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Old 10th June 2011, 20:42   #16
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Default Re: Energy loss in a vehicle

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Originally Posted by Sutripta View Post
For estimating max speed - power reqd (or rather changes in these two) the predominant term is **2. Which is why everyone is familiar with it.

Tyres - ~ 1% of the weight of the vehicle. Doesn't seem like much, but at low speeds, it's a significant dissipative force.

No mention anywhere of the energy carried away by the exhaust. Or of pumping losses.

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Sutripta

Wouldn't exhaust losses be counted in the engine inefficiency (normally thermal loss) itself?

Pumping losses I don't understand, which pumps are we talking about? air inlet and exhaust ?
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Old 10th June 2011, 21:22   #17
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Default Re: Energy loss in a vehicle

^^^
Know this is not really an engine thread, but since people were commenting on engines, was wondering why these were not mentioned.

The IC engine is essentially an air pump. Doesn't like being strangled.

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Sutripta
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Old 10th June 2011, 22:04   #18
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Default Re: Energy loss in a vehicle

I don't know if this is too insignificant to be mentioned but what about the energy loss that happens in a vehicle to electrical outputs? ICE, lights : aren't they all in a way loss of the energy of vehicle? Ultimately the power is derived from the engine.

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Originally Posted by dot View Post
Engine loss = constant as coolant takes care of excess energy in form of heat transfer and that energy is passed on to atmosphere by radiator.
If you observe, when the car remains steady at high speed, the engine temp. actually is lower than when it might not be running at a steady low speed.

So, I'm not sure how engine loss in the form of heat works.

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The much bandied about 25% transmission loss is I think a conspiracy hatched by tuners and modifiers. Even the 10% I'll put on the higher side. Anyway, I've stopped arguing about this a long time back.
Could you elaborate on transmission loss?
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Old 10th June 2011, 22:36   #19
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Default Re: Energy loss in a vehicle

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Originally Posted by Sutripta View Post
No mention anywhere of the energy carried away by the exhaust. Or of pumping losses.
Quote:
Originally Posted by vina View Post
Wouldn't exhaust losses be counted in the engine inefficiency (normally thermal loss) itself?

Pumping losses I don't understand, which pumps are we talking about? air inlet and exhaust ?
I guess Sutripta is also mentioning the kinetic energy of the exhaust gases, which is significant. No idea about the numbers, though.

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Originally Posted by libranof1987 View Post
... what about the energy loss that happens in a vehicle to electrical outputs?
They are not loses. They are requirements for the mechanism called 'automobile' to function and yes, are derived from the engine. If there is a short circuit, then there is a loss.
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Originally Posted by libranof1987 View Post
If you observe, when the car remains steady at high speed, the engine temp. actually is lower than when it might not be running at a steady low speed.

So, I'm not sure how engine loss in the form of heat works.
That is because the outside air is most efficient in cooling the coolant at speeds.

Quote:
Originally Posted by libranof1987 View Post
Could you elaborate on transmission loss?
The power or torque developed by the engine is different when measured at crank shaft and the wheels. The difference is transmission loss and is lost when the power is transmitted from the crank to the wheel.

Last edited by dhanushs : 10th June 2011 at 22:38.
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Old 10th June 2011, 23:04   #20
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Default Re: Energy loss in a vehicle

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Originally Posted by dhanushs View Post
...

They are not loses. They are requirements for the mechanism called 'automobile' to function and yes, are derived from the engine. If there is a short circuit, then there is a loss.

....

Let's call them losses - after all evergy needed by cam to operate, the heat needed to increase the engine's temperature to the point where lubricants can work optimally etc. are also requirements for the automobile to work, and we still call them losses.

Power spent in AC, music system etc. on the other hand is not a loss - though let's account for that too (but separately)
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Old 17th June 2011, 01:12   #21
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Default Re: Energy loss in a vehicle

It is pretty straightforward to figure out what the aero and mechanical rolling resistance losses are in a vehicle. For mechanical rolling resistance, you start rolling at a low speed, say 25 km/h, then shift to neutral, and measure the time it takes to get to a very low speed, such as 5 km/h. Repeat this at different speeds (say, initial velocity 15,20,25,30,35 km/h), and also do equal number of runs in opposite directions to isolate any influence of grade or slope.

