fuel economy

[jerrye]

Earlier post was incorrect. BMW has hydrogen-burning engine in 7-series. See two links below:
http://www.businessweek.com/2000/00_38/b3699304.htm
http://archives.cnn.com/2001/TECH/sc...hydrogen.cars/

[Jim-Iowa]

quote:Originally posted by Kristofor

quote:Originally posted by Jim-Iowa
And if you drive a car built in the last 5 yrs, most are also set up to burn 85% alcohol, very few know that. check yur owners manual for an E85 rating? the only problem with that is a weak distribution network so far.

Well, the other problem is that ethanol has about half the energy content as gasoline so you'll see your mileage drop significantly even though the cost per gallon may be comparable or slightly lower.

Kristofor.

Thats not true at all! I have been using nothing but ethanol since the 70`s. No performance difference in any vehicle I have owned.
Now pure alcohol burns cooler but is less dense than gasoline(70% if I remember corectly).
The racers use it because they can get almost twice the volume of fuel/air in the same area of combustion chamber, therefore higher performance.

[Kristofor]

quote:Originally posted by Jim-Iowa

quote:Originally posted by Kristofor
Well, the other problem is that ethanol has about half the energy content as gasoline so you'll see your mileage drop significantly even though the cost per gallon may be comparable or slightly lower.

Kristofor.

Thats not true at all! I have been using nothing but ethanol since the 70`s. No performance difference in any vehicle I have owned.
Now pure alcohol burns cooler but is less dense than gasoline(70% if I remember corectly).
The racers use it because they can get almost twice the volume of fuel/air in the same area of combustion chamber, therefore higher performance.

Okay, this is my last post on this, as it's too close to a political topic I suppose.

For that reason I'll try to keep this objective.

The energy used to power your combustion engine is derived from the oxidization of the fuel.

Alcohol is essentially a saturated hydrocarbon that has already been partially oxidized (burned). That reduces the amount of energy available to do work for you.

The energy content of Ethanol has 26.68 MJ/kg
The energy content of Gasoline varies but is about 42-44 MJ/kg
Hydrogen (H2) for comparison is 122MJ/kg (but there’s not a practical storage solution at this time)

In the best case scenario Ethanol has ~60% of the energy in a similar mass of gasoline.

Ethanol has a density of 789kg/m^3
Gasoline has a density of about 737kg/m^3
Which gives Ethanol a few percent back due to higher mass per gallon.

If we replace 85% of the gasoline with another fuel that has 64% of the energy we end up with a total energy in the mixture of 15% + (85% * %64) = ~70% of the total energy of straight gasoline.

This of course means you will need to buy about 40% more fuel to run E85. Depending on the cost of the various fuels this may still be less expensive.

The following chart is from the government website that lists the EPA mileage of flexible fuel vehicles when running on gasoline and again when running E85. As expected there is a significant reduction in mileage when using E85

http://www.fueleconomy.gov/feg/byfuel/FFV2005.shtml
[edit: pointed to the current year's models rather than the one from the year my vehicle was made]

In smaller volumes ethanol can be added to gasoline without reducing the energy content quite as much as would otherwise be expected. This is because it will serve the same anti-knock purpose as using higher octane gasoline (which contains less energy than lower octane fuel).

THAT is why race cars will run on methanol (not ethanol), it contains even less energy per unit mass, but because it has a much higher octane rating it allows for a much higher compression ratio without premature ignition. This allows them to compress more air AND more fuel in single compression cycle. This produces more horsepower and uses more fuel in a shorter period of time, advantageous when racing perhaps less so heading to the store. Another benefit of alcohol as a racing fuel is that it is a polar molecule and will dissolve in water. When diluted enough (with a fire hose) it no longer generates enough heat from combustion to sustain a reaction, which is nice if you happen to crash and become soaked with fuel.


Kristofor.

[don_hart]

Jim I agree that we should not be buring oil or natural gas or for that matter coal in our power plants. At present the safest most efficient and cleanest form of power we have at our disposal is nuclear power. We should be replacing all of our feul burning power plants (with the exception of trash burning plants) with nuclear plants.

Unfortunately there is an unreasoning fear of nuclear power in the US. It is one of the best examples of perceived danger as opposed to real danger.

