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What is Engine Load?

What is Engine Load?

(OP)
Dear all,

Hello I'm a new guy to both this forum and engines :)

I have a question (maybe a stupid one) about what is defined by Engine Load and how it affects the fuel consumption of the engine?

Having found no exact definition, I assumed the Load to be dependent on the % of the Throttle being open and, thus, also dependent on the ratio of mixture volume to the full cylinder volume.
WOT causes this ratio to be equal to 1 (or higher, if we have a volumetric efficiency > 100%), % of Throttle being open less than 100 causes the volume of mixture be smaller than the cylinder volume. Right?

But RPM depends on the Throttle opening as well. Does it also mean that the RPM is proportional to the Engine Load?

I feel I have a mess in my head.

Regards,
U6an

RE: What is Engine Load?


Engine load is the power that the outside world takes away from the engine. An engine connected to nothing can have essentially no load, regardless of throttle opening or RPM. If you connect an engine to a dyno or a machine, then you can load the engine.

RE: What is Engine Load?

Further to the above, an engine produces more power and can therefore accommodate more load when its throttle is open wider, and less power, load, when its throttle is less open.

The amount of power available from the engine at 100% throttle will vary over the operating speed range (rpm range) of the engine. At any given speed, the maximum power that the engine can output is "full load."

If the output power of the engine is less than the external load, the engine will decelerate.

If the output power of the engine is greater than the external load, the engine will accelerate.

RE: What is Engine Load?

(OP)
ivymike,

Thank you for your response, not clear for me still.

If we have a car that accelerates, can we then say that the Engine Load is the Tractive Effort?



RE: What is Engine Load?

The engine load is directly related to the tractive effort ... there are losses between the engine and the road which make them diverge a little bit.

Engine load % is normally a comparison of the actual engine output torque to the maximum engine output torque at the current engine operating speed.

RE: What is Engine Load?

Just going down the level road is likely to require HP according to a curve like the red or blue curves here.
http://i1072.photobucket.com/albums/w362/OldTelema...

A chart like in the lower right corner here shows which transmission gears are available at various road speeds during maximum acceleration.
https://www.flickr.com/photos/mr38/5784805058/in/s...

This chart looks to show road load vs speed, and HP available in each gear at full throttle.
http://i237.photobucket.com/albums/ff47/SuperL98ne...

RE: What is Engine Load?

(OP)
ivymike,

Thank you. I will assume then the Engine Load to be approximately equal to the Tractive Effort.

Do you know how to find out the effect of the Engine Load on the fuel consumption?


Tmoose,

I'm not quite sure what you meant..

RE: What is Engine Load?

If efficiency was constant, then engine load would be proportional to fuel consumption. Unfortunately efficiency is not constant, so you'll need a BSFC map to relate engine load&speed to fuel consumption.

see thread71-363722: Understanding BSFC maps

RE: What is Engine Load?

The engine load is the torque output of the engine.

An internal combustion engine is - approximately - a constant torque motor, meaning it can produce the same maximum torque at any rpm. The fact that it happens at a rpm or another, dictates how much power it produces.

Torque is proportional to the amount of force put on the piston, which is proportional to the amount of air being burnt in the combustion chamber, which is why you can relate the engine load to the quantity of air going into the engine, knowing the maximum amount of air that go in at a particular rpm, i.e. at WOT.

RPM does not really depends on throttle opening per say. When an engine is at constant speed, there is only the friction force going against the engine (from the bearings) and some others to run pumps and such, such that the engine can run. This represents the load at idle.

If you give enough heat (fuel combusted) to produce enough torque to go against this load, the engine will idle at constant speed.

If you give more heat, it will produce extra torque which will be transformed into acceleration of the moving parts (F=ma or T=Iα in rotation). Of course, if you give less heat, there will be a deceleration of the rotating components.

But you can increase the load by coupling an external torque to the shaft of the engine (a pump for example or a vehicle that needs to be accelerated). In that case, if you don't increase the heat in the combustion chamber, the engine will begin to decelerate. But if you increase it enough such that the torque converted by the engine equals the torque required by the load, then the speed of the engine will stay constant.

RE: What is Engine Load?

