Investigation of the Burning Behavior of Cryogenic Solid Propellants

Abstract

Cryogenic Solid Propellant (CSP)-technology is a new approach to develop more powerful rocket motors. CSPs include the advantages of classical solid propellants to save weight as well as those of a high energy content and safety of modern liquid propellants. The charges consist of liquid and/or gaseous fuels and oxidizers, both frozen. Two main versions of CSP-technology can be realised: 1. Mono-CSPs show the burning behavior of solid propellants. Experiments with mono-CSPs have been carried out under inert pressure conditions in a window bomb. Mono-CSPs have a stable burning behavior with a constant regression rate which follows the Vieille's law under varying pressure conditions. 2. The advantage of high safety is obtained by assembling oxidizer and fuel in sandwich configurations. The grain geometry governs the burning behavior. Such systems can be externally controlled, e.g. by the heat from a gas generator or they can work self-sustained. A Rod-in-Matrix burner shows self-sustained combustion in an inert pressure atmosphere with overall burning rates in a similar range as solid rocket propellants which obey also a Vieille-like pressure law. Disc stack burners have also been investigated, the combustion of which is strongly dependent on the disc thickness. For a short time Mach's nodes have been observed in the exhaust plume of a disc stack burner. Currently, the temperature ranges are limited to the boiling temperature of liquid nitrogen. Therefore, liquid oxidizers like H2O2 have been used. However, for the first time a propellant strand of polymer rods embedded in solid oxygen was prepared and burnt. The experiments with CSPs end in the combustion of a small rocket motor showing no serious technical obstacles. Simplified models based on the heat flow equation can simulate the burning characteristics of the frozen energetic materials including phase transitions.