Method for determining constant-pressure adiabatic combustion temperature of solid propellant

Abstract

The application discloses a method for determining the constant-pressure adiabatic combustion temperature of a solid propellant, which comprises the following steps: step S1, measuring the stable constant-volume explosion heat value of the solid propellant through an experiment; step S2, calculating the gas mole number of unit mass of the solid propellant; step S3, calculating the actual constant-pressure explosion heat value of the solid propellant according to the stable constant-volume explosion heat value and the gas mole number of unit mass of the solid propellant; step S4, obtaining the theoretical constant-pressure adiabatic combustion temperature according to the known assumed chemical formula of the solid propellant and the raw material enthalpy, and obtaining the theoretical constant-pressure explosion heat value of the solid propellant; and step S5, calculating the actual constant-pressure adiabatic combustion temperature of the solid propellant. The application solves the problems that the traditional contact type thermocouple temperature measurement method cannot measure the combustion temperature of the solid propellant with super-high temperature, and the non-contact optical temperature measurement method has poor test result reproducibility and cannot accurately measure the actual constant-pressure adiabatic combustion temperature.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of solid propellants, and particularly relates to a method for determining the constant-pressure adiabatic combustion temperature of a solid propellant. BACKGROUND

[0002] Direct testing methods for the adiabatic combustion temperature of a propellant include a thermocouple method and an optical non-contact temperature measurement method. The highest measurable temperature of the thermocouple is 2780K, while the combustion temperature of an aluminum-containing high-energy propellant is generally higher than 3000K, which exceeds the temperature measurement range of the thermocouple, and thus the thermocouple cannot be applied to the measurement of the adiabatic combustion temperature of a high-energy solid propellant. The optical temperature measurement method mainly includes a holographic interference temperature measurement technology, a laser spectroscopy temperature measurement technology, an infrared radiation temperature measurement technology, etc. However, the optical temperature measurement has a large focusing difficulty, and the loss through the glass window of the combustion chamber and the influence of intermediate factors such as light refraction are complex, resulting in poor reproducibility of the test results.

[0003] In recent years, the theoretical combustion temperature of a high-energy propellant has been far beyond the temperature measurement range of the thermocouple. The traditional contact thermocouple temperature measurement method cannot measure the ultra-high temperature due to the limited high-temperature resistance of the metal thermocouple wire. The non-contact optical temperature measurement method is affected by the complex intermediate factors such as light refraction due to the high and intense combustion of most solid propellants and the generation of a large amount of carbon particles, which easily pollute the glass window of the optical temperature measurement combustion chamber, resulting in poor reproducibility of the test results. SUMMARY

[0004] The application aims to provide a method for determining the constant-pressure adiabatic combustion temperature of a solid propellant, so as to solve the problem that the traditional temperature measurement technology cannot accurately measure the actual constant-pressure adiabatic combustion temperature of a solid propellant.

[0005] The application adopts the following technical scheme: a method for determining the constant-pressure adiabatic combustion temperature of a solid propellant, which is composed of the following steps:

[0006] Step S1: measuring the stable constant-volume heat of explosion of the solid propellant through an experiment,

[0007] Step S2: calculating the gas moles per unit mass of the solid propellant by using the mass of the solid propellant corresponding to the stable constant-volume heat of explosion and the pressure of the oxygen bomb when the solid propellant of the mass is cooled to 298K after combustion,

[0008] Step S3: calculating the actual constant-pressure heat of explosion of the solid propellant according to the stable constant-volume heat of explosion and the gas moles per unit mass of the solid propellant,

[0009] Step S4: calculating the theoretical constant-pressure adiabatic combustion temperature of the solid propellant by using a thermodynamic software according to the assumed chemical formula of the known solid propellant and the raw material enthalpy, and obtaining the theoretical constant-pressure heat of explosion of the solid propellant by subtracting the total enthalpy of the combustion products at 298K from the raw material enthalpy of the known solid propellant,

[0010] Step S5: Calculate the actual isobaric adiabatic combustion temperature of the solid propellant based on the theoretical isobaric heat of explosion, the theoretical isobaric adiabatic combustion temperature, and the actual isobaric heat of explosion.

