jet fuel specific heat vs. density -- correlation? 1

[brucegrewell]

Trying to determine whether I can infer anything about the specific heat of jet fuel if I know the density (and temperature). Not talking about specific energy, but specific heat as the fuel is used as a coolant in heat transfer.

Of course specific heat and density are predictable over temperature, but I need to know if there is there any correlation between the two, or are they completely independent? Referring to Jet-A, Jet-B, JP-4, -5, -7, -8.

Any advice appreciated!

 

[jmw]

I suspect you will find there is not a sufficiently clear connection.
Fuels are usually blended for specific properties and the density is not one of them but a consequence of whatever refinery processing went on before and whatever feedstocks were used.

One of the problems with aviation fuel reception into storage is to segregate the fuels simply because the density can vary so much from one bridger to another and density is very important to the all-up weight of the aircraft. In other words, density is not a controlled variable.

JMW

http://www.ViscoAnalyser.com

 

[BigInch]

Sorry for the late response, I recently joined Tips.

There is a direct correspondence to Density.

 

[BigInch]

OK not so direct, here's the formula,

SpHeat = (0.6811-0.308*SG+(0.000815-0.000306*SG)*CRF)*(0.055*CRF+0.35) Btu/Lbm-Fº

SG = specific gravity

 

[BigInch]

Oops and CRF is a correction factor = appx 12.0

 

[25362]

A question to BigInch. If the SG is fixed at 60^oF, where is the correlation with temperature ?

I second jmw's answer. Any formula would be so roughly approximate that you may as well take the Cp tabulated values of C₉H₂₀ or C₁₀H₂₂, since these represent about the midpoint components of various kerosine jet fuels. I consider errors would be no more than [±]10%

To get a general idea visit:

http://www.chevron.com/products/prodserv/fuels/bulletin/aviationfuel/pdfs/chapter4.pdf

 

[BigInch]

You already quessed the answer when you said, "If". Its true that SG is usually given at a reference temperature, because SGs vary with temp, but here Temp isn't referenced because SpHeat can indeed be correlated to density or SG which are "bulk properties" that Chevron mentions. (good website that one). So my SG is any temperature at which you have measured (or know) the SG of the fluid. In other words, the temp ref is implicit.

You are also probably correct approximating the Cp by using the midpoint values of the tabulated chains, but I usually don't know what chemicals are in any given hydrocarbon I'm pumping. I usually only get a SG at 60F and have to convert that to actual SG at flowing pressure and temperature to get a mass rate, so I prefer to correlate to SG at any temp.

As for visco's comments, I don't know of any attempt to segrate one jet fuel from another when being received into storage. Gasoline, kerosene and diesel, yes, but not between light and heavy kerosene. Its all kerosene. You can download your Chevron material data sheets for Aviation Turbine Fuel and JP-8 from this page,

http://www.chevrontexacoaviation.com/chevrontexacoaviation/tgam_prod/tgam_prod_home.shtml

These pages show there is essentially no density difference between Aviation Turbine Fuel and JP-8 or kerosene, which is what we actually batch (usually) between diesel batches.

For av turbine fuel,

http://www.chevrontexacoaviation.com/chevrontexacoaviation/tgam_prod/documents/avi_turb_fuel.doc

you see that they give a Density: 0.75 - 0.84 g/ml @ 15°C (59°F)

Open JP-8 and they give a Density: 0.755 - 0.84 g/ml @ 15 ºC

From a pipeline perspective, as well as what Chevron calls "Kerosene" in this MHS, can basically be anything between (our) endpoint gasoline cut + interface + beginning kero cut, and ending kero cut, interface and beginning point diesel cut between continuous serial directly interfaced batch loadings into the pipeline of all three. We distinguish batch changes by densitometer signals, not viscosity, and direct various products to either gas, jet or diesel (or interface) tanks. What we can't distinguish is cut out entirely and put in an interface tank, wich is later reblended back into the diesel, maintaining ppm limits. My understanding is that, after "kerosene" gets to the aviation terminal, they turn it into Jet A-1 or JP-8 by basically running which is really nothing more than some QA/QC tests a run through some filters, maybe adding anti-static, deicer and whatever else they need to do with it before they can call it JP or A-1.

 

[BigInch]

Oh ya. Takeoff runs and aircraft performance in general is planned by weight of fuel (and other items) loaded on board vs air density. This is almost always with the tanks topped off, not the volume of fuel, so they don't have to take into consideration the variable density at different airport fuel tank tempertures. In fact, the heat value of a hydrocarbon liquid is also a bulk property, so if the fuel is heavier, they get more bang out of any given volume, ie. Btu content is directly proportional to the weight of the kero.

