Naked Science Forum
Non Life Sciences => Technology => Topic started by: neilep on 08/12/2008 15:54:08
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Dear Carologists,
D'ya like my new car ?
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Nice eh ?...being delivered next Tuesday. Potato halves and super-glue at the ready to add special decoration !
Does the ambient atmosphere affect the mileage I can get out of my new car ? What about humidity ? hot days ? cold days ?
Ewe see, I just do not know !...I would like to know though.
Thank ewe for helping me know things that I do not know but will soon know.
Neil
Sheepy Soon-To-Be-In-The-Know
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I know that altitude through air pressure affects fuel consumption, so I guess that there is a performance difference according to whether you're getting some nice hot frontals.
Are we still talking cars?
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You will get less MPG on hot or dry days. A certain degree of humidity aids combustion (don't ask me why) and on cooler days more air enters the engine, increasing pressure slightly; although I'm not sure if that holds true for turbo- or supercharged engines.
P.S. Why is my car being delivered to you? [:(!]
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I guess a lot will depend on how the engine is aspirated. I would suppose turbo charging reduces the dependancy on atmospheric pressure and engine performance, but it would depend on how it was carried out.
Leaving out engine performance, both low pressure and drier air (often not accompanying each other) would lead to lower air resistance which could be a dominant effect at high speed.
Neil, if you lend me the car for a year or two I would be happy to produce a report :-)
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In cold weather the fuel contracts so a gallon is more (by weight) than in hot weather.
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And, when you go to the States, a gallon shrinks even more. How's that for an environmental effect?
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You will get less MPG on hot or dry days. A certain degree of humidity aids combustion (don't ask me why) and on cooler days more air enters the engine, increasing pressure slightly; although I'm not sure if that holds true for turbo- or supercharged engines.
I've found just the opposite to be true... my engine runs much stronger on hot days, my fuel economy is much better on hot days, and fuel economy plummets on very cold days. Perhaps because the coolant temperature control on most engines is pretty rudimentary (I mean really, we're in the 21st century, and we're still using bypass thermostats to control engine temperature?).
The reason humidity aids combustion is because water is a part of and a product of combustion.
http://not2fast.com/thermo/water_injection/water_chemistry.txt
To quote part of that post:
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The highest energy particles are the hydrogen atoms - and they penetrate the charge about 5 times as far as the rest of the particles. As they lose energy and return to normal temps - about 5000 k - they begin to react chemically with any surrounding fuel and oxygen particles. The effectiveness of spark ignition is directly related to the availability of free hydrogen. Molecules containing tightly bound hydrogen such as methanol, nitromethane, and methane are far more difficult to ignite than those with less bonds.
During combustion - water - H2O ( present and formed ) is extremely active in the oxidation of the hydrocarbon. The predominate reaction is the following:
OH- + H ==> H2O
H2O + O ==> H2O2
H2O2 ==> OH- + OH-
Loop to top and repeat.
The OH- radical is the most effective at stripping hydrogen from the HC molecule in most ranges of combustion temperature.
Another predominate process is the HOO radical. It is more active at lower temperatures and is competitive with the H2O2 at higher temps.
OO + H ==> HOO
HOO + H ==> H2O2
H2O2 ==> OH- + OH-
This mechanism is very active at both stripping hydrogen from the HC and for getting O2 into usable combustion reactions.
Next consider the combustion of CO. Virtually no C ==> CO2. It's a two step process. C+O ==> CO. CO virtually drops out of early mid combustion as the O / H reactions are significantly faster and effectively compete for the available oxygen.
Then consider that pure CO and pure O2 burns very slowly if at all. Virtually the only mechanism to complete the oxidization ( Glassman - Combustion Third Edition ) of CO ==> CO2 is the "water method".
CO + OH- ==> CO2 + H
H + OH- ==> H20
H2O + O ==> H2O2
H2O2 ==> OH- + OH-
goto to top and repeat.
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So if we were able to put a current through a water tank at just enough voltage to differentiate the water into its OH- (hydroxide) and H3O+ (hydronium) components (ie: separate the low and high pH components of the water) without actually dissociating the water, then pump from the OH- side of the tank and inject that OH- into the engine along with the fuel, we'd greatly increase combustion efficiency without having to go to the bother of running high amps to actually dissociate the water.
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If ewe flipped the picture left-to-right, ewe would be able to get more miles per accident on UK roads...
(I have piloted a left-hand-drive vehicle around the UK - it takes a little effort to get used to it. However, I'm not sure that UK drivers are always ready for it...)
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If ewe flipped the picture left-to-right, ewe would be able to get more miles per accident on UK roads...
Genius. I hadn't even noticed which was the driver's side...