I wonder if the original poster is referring to the parameter that the on-board-diagnostics call "load", if you are watching the engine parameters with a Scangauge or other such tool.

That "load" is more-or-less the percentage of air/fuel delivery going through the engine relative to what it would be at wide-open-throttle (100% "load").

It's not unusual for "load" to be reported in the 25% - 30% range with the engine idling in neutral (zero "actual load" being output), because that's how much it's taking to spin the engine to overcome friction, oil pumping, water pumping, throttling, etc.

The fuel injection system uses this to calculate the correct amount of fuel delivery and also the correct ignition timing, variable-valve-timing actuation (where so equipped), etc.

It is correlated to the output torque, but not directly so.

RE: What is Engine Load?

Engine "load" in technical literature is a dimensionless parameter used to fix any operating point of the engine. The other parameter required is engine speed. Looking at the characteristic map of an engine, the x axis will usually be speed and the y axis may be in units of torque, power or load. The upper limit of the map, the "full power curve" represents 100% load at each speed. Lower values of load at any speed will simply indicate that power and torque are reduced to that percentage.

"Tractive effort" is the linear force produced at the drive wheels. If gear ratio is held constant, "tractive effort" will be proportional to load, but it is not accurate to say that tractive effort = load.

je suis charlie

RE: What is Engine Load?

One more view...

"Load" is a poorly defined and ambiguous term used far too much to mean different things to different people. To me it has one of two usual meanings:

1) Dimensionless. A combination of engine input settings to provide a proportion of the available shaft torque for a given engine speed. Correlated with pedal position (driver demand) in a vehicle. Although continuous, "zero", "part" and "full" are the three most common values used. Modern engine control systems may attempt to make the correlation linear, or at least feel linear.

2) Dimensioned. BMEP. Precisely defined. Normalised for engine size & type, but its range is speed-dependent.

- Steve

RE: What is Engine Load?

Agree with that. "Load" seems to be used interchangeably to describe Power, Torque or BMEP which is OK at a fixed engine speed where all three are proportional.

je suis charlie

RE: What is Engine Load?

Good question. In the engine testing I have done I usually regard that at a certain fixed RPM the maximum torque (or engine load) that can be developed is proportional to the manifold vacuum and thus the fuel consumption is likewise proportional to the manifold vacuum.

RE: What is Engine Load?

Nobody is going to correct this one, eh?

An internal combustion engine is - approximately - a constant torque motor, meaning it can produce the same maximum torque at any rpm. The fact that it happens at a rpm or another, dictates how much power it produces.

LOL

RE: What is Engine Load?

Quote (ivymike)

Nobody is going to correct this one, eh?

An internal combustion engine is - approximately - a constant torque motor, meaning it can produce the same maximum torque at any rpm. The fact that it happens at a rpm or another, dictates how much power it produces.

LOL

What needs to be corrected?

ICE have a "constant torque" because - approximately - the same maximum force can be applied on the top of the piston no matter the rpm. Consequently the power is zero at zero rpm and increases as the rpm increases.

On the other hand, electric motors are considered "constant power" because the same power input (voltage X current) is - approximately - available at any rpm. Consequently, the torque is infinite at zero rpm and decreases as the rpm increases.

RE: What is Engine Load?

"ICE have a "constant torque" because - approximately - the same maximum force can be applied on the top of the piston no matter the rpm. Consequently the power is zero at zero rpm and increases as the rpm increases."

I guess all that work that goes on to tune the power curve of a car is pretty noob, then

TTFN
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Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx

RE: What is Engine Load?

Thank you for that last graph. It shows really well that the torque is at least 75% of the maximum torque throughout the rpm range and that the power varies linearly from idle to 5500 rpm (which means torque is [keyword] approximately [/keyword] constant). Here's another one which compare a gasoline engine with an equivalent electric motor:


Can you tell which one is «constant-torque» and which one is «constant-power»?

RE: What is Engine Load?

I don't suppose it helps the original poster any, but one reason I completely disagree with the statement that "torque is approximately constant" is that the shape of the torque curve is one of the primary factors that makes one IC engine better than another one for a given application. If they're all "approximately equal" then there's really nothing that makes a diesel better than a gasoline engine for pulling a semi up the hill, or one diesel better for marine propulsion and a second one better for a tractor and a third better for racing ... they're all about the same!