 

[BigInch]

OK, as long as they have the air density to lift that fuel weight and get going.

 

[BigInch]

Following excerpted from "Performance Specification, Turbine Fuel, Aviation, Grades JP-4, JP-5, and JP-5/JP-8 ST," MIL-PRF-5624S, 22 Nov 1996 and "Military Specification, Turbine Fuel, Aviation, Kerosene Types, NATO F-34 (JP-8) and NATO F-35," MIL-T-83133D, 29 Jan 1992.

JP-4 (NATO F-40) WIDE CUT GASOLINE TYPE SG = 0.751-0.802
JP-5 (NATO F-44) KEROSENE TYPE SG = 0.788 - 0.845
JP-8 (NATO F-34/F-35) KEROSENE TYPE 0.755 - 0.840
Jet A-1 is the Commercial Equivalent of JP-8

VISCOSITY IS 8.5 cSt for JP-5 (Navy jet fuel), 8.5 for JP-8 & Jet A-1


Differences between these are primarily freeze point is lower for JP-4 (because JP-4 is a slightly wider cut at about 50-60% gasoline and, since 1996, is no longer used due to high flamability, JP-4 higher antioxidant content, JP-5 has lower volatility and higher flash point (60 vs 38ºC for JP-8)for shipboard operations, and JP-8 lower sulfur limits, JP-8+100 has cleaning additives.

JP-1, JP-2, JP-3 have not been used for 30 years or more. JP-6 has not been used since the XB-70 Bomber was cancelled.
JPTS is interesting. Its a U-2 and TR-1 specific fuel, no data on that, but my guess is it allows higher vapor pressure for high cold flights. And another interesting one, JP-7 is for SR-71 only and is not a distillate fuel at all, but composed of "speciality blending stocks" allowing for a very clean burn, low sulfur, low nitrogen and low oxygen impurities. A special additive for lubrication must be added to that one.

So, apparently I have confirmed our operating practice ... proving there is no difference between SG or viscosity between JP-8 and Jet A-1 as they are the same fuels. There can be as much as a 0.5% difference in limits for JP-5 vs JP-8/A-1 but most of the time there will be no difference.

Viscoanalyzer, is your experience any different?

 

[jmw]

Well I'll stand corrected in the current industry but I worked on a project in the UK where they wanted online density at the airport receiving terminal to segregate the fuels by density (as delivered then by tanker).
I also was associated with a tank truck meter application where the density meter was specifically adapted for truck duty.
Now I'm not saying any of these things went ahead or how far ahead they went but they were oil company initiatives.

You quote:
JP-4 (NATO F-40) WIDE CUT GASOLINE TYPE SG = 0.751-0.802
JP-5 (NATO F-44) KEROSENE TYPE SG = 0.788 - 0.845
JP-8 (NATO F-34/F-35) KEROSENE TYPE 0.755 - 0.840
and these show, to me, quite significant density tolerances - a 50kg/m3 spread is significant when you can easily measure online to 0.1-0.15kg/m3.
Sorry, I don't recall the density spread for commercial aviation fuels I was quoted, but I thought the spread was more. Of course, it could be they were quoting the spread across different grades (some time back).

JMW

http://www.ViscoAnalyser.com

 

[BigInch]

Strange. I agree that you can determine the density difference, but I wasn't aware for the need to do so in most cases. The allowable overlap in densities of JP-5 and 8/A1 would make distinguishing them by density impossible. Av gas is also pretty much the same story, but with additives to yield higher volatility and octanes between AvGas grades. Maybe they were simply running QA/QC on the densities, or wanted to distinguish between AvGas and Jet... OMG. You'd think they would get that in different colored trucks, huh?

OK, just wondering if you thought it might be a current practice somewhere so that I wouldn't be caught flat-footed. As long as you're not doing it today, I guess I'm OK. Thx.

 

[jmw]

Well, you couldn't simply use density for an unknown fuel and identify it but if each batch of fuel is analysed then they should be able to report the actual density for that batch. That then lets you "identify" if the fuel you are getting is the fuel you expect.
This is typically how multi product pipeline transfer can use density to discriminate between different grades of gasolene, diesel etc.
Of course, part of the need to measure density is because fuel is sold by mass, not volume.

Re-reading I see that the original question did say "if I know the density"... and my comments were based on the fact that density can vary... sorry.




JMW

http://www.ViscoAnalyser.com

 

[BigInch]

We measure the actual flowing volume with turbine meter pulses, pressure and temperature then correct to get volume and density at the contract custody transfer std. We've got a few densitometers in the lines, but only to ID incoming interfaces for cutout and trigger valve sequence countdowns to direct products to the right tanks.

No problem. As we've found out,... density can vary.