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Old 1st May 2008, 15:25   #1
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Arrow Pumps with fuel density display

Some pumps have installed density meters at the pumps. Here is a interesting read about when to tank up.

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There goes a saying, that you should fuel when the climate is cool, since its generally cooler in the night then in the day, the volume of fuel you get for your money is more than what you would get if you fuel in the daytime instead, since its warmer in the day.

So u get slightly more fuel and a better mileage. Well as you can see in the pics above, a few petrol pumps have gone ahead and installed a display which shows the density of fuel. However in theory, you will get slightly more fuel when the temperature is cooler, but in practice, it doesn't work that way as most gas tanks are buried in the ground, and the fuel is insulated well enough that it won't change temperature noticeably over the course of the day or night. So tank up whenever you feel like, cool or not, it wont make a difference, unless there is large temperature variation between day and night.
Source of above article
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Pumps with fuel density display-dsc00398-large.jpg  

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Old 1st May 2008, 15:39   #2
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You beat me to it.
its been over a month since i've been gassing up in these pumps. the fuel bunk guys don't know what it is...
i've noticed marginal variations of about 3-4% between midday and night fillings.
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Old 1st May 2008, 15:58   #3
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if there ain't no difference, then why did they install the meter?..
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Old 1st May 2008, 16:09   #4
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Originally Posted by nitrous View Post
i've noticed marginal variations of about 3-4% between midday and night fillings.
Variations as in positive during the evenings and later as per common understanding?

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i've been gassing up in these pumps. the fuel bunk guys don't know what it is...
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Old 1st May 2008, 16:10   #5
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Default Great.

Its nice to see such pumps. Till now I havent tried to make out the difference between day and night fillings. I will try out now.


I hope these pump meters become very common as they can really help one make out the difference.
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Old 1st May 2008, 16:22   #6
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its been over a month since i've been gassing up in these pumps. the fuel bunk guys don't know what it is...
Poor chaps! The stink must be bad eh?
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Old 1st May 2008, 16:31   #7
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Quote:
Originally Posted by aaggoswami View Post
I hope these pump meters become very common as they can really help one make out the difference.
The meters shown in the pictures will not help because the displayed density is at 15 deg C (and presumably, atmospheric pressure). You are not seeing the actual density of the fuel at the current temperature as it is pumped into your car. You ought to see the same numbers at those meters regardless of the time of the day, assuming you are getting the same quality fuel. The guy who wrote the article doesn't know some basic physics.

Edit: And note that the article says

Quote:
There goes a saying, that you should fuel when the climate is cool, since its generally cooler in the night then in the day, the volume of fuel you get for your money is more than what you would get if you fuel in the daytime instead, since its warmer in the day.
False! The *volume* is the same as what is indicated at the pumps (i.e., "x" litres) regardless of the time of the day. It is the *weight* of the fuel that changes according to the ambient temperature because of slight variations in density.

Last edited by rks : 1st May 2008 at 16:45.
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Old 1st May 2008, 19:00   #8
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Originally Posted by iraghava View Post
Poor chaps! The stink must be bad eh?
ROFL..ROFL..IShaan..when are you coming here..Atlast NItrous has found a job!!..Poor Fellow attendants..
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Old 1st May 2008, 19:24   #9
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Quote:
the fuel bunk guys don't know what it is...
An innocent guess - Nitro-methane?
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Old 1st May 2008, 19:53   #10
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Quote:
Originally Posted by rks View Post
The meters shown in the pictures will not help because the displayed density is at 15 deg C (and presumably, atmospheric pressure). You are not seeing the actual density of the fuel at the current temperature as it is pumped into your car. You ought to see the same numbers at those meters regardless of the time of the day, assuming you are getting the same quality fuel.
Hi RKS, could the values being displayed be "temperature corrected" to 15 degrees C ? If I remember correct, fuel is bought & sold with a temperature correction to 15 degrees C since as you've mentioned, density varies with temperature.

Plus, if these are invariant values, one would assume that a dynamic display like these would not be needed since density of petrol or diesel at 15 degrees C is a constant.
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Old 1st May 2008, 20:01   #11
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Originally Posted by im_srini View Post
Hi RKS, could the values being displayed be "temperature corrected" to 15 degrees C ?

