The initial rates of heat release produced by the reactions of hydrazine and unsymmetrical dimethylhydrazine with nitric acid were determined in a bomb calorimeter under conditions of forced mixing. Fuel-oxidant weight ratio and injection velocity were varied. The rate of heat release apparently depended on the interfacial area between the propellants. Above a narrow range of injection velocities representing a critical amount of interfacial area, the rates reached a maximum and were almost constant with injection velocity. The maximum rate for hydrazine was about 70 percent greater than that for unsymmetrical dimethylhydrazine. The total heat released did not vary with mixture ratio over the range studied

Feiler, Charles E.

Somogyi, Dezso

English

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GZ 71043
NASA TN D--469
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TECHNICAL
D-/_69
NOTE
LIQUID-PHASE HEAT-RELEASE RATES OF THE SYSTEMS
HYDRAZINE - NITRIC ACID AND UNSYMMETRICAL
DIMETHYLHYDRAZINE - NITRIC ACID
By Dezso Somogyi and Charles E. Feller
Lewis Research Center
C leveZand, Ohio
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON September 1960
https://ntrs.nasa.gov/search.jsp?R=19980228118 2020-06-15T23:29:42+00:00Z

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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
TECHNICAL NOTE D-_69
LIQUID-PHASE }[EAT-RELEASE RATES OF THE SYSTEMS HYDRAZINE - NITRIC
ACID AND UNSYMMETRICAL DIME_RAZINE - NITRIC ACID
By Dezso Somogyi and Charles E. Feiler
SUMMARY
The initial rates of heat release produced by the reactions of
hydrazine and unsyTmmetrical dimethylhydrazine with nitric acid were
determined in a bomb calorimeter under conditions of forced mixing.
Fuel-oxidant weight ratio and injection velocity were varied. The
rate of heat release apparently depended on the interfacial area
between the propellants. Above a narrow range of injection veloc-
ities representing a critical amount of interracial area, the rates
reached a maximum and were almost constant with injection velocity.
The maximum rate for hydrazine was about 70 percent greater than that
for unsymmetrical dimethylhydrazine. The total heat released did not
vary with mixture ratio over the range studied.
INTRODUCTION
Recent findings in rocket combustion studies have led to a com-
bustion model based on vaporization of one of the propellants as the
rate-limiting step for systems such as hydrocarbon-oxygen (refs. i
to 5) and to a distillation theory for systems such as hydrocarbon -
nitric acid (ref. 4). Neither of these models has considered the
effects of liquid-phase reaction and associated heat release on com-
bustion. For systems in which propellants are mixed during injection,
the extent and rate of liquid-phase heat release may be important
factors in combustion.
The objective of this study, therefore, was to obtain data on
the amount and rate of heat release produced by liquid-phase reaction
of typical self-igniting propellant systems. The propellant combina-
tions studied were hydrazine (NzH4) - nitric acid (HNOs) and unsym-
metrical dimethylhydrazine (UDMH) - nitric acid.
The apparatus consisted of a constant-volume calorimeter, in
which the calorimetric fluid also served to quench the reaction, and
a rapid-mixing injection device. Propellants were injected through
a mixing cup of constant area and variable length. On emerging from the
cup the reaction was quenchedand the pressure and temperature rise were
measured. From these data a heat-release rate was obtained as a function
of the injection velocity. An effort was also madeto correlate pressure
and heat-release data in terms of the contr_mtion from each of several
reactions that can occur.
APPARATUSANDPROCEDURE
The apparatus (fig. i) was essentially the sameas the one used in
the investigation of reference 5 except for _omemodifications to adapt
it to the present study. It consisted of a Plexiglas-iined chamber, a
premixing injector, cylinders containing proi_ellant, pistons, and a
quick-opening valve. The chambervolume was divided into two parts:
the upper part, which was about two-thirds or the total volume and con-
tained the quenching medium, and the lower p_rt, which acted as a surge
tank.