RE: What is Engine Load?


another torque and power curve for an internal combustion engine (torque below, power above)

RE: What is Engine Load?

Ok, I'll bite then.

Familiar IC engine torque curves are shaped by breathing inadequacies and the limits of reliable combustion. For NA engines, the available airflow follows the peaks and troughs imposed by the restrictions and tuning of the intke system. For TC engines, the sky (or more often, the PMAX) is the limit.

Designers and calibrators can cut bits out of the available curve to suit applications.

A torque curve flat across most of the operating speed range is becoming more common among light duty automotive applications as TC becomes the norm.

- Steve

RE: What is Engine Load?

I'm talking about the general concept of an ICE compared to other motor types (electric, hydraulic, etc.), not its fine tuning.

Quote (The motor vehicle, 12th ed, p. 16)

1.20 Characteristic speed power curves

If the mean effective pressure (mep) and the mechanical efficiency of an engine remained constant as the speed increased, then both the indicated and brake horsepower would increase in direct proportion to the speed, and the characteristic curves of the engine would be of the simple form shown in fig. 1.5, in which the line marked 'bmep' is the product of indicated mean effective pressure (imep) and mechanical efficiency, and is known as brake mean effective pressure (bmep). Theoretically there would be no limit to the horsepower obtainable from the engine, as any required figure could be obtained by a proportional increase in speed. It is, of course, hardly necessary to point out that in practice a limit is imposed by the high stresses and bearing loads set up by the inertia of the reciprocating parts, which would ultimately lead to fracture or bearing seizure.


Apart from this question of mechanical failure, however, there are reasons which cause the characteristic curves to vary from the simple straight lines of fig. 1.5, and which result in a point of maximum brake horsepower being reached at a certain speed which depends on the individual characteristics of the engine.

Characteristic curves of an early four-cylinder engine of 76.2 mm bore and 120.65 mm stroke are given in fig. 1.6. The straight radial lines tangential to the actual power curves correspond to the power lines in fig. 1.5, but the indicated and brake mean pressures do not, as was previously assumed, remain constant as the speed increases.


On examining these curves it will be seen first of all that the mep is not constant. It should be noted that full throttle conditions are assumed - that is, the state of affairs for maximum power at any given speed.

At low speeds the imep is less than its maximum value owing partly to carburation effects, and partly to the valve timing being designed for a moderately high speed; it reaches its maximum value at about 1800 rev/min, and thereafter decreases more and more rapidly as the speed rises. This falling off at high speeds is due almost entirely to the lower volumetric efficiency, or less complete filling of the cylinder consequent on the greater drop of pressure absorbed in forcing the gases at high speed through the induction passages and valve ports.

When the mep falls at the same rate as the speed rises, the horsepower remains constant, and when the mep falls still more rapidly the horsepower will actually decrease as the speed rises. This falling off is even more marked when the bmep is considered, for the mechanical efficiency decreases with increase of speed, owing to the greater friction losses. The net result is that the bhp curve departs from the ideal straight line more rapidly than does the ihp curve.

[...]

If a suitable scale is applied, the bmep curve becomes a 'torque' curve for the engine that is, it represents the value, at different speeds, of the mean torque developed at the clutch under full throttle conditions - [...]

RE: What is Engine Load?

I agree with JackAction. It is a reasonable and probably useful generalisation to say that reciprocating IC engines produce approximately constant torque across their useful operating range. There are exceptions of course e.g. highly tuned and highly supercharged engines (esp' with centrifugal superchargers).

je suis charlie

RE: What is Engine Load?

That generalization could lead to some baffling results in the context of a discussion of "what is engine load." If available torque is constant across the operating range of the engine, then our OP could leave here with the impression that his car requires the same amount of torque idling in the driveway as cruising the highway at 55 mph (27% load).

RE: What is Engine Load?

The available torque (pedal to the metal) may be approximately constant, but the driver-requested portion of it is not ...

RE: What is Engine Load?

Not sure if you caught what I was saying or not ... since max torque at 800 rpm is much less than max torque at 2000 rpm (typically), if you're reading engine load electronically you might see the same figure (27%) at both idle/no load and at 55 mph constant speed driving. If you take torque to be constant for your engine, that ought to be a surprising result (same power torque!). In reality the low idle no-load torque is less than highway torque, but when expressed as a percentage of max at each speed, the resulting figure is the same.