Plus, if these are invariant values, one would assume that a dynamic display like these would not be needed since density of petrol or diesel at 15 degrees C is a constant.
Yes, the density displayed should be a constant for a particular fuel, regardless of the ambient temperature, since it has been corrected to 15 deg C. The reason it may be displayed is to assure the customer that unadulterated fuel is being supplied. E.g. suppose the petrol is adulterated with kerosene or naptha. Then you will see a variation in the displayed density. Of course for this to be useful you should first know what is the acceptable range for the density of normal unadulterated fuel at 15 deg C.
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Old 2nd May 2008, 01:10   #12
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I feel like most people are missing the main purpose of these meters, which is to prevent / indicate adulterated fuel.

Forget about the "cool in the mornings" theory which will save you a tiny amount, the bigger issue is buying adulterated fuel - which could cost you a lot more.

Quote:
Originally Posted by rks View Post
The meters shown in the pictures will not help because the displayed density is at 15 deg C
Yepp. The readings are temperature stabilized to prevent exactly that.

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Originally Posted by im_srini View Post
If I remember correct, fuel is bought & sold with a temperature correction to 15 degrees C since as you've mentioned, density varies with temperature.
That makes a lot of sense, i didnt know 15*C was the standard, thanks for sharing that info.

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E.g. suppose the petrol is adulterated with kerosene or naptha. Then you will see a variation in the displayed density. Of course for this to be useful you should first know what is the acceptable range for the density of normal unadulterated fuel at 15 deg C.
Exactly! (The lower the density, the more of adulterant has been added to the fuel).

This however makes me wonder if they are going to figure out some way to adulterate fuel without changing the density as much - in which case it probably will be an adulterant that is worse for our car engines than the current adulterants.


I also remember reading this article (probably on TBHP) about another way to detect adulteration - something like very very small amounts (a few parts per million) of substance X are added to all the commonly known adulterants at the time of they are produced.
Hence, to test the fuel, you simply check for any traces of substance X in the fuel, and if it does exist - that means the fuel has been adulterated!

Can anyone find the link to that article?

cya
R
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Old 2nd May 2008, 09:15   #13
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Quote:
Originally Posted by Rehaan View Post
I feel like most people are missing the main purpose of these meters, which is to prevent / indicate adulterated fuel.

Exactly! (The lower the density, the more of adulterant has been added to the fuel).

cya
R
I too wanted to post about this!

I fill up from IOCL pump and use normal diesel. Its always shows 827 of whatever units whenever I fill (mostly morning). I also noticed that the red LED stays ON denoting that its not NORMAL.

The next fueling unit has XtraMile and its reading is 832 or so and its has green LED ON denoting its NORMAL.


As Rehaan said,is it coz Xtra has those extra additives and hence shows normal and the other without those extras and hence ...?
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Old 4th May 2008, 09:13   #14
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Default Yes.

Quote:
Originally Posted by rks View Post
The meters shown in the pictures will not help because the displayed density is at 15 deg C (and presumably, atmospheric pressure). You are not seeing the actual density of the fuel at the current temperature as it is pumped into your car. You ought to see the same numbers at those meters regardless of the time of the day, assuming you are getting the same quality fuel. The guy who wrote the article doesn't know some basic physics.

Edit: And note that the article says

False! The *volume* is the same as what is indicated at the pumps (i.e., "x" litres) regardless of the time of the day. It is the *weight* of the fuel that changes according to the ambient temperature because of slight variations in density.
Yes I agree with you. I had to do some good amount googling to find out and bang, there was your post.



Quote:
I feel like most people are missing the main purpose of these meters, which is to prevent / indicate adulterated fuel.

Forget about the "cool in the mornings" theory which will save you a tiny amount, the bigger issue is buying adulterated fuel - which could cost you a lot more.
Yes that is the main point about the Indian fuel.
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Old 5th May 2008, 16:49   #15
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What should be the ideal display on the meter for unadultered fuel?
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