10 - experimental verification of the thermodynamic properties of jet-a fuel

8/12/2019 10 - Experimental Verification of the Thermodynamic Properties of Jet-A Fuel

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EXPERIHKNTAL V B R I F I C A T I O N O F THE TEERHODYNAHICPROPERTI ES O F A JET A FUELCarmen M. Graci a- Sal cedo, Bonni e J . McBr i de, Theodore A. Brabbs

NASA Lew s Research Cent er, Cl evel and, Ohi o 44135INTROlXJCI ION

Thermodynamc proper t i es f or J et - A fuel are needed f or manycal cul at i ons, i ncl udi ng chemcal equi l i br i umcal cul at i ons. Tof ul f i l l t hi s need, var i ous cor rel at i ons f or t he est i mat i on oft hese proper t i es have been publ i shed (1, 2, 3) . However, t hese aredi f f i cul t t o use and may not be practi cal f or al l appl i cat i ons.I n 1970, Shel l Devel opment Company, under a cont ract f or NASALew s Research Cent er, determned t he thermodynamc proper t i esf or a J et - A f uel (4). I n t he present repor t , we used t heset hermodynamc dat a to der i ve t he coef f i ci ent s necessary t oi ncl ude J et - A ( gaseous and l i qui d phases) i n t he t hermodynam cdat a l i brary of t he NASA Lew s Chemcal Equi l i br i umProgram (5) .To ver i f y the t hermodynamc data and the pol ynomal f i t , t het emperat ures of very r i ch mxt ures of J et - A and ni t rogen wer emeasured and compared t o t hose cal cul ated by t he chemcalequi l i br i umprogramTEERHODYNAWIC DATA ND LEAST SQUARES F I T

To i ncl ude J et - A i n t he t hermodynamc dat a l i brary of t heNASA Lew s Chemcal Equi l i t r i umProgram65) , t he thermodynamcf unct i ons speci f i c heat C ent hal py Ht o be expressed as f unct i gns of t emperaTure i n the f ormof af oyrth ordzr pol ynomal f or Cpo w t h i nt egrat i on const ant s f orHT and ST .and ent ropy STo need

C o = al + a2T + a T2 + a4T3 + a5T4-E 3R2)

HI = al + a2T + a3T2 + a4T3 + a5T4 + asSi = al l nT + a2T + a3T2 + a4T3 + a5T4 + a7- . _ _ - - - -RT 2 3 4 5 T

3)2 3 4

The t hermodynamc data f or a J et - A f uel used f or t hi s r epor twere measured or cal cul ated by Shel l Devel opment Company i n 1970.Most of t hese data were i n an extensi ve unpubl i shed t abl eprovi ded t o NASA Lew s Research Cent er by Shel l .dat a cont ai ned i n t hi s t abl e and addi t i onal f uel i nf ormat i on usedf or t hi s r epor t were publ i shed i n ref erence 4.f romref erence 4 i ncl ude: heat of combust i on val ue used t ocal cul at e t he heat of f ormat i on of t he l i qui d, and a f uelanal ysi s by hydrocarbon t ype and carbon number used t o est i matet he ent ropy of t he gaseous fuel mxture at 298K. The data used

Par t of t heThe dat a used

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from the unpublished table include: heat capacity and enthalpyvalues for gaseous Jet-A for temperatures from 273K to 1273K, theentropy and enthalpy of vaporization at 298K, and enthalpies forliquid Jet-A for temperatures from 298K to 650K. The values forenthalpy given in this table were referenced to liquid Jet-A at273K. Th e chemical equilibrium program requires an assignedenthalpy value at 298K equal to the heat of formation. For thisreason, the enthalphy values from the unpublished table wereadjusted to be relative t o the enthalpy at 298K.The entropy values given in Shell's unpublished table werereferenced to liquid Jet-A at 273K. The chemical equilibrium

program requires the entropy to be zero at 0 K. To estimate theentropy for the gaseous Jet-A, the fuel analysis given in TableXVI of reference 4 was used along with the entropy values of theindividual components from reference 6. The entropy ofvaporization at 298K was obtained from Shell's unpublished tableand ab st ra ct ed from the gas phase entropy to obtain the entropyat 298K for the liquid phase.n updated version of the PAC4 computer code (7), namelyPAC87 was used t o extrapola$e the t$ermodynamic functions for thegas to 6000K 8 ) and fit C and H simultaneously using a leastsquares method.intervals, 298K t o lOOOK and lOOOK to 5000K.For the liquid Jet-A, the heat capacity values in theunpublished table did not match the enthalpies for temperaturesabove 600K. Since the enthalpy was the property measured byShell Development Company (4), it was used in the PAC87 computercode to obtain heat capacity and entropy values for thetemperature range 298K to 650K.

