Advances in Hypergolic Propellants: Ignition, Hydrazine, and Hydrogen Peroxide Research

A review of the literature pertaining to hypergolic fuel systems, particularly using hydrazine or its derivatives and hydrogen peroxide, has been conducted. It has been shown that a large effort has been made towards minimizing the risks involved with the use of a toxic propellant such as the hydrazine. Substitution of hydrazines for nontoxic propellant formulations such as the use of high purity hydrogen peroxide with various types of fuels is one of the major areas of study for future hypergolic propellants. A series of criteria for future hypergolic propellants has been recommended, including low toxicity, wide temperature range applicability, short ignition delay, high specific impulse or density specific impulse, and storability at room temperature. 1. Introduction In typical combustion systems an ignition source such as a spark is needed to begin the combustion reaction [1]. In rocket propellants, there exists a class of materials which ignites spontaneously without the need for an ignition source. A combination of two materials which self-ignites at room temperature is called hypergolic. Because they do not require external ignition forces (compression, spark, heating, catalytic decomposition, etc.), hypergolic mixtures need only a valve to mix the fluids and initiate combustion. This simple mechanism for controlling combustion reduces the number of components in the ignition system which reduces the statistical chances for failure as well as the payload of the system relative to nonhypergolic systems. Therefore, such a system with few mechanical parts and low weight is particularly favorable to extraterrestrial craft. There are several quantifiable properties which are important in any propellant system including specific impulse (the thrust per weight of propellant) and adiabatic flame temperature [2]. Additionally, one of the most important quantities for a hypergolic propellant is the ignition delay, the time between fluid contact and ignition; alternatively, the chemical ignition delay may be used, where the time between the onset of vaporization and ignition is utilized as defined in [3, 4]. In [5, 6] these delay times are used, in part, to describe the preignition behavior of hypergolic propellants. Regardless of definition the time to ignition is important to the performance of a rocket propellant where a long delay leads to combustion outside of the combustion chamber or causes hard-starts, whereas a very short delay risks damaging the injection nozzle [7]. 2. Ignition Measurements There are two main techniques utilized to measure the