RE: What is Engine Load?

(*same torque!)

RE: What is Engine Load?

Let me go back to the original problem and why I gave the answer I did.

The original question is What is Engine Load? and the OP was attempting to relate somehow the engine load with rpm. A big error that needs to be corrected.

ivymike rather explained well the concept of engine load, except that he constantly used the term power instead of torque. It might seem trivial since if we know the rpm, power and torque are related. Unfortunately, people often use these terms like they means the same thing (like when ivymike says same power torque!), but they don't.

That can be confusing because in electricity, a load is a measure of power. But in mechanics, it is a measure of a force or a torque.

Torque is torque, rpm is rpm and power is the combination of both. Since the OP was tempted to relate load and rpm, I thought the distinction was important to point out, i.e. that torque is independent of rpm:

Quote (JackAction)

An internal combustion engine is - approximately - a constant torque motor, meaning it can produce the same maximum torque at any rpm. The fact that it happens at a rpm or another, dictates how much power it produces.

Sorry if my choice of words did not emphasize that fact.

Here is an example to show why the distinction is important and why power is not a mechanical load:

You have 2 cars, one with a gear ratio of 10:1 between the wheels and engine and the other with a gear ratio of 5:1. Both cars have a load of 650 lb.ft at the wheels. What is the engine load?

Answer: The one with the 10:1 gear ratio has an engine load of 65 lb.ft and the other one has an engine load of 130 lb.ft. Note that it is of no importance at what speed the cars are going (or even if they are moving at all) or what are the rpm of the engines. Both engines may produces the same power or they may not. They may even produce 0 hp if the car is not moving (since an engine is not necessarily an internal combustion engine as we know it, we can assume an engine can produce a torque at 0 rpm).

Now let's try with power instead:

You have 2 cars, one with a gear ratio of 10:1 between the wheels and engine and the other with a gear ratio of 5:1. Both cars have a «load» of 25 hp at the wheels. What is the engine load?

If you define the engine load as power, your answer would be 25 hp in both cases. But then again, if both cars have the same speed, the engines will not be at the same rpm. But are they at the same speed? We don't even know.

So, if the cars are not moving (initial acceleration of a dragster at the starting line for example), the power at the wheel is 0 hp, so it would mean that the engine load is zero? I don't think so.

This is why the distinction between torque and power is important and why stating that torque and rpm are independent of one another is also important.



RE: What is Engine Load?

btw, I did mention "Engine load % is normally a comparison of the actual engine output torque to the maximum engine output torque at the current engine operating speed."

Nice straw man argument "if the cars are not moving (initial acceleration of a dragster at the starting line for example), the power at the wheel is 0 hp, so it would mean that the engine load is zero" .. I don't think anyone here would have made that mistake.

RE: What is Engine Load?

If P=0 at an rpm where Pmax=0 what is the load percentage?

Hint: 0/0 does not equal 0

je suis charlie

RE: What is Engine Load?

ivymike,

If we define engine load as torque, these following statements are false and misleading because they all relate engine load to power:

Here you literally define engine load as power:

Quote (ivymike)

Engine load is the power that the outside world takes away from the engine.

Here you compare power with torque (How do you know if 25 hp is more or less than 100 lb.ft of torque?):

Quote (ivymike)

If the output power of the engine is less than the external load, the engine will decelerate.

If the output power of the engine is greater than the external load, the engine will accelerate.

Here, it is a tricky one: Fuel consumption is proportional to torque output, but the torque output is not proportional to fuel consumption as fuel consumption is related to power not torque:

Quote (ivymike)

If efficiency was constant, then engine load would be proportional to fuel consumption.

But these statements are true because they all relate engine load to torque:

Quote (ivymike)

The engine load is directly related to the tractive effort

Quote (ivymike)

Engine load % is normally a comparison of the actual engine output torque to the maximum engine output torque at the current engine operating speed.

Naturally, if we assume engine load is power, the first statements are true and the last ones are false.