[0011] Further, step S1 consists of the following steps:

[0012] Weigh 1-2 grams of solid propellant and measure its constant volume heat of explosion. Then gradually increase the mass of solid propellant weighed and measure its constant volume heat of explosion again until the fluctuation of the constant volume heat of explosion between the two measurements is <100 J / g. Repeat the last measurement process 2-3 times, and take the average of the constant volume heat of explosion measured in these 2-3 measurements as the stable constant volume heat of explosion.

[0013] Furthermore, the mass of solid propellant added each time is equal, and preferably 0.5-1 gram.

[0014] Furthermore, the formula for calculating the number of gas moles per unit mass of solid propellant in step S2 is:

[0015]

[0016] In the formula, V is the volume of the oxygen bomb in the isothermal oxygen bomb calorimeter used for constant-volume explosion heat measurement, and P... e P0 is the pressure of the oxygen bomb in the isothermal oxygen bomb calorimeter when the solid propellant is cooled to 298 K after combustion; P0 is the initial pressure of the oxygen bomb in the isothermal oxygen bomb calorimeter before combustion of the solid propellant; and R is the molar gas constant, taken as 8.314 J·mol2. -1 / kg, n g denoted as the number of gas moles per unit mass of solid propellant, and m as the mass of solid propellant corresponding to the stable constant-volume heat of explosion.

[0017] Furthermore, the formula for calculating the actual isobaric heat of explosion of the solid propellant in step S3 is as follows:

[0018] Q pexp =Q vexp -n g R×298

[0019] In the formula, Q pexp Q is the actual isobaric heat of explosion. vexp To stabilize the constant-volume heat value, n g R represents the number of moles of fuel gas per unit mass of solid propellant, R = 8.314 J·mol⁻¹ -1 / kg.

[0020] Furthermore, the formula for calculating the actual isobaric adiabatic combustion temperature in step S5 is:

[0021]

[0022] In the formula, T pth Q is the actual constant pressure explosion heat value, T pexp Q is the theoretical constant pressure explosion heat value, T pth Q is the actual constant pressure explosion heat value, T pexp Q is the actual constant pressure explosion heat value, T

[0023] The beneficial effects of the present application are: the present application measures the stable constant volume explosion heat value of the solid propellant through experiments, calculates the gas mole number of unit mass of the solid propellant and the actual constant pressure explosion heat value, calculates the theoretical constant pressure explosion heat value and the theoretical constant pressure adiabatic combustion temperature by using the thermodynamic software, and finally calculates the actual constant pressure adiabatic combustion temperature, the absolute error of the actual constant pressure adiabatic combustion temperature obtained by this method and the constant pressure adiabatic combustion temperature calculated by the thermodynamic software is nearly one percent, and the problems that the traditional contact type thermocouple temperature measurement method cannot measure the combustion temperature of the super-high-temperature solid propellant and the non-contact optical temperature measurement method has poor repeatability and cannot accurately measure the actual constant pressure adiabatic combustion temperature are solved. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is a pressure trend graph of the embodiment 1 of the present application. DETAILED DESCRIPTION

[0025] The present application will be described in detail below in combination with the drawings and specific embodiments.

[0026] The present application discloses a method for determining the constant pressure adiabatic combustion temperature of a solid propellant, which comprises the following steps:

[0027] Step S1: measuring the stable constant volume explosion heat value of the solid propellant through experiments, wherein the explosion heat of the solid propellant refers to the heat released when unit mass of the propellant is changed into combustion products at the same temperature (298K) under the condition of a specified initial temperature (the initial temperature is 298K) and oxygen isolation.

[0028] Step S2: calculating the gas mole number of unit mass of the solid propellant by using the mass of the solid propellant corresponding to the stable constant volume explosion heat value and the pressure of the oxygen bomb when the solid propellant of the mass is cooled to 298K after combustion,

[0029] Step S3: calculating the actual constant pressure explosion heat value of the solid propellant according to the stable constant volume explosion heat value and the gas mole number of unit mass of the solid propellant,

[0030] Step S4: According to the assumed chemical formula of the known solid propellant and the raw material enthalpy, the theoretical constant pressure adiabatic combustion temperature is calculated by thermodynamic software based on the principles of minimum free energy, energy conservation and component conservation, and the theoretical constant pressure explosion heat value of the solid propellant is obtained by subtracting the total enthalpy of the combustion products at 298K from the known raw material enthalpy of the solid propellant.

