RESEARCH MEMORANDUM ANALYTIC EVALUATION O F EFFECT OF INLET-AIR TEMPEXATUBE

AND COMBUSTION PRESSURE ON COMBUSTION PERFORMANCE

SLURRIES AND BLENDS OF PENTABOMNE

IN OCTENE-1

QATIONAL PI ADVISORY COMMITTEE

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FOR AERONAUTICS WASHINGTON

Mhy 25, 1956

NACA FiM E56Do2 4

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NATIONAL ADVISORY COMMITTEE ..

r;' N V

FOR AERONAUTICS

ANALYTIC EVaLuATION O F EFFET OF INLET-AIR AND COMBUSTION

PRESSURE ON COMBUSTION PERFORMANCE OF BmON SLURRIES AND

suppT;EMENT I - IPWLIENCE O F PTEW BORIC-OXIDE VAPOR-ESSSURE DATA ON

By Leonard K. Tower

5v"ARY

The theoretical performnce of pentaborane has been recalculated r.

using recent data on the vapor pressure of boric oxide. Previous calcu-

method not aa accurate as that employed in current investigations. The recalculated performance data for pentaborane differ appreciably from previously published data and are considered more accurate f o r evaluation of the re la t ive potent ia l i t ies of boron-containing fuels.

L lat ions were based upon vapor-pressure data obtained same years ago by a

INTRODUCTION

As part of a general 6tu.W of the performnce of high-energy fuels in jet engines, theoretical calculations h v e been made t o evaluate the re la t ive performance poten t ia l i t i es of these fuels. Results of these calculations are reported i n references 1 t o 4. In making calculations for boron-containing fuels the accuracy of the predicted. performance has been dependent upon the accuracy with which the properties of boric oxide have been known. All previous NACA references have based performance calculations on boric-oxide vapor-pressure data reported by Cole and Taylor ( ref . 51 in 1935. Recent vapor-pressure data obtained by Speiser, Naiditch, and Johnston (ref. 6) and Soulen, Sthapitanonda, and &grave (ref . 7) indicate that the ear l ier data (ref. 5) are considerably in

ence 5 are a l s o i n error . - error; consequently, previous performance calculations based upon refer-

II For this reason the present report has been prepared t o show the recent vapor-pressure data on boric oxide (refs. 6 and 7 ) ' and t o

2 NACA RM E 5 0 0 2 6

i l l u s t r a t e t he e f f ec t of these data on performance calculatione of boron- containing fuels. I n addition data are presented to indicate corrections I

t o be made t o data f o r boric oxide previausly reported i n reference 8. For the performance calcubt ions, pentaborane has been asaumed t o be the boron-containing fuel of in te res t . The calculated performance data for pentaborane supersede simllar data reported in reference 3.

SYMBOLS

acceleration due to gravity, 32.17 ft/sec2

enthalpy change due t o formation of substance frm its elements i n atomic gas state divided by RT

sum of sensible enthalpy and chemical energy a t temperature T and a t standard conditions, kcal/mole

equilibrium constant f o r reaction 2B + 30 + %%

mean molecular weight of gas mixture, exclusive of condensed B2°3

universal gas constant, 1545.33fig, ( f t ) ( lb) / ( lb)(oR)

a i r sp-ecif i c impulse,.. ( lb 1 (sec )/lb air

temperature, OK

weight f ract ion of salids or liquids i n exhaust gases

r a t i o of specific heats

equivalence ratio; ratio of actual to stoichiometric f 'uel-air ra t io- . . I . . . - .. . . ~ . - . . - . . - - . - . - -

DISCUSSION AND RESULTS

V a p o r Pressme of Boric Oxide

r

Y

The vapor pressures obtained by Cole and Taylor (ref. 5 ) for boric oxide (Bz03) are compared with data from references 6 and 7 in f igure 1. The more recent vapor-pressure data (refs. 6 and 7 ) are considerably lower than the previously available data (ref. 5). This dlfference in vapor pressure has a significant effect on computations of performance.