Then take the data, plot speed vs deceleration and fit a straight line to it (y=mx+b). m will give you rolling resistance co-efficient.

To measure aero drag, you do the same test, except at higher speeds. Fit a 2nd order line to it (y=nx^2+mx+b), and n will be a very good approximation of Cd or aero drag co-efficient. m will be roughly the same as from the previous test.

Alternatively you can also estimate the frontal area of the vehicle, calculate air density at the test site using temperature and pressure, measure weight accurately, and then calculate the Cd. But I suspect the results will be close to just doing it the non-analytical way.

if it is a small and light vehicle like a go-kart, you can use a fishing scale and a strong person to physically pull the vehicle in a straight line. That will give you the rolling resistance force directly from the scale.
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Old 17th June 2011, 07:19   #22
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Default Re: Energy loss in a vehicle

This pdf which i'm posting is the DEFINITIVE description of all transmission losses & LOTS of other useful info as well. Will definately dispel a LOT of myths, especially the last page.
Attached Files
File Type: pdf Power Tain Performance Vs Engine Performance.pdf (214.0 KB, 227 views)
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Old 17th June 2011, 10:40   #23
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Default Re: Energy loss in a vehicle

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Originally Posted by ananthkamath View Post
It is pretty straightforward to figure out what the aero and mechanical rolling resistance losses are in a vehicle. For mechanical rolling resistance, you start rolling at a low speed, say 25 km/h, then shift to neutral, and measure the time it takes to get to a very low speed, such as 5 km/h. Repeat this at different speeds (say, initial velocity 15,20,25,30,35 km/h), and also do equal number of runs in opposite directions to isolate any influence of grade or slope.

Then take the data, plot speed vs deceleration and fit a straight line to it (y=mx+b). m will give you rolling resistance co-efficient.

To measure aero drag, you do the same test, except at higher speeds. Fit a 2nd order line to it (y=nx^2+mx+b), and n will be a very good approximation of Cd or aero drag co-efficient. m will be roughly the same as from the previous test.

Alternatively you can also estimate the frontal area of the vehicle, calculate air density at the test site using temperature and pressure, measure weight accurately, and then calculate the Cd. But I suspect the results will be close to just doing it the non-analytical way.

if it is a small and light vehicle like a go-kart, you can use a fishing scale and a strong person to physically pull the vehicle in a straight line. That will give you the rolling resistance force directly from the scale.

Hi Ananth

thanks for an easy measurement method. however this will give the numbers for a particular car not a generic analysis. Also the break up of rolling resistance will not be available, and since the engine will be off some resistance components may not be accounted for.


But this seems to be a fun experiment - let me see if I can get time and an open road on the weekend.


Quote:
Originally Posted by 1self View Post
This pdf which i'm posting is the DEFINITIVE description of all transmission losses & LOTS of other useful info as well. Will definately dispel a LOT of myths, especially the last page.

The last page tells you that most car specs are (basically) barely indicative and there is probably a huge variation in manufacturing.

Do you have anything that gives a breakup of how much power is wasted where?

Last edited by vina : 17th June 2011 at 10:47.
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Old 3rd August 2013, 04:50   #24
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Default Re: Energy loss in a vehicle

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Originally Posted by vina View Post
Hi Ananth

thanks for an easy measurement method. however this will give the numbers for a particular car not a generic analysis. Also the break up of rolling resistance will not be available, and since the engine will be off some resistance components may not be accounted for.


But this seems to be a fun experiment - let me see if I can get time and an open road on the weekend.

The last page tells you that most car specs are (basically) barely indicative and there is probably a huge variation in manufacturing.