This is where I chime in the discussion - respectfully and without pointing finger at anyone - and reinforce the position that engine load is in fact a measure of torque, not power. The reason I did not point out your mistake is because I know that you understand what engine load is and I know that by using the term power, you meant torque, an error that many people do, including me.

You then - literally - laughed at me.

I tried to explain myself - quite respectfully, I think - but you are responding with condescending arguments («oh good grief .. we have twins», «Nice straw man argument»).

So, ivymike, here is an easy question that can be answered with only one word and that may help someone who is reading this thread in hope of defining what is engine load:

Is engine load a measure of the engine output torque or power?

RE: What is Engine Load?

I'm sorry, in my previous post there is an error. The following statement is false whether you define engine load as power or torque:

Quote (ivymike)

The engine load is directly related to the tractive effort

  • If you increase the tractive effort, the power of the engine can stay the same if the vehicle speed is also reduced;
  • If you change the gear ratio, you will change the tractive effort without changing the engine torque.
Funny, even though I've admitted making a mistake, I wasn't struck by lightening.shadeshappy

RE: What is Engine Load?

Is engine load a measure of the engine output torque or power?
yes. both, or either.

Load % is typically calculated from torque, but "load" can be interpreted a few ways. Power is easier to explain to someone who just plain doesn't know what "engine load" is.

No, I didn't compare power to torque, that's your assumption based on a narrowly chosen view of what "load" means which is inconsistent with my earlier statement. Same story on the fuel consumption.

(Load) and (load %) are not the same ... and (load %) doesn't have units.

If you don't like being called out for straw man arguments, there's an easy solution: don't make 'em. http://en.wikipedia.org/wiki/Straw_man

... if you think you've been very helpful and informative, then good for you. thumbsup2
I'm going to have to concede that you've won the internet today. (I've got an engine test to prep for. The subject engine will be loaded to max power for the intended application, so that I can confirm the sizing of the cooling system.)











RE: What is Engine Load?

Load is any force that the engine is working against. period.

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

RE: What is Engine Load?

Period?

Ever heard of a "load bank". "Load" is often used to describe power output.

je suis charlie

RE: What is Engine Load?

gruntguru, I am not sure how you would use load to describe engine's power output in a way that totally contradicts what I just got done saying. What are your thoughts? Just to make sure my post was clear, Ivymike's posts about load earlier in this thread are another way of saying what I am trying to say

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

RE: What is Engine Load?

Your post suggested that "load" describes a "force" only.

je suis charlie

RE: What is Engine Load?

Quote (gruntguru)

Ever heard of a "load bank". "Load" is often used to describe power output.

Power only describes load in an electrical context. In a mechanical context, it is always a force or a torque. Load (disambiguation)

But as you said earlier:

Quote (gruntguru)

Agree with that. "Load" seems to be used interchangeably to describe Power, Torque or BMEP which is OK at a fixed engine speed where all three are proportional.

When comparing 2 engines, if the rpm is the same, power is proportional to the torque so it doesn't make a difference to use one or the other WHEN you compare it to a reference value (i.e. max torque or max power).

RE: What is Engine Load?

A lot of pissing and moaning that depends on a definition. Load generally does refer to torque in mechanical systems vs power in electrical systems. But, the OP is asking about fuel consumption so maybe power should be used?

Quote (JackAction)



I'm sorry, in my previous post there is an error. The following statement is false whether you define engine load as power or torque:

Quote (ivymike)


The engine load is directly related to the tractive effort

If you increase the tractive effort, the power of the engine can stay the same if the vehicle speed is also reduced;
If you change the gear ratio, you will change the tractive effort without changing the engine torque.

Funny, even though I've admitted making a mistake, I wasn't struck by lightening.shadeshappy

JackAction - I consider both of your statements wrong. I think there is confusion between tractive effort and tractive force when using the generally accepted automotive definitions. Tractive force is the force produced at the road surface. Tractive effort is the force the engine produces to create the tractive force. So, effort is the output torque of the engine. I would take more issue with the second part of ivymike's statment than the first part, because he was correct and then says there are other loads to consider which are already included in the effort.

I would also never say an ICE is constant torque. This can be reasonable over a certain rpm range but it will not work over the complete engine operating range.