[0031] Step S5: The actual constant pressure adiabatic combustion temperature of the solid propellant is calculated according to the theoretical constant pressure explosion heat value, the theoretical constant pressure adiabatic combustion temperature and the actual constant pressure explosion heat value.

[0032] Wherein, step S1 consists of the following steps:

[0033] 1-2 grams of solid propellant is weighed and the constant volume explosion heat value is measured, then the mass of the weighed solid propellant is gradually increased and the constant volume explosion heat value is measured until the fluctuation of the constant volume explosion heat values of 2 measurements is <100 J / g, the last measurement process is repeated 2-3 times, and the average value of the constant volume explosion heat values of the 2-3 measurements is taken as the stable constant volume explosion heat value, the mass of the weighed solid propellant is equal each time, and preferably 0.5-1 g.

[0034] Wherein, the formula for calculating the gas moles per unit mass of solid propellant in step S2 is:

[0035]

[0036] According to (P e -P0)V=nR×298, it is derived that In the formula, V is the volume of the oxygen bomb of the constant temperature oxygen bomb calorimeter when measuring the constant volume explosion heat value, P e is the pressure of the oxygen bomb of the constant temperature oxygen bomb calorimeter when the solid propellant is cooled to 298K after combustion, P0 is the initial pressure of the oxygen bomb of the constant temperature oxygen bomb calorimeter before the solid propellant is combusted, R is the molar gas constant, taken as 8.314 J·mol -1 / kg, n g is the gas moles per unit mass of solid propellant, and m is the mass of the solid propellant corresponding to the stable constant volume explosion heat value.

[0037] Wherein, the formula for calculating the actual constant pressure explosion heat value of the solid propellant in step S3 is:

[0038] Q pexp =Q vexp -n g R×298

[0039] In the formula, R=8.314 J·mol -1 / kg, n g is the gas moles per unit mass of solid propellant, Q vexpTo stabilize the constant volume bomb heat value, Q pexp Actual constant pressure bomb heat value.

[0040] Wherein, the theoretical constant pressure bomb heat value of the known solid propellant is obtained by subtracting the total enthalpy of combustion products at 298K from the raw material enthalpy of the known solid propellant in step S4, and step S4 consists of the following steps:

[0041] Step S401: According to the raw material enthalpy of the known solid propellant and the assumed chemical formula, the number of moles and mass of all combustion products of 1kg of the propellant under constant pressure at high temperature are calculated by using thermodynamic software under adiabatic combustion to high temperature;

[0042] Step S402: The combustion products of the solid propellant at 298K are determined;

[0043] Step S403: The content of each element is calculated,

[0044] Step S404: The total enthalpy H of the combustion products of 1kg of the fixed propellant at 298K is calculated 298 ,

[0045] Step S405: The theoretical constant pressure bomb heat value of the known solid propellant is obtained by subtracting the total enthalpy of combustion products at 298K from the raw material enthalpy of the known solid propellant.

[0046] Wherein, the formula for calculating the actual constant pressure adiabatic combustion temperature in step S5 is:

[0047]

[0048] In the formula, T pth is the theoretical constant pressure adiabatic combustion temperature, Q pexp is the actual constant pressure bomb heat value, Q pth is the theoretical constant pressure bomb heat value, T pexp is the actual constant pressure adiabatic combustion temperature.

[0049] According to the positive correlation between heat release and temperature, the theoretical constant pressure bomb heat value calculated by the adiabatic high-temperature combustion products under different pressures and at 298K is basically equal to the measured bomb heat value, so it can be considered that the combustion temperature under different pressures is basically equal to the theoretical constant pressure adiabatic combustion temperature. The process of the solid propellant from 298K to the actual constant pressure bomb heat value is very short (<1s), and it does not have time to exchange heat with the outside world, so this process can be approximately considered as an adiabatic heating process, and the highest temperature finally reached is the adiabatic combustion temperature. Then the adiabatic combustion products are always cooled back to 298K, and in this cooling process, the relationship between heat release and adiabatic combustion temperature is In the formula, is the average specific heat capacity of the system, Q is the bomb heat value, and T is the adiabatic combustion temperature.