the computer program. This results in a molecular weight of167.3. A value of 166 was reported in reference 4.are the following:

The data 8ere fitTed in two temperature

The chemical formula C12H23 was used to represent Jet-A in

The coefficients obtained for the liquid and gaseous phasesLIQUID: 298KsT5650Kal = 0.139936393 04a2 =-0.134403663 02a3 = 0.484922453-01a4 3-0.755248823-04a5 = 0.431666873-07a6 =-0.155884863 06a7 =-0.548524143 04

GAS: 298KsTs1000Kal = 0.199351373 01a2 = 0.133839183 00a3 =-0.828912493-04a4 = 0.311809143-07a5 =-0.715287123-11a7 = 0.277445703 02a6 =-0.359034963 05

GAS: 1000KsTs5000Kal = 0.248759753 02a2 = 0.782591033-01a3 =-0.315563533-04a4 = 0.578913943-08a5 =-0.398380323-12as =-0.431105073 05a7 3-0.936339443 02VRRIFICATIONExperimental Apparatuscatalytic flow-tube reactor described in reference 9. Open-endExperiments were conducted in the vaporization section of a


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w t h si x i n a ci r cl e and one i n t he center . Fuel was del i veredt o each cone t hrough t ubes of equal l engt h and of 0 04 cm I DThese t ubes were l ocated t o spray the fuel i n the di rect i on of

operat i ng procedureThe standard operat i ng procedure was t o warmup t he react or f orabout t wo hours w t h hot ni t rogen t o at t ai n a st eady stat etemperature. Then, l i qui d f uel i s added and t he mxturet emperature 68 cmdownst reamof t he poi nt of f uel i nj ect i on wasmoni tored.f or about 5 mnutes. Thi s t ook about 30 mnut es f or t he f i r stpoi nt . Then t he f uel f l ow was i ncreased or decr eased, and dat awere t aken i n t he same manner. For t he second poi nt on, dat acoul d be taken every 10 mnutes.

Ni t rogen i s heated t o about 800K w t h an el ectr i c heat er .

No data was r ecorded unt i l t he temperature was st eady

Experi ment al ApproachThe obj ect i ve of t hi s st udy i s t o ver i f y the t hermodynamcproper t i es of a J et - A f uel by measur i ng t he temperatures of very. r i ch vapor i zed f uel / ni t rogen mxtures. I n a pr i or st udy (9) i twas observed t hat t he addi t i on of l arge quant i t i es of l i qui d f uelt o a hi gh t emperat ure gas st reamcaused a l arge reduct i on i n t hest reamt emperat ure ( 2 00 t o 300K) . Thi s mxture temperat ure canbe cal cul at ed usi ng t he chemcal equi l i br i umprogram and t het hermodynamc proper t i es of t he f uel ( l i qui d and gas) andni t rogen. We found t hat i n such a syst em t he t emperature wasvery dependent upon the t hermodynamc proper t i es of t he f uel .For exampl e, a f 5 change i n t he gas phase heat capaci t y of t hef uel caused a T7K change i n t he cal cul at ed mxture temperat ure.

Fi r st , t he feasi bi l i t y of t he exper i mental t echni que w l l bedemonst rated by st udi ng i so- oct ane, a f uel f or whi ch t het hermodynamc proper t i es are wel l known. Second, t he data f ori so- octane w l l be used as a st andard f or det ermni ng any non-adi abat i c behavi or of t he apparatus. Fi nal l y, J et - A w l l bestudi ed under i dent i cal condi t i ons.Resul t s nd Di scussi oni nj ector A Temperatures of f uel / ni t rogen mxtures were measuredf or di f f erent amount s of f uel i nj ected i nt o t he hot ni t r ogenst ream These measurement s were compared t o the t emperatures

