Chemistry Reference
In-Depth Information
number of works (for example, see [6, 11, 12, 13]). Due to the absence of kinetic
data for temperatures close to the surface temperature of the ignited or burning fuel,
a quantitative analysis of the contribution of condensed-phase reactions to the over-
all process was previously not possible. However, this can now be achieved using the
kinetic data presented in this chapter and in Chap. 5, although it is worth noting that
only cases where the reacting mixture can be assumed to be pseudohomogeneous
can be considered. In other words, the reacting layer thickness should significantly
exceed the characteristic heterogeneity scale (in this case, the AP crystal size).
Practically speaking, this means that the obtained kinetic parameters can be
used to analyze processes characterized by an ignition delay (induction) period of
more than 0.5 s. Such an induction period is characteristic of solid-propellant rocket
charges undergoing aerodynamic heating for example. The obtained kinetic con-
stants can also be used to quantitatively analyze the role of condensed-phase reac-
tions in AP-based composite solid propellant burning at subatmospheric pressures.
At
P
0
.
1 MPa, the reaction rates for most AP-based composite solid propellants
are quite low. Therefore the reaction zone can be treated as being homogeneous,
since its thickness significantly exceeds the AP grain size.
First, let us compare kinetic data obtained by DTA and the method of ignition
using a hot metal block (Sect. 5.4) for two samples of NG-2-60-DTM commercial
polyurethane composite solid propellant (with and without the combustion catalyst,
Fe
2
O
3
).
The values of
Qk
0
and
E
ign
were obtained by experiments on ignition in the
temperature range of 350-430
◦
C. In this case, a term characterizing the conversion
degree for the pre-ignition time was neglected in Eq. (5.5)
≤
0
3
/
2
)(1 +
τ
ign
=(1 + 1
.
6
Θ
0∞
+ 0
.
2
Θ
)(1 + 8
Θ
0∞
γ
β
)
.
∞
= R
T
S
c
/
QE
;
Q
is determined by thermography), into account, refined data for
E
ign
were obtained
(Table. 9.3).
The difference between
E
ign
and
E
ign
was found to be approximately 3 kJ mol
−
1
,
which is within the experimental error.
3
/
2
, which includes the thermal effect
Q
(
By taking the term 8
Θ
∞
γ
γ
0
Table 9.3
Determination of the conversion degree
ign
on the surface of the composite solid pro-
pellant at its ignition (comparison of data obtained by the ignition method and DTA)
Composition
η
Ignition on a metal block
DTA with thermal dilution
Data from Chap. 5
Refined data
E
ign
,
kJ mol
−
1
E
=
E
ign
,
kJ mol
−
1
E
ign
,
kJ mol
−
1
lg
Qk
0
,
Jg
−
1
s
−
1
lg
Qk
0
,
Jg
−
1
s
−
1
η
ign
lg
Qk
0
,
Jg
−
1
s
−
1
AP-polyurethane 178
16.4
182
16.8
182
0.3
16.6
AP-
polyurethane+
Fe
2
O
3
129
13.2
131
13.6
131
0.17
13.4
