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samtheman
Dodge Dakota
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11/14/2002
17:58:32
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 Subject: Engineers, scientists or anyone! Fuel??
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It's 7/1 and 90 degrees in NYC. Your engine is fully warmed and you fill up. You travel thru that light 90 degree air to Chicago. It's 1/1 and 15 degrees in NYC. Again you fill your fully warmed vehicle and make the same trip. Now your cold air intake is truely sucking in cold air, efficiency is at its highest! However, you must push that vehicle thru that heavy, dense air. Which trip would you use the least amount of gas?
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Rrrockhound
GenIII
11/14/2002
19:31:33
|  RE: Engineers, scientists or anyone! Fuel??
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The January trip will burn more gas. Cold fuel burns less efficiently, which is why gas mileage goes down the toilet in the winter. The air density difference should be negligble, and anyway, winter air is drier (less humid) than summer air, so it's probably not heavier at all. On the plus side, though, you'd have a tail wind going from Chi-town to NYC.
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j
GenIII
11/14/2002
20:31:15
| RE: Engineers, scientists or anyone! Fuel??
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Dry air is heavier than humid air. It is more dense. But I agree that the difference in air resistance would probably not be a factor. If the temp is really cold, you might use more fuel because, since the air is denser, your engine is getting more air so it must give it more fuel too.
On the other hand, it will be running more efficiently (getting more power out of each power stroke) with the denser air so you won't have to put your foot as far into it for the same speed.
...hopefully, you are totally confused now.
2000 4.7 CC auto, clear corners, Magnaflow catback, Kenne Bell s/c.
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Lab Rat
GenIII
11/14/2002
21:30:00
| RE: Engineers, scientists or anyone! Fuel??
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Cold fuel does not burn less efficiently, the opposite is true. Why do you think racers pack cool cans full of dry ice? Why did Benz use fuel coolers for several years? Cooling it increases it's density and therefore the available BTU/lb (enthalpy).
The same holds true for air.
LR
Gibson Dual Sport, AirForce One air intake, Jet II, Jet TBS, 180 stat, IAT, TPS, no viscous fan, Lakewood traction bars, "Wilson" antenna ball...when are we gonna see some real parts??!!
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Funkycheeze
Dodge Dakota
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11/15/2002
02:37:06
| RE: Engineers, scientists or anyone! Fuel??
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cold engines burn the fuel less efficiently though
so it would break down like this
cold air = good
cold gas = good
cold engine = bad
sot it depends on how long you have driven the truck before filling it up - but you said it would be warmed up so thats not an issue
the only benifit to the cold fuel is the fact that it is more dense, so if you did it by dollar value (since the price of fuel is volume adjusted) you would be removing that from the equation
the air resistance on the truck would be negligible, even at high speed
you must also make sure the tires have the same pressure since the cold air in the tires will make them 'flatter' unless adjusted - and flatter tires have higher rolling resistance greatly affecting mileage
you must also remember that although the engine gets more air since its cold and dense, that only makes it ABLE to burn more gas in one stroke (as adjusted by the ECU from the O2 sensor), but you dont get much better mileage during normal driving since you dont have the throttle body the whole way open so it doesnt need that extra 'fuel burning ability' and will use the same amount (as in # of molecues, not volume) of fuel
i would say, if the tires have the exact same pressure ino both cases, if the roads are bare, and if the volume used is temperature adjusted the winter trip will use the exact same amount of gas
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yates-in-DE
GenIII
11/15/2002
05:46:49
| RE: Engineers, scientists or anyone! Fuel??
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Also have to factor winter fuel blend in. It's oxygenated and there for getting less fuel per gallon. (I hope you are fully confused) The oil companies do this because in the winter if the gas wasn't 'Fluffed Up' you would get a gallon of cold gas that weighed 7.3 #'s, instead of the 6.9 #'s factored at 60 deg, you get in the summer. So you would get more miles per tank full and what oil company in their right mind wants this.
Later,
Lynn
Cool Forum Click on Pic
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Dominic
Dodge Dakota
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11/15/2002
10:40:13
| RE: Engineers, scientists or anyone! Fuel??
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I do not believe that colder fuel burns more efficiently than warm fuel. There are two reasons why I don't believe this:
1. I had a motorcycle with a fuel preheater that increased the temperature of the fuel before entering the carbs.
2. The company I work for builds large gas turbines with HUGE heat exchangers that preheat the fuel going to these engines.
