33 mpg 2004 Civic

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Edward W. Thompson wrote:


Actually, I taught science 101. If the gas is denser, that means that in every gallon or liter that is colder, you get more energy. More energy means you go farther.
If the gas is 20 degrees F colder, it contains about 1% more energy or about a 0.4 mpg difference. If the gas is stored in an underground container, the gas temperature should be pretty constant. However, the gas can get colder or warming in transport and when going through the pipes in the ground.
http://www.users.qwest.net/~taaaz/AZgas.html
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wrote:

Haven't you moved the goal posts? You now are saying that the temperature of the gas from an underground storage tank will be essentially constant. We can agree upon that, so a gallon of fuel in the winter is essentially the same volume as that in the summer. Hence in energy terms a gallon of 'summer' fuel is the same as that of 'winter' fuel. Please explain why winter driving is more fuel efficient than summer driving. Winter driving is often more fuel efficient as the driver generally will operate his vehicle more conservatively due to road conditions.
Where 'benefit' may occur at low ambient temperature is the air is more dense hence for a given volume, cylinder capacity, a greater charge of air can be ingested per stroke which will allow more fuel to be burned hence greater output. That is why intercoolers are used tp cool the air in turbo charged engines, in case you didn't know. This has nothing to do with increase in fuel efficiency, simply a potential increase in power for a given size of engine.
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Jeff wrote:

yes, colder is denser, but formulation changes seasonally. winter gas has more ethanol, and ethanol has a lower calorie content, hence lower mpg.
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jim beam wrote:

yes, I already pointed out that E15 has about 4.5% less energy that E0 gas.
I don't know how much difference the cold temperature makes, because most tanks are underground. In theory, none, because the underground temperature is fairly constant usually about 10 to 15 C, but, the gasoline may be significantly colder when it is dumped from the trucks into the ground. And gasoline is not immediately heated or cooled in those huge underground tanks. It might take a couple of days until it reaches a steady temperature of about 15 C. But the gasoline might not last that long in the tank. In addition, the gasoline might be cooled as it is passing through the pipes in the ground. If the gas is around 0 C, when it warms up to 15 C (about 59 F), it will expand by about 1.5%.
So the question is, what is the temperature at the point where the gasoline volume is measured as it is pumped?
http://www.users.qwest.net/~taaaz/AZgas.html http://www.usatoday.com/news/nation/2007-07-04-hot-fuel_N.htm
Jeff
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Jeff wrote:

gasoline shouldn't be sold by volume, it should be sold by the therm, like natural gas. that way, there's no gaming of the energy content, no class action lawsuits over gas being sold short in the summer because it's warm, etc...
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jim beam wrote:
<...>

That's an excellent idea. Plus, why should we pay the same tax on E10 as E0 when it has 3% less energy per gallon? Or E85, which has 35% less energy?
It shouldn't be hard to determine the energy content of different gasolines and adjust them for the temperature and any additives, like the oxygenates (usually ethanol) that are added to keep the exhaust clean.
Jeff
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Jeff wrote:

better yet, why should we subsidize farmers to produce the stuff and give tax credits to the oilcos to use it? we're getting the hose /three/ ways, not just with lower gas mileage.

just like natural gas.

that smells bogus. it adds to the "oxygen content" going in, but fwiu, since that oxygen atom is already bound in the molecule, it yields nothing to the reaction. adding a compound with nitrates would add to the reaction since they yield free oxygen, but that would add calorific value too, and that ain't gonna be allowed!
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On Thu, 24 Jan 2008 19:09:58 -0800, jim beam

It would still likely be metered by volume so you still have to either compensate for temperature or... not. The density of gas might vary by +/- 2% over any reasonable temperature range compared to it's density at 60F which is where it is theoretically sold. You get cheated a little in the summer and you cheat them a little in the winter, unless someone is intentionally heating it up.
Energy content by mass varies +/- 4% around the nominal 44.4 Mj/kg. 10% ethanol knocks it down another 3.3%. Economists would argue that the market is already compensating for this variability (in temperature and energy content), but economists never compensate for the fact that the butcher has his finger on the scale.
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Gordon McGrew wrote:

i'll take another 7.3% increase in revenue please! if you sell food, you're a brewer or a public utility, you get slammed for that game. oilco's? no problem!

indeed. well said.
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Gordon McGrew wrote:

I am sure that if they are delivering 1% more gasoline, they are increasing the price by 3%. But, I am not sure that in the summer that they lower the price by that amount.

No, the market is not compensating for either of these. The competition is based on the volume of gas, not the energy content. I have yet to see a sign that says, "our gas has 44,000 kJ per kg." And I rarely see signs that tell you if there is any ethanol in gasoline (I only remember one at a Sunoco station).
Most consumers are not aware that ethanol has less energy content that gasoline nor are they aware of the energy content of their gasoline or even if there is ethanol in their gas.
So the market doesn't compensate for the different energy contents.
A lot of people want to buy high octane gas to give their car a treat. People don't always make logical decisions. And, they don't gather info to make decisions.
Jeff
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wrote:

The argument is that, if I own a gas station, I have to make $X in profit per month to make it worthwhile. All the other gas station owners are in the same boat. If we all get busted for selling hot/low energy gas and we have to reform our ways and price our fuel by the joule, we will adjust our prices so that we will still earn at least $X per month or higher if the market will bear. Not saying I buy into this fully, but there is a kernel of truth to this.

Probably true. But I know it and what good does it do me? I still get my 10% ethanol gas at the same price as everyone else. In Illinois, you have no choice. I don't know if it provides any benefit to the gasoline industry either. If they are paying as much or more per gallon for ethanol as they do for gasoline, they aren't going to make any more money even if you are paying more per Mj.

Not directly, but it is not certain that the price would be any lower if they did.

Hence, the Hummer. Kind of puts the low density gas thing in perspective.
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i have an 03 civic lx coupe. in the summer i can get 46mpg by adding a bottle of stp to the oil, keep the tire pressure at 34lbs and drive 65mph.
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Timothy Stoughton wrote:

And you would get 46 mpg if you kept the tire pressure at 34 lbs and drove at 65 mpg and added a bottle of gas to the gasoline (i.e., the same volume of the STP).
You'd save money if you didn't use STP.
Jeff
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