EP3770136B1 - Composite solid propellant - Google Patents

Description

Technical area

Disclosed is a composite propellant having a combustion rate exhibiting reduced sensitivity to pressure changes. The invention also relates to the application of this composite propellant as a propellant change of a rocket engine.

Prior art

Composite propellants are known for rocket propulsion and generally use a binder in which energetic charges are dispersed. A ballistic catalyst can be added to these compositions in order to increase the combustion rate and the thrust produced. Thus, the use of iron oxide Fe ₂ O ₃ as a ballistic catalyst is known. However, it remains desirable to reduce the sensitivity of the combustion rate to the pressure in the combustion chamber. US 3,255,059 discloses a composite solid propellant comprising a binder, a perchlorate oxidizing charge having a bimodal size distribution, a reducing charge and a ballistic catalyst.

Disclosure of the invention

• une charge oxydante comprenant des particules de perchlorate inorganique, la charge oxydante présentant une distribution de taille bimodale avec (i) un premier ensemble de particules de perchlorate inorganique présentant une première taille D50 comprise entre 150 µm et 250 µm et présent à raison de 50% à 60% en masse dans le propergol solide composite, et (ii) un deuxième ensemble de particules de perchlorate inorganique présentant une deuxième taille D50 comprise entre 5 µm et 20 µm et présent à raison de 7% à 17% en masse dans le propergol solide composite,
• une charge réductrice comprenant des particules d'aluminium et/ou d'un composé d'aluminium, et
• un catalyseur balistique comprenant des particules d'oxyde de cuivre CuO.

The invention relates to a composite solid propellant comprising a binder comprising a crosslinked polymer polyol in which are present:

• an oxidizing charge comprising particles of inorganic perchlorate, the oxidizing charge having a bimodal size distribution with (i) a first set of particles of inorganic perchlorate having a first size D50 of between 150 µm and 250 µm and present in an amount of 50% at 60% by mass in the composite solid propellant, and (ii) a second set of inorganic perchlorate particles having a second size D50 of between 5 µm and 20 µm and present at a rate of 7% to 17% by mass in the propellant solid composite,
• a reducing filler comprising particles of aluminum and / or an aluminum compound, and
• a ballistic catalyst comprising particles of copper oxide CuO.

Unless otherwise stated, the term “size D50” is understood to mean the dimension given by the statistical particle size distribution to half of the population.

The incorporation of a CuO copper oxide ballistic catalyst within the composite solid propellant formulation described above jointly achieves a high burn rate associated with a significant reduction in the pressure exponent, and this over a wide pressure range. The pressure exponent corresponds to the exponent n in Vieille's law which is verified by the propellant and which has the expression: Vc = aP ⁿ , where Vc denotes the combustion rate of the propellant, P the pressure in the chamber of combustion and has a pre-exponential factor. The reduction of the pressure exponent n makes it possible to reduce the dependence of the combustion speed on the pressure and thus makes it possible to envisage being able to access a significant reduction in the operating dispersion of a solid propellant engine. Indeed, the reduction of the pressure exponent makes it possible to reduce the operating fluctuations linked to the pressure fluctuations during the operation of the engine, thus leading to obtaining a more stable operating point of the engine. The reduction in operating dispersions contributes in particular to reducing the mechanical stresses to which the engine structure could be subjected in the event of maximum internal pressurization. Thus, it is possible to envisage being able to use optimized engine architectures (reduced structure mass) for the same level of engine operating reliability, or with isosizing of the engine, at an increase in the level of engine operating reliability. The beneficial effect of the copper oxide CuO ballistic catalyst is obtained for a composite solid propellant exhibiting the bimodal size distribution described above for the oxidizing charge. Such a propellant is suitable for integration as a propellant charge for a space vehicle. As will be recalled in the experimental part, the effect of lowering the pressure exponent following the incorporation of copper oxide CuO is not significantly obtained if the particle size of the oxidizing charge differs from that described above.

In an exemplary embodiment, the copper oxide particles CuO have a BET specific surface area greater than or equal to 10 m ² / g.

Such a specific surface area advantageously makes it possible to further increase the rate of combustion of the propellant.

In an exemplary embodiment, the mass content of copper oxide particles CuO is between 0.01% and 1%.

• le polymère polyol réticulé en une teneur massique comprise entre 9% et 12%,
• les particules de perchlorate inorganique en une teneur massique comprise entre 64% et 70%,
• les particules d'aluminium et/ou du composé d'aluminium en une teneur massique comprise entre 17% et 23%, et
• les particules d'oxyde de cuivre CuO en une teneur massique comprise entre 0,01% et 1%.