Now, I am no combustion expert, but I believe they do this to help meet emmission standards (which in my mind means a more complete combustion of the fuel = more efficient engine).
By the way, I always thought that racers used the dry ice for the air intake to cool the incoming air.
Dominic
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Texas Todd
Dodge Dakota
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11/15/2002
11:14:18
|  RE: Engineers, scientists or anyone! Fuel??
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Dominic,
OK,
preheating the fuel,
anyway, the dry ice trick goes around the air intake tube, not drastically doing alot, but it helps.
If you put it in the intake, like before the filter, you'd be adding C02 to the intake, NOT good for the fuel mixture. I'm sure you knew that, just thought I'd add it in writing.
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Canucker
Dodge Dakota
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11/15/2002
12:07:36
| RE: Engineers, scientists or anyone! Fuel??
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Warm fuel DOES burn more efficiently ... from a thermal efficiency stand point. Ideally, you'd want the fuel temp to be just a bit cooler than its self combustion temp before igniting it.
Why then do you get more power with colder fuel? simple. the cold fuel cools off the air intake and allows for more timing advance before knock (self igniting of fuel).
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Duner
Dodge Dakota
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11/15/2002
13:54:44
| Justa Wild Guess?
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You didn't specify which Dodge engine, year, make or model.
If you are talking about a "modern" late model Dodge engine with a returnless fuel system - then the winter trip SHOULD* net the better fuel mileage.
During the summer the fuel rails heat up causing the passenger side of the engine to get less fuel due to temp/density issues. This causes an imbalance in the engine that hurts efficiency. We register it as the truck feeling sluggish in the heat. The problem isn't as bad during the winter months.
The same holds true for the IAT sensor/PCM issue. Higher ambient air temps mean higher IAT sensor readings. When the PCM sees higher IAT readings it retards the ignition timing which makes the engine work harder. Working harder burns more fuel and is less efficient. Cooler air temps and IAT readings and the PCM will allow more ignition timing. More ignition timing lets the engine work easier. Working easier means less fuel burned for the same result.
Add both of those things together and the result SHOULD* be better fuel economy.
*Now you have to factor the oxygenated fuel back into the mix. For that I have no real answer! You would have to test this for yourself. The fuel companies say that the difference is only 2-5% or so difference in fuel economy..... does anybody actually know?
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Freakinsmart
Dodge Dakota
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11/15/2002
14:20:02
| RE: Engineers, scientists or anyone! Fuel??
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Hot air is less dense, and will have a lower number of oxygen molecules per cubic foot than cold air. The explosions in the combustion chamber depend on oxygen. If there is less oxygen, the explosion will be weaker and create less power.
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nate
Dodge Dakota
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11/15/2002
15:15:13
| RE: Engineers, scientists or anyone! Fuel??
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Dominic -
There is a slight difference in how a turbine works and how an automobile engine works.
Recapturing heat in a turbine cycle improves by re-introducing heat into the system during the combustion process that would otherwise be lost to the atmosphere. More heat in = more heat out.
The same is not true for the 4-stroke engine. Cold fuel = dense fuel = more fuel / unit volume
Cold air = dense air = more oxygen / unit volume
more fuel + more oxygen / volume = more energy per cylinder. (after the engine reaches operating temperature).
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Tim
Dodge Dakota
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11/15/2002
15:43:42
| RE: Engineers, scientists or anyone! Fuel??
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I'm currently into the second stage of development of my own heat exchanging engine. I'm using the heat from the water to heat the gasoline. Hot fluids expand, it also allows the fuel to atomize more readily with air for consumption, reducing amount of fuel needed, reducing emissions and the like. Second, I'm now installing a heat exchanger to use the water from the thermostat to heat the air through a duct going into the engine. I'm running an old 77 dodge pickup with 35 inch tires and a 4 barrel carb, and getting 26 miles to the gallon doing it.
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Duner
Dodge Dakota
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11/15/2002
16:01:34
| RE: Engineers, scientists or anyone! Fuel??
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Tim - Getting fuel mileage like that out of a '77 with those big tires is awesome! Now for the other side of the coin.... How's the performance? What kind of an engine are you using? What kind of 4bbl?
So far the best my 4.7 has gotten on a trip from LA was 21.89 mpg. It might have done slightly better - but I had to "play" a little bit on the way.
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Art
Dodge Dakota
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11/15/2002
16:44:36
| RE: Engineers, scientists or anyone! Fuel??
