like the slope, load etc) is controlled by the drivers right foot.