The i ni t i al data were t aken w t h i so- octane and f uel

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cal cul at ed by t he chemcal equi l i br i umprogramf or 298K l i qui df uel and 800K ni t rogen. Si nce t he exper i ment al f uel and ni t rogent emperat ures coul d not be mai ntai ned at exact l y these condi t i ons,smal l cor r ect i ons were r equi red t o reduce t hese t o t he samest ar t i ng condi t i ons. The data f or i so- octane are shown i n Fi gure2. I t was observed that f or l ow f uel mol e f ract i ons theexper i ment al t emperat ures were bel ow t he cal cul at ed ones. Thi sbehavi or i s expect ed when t he exper i mental apparat us i s notadi abat i c. . However , at hi gher f uel mol e f ract i ons, t he measuredt emperatures were much hi gher than t he cal cul ated ones and tendedt o l evel of f . Thi s suggest s t hat compl et e vapor i zat i on had notbeen obt ai ned at t he moni t or i ng st at i on 68 cmdownst reamof t hepoi nt of f uel i nj ect i on. I n di scussi ons w t h I ngebo (l o), i t wassuggest ed t hat vapor i zat i on coul d be i mproved by i ncreasi ng t hegas vel oci t y and provi di ng a const ant area sect i on t o account f ort he st reambreak-up di st ance (about 2.5 cm. I nj ector A wasmodi f i ed by at t achi ng a 3.0 cmaddi t i on at t he i nl et of eachnozzl e, as shown i n Fi gure l b. The cal cul at ed drop si ze obtai nedw th the modi f i ed f uel i nj ector i s about 22 pm Wt h t heprevi ous desi gn, cal cul at ed f uel drops were about 44 pmat t hethroat of t he nozzl es, but dropl et s 2.5 t i mes l arger werecal cul at ed at a di st ance 2.5 cmdownst reamof the throat . Thesemodi f i cat i ons shoul d si gni f i cant l y i mprove vapor i zat i on.t he i so- octane dat a i n Fi gure 3. Al l t he exper i ment al l y measuredtemperatures were bel ow t he cal cul at ed curve and t he data showeda si ml ar shape. Thi s suggest s t hat vapor i zat i on was compl ete.The temperat ure di f f erence can be at t r i but ed to apparat us heatl osses. These heat l osses i ncrease as t he mxture t emperat urei ncreases, whi ch i s t he behavi or expected f or a non- adi abat i csystem A cur ve f i t t o t he exper i mental data i ndi cated a heatl oss varyi ng f rom7 degrees at 460K t o 23 degrees at 580K. Thesystemwas cal i brat ed by pl ot t i ng t he di f f erence bet ween t hi scurve and t he cal cul at i on as a f unct i on of t emperat ure.

The measured temperat ures for J et - A/ ni t rogen mxtures areshown i n Fi gur e 4a. The behavi or i s exact l y that observed f ort he i so- octane data. Cor rect i ng t he exper i ment al dat a poi nt s f ort he heat l osses f romthe cal i brat i on curve produced t he resul t sshown i n Fi gure 4b These data are i n excel l ent agreement w t ht he t emperat ures cal cul at ed usi ng t he coef f i ci ent s der i ved f romt he thermodynamc dat a f or J et - A.

The extent of vapor i zat i on of a f uel w t h an end boi l i ngpoi nt of 532K (4) was checked by usi ng the Cl apeyron equati onwhi ch r el at es t he boi l i ng temperature (T) of a l i qui d w t h i t svapor pressure (P)

Fuel i nj ector B proved to be very successf ul , as shown by

I n P = A + B T 4)Dat a of vapor pressure reported i n ref erence 4 were used t odet ermne the const ant s A and B The l i ne obt ai ned f romtheequat i on i s shown i n Fi gure 5. The regi on under t he l i ne ( regi on

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Figure 1 Fuel In jectorsa) Fuel Injector A

Throat diarn = 0.508 cm

1.37 cml ow

10 cmb) Fuel Injector B

Throat diam. = 0.254 cm

1.37 c m

Figure 2 Exper imenta l Da t a for Iso-Octane Fuel Inje ctor A

600580

* 560540

520

5 0 0

2 480460

440

Experimental oto- alculated Vap. Temp.a

?E4

5 6 7 8 9 10 1 1 12.Fuel Mole Percent

880

t


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Figure 3 Exper imenta l Data fo r Iso-Octane Fuel In jector B620600580560

@ 540y 520

500

u

W

WI 480

4604 4 0 L , , , , , , , I , , , I 1 , I , , , , , , , , I , , , I j

5 6 7 8 9 10 11 12Fuel Mole Percent

Figure 4 - Exper imenta l Data fo r Jet -A Fuel In jector 6

a) Raw Data

Experimental Doto

3 4 5 6 7 8 9 1 0

Fuel Mole Percent

b) Data Corrected fornon-adiabatic conditions

620

Mx)

mv 56

alculated Vap. Temp.

y 540y 520

0

500

k460

440

3 4 5 6 7 8 9 10Fuel Mole Percent

881


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Figure 5 Vaporizat ion Temperature for Jet-ATemperoture, deg K

6 5 400 300 25100--.Eu 10

QIa , 1

0.1

p 0.01mma-; 1E-3aL

1E-4

I l l I 1

lopeyron Eqtn. Ref. 4)Experimental doto\

1.5 2.0 2.5 3.0 3.5 4.0Reciprocol Temperature 1000, Kpl

10 - experimental verification of the thermodynamic properties of jet-a fuel

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