You are wrong about an electric motor being constant HP and having infinite torque at zero speed. They are basically constant torque machines from 0 speed until rated speed (or until you run out of voltage). This is the range electric motors are operated in probably 99% of the time. You can clearly see this constant torque portion of the curve in the graph you posted. They then switch to constant power machines once you run out of voltage.

RE: What is Engine Load?

Quote (LionelHutz)

Tractive force is the force produced at the road surface. Tractive effort is the force the engine produces to create the tractive force.

Traction, or tractive force, is the force used to generate motion between a body and a tangential surface, through the use of dry friction.

In automotive engineering, the terms [tractive force & tractive effort] are distinctive: tractive effort is generally higher than tractive force by the amount of rolling resistance present

[Tractive effort applies] to different operating conditions, but are related by common mechanical factors: input torque to the driving wheels, the wheel diameter, coefficient of friction (μ) between the driving wheels and supporting surface, and the weight applied to the driving wheels (m).

The driving wheel torque is not the engine torque. An engine can produce any value of torque and still produce the desired wheel torque through a proper transmission.

Quote (LionelHutz)

I would also never say an ICE is constant torque.

[...]

You are wrong about an electric motor being constant HP and having infinite torque at zero speed.

When I state these facts, it is on a theoretical point of view.

In theory, with an ICE, the same quantity of fuel mixture goes inside the engine (it depends on the engine's displacement). Once this fuel mixture has burned, it produces a certain force, creating a certain torque. So the same torque is produced by every cycle, no matter the rpm. Thus the rpm of the engine determines the power output. So only a certain defined amount of torque is produced.

In theory, with an electric motor, only a certain amount of power can be accepted (current X voltage). Since an electric motor is machine that convert electrical power to mechanical power and that power is always conserved, therefore the torque is inversely proportional to the motor rpm. For example, with a DC motor, torque depends on the input current and speed on the input voltage. Both of these can easily be set to any value with the help of a transformer, but their product will always remain the same, i.e. same power input.

In practice, with an ICE, fuel mixture quantity can vary depending if the cycle is at a rpm or another. The combustion quality can also vary depending if the cycle is at a rpm or another, affecting the force available on top of the piston. Of course, there are no free lunch, and an engine cannot produce an infinite amount of power, just by indefinitely increasing the rpm. Flow restriction and mechanical failure comes into play at one time or another.

In practice, with an electric motor, torque will not be infinite at zero rpm. Limits are imposed depending on their construction and, as with an ICE, mechanical failure. If you have a big enough motor, of course you can have your rpm range within that upper torque limit.

RE: What is Engine Load?

gruntguru - What else would you call a force that an engine is applying torque to?

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

RE: What is Engine Load?

Wow, I can quote Wikipedia too.

Tractive effort is the force generated by a vehicle's engine or motor in order to generate motion through tractive force. Tractive effort differs from tractive force, which is the actual force applied at the road surface, by the amount of rolling resistance present.

Once again - definitions....

As for the rest of your post, good for you and your theories. Even theory has different meanings. Apparently, your definition is abstract. Mine is more scientific and says that a motor design has a safe current limit. This current limit will limit the possible torque the motor can produce. This current limit makes your "in practice" statement completely wrong too.

You first made your statements without any "in theory" attached and now you're justifying both by using "in theory". Big surprise.


Panther140 - yes, I would agree that the load on a ICE is always the force it's working against. An ICE produces a twisting force at the crankshaft so it's rather hard for the load to be anything else.

RE: What is Engine Load?

Quote (LionelHutz)

Mine is more scientific and says that a motor design has a safe current limit.

Quote (JackAction)

In practice, with an electric motor, torque will not be infinite at zero rpm. Limits are imposed depending on their construction and, as with an ICE, mechanical failure.

That seems pretty much the same to me.

Quote (LionelHutz)

You first made your statements without any "in theory" attached and now you're justifying both by using "in theory". Big surprise.

From the reference in my earlier post (7 Mar 15 02:07):

Quote ((The motor vehicle, 12th ed, p. 16))

Theoretically there would be no limit to the horsepower obtainable from the engine, as any required figure could be obtained by a proportional increase in speed.

