Internal Combustion Engine Loading

[Sohan]

Hey people
I intend to self learn IC engines.
I am a a little confused by what this sentence says in my textbook.
"An idling engine is one which operates at no load and with nearly closed throttle"
I basically want to know what loading means in this particular context?
And what else can loading mean in other contexts regarding IC engines.
please help!
thank you

 

[Danger]

Idling under no load is considered to be what the engine does with the transmission in neutral with no input from the throttle pedal. That can be altered by changing the idle setting on the carb, or by some tweeking of the injectors if your vehicle is so equipped. Idling under load would be in a situation of an automatic transmission in drive, but with your foot on the brake. It could also apply to a driving situation in which you remove any throttle input, such as "coasting" down a hill. In that case, it works as a braking device.

 

[xxChrisxx]

A 'load' on an engine is basically anything acting to stop the engine from spinning.

'No load' as Danger said can only be achieved if the clutch is disengaged. If you've even driven a car you'll know that just tapping the throttle in neutral will cause the revs to raise and fall very quickly.

'Full load' would be the engine operating at full throttle but not increasing in rpm. eg going up a hill in a high gear with the throttle fully open.

Typically you don't include inherent losses that occur from running the engine as 'load', so running any ancillaries aren't counted.

 

[brewnog]

No load is when the energy you're putting in isn't being used to do anything other than keep the engine running, overcome friction, and power any water/oil pumps required for operation of the engine.

Chris, I don't agree that 'no load' can only be achieved with an open clutch; under steady conditions the clutch plate doesn't consume energy. As long as no useful work is being done, there's no load. Nor do I agree that 'full load' requires fixed rpm; at wide open throttle you have full load regardless of gear, engine speed, or rate of change of engine speed. The notable exception is with a turbocharged engine under a transient event where the required boost pressure has not been achieved due to lag.

 

[Danger]

Chris, I don't agree that 'no load' can only be achieved with an open clutch; under steady conditions the clutch plate doesn't consume energy. As long as no useful work is being done, there's no load.

Now I am very confused. If there is no useful work being done, even on a dyno, how can the engine continue to run? Just operating the radiator fan requires work. I know that you qualified that in your post regarding parasitic losses as out-of-bounds, but where do you draw the line? For instance, a 6-71 Roots might draw 150 hp from your engine, but provide 300. Net gain 150 hp. Would that 3" Gilmer belt be considered a parasitic loss, or an investment in something better?
I'm not playing Devil's Advocate here; these are questions that I would seriously like some insight into.

 

[brewnog]

Yes, good question. There's no strict convention for what's counted and what's not in terms of anciliarries, so it's best to define it if you're quoting anything. I consider engine mounted water and oil pumps, and a battery charging alternator (fully charged batteries) to be pretty typical. For an engine driven radiator fan, I quote gross power (flywheel power plus fan power) and net power (flywheel power only).

Anyway, by "zero useful work" I mean "no work being done by the flywheel".

 

[Danger]

Ahhh...
Thanks for the clarification, mate. It makes more sense now.

 

[xxChrisxx]

Chris, I don't agree that 'no load' can only be achieved with an open clutch; under steady conditions the clutch plate doesn't consume energy. As long as no useful work is being done, there's no load. Nor do I agree that 'full load' requires fixed rpm; at wide open throttle you have full load regardless of gear, engine speed, or rate of change of engine speed. The notable exception is with a turbocharged engine under a transient event where the required boost pressure has not been achieved due to lag.

By open clutch I meant 'engine not connected to wheels'. I suppose no useful work is a better way to put it.

And sadly, I now disagree with my own post re: full load. Damn.

 

[brewnog]

No bother Chris!

 

[JaredJames]

I think the key in the OP is the use of "idling".

An engine under no load isn't necessarily idle. The OP wanted to know what load meant in the context of idling.

In so far as no load when idling goes, it would be the engine running with the clutch disengaged and no ancilleries running (these being items you can manually disengage from the cockpit). Anything you have no control over should be considered part of the engine in so far as it has to run and so for the engine to idle, the rpm needs to include these.

For me, the idle speed is pretty much as slow as you can get the engine to run without stalling (when no user controlled items are activated). On a cold day, the engine will idle at a higher rpm than on a warm day.

So to finish, load would be considered anything drawing power off the engine that the user has control over.