In an exemplary embodiment, the propellant comprises:

• the crosslinked polymer polyol in a mass content of between 9% and 12%,
• particles of inorganic perchlorate in a mass content of between 64% and 70%,
• particles of aluminum and / or of the aluminum compound in a mass content of between 17% and 23%, and
• particles of copper oxide CuO in a mass content of between 0.01% and 1%.

The invention also relates to a propellant comprising a propellant body defining a combustion chamber in which a charge of the composite propellant as described above is present.

The invention also relates to a space vehicle comprising a thruster as described above. The space vehicle can be a rocket launcher.

Brief description of the drawings

• [ Fig. 1 ] The figure 1 schematically illustrates the bimodal size distribution for the inorganic perchlorate particles that can be used within the scope of the invention.
• [ Fig. 2 ] The figure 2 represents a propellant body incorporating a composite solid propellant according to the invention.
• [ Fig. 3 ] The figure 3 compares the evolution of the combustion speed as a function of the pressure for different propellant compositions.
• [ Fig. 4 ] The figure 4 compares the evolution of the pressure exponent as a function of the pressure for different propellant compositions.
• [ Fig. 5 ] The figure 5 compares the evolution of the combustion speed as a function of the pressure for different propellant compositions.
• [ Fig. 6 ] The figure 6 compares the evolution of the combustion speed as a function of the pressure for different propellant compositions.
• [ Fig. 7 ] The figure 7 compares the evolution of the pressure exponent as a function of the pressure for different propellant compositions.

Description of the embodiments

The propellant comprises a binder comprising a crosslinked polymer polyol. The crosslinked polyol polymer is, for example, a crosslinked hydroxytelechelic polybutadiene (PBHT). The polymer polyol is crosslinked by a crosslinking agent. The crosslinking agent can be a diisocyanate. In this case, a polyurethane is obtained by crosslinking the polyol with the crosslinking agent diisocyanate. The binder can comprise a polymer polyol chain extender in a manner known per se. The oxidizing and reducing charges can be dispersed in the binder. The binder can constitute a polymer matrix coating the oxidizing and reducing charges.

The oxidizing charge comprises particles of inorganic perchlorate. The inorganic perchlorate can be ammonium perchlorate (NH ₄ ClO ₄ ). As indicated above, the inorganic perchlorate particles exhibit a bimodal size distribution with (i) a first set of inorganic perchlorate particles exhibiting a first size D50 of between 150 µm and 250 µm and present in an amount of 50% to 60% by mass in the composite solid propellant, and (ii) a second set of inorganic perchlorate particles having a second size D50 of between 5 μm and 20 μm and present in an amount of 7% to 17% by mass in the composite solid propellant. The inorganic perchlorate particles can be present in the composite solid propellant in an overall mass content of between 64% and 70% (corresponding to the sum of the contents of the particles of the first and second sets).

The size distribution of the inorganic perchlorate particles can be determined by laser diffraction technique, in a manner known per se.

The figure 1 illustrates the bimodal size distribution of the inorganic perchlorate particles which can be used within the scope of the invention. In this figure, for a given size x of particles, the ordinate indicates the mass content in the propellant of the particles having this size x. The inorganic perchlorate particles define a first set E1 of perchlorate particles inorganic and a second set E2 of inorganic perchlorate particles. The bimodal distribution is asymmetric. The bimodal distribution presents two distinct peaks (maxima) P1 and P2. The height of the peak P1 of the distribution of the first set E1 may be different, for example greater than the height of the peak P2 of the distribution of the second set E2.

The distribution of each of the first and second sets E1 and E2 can correspond to a normal distribution. The particles of the first set E1 have a first size D50 TM1 and the particles of the second set E2 have a second size D50 TM2. The first size D50 TM1 is larger than the second size D50 TM2. The second size D50 TM2 can be spaced from the first size D50 TM1 by at least two, or even at least three, standard deviations of the distribution of the first set E1.

The reducing filler comprises particles of aluminum and / or an aluminum compound. The aluminum compound can be at least one of an aluminum alloy or alumina (Al ₂ O ₃ ). The particles of aluminum and / or of the aluminum compound can be present in the composite solid propellant in a mass content of between 17% and 23%.

