talking about fuel...
27-06-2014, 05:41 PM
#1
talking about fuel...
Can anyone explain to me how fuel economy works?
Using my own car as an example it will do 30mpg on the motorway at 60 mph, it's got a 60 litre tank which means it'll do 400 miles before it runs out
So in 6 hours and 40 minutes it'll be out of fuel
On my daily commute it does 20 mpg and it takes 30 minutes each way to do the 10 miles, but going by that logic it's going to last me twice as long doing less mpg but running for a longer time
So, how does that work?
Using my own car as an example it will do 30mpg on the motorway at 60 mph, it's got a 60 litre tank which means it'll do 400 miles before it runs out
So in 6 hours and 40 minutes it'll be out of fuel
On my daily commute it does 20 mpg and it takes 30 minutes each way to do the 10 miles, but going by that logic it's going to last me twice as long doing less mpg but running for a longer time
So, how does that work?
27-06-2014, 05:58 PM
#2
PassionFord Post Whore!!
You're trying to compare Apples to Oranges with holes in.
LESS MILES TRAVELLED
If you left the car sat on the drive ticking over it would keep running for days.
LESS MILES TRAVELLED
If you left the car sat on the drive ticking over it would keep running for days.
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28-06-2014, 07:20 AM
#8
It's all about efficiency mate. It takes a lot of energy to accelerate something, but very little to maintain its velocity.
Try to think of it this way.... Imagine how hard it is to push a car yourself from a standstill, to actually get it up to say, 20mph. Getting it moving is hard.
Now think how hard it is to just keep it rolling at that speed. Pretty easy.
Engines are the same, but their energy is provided by fuel. To maintain 60mph in your average sized car requires only about 5bhp worth of fuel.
To accelerate it from 20 to 30 requires a lot more, and in the city commute your accelerating constantly in stop start traffic.
If I asked you to walk along and maintain a cars speed at 20mph on a flat road for an hour you could probably manage it.
If I asked you to stop and start the same car up to 20mph then back to zero and repeat it constantly, I bet you could manage about 3 attempts before you collapsed. Lol
Try to think of it this way.... Imagine how hard it is to push a car yourself from a standstill, to actually get it up to say, 20mph. Getting it moving is hard.
Now think how hard it is to just keep it rolling at that speed. Pretty easy.
Engines are the same, but their energy is provided by fuel. To maintain 60mph in your average sized car requires only about 5bhp worth of fuel.
To accelerate it from 20 to 30 requires a lot more, and in the city commute your accelerating constantly in stop start traffic.
If I asked you to walk along and maintain a cars speed at 20mph on a flat road for an hour you could probably manage it.
If I asked you to stop and start the same car up to 20mph then back to zero and repeat it constantly, I bet you could manage about 3 attempts before you collapsed. Lol
Last edited by Stu @ M Developments; 28-06-2014 at 07:23 AM.
28-06-2014, 07:22 AM
#9
15K+ Super Poster!!
Also, in town driving, you are constantly accelerating the car from a standstill. This requires much more power and energy than simply maintaining a reasonable speed.
Rick
02-07-2014, 08:19 AM
#10
It's all about efficiency mate. It takes a lot of energy to accelerate something, but very little to maintain its velocity.
Try to think of it this way.... Imagine how hard it is to push a car yourself from a standstill, to actually get it up to say, 20mph. Getting it moving is hard.
Now think how hard it is to just keep it rolling at that speed. Pretty easy.
Engines are the same, but their energy is provided by fuel. To maintain 60mph in your average sized car requires only about 5bhp worth of fuel.
To accelerate it from 20 to 30 requires a lot more, and in the city commute your accelerating constantly in stop start traffic.
If I asked you to walk along and maintain a cars speed at 20mph on a flat road for an hour you could probably manage it.
If I asked you to stop and start the same car up to 20mph then back to zero and repeat it constantly, I bet you could manage about 3 attempts before you collapsed. Lol
Try to think of it this way.... Imagine how hard it is to push a car yourself from a standstill, to actually get it up to say, 20mph. Getting it moving is hard.
Now think how hard it is to just keep it rolling at that speed. Pretty easy.
Engines are the same, but their energy is provided by fuel. To maintain 60mph in your average sized car requires only about 5bhp worth of fuel.
To accelerate it from 20 to 30 requires a lot more, and in the city commute your accelerating constantly in stop start traffic.