Injection was accomplished by triggerin_ the quick-opening valve_
which discharged high-pressure nitrogen gas _gainst the driver piston
to force the propellants to break through the Teflon gasket and be
mixed in the cup. Whenthe mixture emerged from the cup, the reaction
was stopped before going to completion by th_ quenching fluid. The
temperature rise of the quenching fluid was neasuredby a resistance
thermometer and recorded by a potentiometer. The temperature was
extrapolated back to zero time to compensatefor the heat lost during
the time of temperature rise. The heat release was calculated from
the extrapolated temperature (shown in fig. _), the mass, and the
specific heat of the quenching fluid. The pressure rise due to the
reaction was measuredby a Bourdon tube pressure gage.
The apparatus was checked for accuracy _ith solutions of hydrogen
chloride and sodiumhydroxide. The difference between the experimental
heat release and the theoretical value was less than one-half of
i percent.
The mixing efficiency of the injector _as determined with aqueous-
dye-solution injection by the method described in reference 6 and was
found to be 94 percent. Water injection was used to determine the flow
velocity through the mixing cup. For this determination the mixing
cup waswired as shown in figure 3. Water shorted out the wires as it
flowed through the cup, and the resulting electrical signals were
recorded by an oscilloscope. The flow velocity was calculated from
the distance between wires and the time between signals. Velocity as
a function of driver gas pressure is also shownin figure 3. Similar
results for this type of apparatus were found in reference 7, where it
is stated that the injection rate of water was constant throughout the
injection period.
I
_O
Mixing-cup length varied from 0.31 to 1.06 inches_ while the driver
gas pressures were ZOO, SO0_ 800_ i000, ISO0_ and 2000 pounds per square
inch l_a_e (which correspond to injection velocities from 60 to 190 ft/sec).
Throughout this experiment the total volume of propellants was held con-
stant at 2 cubic centimeters. The volume ratios of acid to fuel studied
and the correspouding weight and mole ratios are sulmnarized in the
following table :
Volume ratio
Weight ratio
Hole rat io
1.0 1.50
1.S 2.85
0.76 1.14
0.67 1.00 1.SO
1.28 1.91 2.87
1.22 1.88 2.73
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2)
RESULTS AND DISCUSSION
Total Heat Release and Equilibrium Pressures
The experimental total heat release in the reaction of hydrazine
and UDHH with nitric acid is sho_m in figure 4 as a function of mixing-
cup length. A linear increase in heat release with cup length was
observed for both fuels (fig. 4(a)). The quantity of heat reached a
maximum at a driver pressure of about i000 pounds per square inch gage
and at this pressure was about S0 percent larger for hydrazine than for
UDP_. The total heat released was independent of mixture ratio over
the range studied (fig. 4(b)). At zero cup length a finite constant
heat release was obtained experimentally. This heat was probably com-
posed of heat of solution of unreacted or excess fuel or acid in water
and of heat of neutralization of acid with fuel.
The equilibrium pressures produced by the reactions are shown in
figure 5 as a function of mixing-cup length. The pressure rise and
the heat release were from i0 to 30 percent of the theoretical values
for complete combustion_ which indicated that appreciable quantities
of gaseous products were formed.
Heat-Release Rates
Evolution of gas in the mixing cup could result in an accelerating
flow whose rate would have to be kno_m in order to obtain heat-release
rates. It is possible to obtain an initial heat-release rate by
assuming that the velocity at the entrance to the mixing cup was equal
to that measured in cold-flow calibrations. Thus, the heat-release
rate at zero cup length is given by
:\TJ L-_ V i
where Qexp is the experimental heat relea3ed, L is the mixing-cup
length, t is time_ (dQexp/dL)L_ _ is the gradient of the heat release with
with cup length at zero, and (dL/dt)L_ _ is the injection velocity (Vi).
Values of (dQexp/dL)L_ _ expressed in kcal/(ft)(mole acid) were obtained
at each pressure from the curves of figure i(a), while injection veloc-
ities were obtained from figure S. The variation of dQexp/dtL_ _
(hereinafter called the heat-release rate) with injection pressure or
velocity is shown in figure 6. The two fuels gave heat-release-rate
curves of similar shape. The abrupt increase in slope indicates the
existence of a critical injection velocity ar pressure whose value is
about the same for each fuel.