[0050] Obviously, dissociated material will combine and phase change during the cooling process, so the specific value of T cannot be solved. Therefore, the theoretical constant pressure adiabatic combustion temperature T pth and the theoretical constant pressure explosion heat Q pth are introduced. For the system, it can be considered that T is a function only related to temperature; because the small range change (within 100K) of temperature causes relatively small change of T , it is considered that the theoretical average specific heat capacity C is approximately equal to the actual average specific heat capacity C , and the formula for calculating the actual constant pressure adiabatic combustion temperature can be obtained.

[0051] Example 1

[0052] A propellant formula is known, the enthalpy of raw material is -527.19kJ / kg, and it is assumed that the chemical formula is C 11.9634 H 26.9794 O 24.740 2N 15.7296 Cl 0.9361 Al 6.6729 . The stable constant volume explosion heat value is measured by a constant temperature oxygen bomb calorimeter, and the volume of the oxygen bomb of the constant temperature oxygen bomb calorimeter is 0.287L.

[0053] Step S1: measuring the stable constant volume explosion heat value of the solid propellant

[0054] Table 1: stable constant volume explosion heat value test process of solid propellant

[0055]

[0056]

[0057] The constant volume explosion heat value of the solid propellant shows a trend of increasing with the increase of the sample mass, and after the sample mass increases to a certain degree, the constant volume explosion heat value begins to stabilize. Considering the safety problem of the experiment, the sample mass is not increased any more for verification, and at this time the sample mass corresponding to the constant volume explosion heat value is 4.5g, the constant volume explosion heat value is measured twice, and the average value of the constant volume explosion heat value of the two times is taken as the stable constant volume explosion heat value of the solid propellant under the condition of 0.287L, and the stable constant volume explosion heat value Q vexp is 7033.5kJ / kg.

[0058] Step S2: calculating the number of moles of gas per unit mass of solid propellant

[0059] The pressure changes of the oxygen bomb equipped with a pressure sensor during the test are collected to obtain the values of P0 and P e , and the specific pressure trend graph is as follows:​Figure 1 The oxygen bomb was then charged with 4.5 g of solid propellant and measured, and the theoretical constant pressure heat of explosion was calculated according to where V = 0.287 L, R = 8.314 J-mol -1 / kg, T = 298 K, m = 4.5 g, P0= 0.0622 MPa, P e = 1.2375 MPa, and n g = 30.31 mol.

[0060] Step S3: Calculate the actual constant pressure heat of explosion value

[0061] According to Q pexp = Q vexp -n g R x 298, where R = 8.314 J-mol-1 / kg, n g = 30.31 mol, Q pexp = 7033.5 kJ / kg-30.31 x 8.314 J-mol -1 / kg x 10 -3 x 298 K = 6958.40 kJ / kg.

[0062] Step S4: Calculate the theoretical constant pressure adiabatic combustion temperature by thermodynamic software, and subtract the total enthalpy of the combustion products at 298 K from the enthalpy of the raw materials of the known solid propellant to obtain the theoretical constant pressure heat of explosion value of the propellant.

[0063] The Factsage software was used to calculate the theoretical adiabatic combustion temperature and the number of moles of main combustion products of the solid propellant under adiabatic combustion to 6.86 MPa, 10 MPa, 15 MPa, and 20 MPa, as shown in Table 1.

[0064] Table 1 Theoretical constant pressure adiabatic combustion temperature and main combustion products of 1 kg of propellant under different pressures

[0065]

[0066]

[0067] According to the adiabatic combustion products, the combustion products at 298 K were determined to be CO, CO2, H2, H2O, N2, HCl, AlCl3, and Al2O3, and based on the enthalpy of the raw materials minus the enthalpy of the products, the theoretical constant pressure heat of explosion Q pth of the solid propellant was calculated.