If I asked you to walk along and maintain a cars speed at 20mph on a flat road for an hour you could probably manage it.
If I asked you to stop and start the same car up to 20mph then back to zero and repeat it constantly, I bet you could manage about 3 attempts before you collapsed. Lol
When idling the engine is using 100% of it's power just to overcome its own resistances. At very low speeds most of the power is being used for internal losses and the a little to actually move you forward. As you increase speed the engine becomes more economical as the balance between useful work and internal loss improves. Then, after a certain speed - which depends on vehicle - the economy will drop off due to friction in the drive train and aero.
Also, in town driving, you are constantly accelerating the car from a standstill. This requires much more power and energy than simply maintaining a reasonable speed.
Rick
Also, in town driving, you are constantly accelerating the car from a standstill. This requires much more power and energy than simply maintaining a reasonable speed.
Rick
i'm using more fuel but the engine is being run for a longer time, how is that scenario possible?
unless you have to assume that lots of time spent idling means it's not using any fuel at all? but it's constantly running and 20 mpg, regardless of how you look at it is worse than 30 mpg so which part of this conundrum am i missing?
or can i not see the forest for the trees
or am i not explaining it properly
02-07-2014, 09:09 AM
#13
However, you could then leave the car running outside work all day and use another 1 gallon of fuel going nowhere and drop that days MPG down to 15 miles per gallon as you have now used 2 gallons of fuel, but only traveled 30 miles. Does that help?
02-07-2014, 10:02 AM
#14
they penny has dropped after that post stu, thanks for the info 
i had been wondering about it for years ever since we went to the motorshow at the excel centre and the guy's who were doing the range rover off road course said that they'd only used half a tank of fuel in 3 days, now i know why
i had been wondering about it for years ever since we went to the motorshow at the excel centre and the guy's who were doing the range rover off road course said that they'd only used half a tank of fuel in 3 days, now i know why
02-07-2014, 10:51 AM
#15
WORK DONE consumes fuel.
Two types of work your engine needs to do:
Acceleration
Maintain momentum by overcoming friction and wind resistance etc
In stop-start driving you are doing lots of accelerating which uses a lot of fuel, at a steady held speed you arent.
also, idling in traffic gets you 0mpg for as many minutes as you are doing it of course.
(edit - should have read replies first, a lot of that is repeated!)
Two types of work your engine needs to do:
Acceleration
Maintain momentum by overcoming friction and wind resistance etc
In stop-start driving you are doing lots of accelerating which uses a lot of fuel, at a steady held speed you arent.
also, idling in traffic gets you 0mpg for as many minutes as you are doing it of course.
(edit - should have read replies first, a lot of that is repeated!)
02-07-2014, 10:36 PM
#16
PassionFord Post Whore!!
It's all about efficiency mate. It takes a lot of energy to accelerate something, but very little to maintain its velocity.
Try to think of it this way.... Imagine how hard it is to push a car yourself from a standstill, to actually get it up to say, 20mph. Getting it moving is hard.
Now think how hard it is to just keep it rolling at that speed. Pretty easy.
Engines are the same, but their energy is provided by fuel. To maintain 60mph in your average sized car requires only about 5bhp worth of fuel.
To accelerate it from 20 to 30 requires a lot more, and in the city commute your accelerating constantly in stop start traffic.
If I asked you to walk along and maintain a cars speed at 20mph on a flat road for an hour you could probably manage it.
If I asked you to stop and start the same car up to 20mph then back to zero and repeat it constantly, I bet you could manage about 3 attempts before you collapsed. Lol
Try to think of it this way.... Imagine how hard it is to push a car yourself from a standstill, to actually get it up to say, 20mph. Getting it moving is hard.
Now think how hard it is to just keep it rolling at that speed. Pretty easy.
Engines are the same, but their energy is provided by fuel. To maintain 60mph in your average sized car requires only about 5bhp worth of fuel.
To accelerate it from 20 to 30 requires a lot more, and in the city commute your accelerating constantly in stop start traffic.
If I asked you to walk along and maintain a cars speed at 20mph on a flat road for an hour you could probably manage it.
If I asked you to stop and start the same car up to 20mph then back to zero and repeat it constantly, I bet you could manage about 3 attempts before you collapsed. Lol
Just being picky mate but I know what you mean lol.
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