(4) Effect of deviation between pressure index and temperature sensitivity coefficient of grain
The influence of the deviation between the pressure index and the
temperature-sensitive coefficient of the grain requires that the physical and
chemical properties of the grain be relatively stable.
1. The influence of pressure index deviation on combustion pressure deviation.
For example, if the pressure index and its allowable deviation of a retarded
charge are n Æ Dn ¼ 0:28 1 Æ 11%
ð
Þ%0:28 Æ 0:03, i.e., change in the
range of 0:25 $ 0:31, the corresponding combustion pressure will change in
the range of 3:637 $ 4:069 MPa at low temperature À40
C, with deviation
of Æ6% from the nominal value.
2. The influence of temperature sensitivity coefficient deviation on combustion
pressure deviation. For example, if the temperature sensitivity coefficient
and its allowable difference of a retarded charge are a T Æ Da T ¼
0:00282 1 Æ 6%
ð
Þ% 0:00282 Æ 0:00017
ð
Þ =K,
i.e.,
the
range
of
0:00265 $ 0:00299, the corresponding combustion pressure deviation at low
temperature À40
C is Æ2:5% of the nominal value.
Countermeasure: In order to reduce the influence of the deviation of physical
and chemical performance parameters such as pressure index and temperature
sensitivity coefficient on gas pressure and gas power, strict quality control must
be carried out on the raw material formulation and manufacturing process of the
grain to ensure the relative stability of physical, chemical, and thermodynamic
properties of the bulk production grain.
(5) Effect of the tolerances of main parameters on the comprehensive deviation of
combustion pressure
Considering the influence of the main parameters tolerance of retarded propellant on the comprehensive deviation of combustion pressure, it is necessary
to reasonably distribute and calculate the tolerance.
1. Allocation of tolerances for main parameters
Allocation criteria: Adjustment and control are made according to the
process accessibility and degree of difficulty of combustion pressure tolerance to the related main influencing parameter tolerances.
As mentioned above, the main parameter deviations affecting the combustion pressure deviation are sorted as follows according to the magnitude of
their effects:
(a) The relative deviation Æ11% of the grain pressure index affects the
combustion pressure deviation d 2 ¼ Æ6%.
(b) The relative manufacturing accuracy of nozzle diameter and grain
diameter are þ 1:3% and À0:13%, respectively, which affect the
combustion pressure deviation d 1 ¼ À5:5%.
(c) The relative deviation Æ6% of the grain temperature sensitivity coefficient affects the combustion pressure deviation d 3 ¼ Æ2:5%.
9.3 Design Principle of Gas Generator
133
The influence of the deviation between the pressure index and the
temperature-sensitive coefficient of the grain requires that the physical and
chemical properties of the grain be relatively stable.
1. The influence of pressure index deviation on combustion pressure deviation.
For example, if the pressure index and its allowable deviation of a retarded
charge are n Æ Dn ¼ 0:28 1 Æ 11%
ð
Þ%0:28 Æ 0:03, i.e., change in the
range of 0:25 $ 0:31, the corresponding combustion pressure will change in
the range of 3:637 $ 4:069 MPa at low temperature À40
C, with deviation
of Æ6% from the nominal value.
2. The influence of temperature sensitivity coefficient deviation on combustion
pressure deviation. For example, if the temperature sensitivity coefficient
and its allowable difference of a retarded charge are a T Æ Da T ¼
0:00282 1 Æ 6%
ð
Þ% 0:00282 Æ 0:00017
ð
Þ =K,
i.e.,
the
range
of
0:00265 $ 0:00299, the corresponding combustion pressure deviation at low
temperature À40
C is Æ2:5% of the nominal value.
Countermeasure: In order to reduce the influence of the deviation of physical
and chemical performance parameters such as pressure index and temperature
sensitivity coefficient on gas pressure and gas power, strict quality control must
be carried out on the raw material formulation and manufacturing process of the
grain to ensure the relative stability of physical, chemical, and thermodynamic
properties of the bulk production grain.
(5) Effect of the tolerances of main parameters on the comprehensive deviation of
combustion pressure
Considering the influence of the main parameters tolerance of retarded propellant on the comprehensive deviation of combustion pressure, it is necessary
to reasonably distribute and calculate the tolerance.
1. Allocation of tolerances for main parameters
Allocation criteria: Adjustment and control are made according to the
process accessibility and degree of difficulty of combustion pressure tolerance to the related main influencing parameter tolerances.
As mentioned above, the main parameter deviations affecting the combustion pressure deviation are sorted as follows according to the magnitude of
their effects:
(a) The relative deviation Æ11% of the grain pressure index affects the
combustion pressure deviation d 2 ¼ Æ6%.
(b) The relative manufacturing accuracy of nozzle diameter and grain
diameter are þ 1:3% and À0:13%, respectively, which affect the
combustion pressure deviation d 1 ¼ À5:5%.
(c) The relative deviation Æ6% of the grain temperature sensitivity coefficient affects the combustion pressure deviation d 3 ¼ Æ2:5%.
9.3 Design Principle of Gas Generator
133