As for a reference for an electric motor, you are right, I did not provide one. There is one I had in mind since the beginning of the thread, but couldn't find a copy of the extract I needed online and my paper version is not close by (Then again, I never thought I would have to explain myself that much). Luckily, it did show up on the Google preview this time, so you have an extract from Theory of Ground Vehicles, p. 227 in the image attached to this post (Sorry. p.228 was not shown on Google preview so fig. 3.20 wasn't available, but from the context you can imagine it looks like fig. 3.19).

As you can see, I can quote more than Wikipedia. And when I do quote Wikipedia, I used text that is referenced. The reference for my quoted text stating that it is input torque to the driving wheels (as opposed to engine torque), clearly relates the traction effort to engine power, not torque. Even in your link, it says (although unreferenced) that the traction effort available is limited by the available power; which is inconsistent with relating it to engine torque.

Funny thing. I read p.255 of the previous Wikipedia reference - which talks about fully electric haulage locomotives - and it says:

Quote (Handbook of railway vehicle dynamics (p. 255))

At low speeds the traction system is limited by current so tractive effort is applied proportionally to throttle notch level. Tractive force delivered in this region may be independent of speed, or reduce with speed, depending on the locomotive characteristics and control. At higher speeds the system is limited by power so the tractive effort available decreases at increased speeds according to force velocity product P = Ft/dbv.

Look at the figure going with the text showing typical tractive effort performance curves: The «high speed» range is at least 70% of the whole speed range. I would consider the «constant power» section being more predominant than the «constant torque» section.

By the way, theory is often abstract. That is how you differentiate it from practice.

RE: What is Engine Load?

Yes, a theoretical limitless hp and an ICE being constant torque are exactly the same thing. How could I have missed that point. rofl

Of course traction effort is limited by available power. There is nothing inconsistent about that statement.

You posted that complete nonsense about electrical motors being constant HP and having limitless torque at low rpm's as if it was a fact. You backpedaling with this "in theory" BS to justify your claims. Now you're saying they are constant torque up to a certain speed, but that doesn't matter because it's only a small portion of the operating range? I can't even follow what you're claiming anymore.

The fact that the locomotive specific application runs a motor well above the voltage limit doesn't change anything about what I posted. The motor is constant torque until you can't increase the applied voltage. The locomotive is a rather specialized application. I work with electric motors every day and 99.99% of the applications I deal with never take the electric motor above it's constant torque operating range.

You should really be more careful with your broad generalized use of "electric motors". The series wound DC locomotive motor in not the only type of electric motor.

RE: What is Engine Load?

Quote (LionelHutz)

Yes, a theoretical limitless hp and an ICE being constant torque are exactly the same thing. How could I have missed that point.

I can't believe how condescendant you are, but I'm sorry if I'm not sure what you don't understand. This might be a quote of interest from the same earlier post:

Quote ((The motor vehicle, 12th ed, p. 16))

If the mean effective pressure (mep) and the mechanical efficiency of an engine remained constant as the speed increased, then both the indicated and brake horsepower would increase in direct proportion to the speed, and the characteristic curves of the engine would be of the simple form shown in fig. 1.5

And before you say anything, torque is directly proportional to mep (in theory; in practice, I know that you have to considered friction mep as well). So, in theory, the torque also remained constant as the speed increases. The rest of the post (not me, the reference) explains why practice differs from theory.

Quote (LionelHutz)

You posted that complete nonsense about electrical motors being constant HP and having limitless torque at low rpm's as if it was a fact. You backpedaling with this "in theory" BS to justify your claims. Now you're saying they are constant torque up to a certain speed, but that doesn't matter because it's only a small portion of the operating range? I can't even follow what you're claiming anymore.

I said in theory electric motors have infinite torque at zero rpm. Of course, there is an actual limit in practice (as I have stated). And that limit will apply within a certain speed range, i.e. when you will reach rpm = Pmax / Tmax. I think I clearly demonstrate, with appropriately referenced real world examples, that it is a small portion of the rpm range (Of course, one can use an oversize motor for their needs and use it only in the lower rpm range). You have to be of bad faith to twist my words that way.

Quote (LionelHutz)

The fact that the locomotive specific application runs a motor well above the voltage limit doesn't change anything about what I posted. [...] The locomotive is a rather specialized application.