A possible explanation of the behavior of these curves may be
obtained from consideration of the followin_ expression for the heat-
release rate:
l_Qex%_
= 1
where k is a rate constant (in kcal/(sec) mole acid)), E is the
activation energy for the reaction, R is t]_e universal gas constant,
T is temperature, and F(M) is the fracti,_n of total propellant that
is mixed. It is assumed that mixing occurs in the interracial surfaces
between fuel and acid and thus the fraction of material mixed will
increase with interfacial area. Previous s;udies with the type of
apparatus used in this study have shown tha; mixing increases with flow
velocity (ref. 8).
The increase in heat-release rate with injection velocity at the
lower velocities (fig. 6) may thus be attri:_uted to an increase in
interfacial area or in F(M). The rapid ri_e in heat-release rate
observed at injection velocities of 120 to _40 feet per second is
attributed to an increase in temperature, fin this velocity range it
appears that heat generated in the interracial area can no longer be
dissipated to the surrounding fluid at a sufficient rate, and therefore
the temperature of the reacting material in.:reases, which results in
an exponential increase in heat-release rate. At velocities greater
than about 140 feet per second the heat-rel_ase rates attain constant
S_D
O_
I
values or perhaps decrease slightly, which indicates that temperature
has attained a constant value. This temperat_ire is probably a character-
istic temperature of the propellant system such as the flame temperature.
It is possible that gas evolution rates accompanying the reaction are
sufficient at the highest injection velocities to inhibit the mixing
process. The resulting decrease in F(H) would thus account for a
decrease in the heat-release rate.
A comparison of the maximum heat-release rates shows that hydrazine
has a rate about 70 percent larger than UDMH. The values are 85,000 and
48,000 kcal/(sec)(mole acid) for hydrazine and UDMH, respectively. In
reference 9 it was found that the combustor volume needed for complete
combustion of hydrazine was about half that required for UDHH. This
result agrees with the relative heat-release rates found for the two
fuels.
Correlation of Equilibrium Pressures with Heat-Release Data
The equilibrium pressures shown in figure S should correlate with
and serve to check the heat-release data. The equilibrium pressure
and the bulk of the heat evolved in these experiments appear to be due
to the combustion reaction. From the two measurements, pressure and
heat release, it was possible to calculate independently two values
of the extent of the combustion reaction expressed as the number of
moles of acid reacted. The combustion reactions assumed were
Cm os(z) + 5%He(Z) leS2o(z) + rs2(g)
16m o:(z) + s(c%)2ssHs(Z) - SSH20(Z)+ lSHS(g) + 1OC02(Z,g)
Pressures were thus due to nitrogen and a part of the carbon dioxide
given by Henry's law. By use of experimental pressures in the ideal
gas law for the stoichiometric quantities, it was possible to calculate
the moles of acid that had reacted.
To arrive at a comparable value from the heat data requires a
determination of that portion of heat due to combustion. In addition
to combustion_ sources of heat were the neutralization reaction and
the heat of solution of unreacted material and products of reactions
in the water. Among the products of reaction only a part of the
carbon dioxide, given by Henry's law_ dissolved in water. Since this
was a small amount and the heat of solution is small, this quantity
was neglected.
6A material balance maybe written as foi.lows:
X = X 1 + X2 + X 3
Y = YI + Y2 + Y3
where X and Y are the number of moles of acid and fuel injected,
respectively, and the subscripts i, 2, and 5 are the number of moles
reacting by combustio% neutralizatio% and _olution, respectively.
The number of moles neutralized does not inci_ude those that subse-
quently were combusted.
The heat balance may then be written
Qexp = QiX1 + Q2X2 + QsX3 + Q_Y3
where Qexp is the total heat measured experimentally, QI' Q2_ and
Q3 are, respectively, the heats of combusti,m, neutralization, and
solution per mole of acid, and Q_ is the h_at of solution per mole
of fuel.
In addition there are several acid-fuel ratios:
X
Input ratio =
XI
Stoichiometric combustion r_tio =--
YI
X 2
Neutralization ratio = --
YZ
Also_ either X 3 or Y3 is zero depending )n the input ratio. For
all input ratios studied except one, acid wa_ in excess and Y3 = 0.
