Range : Jet A versusJet B
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Range : Jet A versusJet B
1000 litres of Jet B weighs 1770 lbs @ 15 degrees C., 1000 litres of Jet A1 weighs 1850 lbs @ 15 degrees C. Jet B reportedly has a higher calorific value.
Here is the question; which will take you farther a litre of Jet A or a litre of JetB?
Formulas welcome.
IHL
Here is the question; which will take you farther a litre of Jet A or a litre of JetB?
Formulas welcome.
IHL
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Interesting...
The figures given (above) for Jet B would give it a lower SG (around .804 against the .840 given for A1) so I'd be surprised if the calorific value where higher (not checked).
Following Gem's thought though, it may be that the lighter of the two fuels would be burned at a faster rate if fuel burn relies on Lbs. per hour (but that rating would have been given for only one specific fuel).
If its calorific value is higher it may result in eng. overtemp.
Is the hypothetical engine rated for both fuels? Is it a hypothetical engine?
The figures given (above) for Jet B would give it a lower SG (around .804 against the .840 given for A1) so I'd be surprised if the calorific value where higher (not checked).
Following Gem's thought though, it may be that the lighter of the two fuels would be burned at a faster rate if fuel burn relies on Lbs. per hour (but that rating would have been given for only one specific fuel).
If its calorific value is higher it may result in eng. overtemp.
Is the hypothetical engine rated for both fuels? Is it a hypothetical engine?
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SPS :
Jet be is a mix of 60% kerosene and 40 % naptha(if my memory serves me correctly), it burns hotter and is definietly easier to get a light-off in cold temperatures. The engines in the question are not theoretical but certified civilian engines.
I think with a 1000 litres of Jet A an A/c would go farther than with Jet B. That being said I've had pilots argue that you get the same range because Jet B gives the same performance as Jet A with reduced fuel burn allowing one to go the same distance on 1770 lbs of Jet B as 1850 lbs of Jet A1.
Never been able to find the proof in text, to dispell or confirm the difference.
IHL
Jet be is a mix of 60% kerosene and 40 % naptha(if my memory serves me correctly), it burns hotter and is definietly easier to get a light-off in cold temperatures. The engines in the question are not theoretical but certified civilian engines.
I think with a 1000 litres of Jet A an A/c would go farther than with Jet B. That being said I've had pilots argue that you get the same range because Jet B gives the same performance as Jet A with reduced fuel burn allowing one to go the same distance on 1770 lbs of Jet B as 1850 lbs of Jet A1.
Never been able to find the proof in text, to dispell or confirm the difference.
IHL
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Well its a very interesting problem and let's see if anyone will enlighten us!
I'd be with you I think, A1 is heavier and if we stick with Lbs per hour then less volume will be burned for that weight?
But then, as you've said, more heat per weight (as with 'B')would give more reaction and that would also affect range.
Which one wins?
I'd be with you I think, A1 is heavier and if we stick with Lbs per hour then less volume will be burned for that weight?
But then, as you've said, more heat per weight (as with 'B')would give more reaction and that would also affect range.
Which one wins?
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I was lead to believe during my instructor days, that the SG of the fuel doesn't affect fuel burn rate, but does affect the gauge reading, i.e. density Vs volume. If a fuel with a lower density is put in, the gauge will over read and therefore lead one to believe they have more fuel than really exists! [provided your fuel tank sensors cater for density of course].
My head hurts now.....too dense, methinks
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Thermal runaway.
My head hurts now.....too dense, methinks
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Thermal runaway.
Guest
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TC,
You are right. Fuel flow meters work via an impellor in the fuel stream i.e. they actually measure volume flow so if the SG differs they will not know the difference in in weight. Some fuel contents gauges (electrical capacitance type for certain) also tell porkies if the SG is different to that at which they were calibrated.
If a fuel weighs less and has better calorific value it must be a better fuel. Less energy will be expended carrying it and the fuel flow required to get the same power output will be less, although there may be T4 limiting problems requiring engine adjustment. I remember years ago when our sqn went to RAFG the engineers had hours of fun resetting the fuel flows due to the fuel difference.
You are right. Fuel flow meters work via an impellor in the fuel stream i.e. they actually measure volume flow so if the SG differs they will not know the difference in in weight. Some fuel contents gauges (electrical capacitance type for certain) also tell porkies if the SG is different to that at which they were calibrated.
If a fuel weighs less and has better calorific value it must be a better fuel. Less energy will be expended carrying it and the fuel flow required to get the same power output will be less, although there may be T4 limiting problems requiring engine adjustment. I remember years ago when our sqn went to RAFG the engineers had hours of fun resetting the fuel flows due to the fuel difference.
Guest
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Jet A vs. Jet B depends on how you’re looking at it, by weight or by volume. The following uses numbers from Canada, and I have no idea if European, Aussie, or other fuels are slightly different.
Jet A has a caloric value of 18,300 BTUs/lb.
Jet B has a caloric value of 18,400 BTUs/lb.
Therefore, Jet B has roughly 0.54% more caloric value/lb. , and if you compare by weight, is a slightly more energetic fuel.
On the other hand, Jet A is approx 5.5% heavier than Jet B at 15ºC, so the same volume will weigh in higher. Therefore, if the comparison is by volume, you’ll go further on Jet A than you will on Jet B.
Hope this helps you out.
[This message has been edited by CTD (edited 20 March 2001).]
Jet A has a caloric value of 18,300 BTUs/lb.
Jet B has a caloric value of 18,400 BTUs/lb.
Therefore, Jet B has roughly 0.54% more caloric value/lb. , and if you compare by weight, is a slightly more energetic fuel.
On the other hand, Jet A is approx 5.5% heavier than Jet B at 15ºC, so the same volume will weigh in higher. Therefore, if the comparison is by volume, you’ll go further on Jet A than you will on Jet B.
Hope this helps you out.
[This message has been edited by CTD (edited 20 March 2001).]