I'm sorry if the theory that I did not create - that I can provide references from other quality sources - do not match your unreferenced statements. I'm sorry if electrical motors used in cars and locomotives do not match you electric motor experience.

Quote (LionelHutz)

You should really be more careful with your broad generalized use of "electric motors". The series wound DC locomotive motor in not the only type of electric motor.

I'm not specialized in electrical motors, so sorry if I did not mentioned «series-wound» electric motors as was specified in one of my source. One would think that someone specialized in that domain would of understood what I was referring to.

I just brought up the electric motor to explain to another person how we can approximately generalize a power curve for different power sources, which was not even an important statement by itself. banghead

Because, in the end, my point is that engine load is a synonym for engine torque. Period (as would say Panther140).

Now, if some people want to twist my words by selecting them one by one and then taking something out of their head with absolutely no reference other than «I'm right because I know», have your fun at it. But if you will accuse me of being wrong and laugh at me, I will defend myself with arguments and references.

RE: What is Engine Load?

"Because, in the end, my point is that engine load is a synonym for engine torque. Period (as would say Panther140).

Now, if some people want to twist my words by selecting them one by one and then taking something out of their head with absolutely no reference other than «I'm right because I know», have your fun at it. But if you will accuse me of being wrong and laugh at me, I will defend myself with arguments and references."

This is a good thread with opposing viewpoints, not adversary ones! This is engineering stuff its supposed to be fun!!

Just to clarify what I mean when I say that Engine load is the sum of all forces acting against the engine:
- An engine that makes 100 ft/lbs of torque at XXXX RPM under WOT would be under 100% load if it were spinning something that required 100 ft/lb of torque to move at whatever RPM it is at.
- Load can be independent of available engine torque
- Load and available Torque at XXXX rpm are independent variables
- Acceleration and deceleration of the system compensate for differences in Available torque and engine load.. until other limiting factors come in to play.
- An engine's own parts can add to the load it faces (picture a 2 ton crankshaft in a 4 cylinder engine, or a massive flywheel)

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

RE: What is Engine Load?

The best I can say,or what I am acqainted about it,is when I had installed megajolt onto one of my cars. I've known it to be the plenum vacuum

RE: What is Engine Load?

I swore to myself I wouldn't peek at this thread again... but I'm feeling ill to my stomach and thought this might help resolve it.

Not that it really matters, but those who would say that "engine load" can only mean "torque" might struggle to explain why SAE J1995 would offer "a method for determining gross full load engine power with a dynamometer." If "load" can only mean torque, then there's no single value for "full load engine power" on a variable speed engine, is there?

In fairness, that was the original version (1995 - 2013) and in the revised version (2014) the omit the term "load" altogether. Guess some folks found it confusing.



RE: What is Engine Load?

Quote (ivymike)

but those who would say that "engine load" can only mean "torque" might struggle to explain why SAE J1995 would offer "a method for determining gross full load engine power with a dynamometer." If "load" can only mean torque, then there's no single value for "full load engine power" on a variable speed engine, is there?

I don't have a copy of J1995, but J1349 (2004) - which is the same standard but for net values instead of gross values - mentions also «A method for determining net full load engine power and torque with a dynamometer».

Looking at the definition section:

Quote (J1349)


3.1 Net Brake Power and Torque

The power and torque produced by an engine at any speed [...]

So these values are measured with respect to a given rpm. There is not just a single value for an engine (As opposed to «Rated Net Power and Torque» also defined in the standard and means «the peak Net Brake Power and Torque produced by the engine within the operating speed range»).

So, according to the standard definitions, «net full load engine power and torque» means «net engine power and torque @ full load condition» which also means that all 3 values (power, torque & load) are rpm dependent.

There are no definition for «load power» or «load torque» in the standard.

RE: What is Engine Load?

You have a MJLJ running on the MAP sensor (I also have one). You can get a MJLJ that uses a TPS to find laod, in which load is measured as a percentage based on Throttle Position. If you boost your car with the MAP sensor, then it will tell you that your engine is operating with 230 kpa in the intake manifold. Does that mean your engine is at 230% load? How could it when the TPS version simply says its at 100% load?

Conclusion: Manifold pressure is just a sypmtom/effect. Engine load is the cause of it.

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

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