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NACA RM E56D02 9

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- Slight adjustments have been made in the lower curve of figure 1 t o make the data consistent with tabulations of properties of gaseous Bz03 contained in reference 8. These adjustments are such that entropy and specific-heat data for gaseoy B203 in reference 8 a r e unchanged. The new values of vapor pressure shown i n figure 1 render the tabulated values of log K and I$ in reference 8 obsolete. Tabulated data of reference 8 can be corrected to the new standazds by means of the following relations:

(%Inew = (€!$old + 12.2174 kcal/mole a

In these relations, conversions to Btu may be d e by multiplying kilo- calories by 1798.82. These corrections to the data of reference 8 should be regarded a8 interim values, which may be used u n t i l a formal revision

* of thermal data fo r t he boron oxides is available.

d H e a t of Vaporization of Boric Oxide d

The Clausius Clapeyron equation was used t o compute the variation of heat of vaporization w i t h temwature. This re la t ion is shown in figure 2 and is based on the recent vapor-pressure data (fig. 1, refs. 6 and 7).

Combustion Temperatures of Pentaborane

The data described i n the preceding paragraphs w e r e used to ca lcu la te the variation of conibustion temperature with equivalence r a t i o f o r penta- borane (B,&> In the region of B203 vaporization. The molecules consid- ered as possible combustion products w e r e : %03 (gas and l iquid), H20, IT2, 02, and NO. Because OH, BO, and other substances w e r e overlooked, the calculations w e r e limited t o less than 4000° R. The variation of conibustion temperature with equivalence r a t i o is shown i n figure 3, and a comparison is &own of the r e su l t s based on old and new vapor-pressure data f o r B2O3. A t temperatures above 3900° R where vaporization i s com- plete, the solid curve represents reasonably w e l l the couibustion tempera- . tu re data using old and new vapor pressures.

. A i r Specific Impulse of Pentaborane

mom the conibustion temperatures shown in figure 3 the air specific impulse of pentaborane w a s computed by the method described in reference

r

4 - NACA RM E56Do2

3, which assumes frozen composition during expamion. Necessary thermal properties y, R, and X consistent with the conibustion temperatures based on the new Bz03 v a p r pressures are shown i n figure 4. Figare 5

compares the var ia t ion of air specific impulse with equivalence r a t i o for both old and new vapor-pressure data.

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Consumption of Pentaborane

O f particular interest in the evaluation of boron-containing fuels is the consumption r e l a t i v e t o hydrocarbons. A comparison of t h i s type is reported in reference 3 for pentaborane; however, the calculation vas based on the old vapor-pressure data far B203 as reported in reference 5. For this reason consumption data have been recalculated on the basis of the new vapor-pressure data reported. i n r e f e r e x e s 6 and 7. The results are shown in f igure 6 for consumption of B& re la t ive to octene-1. The conditions chosen f o r t h i s comparison w e r e 560° R inlet-air temperature and a pressure of 2 atmospheres.

0 rn P 03

Use of the new data r e su l t s i n a significant decrease in re la t ive fue l consumption a t cer ta in levels of a i r spec i f ic impulse. Also, t h e same leve l of re la t ive fue l consumption is reached a t higher air specific impulses. For example, the new data. indicate that a re la t ive fue l con- I

sumption of 0.838 is reached about 10. seconds higher than was previously estimated from the old vapor-pressure data.

8

The comparison of fuel consumption is based on frozen composition in the expansion process. If the composition adjusts during expansion, lower fue l consumptions can be attained with pentaborane fuel, particu- larly at high a i r spec i f ic impulse levels.

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CONCLUDING REMARKS

Small inconsistencies between figures 4 to 6 are largely a resu l t of simplification i n the calculations. Refined calculations will alter these figures some, although the general performance levels w i l l not be greatly changed. Until better calculations are made, figures 4, 5, and 6 must be regarded aa tentative. Further refinements in calculat ion may also a l ter the re la t ive fuel consumption f o r pentaborane at elevated temperatures above the vaporization region.. .. ., .. . L

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A simplified method fo r obtaining approximate combustion tempera- tures and thrust performances .& baran-mtaining fuels is presented i n reference 9 . The thermal data ta-bulated therein incorporate the new vapor pressures for boron oxide. . . . ..

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L e w i s Flight Propulsion .h&orat.ory National Advisory Committee fo r Aeronautics . .

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Cleveland, Ohio, -April 3, 1956 " -

W A RM E56D02 5

1. Breitwieser, Roland, Gordon, Sanford, and Gammon, Benson: Summary Report on Analytical Evaluation of Air and Fuel Specific-hpulse Characteristics of Several Nonhydrocarbon Jet-Engine Fuels. NACA RM E52L08, 1953.