The propellant further comprises a ballistic catalyst comprising particles of copper oxide CuO. As indicated above, the mass content of copper oxide particles CuO in the propellant can be between 0.01% and 1%, for example between 0.1% and 1%, for example between 0.1% and 0.3% or between 0.3% and 1%. According to one example, the copper oxide particles CuO may have a BET specific surface area of greater than or equal to 10 m ² / g.

Copper oxide CuO may be the sole ballistic catalyst present in the composite solid propellant. The composite propellant may be devoid of at least one of the following ballistic catalysts: a copper salt, an iron oxide, the catalysts based on ferrocene, a chromium oxide, a nickel oxide, a cobalt oxide, a salt metallic lead, a salt of bismuth.

The composite propellant can be devoid of at least one of the following compounds: nitrocellulose or nitroglycerin.

The propellant can be made from the constituents mentioned above by using mixing and crosslinking techniques known to those skilled in the art which are not repeated here for the sake of brevity.

The figure 2 shows a thruster body 1 comprising a structural casing 11 defining a combustion chamber in which is present the charge of composite propellant 10. The thruster body comprises an igniter (not shown) intended to initiate the charging of propellant 10. The body of the propellant thruster can be part of a rocket engine and be a rocket launcher thruster body. Advantageously, the composite solid propellant may have a pressure exponent n in Vieille's law less than or equal to 0.2, preferably less than or equal to 0.1, over all or part of the pressure range 8-15 MPa in the combustion chamber.

Examples Example 1: comparison between the use of copper oxide CuO and iron oxide Fe ₂ O ₃ as a ballistic catalyst in a propellant formulation incorporating a bimodal distribution of oxidizing charge

• granulométrie D10/D50/D90 d'environ 0,5µm/5,0µm/20 µm (valeurs mesurées par un granulomètre à diffraction laser),
• surface spécifique de 11,6 m²/g (BET),
• densité de 6,28 g/cm³ (pycnomètre à gaz), et
• pureté 98,3%.

The formulation used in this test exhibited a bimodal load distribution of ammonium perchlorate (AP). This composite propellant formulation is suitable for forming the propellant charge of a space launcher. The grade of copper oxide CuO used was in the form of a fine solid powder, corresponding to the grade "Copper (II) oxide Special Ultra Fine" (CAS No. 1317-38-0) supplied from the producer TIB Chemicals. The characteristics of the copper oxide CuO which was used were as follows:

• D10 / D50 / D90 particle size of approximately 0.5µm / 5.0µm / 20µm (values measured by a laser diffraction particle size analyzer),
• specific surface of 11.6 m ² / g (BET),
• density of 6.28 g / cm ³ (gas pycnometer), and
• purity 98.3%.

• charge oxydante de PA à raison de 66,75% massique,
• charge réductrice d'aluminium à raison de 20% massique,
• liant polyol réticulé à raison de 13% massique, et
• catalyseur balistique (Fe₂O₃ ou CuO) à raison de 0,25% massique.

The formulations having the composition below were prepared and evaluated:

• oxidizing charge of PA in an amount of 66.75% by mass,
• reducing load of aluminum at a rate of 20% by mass,
• 13% by mass crosslinked polyol binder, and
• ballistic catalyst (Fe ₂ O ₃ or CuO) at a rate of 0.25% by mass.

• 54,75% massique de classe granulométrique de dimension moyenne centrée sur 200 µm correspondant au premier ensemble de particules de perchlorate inorganique, ces particules avaient été obtenues par cristallisation, et
• 12% massique de classe granulométrique de dimension fine centrée sur 9 µm correspondant au deuxième ensemble de particules de perchlorate inorganique, ces particules avaient été obtenues par broyage à partir des particules de classe granulométrique de dimension moyenne centrée sur 200 µm.

The 66.75% by mass of loads of PA used were distributed as follows:

• 54.75% by mass of particle size class of average size centered on 200 μm corresponding to the first set of inorganic perchlorate particles, these particles had been obtained by crystallization, and
• 12% by mass of particle size class of fine dimension centered on 9 μm corresponding to the second set of inorganic perchlorate particles, these particles had been obtained by grinding from particles of particle size class of average size centered on 200 μm.

The aluminum powder used was a variety characterized by a regular grain morphology, obtained by atomization under an inert atmosphere (nitrogen) and of size D50 of about 30 μm.