[0068] Table 2 Results of cooling the high-temperature products of the solid propellant to 298 K under different pressures

[0069]

[0070] The content of the main combustion products and the theoretical constant pressure explosion heat value of the high temperature products cooled to 298K under various pressures are shown in Table 2. From the data in Table 2, the sum of the enthalpy of each product is constant, and the effect of pressure on the total enthalpy is not more than one thousandth, i.e. the combustion products at the end state of the explosion heat test are determined by cooling the adiabatic combustion products at the specified pressure to 298K, and the calculated theoretical constant pressure explosion heat value is a unique value. The final constant pressure explosion heat value Q of the solid propellant can be taken as the average value 7054.6571 kJ / kg. pth

[0071] Step S5: calculating the actual constant pressure adiabatic combustion temperature

[0072] According to The calculated actual constant pressure adiabatic combustion temperature of the propellant under different pressures is shown in Table 3.

[0073] Table 3 actual constant pressure adiabatic combustion temperature of the solid propellant

[0074] Pressure / MPa Theoretical constant pressure adiabatic combustion temperature / K Actual constant pressure adiabatic combustion temperature / K 6.86 3739.29 3692.34 10 3780.17 3732.66 15 3821.98 3773.90 20 3850.13 3801.66

[0075] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.​

Claims

1. A method for determining the constant-pressure adiabatic combustion temperature of a solid propellant, characterized in that, It consists of the following steps: Step S1: measuring the stable constant volume explosion heat value of the solid propellant by experiment, Step S2: calculating the gas mole number per unit mass of the solid propellant by using the mass of the solid propellant corresponding to the stable constant volume explosion heat value and the pressure of the oxygen bomb when the solid propellant of the mass is cooled to 298K after combustion, Step S3: calculating the actual constant pressure explosion heat value of the solid propellant according to the stable constant volume explosion heat value and the gas mole number per unit mass of the solid propellant, Step S4: calculating the theoretical constant pressure adiabatic combustion temperature by using thermodynamic software according to the assumed chemical formula and the raw material enthalpy of the known solid propellant, and obtaining the theoretical constant pressure explosion heat value of the solid propellant by subtracting the total enthalpy of the combustion products at 298K from the raw material enthalpy of the known solid propellant, Step S5: calculating the actual constant pressure adiabatic combustion temperature of the solid propellant according to the theoretical constant pressure explosion heat value, the theoretical constant pressure adiabatic combustion temperature and the actual constant pressure explosion heat value.

2. The method of claim 1, wherein, Step S1 consists of the following steps: 1-2 grams of the solid propellant is weighed and the constant volume explosion heat value is measured, then the mass of the solid propellant is gradually increased and the constant volume explosion heat value is measured until the fluctuation of the constant volume explosion heat values measured twice is <100J / g, the last measurement process is repeated 2-3 times, and the average value of the constant volume explosion heat values measured 2-3 times is taken as the stable constant volume explosion heat value.

3. The method of claim 2, wherein the method further comprises: The mass of the solid propellant weighed each time is equal and is 0.5-1 gram.

4. The method of claim 1, wherein, The formula for calculating the gas mole number per unit mass of the solid propellant in Step S2 is: ； wherein, V V0 is the volume of the oxygen bomb of the constant volume oxygen bomb calorimeter for measuring the constant volume explosion heat value, P e P0 is the pressure of the oxygen bomb of the constant volume oxygen bomb calorimeter for measuring the constant volume explosion heat value when the solid propellant is cooled to 298 K after combustion, P 0 P0 is the initial pressure of the oxygen bomb of the constant volume oxygen bomb calorimeter before the solid propellant is combusted, R R is the molar gas constant, taken as 8.314 J·mol -1 / kg, n is the number of moles of gas per unit mass of the solid propellant, m m is the mass of the solid propellant corresponding to the stable constant volume explosion heat value.

5. The method of claim 4, wherein the method further comprises: The formula for calculating the actual constant pressure explosion heat value of the solid propellant in Step S3 is: ； wherein Q pexp is the actual constant pressure bomb heat value, Q vexp is the stable constant volume bomb heat value, is the number of moles of gas per unit mass of solid propellant, R = 8.314 J·mol -1 / kg.

6. The method of claim 5, wherein the method further comprises: The formula for calculating the actual constant pressure adiabatic combustion temperature in Step S5 is: ； wherein T pth is the theoretical constant pressure adiabatic combustion temperature, Q pexp is the actual constant pressure heat of explosion, Q pth is the theoretical constant pressure heat of explosion, T pexp is the actual constant pressure adiabatic combustion temperature.

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