Why the difference in Winter Fuel Mileage??

[hammersley]

OK - I can usually get OVER 25 MPG if on a Trip I drive around 55 - This weekend I took a trip where in 150 miles at 57-58 - I could only get 22... . No Wind or bad weather and no fast acceleration... ... what is it in the winter blend that does this?????

 

[BILLVO]

a simplified explanation

Number 1 diesel fuel doesn't have nearly as many BTU's as Number 2 fuel. Less Btu's equals less energy which means it takes more fuel to do the same as usual #2.

 

[rbattelle]

Number 1 diesel fuel doesn't have nearly as many BTU's as Number 2 fuel. Less Btu's equals less energy which means it takes more fuel to do the same as usual #2.

What's interesting is that on a gravimetric basis, #1 has more energy than #2:



#1 = 18250 btu/lbm

#2 = 18000 btu/lbm

(Lower heating values)



But on a volumetric basis, #1 has more energy.



Specific gravity of #1 = 0. 876

Specific gravity of #2 = 0. 920



Let's say we take 30 gallons of each type of fuel. Which has more energy content?



#1:

(0. 876)*(8. 34 lbm/gal)*(30 gal)*(18250 btu/lbm) = ~4e6 btu



#2:

(0. 920)*(8. 34 lbm/gal)*(30 gal)*(18000 btu/lbm) = ~4. 14e6 btu



On a volumetric basis, #2 has ~3. 5% more energy than #1.



This is one reason some people say it's a crime that we buy fuel on a volume basis rather than an energy-content basis.



Ryan

 

[WDaniels]

You must also consider that cooler weather will make everything stiffer. Bearing grease and everything gets stiff taking more power to keep the same speed. Last year starting in the summer I took readings on the way to and from work starting in the summer time through the winter and into the next summer. The readings were taken at the same time of day, same place, same speed on cruise control that had stabilized, everything was the exact same from day to day. The only thing different was the temperature of the day and the fuel. It showed me that during the winter it costs more to operate due to reduced fuel economy. At -35 and lower the boost at cruise rose to about 7 or 8lbs on flat ground. During the summer it was less than 2. Egt's during the winter were around 600 and during the summer it was about 550 to 600.
Also, I find it difficult to believe that in Washington that they don't keep #2 year around. It doesn't get cold enough to gell there. I keep #2 in the tank to about -25 to -30 with additive of course.
WD

 

[Vaughn MacKenzie]

Also with this frigid air mass hanging around the air density creates more wind resistance.



Heh. . . you drove less than 60 on an entire trip. . . I hardly go under 65 anywhere in eastern Washington, usually 70 everywhere I go

 

[TAbbott]

The #2 fuel may not gel in Washington, but #2 fuel pumped into the tank of a truck in Washington and taken to Montana or BC or Alberta, which aren't that far away, could sure gel up there!

 

[mhenon]

What's interesting is that on a gravimetric basis, #1 has more energy than #2:



#1 = 18250 btu/lbm

#2 = 18000 btu/lbm

(Lower heating values)



But on a volumetric basis, #1 has more energy.



Specific gravity of #1 = 0. 876

Specific gravity of #2 = 0. 920



Let's say we take 30 gallons of each type of fuel. Which has more energy content?



#1:

(0. 876)*(8. 34 lbm/gal)*(30 gal)*(18250 btu/lbm) = ~4e6 btu



#2:

(0. 920)*(8. 34 lbm/gal)*(30 gal)*(18000 btu/lbm) = ~4. 14e6 btu



On a volumetric basis, #2 has ~3. 5% more energy than #1.



This is one reason some people say it's a crime that we buy fuel on a volume basis rather than an energy-content basis.



Ryan

Ryan... thanks for that. I'm going to keep those two formulas running in my head (casino style) as I fill up next time... just to pass the time.

Mike

 

[steved]

I found ambient temp plays more into fuel mileage than anything... just sucking in the really cold air causes a decrease in mileage IME, with everything else the same.



steved

 

[Grizzly]

An engine will not run as efficient when cold.