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Comparative tests of two types of nozzle closures for solid propellant rocket motors

Wacko Krzysztof, Kindracki Jan, Woźniak Przemysław, Mężyk Łukasz

Materiały Wysokoenergetyczne

2023

T. 15

71--80

The ignition of a propellant is one of the most important stages of a rocket motor operation, and so it is essential to provide the proper conditions for this to occur. The igniter used in such motors generates ignition gases, which increase the chamber pressure and temperature and initiate grain combustion. Hence, it is necessary to use a component which enables a sufficiently high pressure in the chamber for the combustion process to become fully developed and maintained. To this end, closures are used, which are pushed out of the nozzle once the required pressure is reached. In addition to ensuring proper ignition conditions for the propellant, they protect the grain from the adverse effects of e.g. weather (contamination, moisture). Proper selection of this component of motor reduces pressure accumulation time in the motor chamber, thereby improving the ignition characteristics, which in turn has a critical impact on the further combustion and performance of the motor. Experiments tested the adhesive bonding using 5 different adhesive types with the bonds being made at both room and increased temperature. For testing membrane, 3 materials were used: copper, brass and polypropylene, in which two thicknesses were tested: 100 and 200 μm. The results of the bonding showed high non-reproducibility and it was not possible to determine working pressure values with great confidence. However, for the membrane, the results were much more reproducible and a relationship was established between membrane diameter and its burst pressure, which may be put to practical use in tests or in micro rocket motor applications.

Zapłon materiału pędnego stanowi jeden z ważniejszych etapów pracy silnika rakietowego, zatem niezbędne jest zapewnienie mu właściwych warunków ku temu. Stosowany w silnikach rakietowych na stały materiał pędny zapłonnik, generuje gazy zapłonowe, które podnoszą ciśnienie i temperaturę w komorze oraz inicjują spalanie ziarna. Dlatego konieczne jest zastosowanie elementu, który pozwoli na utrzymanie odpowiednio wysokiego ciśnienia w komorze, aby mógł się w pełni rozwinąć proces spalania. W tym celu stosowane są zatyczki, które po osiągnięciu odpowiedniego ciśnienia zostają wypchnięte z dyszy. Oprócz zapewnienia właściwych warunków zapłonu materiału pędnego, pełnią m.in. rolę ochrony ziarna przed negatywnym wpływem zewnętrznych warunków atmosferycznych (zanieczyszczenia, wilgoć). Odpowiednie dobranie tego elementu silnika pozwala na zmniejszenie czasu narastania ciśnienia w komorze silnika, poprawiając charakterystyki zapłonowe, co z kolei ma kluczowy wpływ na dalszy przebieg spalania i osiągi silnika rakietowego.

HTPB-based Binder Surrogates and their Effects on Preliminary Rocket Motor Analyses

Okniński Adam

Central European Journal of Energetic Materials

2022

Vol. 19, no. 3

209--230

This paper presents a comparison of the hydroxyl-terminated polybutadiene (HTPB) models used during conceptual and preliminary rocket propulsion analyses. The HTPB molecular formulas and enthalpies of formation from various literature sources, obtained by different methods, are discussed. It is shown that the range of heats of formation and properties of HTPB-based binders presented in these references are very wide. The Benson additivity rule was used to estimate the HTPB enthalpy of formation and to compare it with values found in the literature. The HTPB binder models are set side by side in terms of solid rocket motor performance and observable combustion products, using chemical equilibrium software. Moreover, simple heat transfer and aluminum combustion models are used to present the impact of using different models of binders on design calculations. It isshown that ammonium perchlorate/ HTPB propellant thermochemical output data may not be valuable, if used without caution. Taking appropriate contingencies into account and understanding what type of model is being used is necessary. The objective of this paper is to turn the attention of the propellant and explosives community to a class of problems that are often overlooked during initial design phases due to propellant composition simplification.