The single exception occurred at the fuel-rizh ratio with hydrazine.
The input ratios are tabulated in the precedLng section. Values of
the various Q's and ratios are given in th_ following table:
N2H 4
QI _
kcal
Q2 '
kcal
Qs,
kcal
Q_ _ X I X 2
kcal YI Y2
mole acid mole acid mole acid mole fuel
177 18.5 6.1 6.6
152 19.0 6.1 ---
0.8 1.0
.2 1.0
!
LM
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Values of QI were calculated for the stoichiometric quantities given
previously_ while Q2 and Q3 were determined experimentally for the
dilute solutions involved in this study; Q2 thus includes the heat of
solution or dilution of neutralization products.
These equations were solved for XI; the moles of acid reacting
by the combustion reaction. Values of X I obtained from pressure
measurements are plotted against those from calorimetric data in
figure 7. A perfect correlation would have resulted in a slope of
unity as sho_m. The agreement found was considered reasonable in
view of the possible sources of error in the calculations and in the
experimental data.
Suggested Combustion Mechanism
The combustion mechanism postulated for these highly reactive
propellant systems under conditions of forced mixing is reaction at
fuel-acid interfaces. Provided the interfacial area or mixing is
great enough_ reaction or heat release appears to proceed at a rate
characteristic of the propellants. If the mixing becomes too great_
it appears that the heat-release rate may be decreased because of gas
evolution that forces the propellants to separate. It is also possible
that gas evolution could lead to additional breakup of the fluid to
smaller drops. As shown in references i and 2, small drops are desir-
able in a rocket engine because they give the largest conversion rates
with propellant systems that are not self-ignitingJ Further studies
are indicated to determine whether there is an appreciable effect of
gas evolution on resultant drop size.
The heat-release rates found in this study were compared with
approximate rates of convective heat transfer to a burning drop using
the expressions of reference 2. For drops of about i00 microns in
diameter the two rates were the same order of magnitude. Thus the
heat release found in this study is appreciable and could considerably
modify the vaporization theory.
SUMMARY OF RESULTS
The liquid-phase heat-release rates of unsymmetrical dimethyl-
hydrazine (UDMH) and hydrazine with nitric acid were determined in a
bomb calorimeter under conditions of forced mixing. The results may
be summarized as follows:
I. The maximum rate of heat release of hydrazine was about
70 percent greater than that of UDMH, the values being 83_000 and
48,000 kcal/(sec)(mole acid) for hydrazine and UDMH, respectively.
82. The rate of heat release appears to depend on the interfacial
area between the propellants or on the degree of mixing. Above a narrow
range of injection velocities representing a critical amount of inter-
facial area, the rates were almost constant with injection velocity.
5. Within the range mixture ratio was varied it had no effect on
the total amount of heat released.
Lewis Research Center
National Aeronautics and SpaceAdministration
Cleveland_ Ohio, May51, 1960
REFERENCES
i. Prlem, Richard J., and Heidmann,Marcus F.: Propellant Vaporization
as a Design Criterion for Rocket-Eng_e CombustionChambers. NASA
TR R-67, 1960.
2. Ingebo_ Robert D.: Heat-Transfer and Drag Coefficients for Ethanol
Drops in a Rocket ChamberBurning EthEnol and Liquid Oxygen.
Paper prepared for 8th International Symposiumon Combustion,
California Institute of Technology, A[gust 1960.
5. Baker, Louis, Jr.: A Study of the Combtstion Rates of Hydrocarbon
Fuels with Red Fuming Nitric Acid in _ Small Rocket Engine.
NACARME58DO3a,1958.
4. Wood, Bernard J., Wise, Henry, and InamJ, S. Henry: Heterogenous
Combustion of Multicomponent Fuels. FASA TN D-206, 1959.
5. Schalla, Rose L., and Fletcher, Edward ;.: The Behavior of the
System Triethylamine - White Fuming N_tric Acid under Conditions
of Rapid Mixing. Sixth Symposium (International) on Combustion,
Reinhold Pub. Corp., 1957, pp. 911-91].
