Can diesel vary in amount of BTU's(?) or power potential?

[ChesterRam]

I've been buying flying J diesel almost exclusivly now for 30k miles, I average about 19. 2 mpg (via the computer). Well the other day I got really low and just had to take on a load from a supermarket station... . And my average for the load went up at least 2 mpg.

I thought truck stop stuff was the best?

Any reason this might have happened? Driving conditions and practice were essentially unchanged.

Thanks,

chris

 

[illflem]

The amount of energy in diesel is measured as cetane, some pumps post the value. 48 is about average cetane, but I've seen it as low as 40. Some places sell premium diesel, it doesn't mean the cetane is higher, it just has additives that are cheaper to add yourself. Most all brands of #2 diesel in a geographical area will have came from the same main supply lines/tanks and the cetane number is the same, what can vary is the #1 blend and additives. The truck stop diesel you used could have a higher ratio of #1 added for winter.

 

[Shovelhead]

48 cetane??

Dang Bill, around the this Washington,... . DC that is,... . 90% of the stations only carry 40 cetane #2.

I've found one station with 42c, and one with 43c.

Maybe I need to get a big aux. tank and come out there for fuel.

No wonder you guys are posting such high mpg numbers.



edit: fuel prices vary from a low of $1. 13 to as high as $1. 55.

Again diesel fuel is $. 10 higher than premium gasoline. :-{}

 

[Ray Torresdal]

btu's

#1 fuel would have less energy than #2 - I would bet that Flying J's fuel is more heavily blended with #1 than the other fuel source. I haven't been able to discern any difference in mileage in my two local suppliers, but some of the area truckers swear by one over the other. At least fuel isn't higher than gas right now - $1. 26 locally. Ray

 

[klenger]

Could it be that Flying J is still selling winter blend and the other was selling summer blend?

 

[illflem]

Another thing I learned just recently is as winter ends (like today) many stations and fuel suppliers will up the ratio of #1 to #2 in a effort to eliminate stockpiles of #1 that would otherwise have to be stored till next year. Best bet if you want better fuel economy and power is to buy straight #2 if available and add your own winter additive till things finally warm up.

 

[Rammin On]

The amount of energy in diesel fuel is measured by the API gravity or specific gravity of the fuel. The recommended API gravity of fuel for Cummins engines is 42 to 30 degrees at 60 drgrees F. Using high density ( low API gravity) will produce more power. As a general rule ... there is about a 3-5% decrease in thermal energy for every 10 degree increase in API gravity. #2 fuel has a minimun API gravity of 30 ... For example ... fuel with an API gravity of 35 weighs 7. 076 lbs/gallon. The higher the weight or heavier the fuel the greater the BTU content. Basically ... the power obtained from diesel fuel is determined by the BTU content which is in direct relation to its weight per gallon.



The cetane number is just a measure of the ignition quality of the fuel. Kinda like octane ... in reverse. cetane # is the ability of the fuel to ingnite ... octane is the ability of the fuel to resist ignition.