The figures 3 and 4 provide the results of the comparison of the ballistic characteristics obtained with this formulation depending on whether copper oxide CuO or iron Fe ₂ O ₃ is used as a ballistic catalyst. The formulation using copper oxide CuO incorporated at a rate of 0.25% by weight corresponds to curve “A” in these figures. The reference formulations using iron oxide (Fe ₂ O ₃ ) as ballistic catalyst, incorporated at the same mass rate of 0.25% in the propellant, correspond to curves “B” to “E”. Different grades of iron oxide Fe ₂ O ₃ were evaluated, corresponding to products of different particle size and / or specific surface area and / or purity and / or obtained by different manufacturing processes in order to demonstrate in each case l 'advantageous effect produced by the use of copper oxide CuO. These Fe ₂ O ₃ grades have been sourced from various producers / suppliers in the field and are representative of Fe ₂ O ₃ grades which can be used as a ballistic catalyst in space vehicle propellants.

The propellant samples were made on the same manufacturing means, namely a horizontal type mixer with a capacity of 5 liters. The formulations were identical except in terms of the nature of the ballistic catalyst (CuO or Fe ₂ O ₃ ). The propellant firing time was identical in each of the tests carried out. The means and the test parameters were identical for the characterization ballistic. The combustion rate was measured by ultrasonic echo analysis, the samples having been preconditioned at + 20 ° C. before testing.

The results obtained are provided to the figure 3 which shows the curves of combustion rate (Vc in mm / s) as a function of pressure (in MPa) for formulations catalyzed with CuO in comparison with those catalyzed by Fe ₂ O ₃ . The figure 4 shows the variation of the pressure exponent (n) as a function of the pressure (in MPa) for formulations catalyzed with CuO in comparison with those catalyzed by Fe ₂ O ₃ .

The figures 3 and 4 illustrate the favorable impact generated by the use of copper oxide CuO on the ballistic characteristics of the propellant. In particular, there is a notable flattening of the shape of the combustion rate curve over the 9-15 MPa range when CuO is used, which results in a very significantly lower pressure exponent value n (n less than or equal to at 0.2 over the 8-15MPa range and with n close to or less than 0.1 over the 10-14MPa range). This result should be compared with those obtained when Fe ₂ O ₃ is used for which the pressure exponent n is greater than or equal to 0.3 over the range 7-15 MPa. It is also noted that one obtains, over the pressure range 2-9 MPa, a combustion rate equivalent to that obtained with Fe ₂ O ₃ when CuO is used.

In the engine architectures for space launchers implementing the formulation having the basis detailed above without a CuO catalyst, the nominal operating pressure range of the engine is between 4 MPa and 9.5 MPa. The maximum pressure, taking into account the possible operating fluctuations during the combustion of the propellant charge, is around 10 MPa. The figure 3 shows that the use of CuO makes it possible to reach combustion speed levels quite comparable to those obtained with Fe ₂ O ₃ over the operational operating range of the engine.

When CuO is used, the pressure exponent value decreases very sharply as it approaches 10 MPa, which corresponds to the upper limit of the operating range. Thus, the risk of pressure fluctuation which can generate a fluctuation of the operating point, and possibly a mechanical overpressure of the engine structure which can adversely affect its integrity, is significantly reduced. In this configuration, the ballistic characteristics induced by the use of CuO thus make it possible to consider accessing more stable engine operations in this pressure range (when approaching the upper limit of 10 MPa), or even to consider being able to access optimized engine architectures as indicated previously. .

The figure 5 makes it possible to indirectly confirm the advantageous impact induced by the use of CuO. In this test, the evolution of the combustion speed as a function of the pressure was determined for two formulations of propellant for space launchers: The first formulation evaluated was identical to that described above but catalyzed with 0.20% by mass of Fe ₂ O ₃ and implementation on a mixer of different technology (mixer with vertical blades with a capacity of 1 Gallon). The curve marked "F" at figure 5 corresponds to the results obtained for this first formulation. The mass content of AP of average dimension centered on 200 μm was 54.8% by mass. The second formulation evaluated was identical to the first formulation but without Fe ₂ O ₃ ballistic catalyst. In this second formulation, the Fe ₂ O ₃ content was transferred to the AP content of average dimension centered on 200 μm, which then represented 55% by mass. The curve noted "G" at the figure 5 corresponds to the results obtained for this second formulation.

The figure 5 illustrates the fact that the incorporation of Fe ₂ O ₃ within a composite propellant formulation leads, compared to an uncatalyzed base, to a notable increase in the value of the combustion rate over the operational operating range of the engine for space launcher. However, there is no significant improvement in the value of the pressure exponent over this same functional range compared to a non-catalyzed formulation (ie free of Fe ₂ O ₃ ). This result illustrates the fact that the strong lowering of the pressure exponent value observed previously with CuO is not intrinsically inherent in the uncatalyzed base formulation, and that the addition of a conventional ballistic catalyst (in this example Fe ₂ O ₃ ) is certainly not sufficient to lower this exponent value but is content to increase the combustion speed value, thus demonstrating in the end that the lowering of the pressure exponent value associated with a increase in Vc is indeed induced by the use of copper oxide CuO.