2. Tower, Leonard K., and -n, Benson E.: An&l;ytical Evaluation of Effect of Equivalence Ratio, Inlet-Air Temperature, and Conibustion Pressure on Performance of Several Possible Rsm-Jet n e b . NACA RM E53G14, 1953. . .

3. Tower, Leonard K.: Analytic Evaluation of Effect of Inlet-Air Tem- perature and Combustion Pressure on Cmbustion Performaace of Boron Slurries and Blends of Pentaborane i n Octene-1. NACA RM E55A31, 1955.

4. Olson, W a l t e r T., Breitwieser, Roland, and Gibbons, Louis C.: A Review of NACA Research Through 1954 on Boron Compounds as Fuels fo r Jet Aircraft (Project Zip). NACA RM E55BO1, 1955. -

5. Cole, S. S . , and Taylor, N. W.: System Na2GB203. I V - Vapor Pres- sues of Boric Oxide, Sodium Metaborate, and Sodium Diborate Between l l 5 O o and 1400° C. Jour . Am. Ceramic SOC., vol. 18, no. 3, Mar. 1935, pp. 82-85.

6. Speiser, Rudolph, Haiditch, %M, and Johnston, Herrick L. : The Vapor Pressure of Inorganic Substances. I1 - %Os. Jour. Am. Chem. Soc., vol. 72, no. 6, June 1950, pp. 2578-2580.

7. Soulen, John R., Sthapitanonda, Prasom, and Margrave, John L. : V a p o r i - zation of horganic Stibstances: +03, Te02 and W3NZ. Jour. Phys.

Chem., vol. 59, no. 2, Feb. 1955, pp. 132-136.

8. Huff, V e a r l N., Gordon, Sanford, and Mrrel l , Virginia E. : General Method and Thermodynamic Tables fo r Computation of Equilibrium Composition and.Temperature of Chemical Reactions. NACA Rep. 1037, 1951. (Supersedes NACA TN*s 2113 and 2161.)

9. Hall, Eldon W. , and Weber, Richard J. : Tables and Charts f o r Thermodynamic Calculations Involving A i r and Fuels Containing Boron, Carbon, Ey-drogen, and Oxygen. NACA RM E56B27, 1956.

6 NACA RM E56D02 t

Temperature, %

f I _ _ _ I I I .?so0 3000 '3565 ' I ". . . " - - ~ - - " - " -15oa

. . .

Temperature, 9

Figure 1. - Vapor pressure of b o r i c x a i d e (+03>.

R

.

4 8 B ?3

. . . .. ...

C i

78

I7

76

75

76

75

72

1 b

~. . .

5018 .. . . . ... . .I

I .

u Ln

N 0

I

-3

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0 wi

5000

4000

3000

2000

1000 0 .2 .4 .6 .a 1.0

Equivalence ratio, cp

Figure 3. - Combustion temperature of pentaborane (%Hg) at 560° R inlet-& temperature and 2 atmospheres pressure.

NACA RM E56D02 9

Temperature, % .08

0

56

g%

53 .40 .44 -48 .52 .56 .60

Equivalence rat io , cp

Figure 4. - Thermal properties of pentaborane (BgHg) couibustion products in region of boric oxide (B203) vaporization f o r ideal conibustion using data of references 6 and 7. -

10

st ‘32 0 aJ a

u3 1

180

17 0

160

150

140

3-30

120

110 .2 .3 .4 .5 . .6 .7 .8

Equivalence ratio, rp

Figure 5. - A i r specific Inpulse of pentaborane (BgHg) at 560° R inlet-air temperature and 2 atmospheres pressure. .

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s

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L I b

ri

4 4J u V 0

B

. .. . .

I

F F

I OJ

Air epecFPlc lmpulae, Ea, (lb) (sec)/lb alr

1600 2000 2400 2800 3200 3600 4000 Combustion temgerature of octene-1, OR

Figure 6. - Coneumption of pentaborme relative to that o r octcm-1 again& air 8pec i r lc impulee f o r 2 Btu106ph0ES combustion pressure 8 n ~ 560' R m e t - & temperature. ::

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c