Do you have anything that gives a breakup of how much power is wasted where?
There is little else on the planet more inefficient than a motor car, especially when it is nearly new, will last only ten years due to uneconomic repair expense as it becomes older and is one of the bigger and faster incarnations of our beloved machine. In Britain, for example, air pollution kills as many people as road accidents do. Now we have much less road-kill than in India, but this is still a very significant statistic. It is also an aspect of the motor vehicle's inefficiency. The energy cost of a road traffic accident is enormous, even (more so) if the victim survives - think of the congestion, medical treatment, loss of production and so on.

So the breakdown of how much energy is wasted where? Rather than give a percentage approximation of how much more energy is lost in third gear rather than fifth or sixth, of how much more is lost when greases and oils are gloopy due to age or temperature, perhaps I should focus peoples' minds on how totally inefficient a new luxury car is. Rather than go in to great detail about all this, there is a basic law which suggests that the more money you spend, the more damage you do to the world.
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Old 17th August 2013, 01:53   #25
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Default Re: Energy loss in a vehicle

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There is little else on the planet more inefficient than a motor car,
especially when it is nearly new, will last only ten years due to uneconomic repair expense as it becomes older and is one of the bigger and faster incarnations of our beloved machine.
...
Interesting, I always thought older cars are are more inefficient. Do you have any numbers?

Also I didn't understand the in-car-nation part

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In Britain, for example, air pollution kills as many people as road accidents do. Now we have much less road-kill than in India, but this is still a very significant statistic. It is also an aspect of the motor vehicle's inefficiency. The energy cost of a road traffic accident is enormous, even (more so) if the victim survives - think of the congestion, medical treatment, loss of production and so on.
I'm not sure this is relevant or even appropriate for a "Tech Stuff" thread

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So the breakdown of how much energy is wasted where? Rather than give a percentage approximation of how much more energy is lost in third gear rather than fifth or sixth, of how much more is lost when greases and oils are gloopy due to age or temperature, perhaps I should focus peoples' minds on how totally inefficient a new luxury car is. Rather than go in to great detail about all this, there is a basic law which suggests that the more money you spend, the more damage you do to the world.

Again who ever talked of the luxury car? Why are we talking about this on "Tech Stuff"?

And kindly don't tell the last part of your wisdom to the ilk of Bill and Melinda Gates.
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Old 17th August 2013, 03:57   #26
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Default Re: Energy loss in a vehicle

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Interesting, I always thought older cars are are more inefficient. Do you have any numbers?
I am considering more than just the obvious, Mr Vina. Energy consumed by a car isn't measured simply through fuel consumption alone. Although the heavier a car, the more fuel it is likely to consume. And cars have steadily become less light down the years. By 1994 good cars had become very efficient in the engine department - an early 90s Golf TDi will easily beat 60 mpg.
It's easy to forget the energy consumed in making the car and the materials it's formed from in the first place. It follows that the older it is, the less its carbon footprint from its manufacture, per mile. http://portal.unesco.org/education/e...and+energy.pdf

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Also I didn't understand the in-car-nation part
https://en.wikipedia.org/wiki/Incarnation

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Originally Posted by vina View Post
Again who ever talked of the luxury car? Why are we talking about this on "Tech Stuff"?
So should I place a reply to this in a different section? It could get rather confusing. Besides, the reply was about energy efficiency. Which is broadly related to energy loss. Which is the title of this thread.

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And kindly don't tell the last part of your wisdom to the ilk of Bill and Melinda Gates.
He would completely understand - as would most who are educated in the challenges of the 21st century. Embodied energy is an important concept. Energy production generally means pollution, and there is a basic correlation between the energy embodied in a product and its cost. (In fact, embodied energy is usually under-priced, since we are storing up pollution for our descendants.)

There is a difference between spending money on a well for a remote village and somebody buying a new mobile phone every year. This is a good example of how the cost/embodied energy rule of thumb cannot be blindly applied. Not only does a well benefit many people, but it can help prevent disease and uses little or no energy once it is built. In contrast, the latest mobile phone is a cornucopia of energy density and pollution.
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