Bob I would have to agree that hydrogen is lighter than air. It is not just highly flammable it is explosive. Contary to what we see in the movies it is actually quite difficult to create a gasoline explosion. To get a true gasoline explosion it is nessesary to disperse gasoline as an areosol or to create a large enough volume of concentrated fumes . Hydrogen on the other hand has a naturally gaseous state and even lightly contained will reach an explosive mixture with air quite quickly.

Yes you will not get pools of burning feul on the ground but is it much better to have a burning pool of gas than a feul air explosion.

[pierhogunn]

One of the things that did allow some of the passengers of the hindenburg to escape is that as it burns, Hydrogens goes up into the atmosphere, so the ground hugging fireballs that you get from misted gasoline.

There is a neat article at www.sciam.com about a technique for turning exhaust into O2 and Water using blue-green alge, sunlight, and plastic mesh... good read

Dan

[Kristofor]

quote:Originally posted by don_hart

At present the safest most efficient and cleanest form of power we have at our disposal is nuclear power. We should be replacing all of our feul burning power plants (with the exception of trash burning plants) with nuclear plants.

I agree, and in fact there has been a bit of a shake up in a few well known environmental conservation groups where prominent members have called for people to look to nuclear as the "least bad" large scale generator technology.

Fission isn't an ideal process (potential weapon precursors from some designs, medium lenght half-life isotopes produced, etc) but it's clearly better than burning even "clean" coal or oil and even better than burning natural gas or propane if one is concerned about CO2 emissions. There is also plenty of capacity to add these plants and run them for years.

The various other technologies like solar or kinetic generation (hydro, wind, wave, tidal) are also attractive to a greater or lesser extent though they all have their own environment concerns as well. Long term everyone hopes that ITER will pan out and prove deuterium/tritium is commercially viable with the hope for deuterium/deuterium reactions down the road, but I wouldn't hold off on building more capacity today on hopes that are decades away.

Kristofor.

[Tom J]

I wish I knew the answers. I remember when gas prices went from $.30 a gallon to $.50+ in 1973. We were quickly inunidated with small fuel efficient cars. These cars were, by in large, terrible to drive. However, they paved the road for more efficient well built cars. If my memory serves me correctly, by the late 1980's and early 1990's most family sedans got at least 20 to 25 mpg and seemed adequately powered. I am not sure if it was marketing, shortsightedness or what, but by the end of the 1990's everyone seemed to want an SUV. I succumbed to this and now have a 1999 Explorer with an V8 sitting in my driveway. I don't think it is a bad automobile, but it gets 18 mpg on the highway and probably no more than 12 mph in town. Filling it up requires a second mortgage. But of course we are able to travel the two miles of dangerous pavement between our house and the grocery store with no problem. Why we bought or even thought we needed such a vehicle is beyond me, but it seems everyone in our neighborhood has one.

Excuse the ramblings, but it seems that we never learn. I know that at an early age I decided that my driving pattern necessitated only that the car get me from point A to point B in relative comfort with a minimum of trouble. Nothing has changed in my driving pattern, nor do I believe that my earlier decision was wrong, but I sure as **** did not follow it and now I am literally paying the prie.

[Jeff]

I vote Nuke. Small rods, lotsa water. You won't even have to turn your heater on in the winter. The car will be warm when you get in it.
North Korea will probably punch out a bunch of fuel-rod nuke-powered Hyundais before too long, especially since they "are not using them for missles".

[Stick]

[quote]quote:Originally posted by Kristofor

Originally posted by don_hart

At present the safest most efficient and cleanest form of power we have at our disposal is nuclear power. We should be replacing all of our feul burning power plants (with the exception of trash burning plants) with nuclear plants.

The scary part about nuke generation isn't even the chance of an accident, but the thought of how you de-commission a nuke plant when it's past its useful life expectancy. General life expectancy of a Hydro plant is around 75-100 years, steam of any sort, around 50 years. Nukes generate by making steam. So now after that 50 years, what do you do with the radioactive sections of the plant and its waste fuel for the next 40,000 years or more? With a hydro plant, you can re-divert the river around it and build a new one, or just open the spillway and let it go back to the way it was before. Here in Canada we have HUGE undeveloped hydro sites that would flood only existing river banks, unused because a few bats nest in the river banks. Excuse me for living, but what is the alternative? Chernobyl? Three eyed cows? Acid rain? No electricity? Screw the bats!