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Sheesh guys. Nice discussion regarding the density of air molecules but the correct answer is obvious. You will always get better gas mileage in the winter than the summer. Why? In the summer (90 degrees) the engine is turning the air conditioning compressor which steals a ton of available engine power and therefore gas. In the winter, all available engine power goes to the wheels. Sure, air density and temperature have a minor effect but they add up to nothing compared to the extra hp (gas) required to turn your compressor to cool your behind. Of course, you could always drive from New York to Chicago with your windows down in 90 degree heat *smile*.
Cheers
Art
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Duner
Dodge Dakota
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11/15/2002
16:52:43
|  We don' t need no steenkin' air conditioning!
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If you drive with the defrost turned on in the winter - it runs the AC compressor too! LOL
Some people would be willing to drive during the summer without their AC turned on to save a few bucks on fuel mileage..... but I'm certainly NOT one of them!
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imsosmart
Dodge Dakota
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11/15/2002
17:08:32
| RE: Engineers, scientists or anyone! Fuel??
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P*V=n*R*T
Gay-Lussac's law explains the limitations of the traditional engine.
At the moment of combustion you want "P" (pressure) to be as high as possible so that power is maximized. The only variable you can control is "T"(temperature) (assuming as a first approximation that "V"(volume) of the cylinder is constant during combustion).
A metal cylinder can operate at a temperature of about 1000K (Kelvin). Any higher and it will suffer damage.
A ceramic cylinder will operate at the highest temperature combustion will provide: about 3000K. An astonishing factor 3 improvement in power!
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Duner
Dodge Dakota
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11/15/2002
17:36:38
| RE: Engineers, scientists or anyone! Fuel??
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Are you talking about gasoline powered internal combustion engines?
Temperature is the only variable you can control? What about fuel quality?
With the production engines in cars/trucks today the metal cylinders aren't the problem.... Detonation is the problem. The quality of fuel is the problem. Detonation kills head gaskets, pistons, rod bearings, crank shafts.... well you get the picture.
What kind of fuel will you use that won't pre-ignite before getting to full pressure? Does that mean you would run ceramic pistons as well?
C'Mon spill it! Tell us about this new kind of engine that will make 3X the power!
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j
GenIII
11/15/2002
17:46:39
| RE: Engineers, scientists or anyone! Fuel??
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Temp is not the only variable you can control. You can also control n. The more oxygen molecules (and the fuel to go with it) you put in the chamber, the higher the pressure is going to be.
2000 4.7 CC auto, clear corners, Magnaflow catback, Kenne Bell s/c.
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Canucker
Dodge Dakota
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11/15/2002
18:31:36
| RE: Engineers, scientists or anyone! Fuel??
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A/C !?? who needs it :) I don't have it.
FYI:
the PV=mRT equation would only apply to the air .. and would be a very, very loose approximation (loose like Debbie in the critically acclaimed film 'Debbie Does Dallas').
a more correct equation (again, just for the air) would be PV=ZmRT where the Z is a corrected factor that is tabulated and varies with temp, pressure and type of gas ...
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dfkj
Dodge Dakota
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11/16/2002
11:56:03
| RE: Engineers, scientists or anyone! Fuel??
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the only one that got it right so far is Yates the rest are moot points that do not factor in the fact that in the north the oxygen content on the fuel changes seasonally, thank you EPA for wasting fuel in the winter.
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Bill Smith
Dodge Dakota
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11/16/2002
15:19:59
| RE: Engineers, scientists or anyone! Fuel??
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the other thing you have to consider with the A/C input... is the extra fuel used in turning the compressor is USUALLY overriden in fuel mialage in the drag caused by having the windows open in 90 degree heat! think about it ... some SUV's have so much room in the back to catch air,it's like driving with a parachute out the back with the windows open! drag = more fuel consumption,so in certain instances.... you can get better or the same mialage with the a/c on as with it off. something to think about
Bill
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Lab Rat
GenIII
11/16/2002
15:28:55
| RE: Engineers, scientists or anyone! Fuel??
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The A/C compressor doesn't consume any more than about 5 HP; pretty negligable.
LR
Gibson Dual Sport, AirForce One air intake, Jet II, Jet TBS, 180 stat, IAT, TPS, no viscous fan, Lakewood traction bars, "Wilson" antenna ball...when are we gonna see some real parts??!!
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