A Computational Study of the Combustion of Hydrazine with Dinitrogen Tetroxide

1. Introduction

Throughout time there has been an increasing interest in outerspace (Edwards, Kuznetsov, & David, 2007). Chemical combustion-based space transportation is a leading technology in comparison to nuclear or ionic propellants. While we currently use cryogenic oxidizers and petroleum-based fuels to put humans in space, the most favorable method would be hypergolic fuel maintaining an ability of spontaneous combustion upon contact of the oxidizer with the fuel (Zhang & Shreeve, 2014). The major downfalls of hypergolic fuel are its toxicity, limited stability, which is why this fuel source is used strictly for unmanned spacecraft (Boice et al., 2006).

In many hypergolic reactions, the terminal product is toxic such as nitrous acid (HONO) (Konnov, 2008). The determination of a way to yield non-toxic byproducts would provide space exploration programs and space agencies one step closer to cheaper and more efficient fuel / oxidizer components for space travel. In order to do this, it is imperative to further explore available combustion pathways for commonly used fuel and oxidizer pair such as hydrazine (N₂H₄) and dinitrogen tetroxide (N₂O₄) (Edwards, 2003). Determining the mechanism, byproducts, and fuel to oxidizer ratio will allow for future research to predict a better selection of propellant components.

There have been extensive studies on the combustion of hydrazine or hydrazine derivatives with various oxidizers (Daimon, Terashima, & Koshi, 2014; Davis & Yilmaz, 2014; Gehring, Hoyermann, Wagner, & Wolfrum, 1969; Gray & Lee, 1954; Kanno et al., 2015; Lai, Zhu, & Lin, 2012; Liu et al., 2013; Liu, Zybin, Guo, van Duin, & Goddard, 2012; Miyajima & Sakamoto, 1973; Niemeier & Kjell, 2013; Raghunath, Lin, & Lin, 2014; Sawyer & Glassman, 1967; Spada, Ferrão, Roberto-Neto, Lischka, & Machado, 2015; Spada, Ferrão, Rocha, et al., 2015; Tani, Terashima, Koshi, & Daimon, 2015). For example, Gray and Lee examined the explosive combustion of N₂H₄ with O₂ giving rise to N₂ and H₂O (Gray & Lee, 1954). Gehring et al. studied the reaction of N₂H₄ with atomic oxygen and reported the main product of N₂H₂ and H₂O (Gehring et al., 1969). Sawyer and Glassman investigated the reaction of N₂H₄ with NO₂ and found the reaction characterized with two distinct steps, each of which involved the formation of N₂ and H₂O (Sawyer & Glassman, 1967). Tani et al. numerically simulated the hypergolic ignition and flame structures of N₂H₄ with NO₂-N₂O₄ and proposed the detailed chemical kinetics mechanisms based on the experimental work by Miyajima and Sakamoto (Miyajima & Sakamoto, 1973; Tani et al., 2015). The numerical simulations illustrate two types of chemical reactions in the hypergolic ignition processes: sequence of hydrogen abstraction from N₂H₄ by NO₂ and thermal decomposition of N₂H₄, the former of which plays a dominant role in preheating the mixture gas (Tani et al., 2015).