Example 1 demonstrated the advantage linked to the incorporation of copper oxide CuO as a ballistic catalyst. The tests in Example 1 were conducted on a propellant basis having a particular bimodal oxidative charge distribution which is suitable for use in a space vehicle. Example 2 to follow will now focus on evaluating the influence of the particle size of the oxidizing charge on the ballistic characteristics obtained for the propellant.

Example 2: influence of the particle size of the oxidizing charge on the ballistic characteristics of the propellant

In this example, the propellant base used included an oxidizing charge of PA with a significantly lower average particle size and in the form of a trimodal distribution (outside the invention) and no longer bimodal as in example 1. In In this test, the inventors compared the performance obtained between such a propellant incorporating either copper oxide CuO or iron oxide Fe ₂ O ₃ instead of copper oxide CuO.

• d'oxyde de cuivre CuO (courbe notée « H » aux figures 6 et 7), et
• d'un catalyseur balistique oxyde de fer (Fe₂O₃) (courbe notée « I » aux figures 6 et 7)

The figures 6 and 7 illustrate the comparison of the ballistic characteristics obtained with use:

• of copper oxide CuO (curve denoted "H" at figures 6 and 7 ), and
• an iron oxide ballistic catalyst (Fe ₂ O ₃ ) (curve denoted "I" at figures 6 and 7 )

In both of these cases, the catalysts were incorporated at a comparable rate into the propellant.

The figure 6 illustrates the fact that the incorporation of CuO induces a catalytic effect leading to a combustion rate level equivalent to that of the Fe ₂ O ₃ ballistic catalyst. However, the use of CuO in such a formulation of composite propellant with distribution of PA oxidizing charges outside the invention does not induce a significant reduction in the value of the pressure exponent compared to a formulation catalyzed with Fe ₂ O _3. , unlike what was observed previously for a propellant formulation having a bimodal distribution of the oxidizing charges (see figure 7 ).

Thus, it is observed that when the particle size of the oxidizing charge is modified, the incorporation of copper oxide CuO does not lead to a significant lowering effect of the pressure exponent compared to the use of oxide of iron Fe ₂ O ₃ . The advantage linked to the incorporation of copper oxide CuO does not appear systematically within any formulation of composite propellant but results from the combination with oxidizing charges of specific particle size.

The expression "between ... and ..." should be understood as including the limits.

Claims (6)

1. A composite solid propellant (10) comprising a binder comprising a crosslinked polyol polymer in which are present:

   - an oxidizing filler comprising particles of inorganic perchlorate, the oxidizing filler having a bimodal size distribution with (i) a first set (E1) of particles of inorganic perchlorate having a first size D50 (TM1) comprised between 150 µm and 250 µm and present in an amount of 50% to 60% by mass in the composite solid propellant, and (ii) a second set (E2) of particles of inorganic perchlorate having a second size D50 (TM2) comprised between 5 µm and 20 µm and present in an amount of 7% to 17% by mass in the composite solid propellant,

   - a reducing filler comprising particles of aluminum and/or of an aluminum compound, and

   - a ballistic catalyst comprising particles of copper oxide CuO.
2. The composite solid propellant (10) as claimed in claim 1, wherein the particles of copper oxide CuO have a BET specific surface area greater than or equal to 10 m²/g.
3. The composite solid propellant (10) as claimed in claim 1 or 2, wherein the mass content of particles of copper oxide CuO is comprised between 0.01% and 1%.
4. The composite solid propellant (10) as claimed in claim 3, wherein the propellant comprises:

   - the crosslinked polyol polymer in a mass content comprised between 9% and 12%,

   - the particles of inorganic perchlorate in a mass content comprised between 64% and 70%,

   - the particles of aluminum and/or of the aluminum compound in a mass content comprised between 17% and 23%, and

   - the particles of copper oxide CuO in a mass content comprised between 0.01% and 1%.
5. A thruster comprising a thruster body (1) defining a combustion chamber in which a charge (10) of the composite propellant as claimed in any one of claims 1 to 4 is present.
6. A spacecraft comprising a thruster as claimed in claim 5.

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