6. Somogyi, Dezso, and Feiler, Charles E.: Mixture Ratio Distribution
in the Drops of Spray Produced by Impfnging Liquid Streams.
ARS Jour., vol. 50, no. 2, February i_60_ p. 185.
7. Kilpatrick, Martin, and Baker, Louis L._ Jr.: A Study of Fast
Reactions in Fuel-Oxidant Systems. Fifth Symposium (Inter-
national) on Combustion, Reinhold Pub. Corp., 1955, pp. 196-205.
8. Roughton_ F. J. W., and Chance, B.: Investigation of Rates and
Mechanisms of Reactions. Vol. 8 of Technique of Organic Chemistry,
A. Weissberger, ed._ Interscience Publ., 1955, p. 669.
9. Feiler, Charles E., and Baker, Louis, _-.: A Study of Fuel-Nitric
Acid Reactivity. NACA RMES6A19, 195(!.
I
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FJgmre i. - Bomb-calorlmeter assembly.
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1.4
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1.0
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[Q
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40
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i
Driving gas pressure_ /
ib/sq[] 200in"gage /_ i
<> 5oo "
_7 800 /" /,
_ Iooo //,_,0 1500
,_ 2000 i,/
,- //
-I .-,°
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•4 __oints for all _iver presage;
.2
0xidant-fuel 0xidant-fuel
weight ratio volume ratio
r
Open symbols Nitric acid i. 91 1
and UDMH
Solid symbols Nitric acid i. 50 i
and hydraz: ne
I I I I .I I I I i
.2 .4: .6 .8 1.0
Mixing-cup length _ in.
(a) Various driver pressures.
Flgure 4. - Experimental h_#at-release curves.
1.2
13
1.6
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1.2
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,--t
-0
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4._
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-r'-I
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N
/
/
/
/' Ai
/ _f 0xidant-fuelweightratio
/ • i° 50_ Nitric acid and hy_azine
_ 2.25 !
1.28 Nitric acid and _
2.87
.2
.2 ._ .6 .8 1.0
Mixing-cup length, L_ in.
(b) Various oxidant-fuel ratios. Driving gas pressure;
1500 pounds per square inch gage.
_Igure _o - Concluded. Experimen%al heat-release curves.
1.2
14
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bD
bD
6O
r_
_ _o
m
©
%
r-t
-o
_ _o
-H
%
bl
Figure 5.
Open symbols
__ Solid symbols
Driver gas pressure,
lb/sq in. gage
I-I 200
0 500
800
i000
0 1500
2000
Nitric acid and UD_
(oxidant-fuel weight ratio, i. 91)
Nitric acid and hy4razine
(oxidant-fuel weight ratio, 1.50)
.2
9 1
- /
.A .6 .8 1.0
Mixing-cup length, L, in.
1.2
Experimental pressure measurements. Equilibrium conditions.
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100XlO 5
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"_" 80
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G 80
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e 40
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r-_
%
I
..p
e 2o
N
I I i t I
0x idant- fue i
weight ratio
Nitric acid
and hydrazine i. S0
Nitric acid and
UDMH i. 91 /
_o
Figure 8.
80 120 160 200
Injection velocity, Vi, ft/sec
[ I I I i I
200 S00 800 i000 1500 2000
Driver pressure, ib/sq in. gage
- Heat-release rate as function of injection velocity.
240
16
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h
q_
4_
,H
H
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o
o
4_
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rH
• OO8
• 006
• OO4
• 002
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i
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@
°,,,4io
n
/
i
Theoretical
,/
/
/
/
0_° o _it_io ao_dan__
_ 0 Nitric acid and hyd_azine
.002 .004 .006 .008 .010
Moles of nitric acid reacted calculated from heat release
Figure 7. - Correlation of heat releas_ with pressure data.
NASA - Langley Field, Vs. E-913


Liquid-Phase Heat-Release Rates of the Systems Hydrazine-Nitric Acid and Unsymmetrical Dimethylhydrazine-Nitric Acid

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