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Chemical Rocket Propellants
Published in D.P. Mishra, Fundamentals of Rocket Propulsion, 2017
Nitric acid (HNO3) is considered as an oxidizer in rocket engine, particularly when freezing point is not an issue. Generally, HNO3 is not used directly, rather nitric acid mixtures are being preferred in rocket engine. The nitric acid formulation most commonly used is the red fuming nitric acid (RFNA), which consists of HNO3, 5%–15% N2O4, and 1.5%–2.5% H2O. When the solution contains more than 86% HNO3, it is referred to as fuming nitric acid. The red color of RFNA is due to the presence of the nitrogen dioxide that is formed during the breaking down of N2O4. RFNA, along with other substances like amine nitrates, can be used as monopropellant. But it is usually used as bipropellant in rocket engine. Note that HNO3 is quite corrosive in nature. In order to reduce its corrosiveness, 0.4%–0.7% HF is added as a corrosion inhibitor and, hence, it is known as inhibited red-fuming nitric acid (IRFNA), which is being used in rocket engines. IRFNA along with aromatic amine fuels like aniline (C6H7N) and xylidine (C8H11N) had been used for missile applications. But IRFNA is quite toxic and volatile in nature as it contains large percentage of N2O4. In order to reduce its toxicity and volatility, less amount of N2O4 (less than 0.5%) is dissolved and it is known as white-fuming nitric acid (WFNA), which is considered as a safe and storable liquid oxidizer along with kerosene and hydrazine rocket fuel. Similarly, when 0.4%–0.7% HF is added to WFNA as a corrosion inhibitor, it is known as inhibited red-fuming nitric acid (IWFNA). Although WFNA has a somewhat less performance level as compared to the RFNA, it is used due to its nontoxic and low volatile nature. Nitric acid along with Aerozine has been used in the Titan family of launch vehicles and the second stage of the Delta II rocket engine. For tactical missiles, the US army had used IRFNA/UDMH. Note that Kosmos-3M is the most launched light orbital rocket with specific impulse of 291 s, in which IRFNA was used as an oxidizer along with UDMH fuel.
Performance of neat and gelled monomethylhydrazine and red fuming nitric acid in an unlike-doublet combustor
Published in Combustion Science and Technology, 2018
Jacob D. Dennis, Jared D. Willits, Timothée L. Pourpoint
The possibility of increased safety and performance over current propellant technologies has led to research into gelled hypergolic propellants. Hypergolic propellants offer the unique benefit of rapid ignition upon contact eliminating the need for a dedicated ignition system and the gelling process reduces risks associated with these very reactive propellants. Potential safety improvements come through spill reduction during storage and handling, insensitive munitions compliance, reduced toxic vapor outgassing, and slosh reduction (Hodge, 1999). Gelled propellants could also offer high energy density when loaded with energetic materials. Rahimi et al. (2004) describe a number of applications that may benefit from gelled propellants including tactical missiles, attitude control systems, and launch or in-space propulsion systems. Research in the late 1990s and early 2000s focused on hydrazine and monomethylhydrazine (MMH) gelled with cellulose derived gelling agents, such as hydroxypropylcellulose (HPC) (Hodge, 1999; Kubal, 2010; Rahimi, 2004; Solomon, 2013). The majority of these studies also use particulate gelling agents, primarily fumed silica, to gel the oxidizer, either red fuming nitric acid (RFNA) or inhibited red fuming nitric acid (IRFNA).
Early Liquid and Gas Phase Hypergolic Reactions between Monomethylhydrazine and Nitrogen Tetroxide or Red Fuming Nitric Acid
Published in Combustion Science and Technology, 2019
Ariel T. Black, Michael P. Drolet, Timothée L. Pourpoint
Monomethylhydrazine (MMH, CH3NHNH2), purchased from Sigma-Aldrich (PN: 67540, ≥98% purity), is a clear, colorless, hygroscopic, liquid fuel. MMH is a hydrazine (N2H4) derivative where one hydrogen has been replaced with a methyl group (CH3). Nitrogen dioxide (NO2) and nitrogen tetroxide (N2O4, NTO) coexist in equilibrium which readily shifts to favor either compound based on changes in the temperature and/or pressure of the mixture (Leenson, 2000). NO2 is a reddish-brown gas, while N2O4 is colorless as a liquid, but manifests as orange-brown due to the presence of dissolved NO2. Often, liquid N2O4 exhibits a bright green color which is an indication of minute and often negligible water contamination. The NTO used in this study was obtained from Sigma-Aldrich (PN: 295582, ≥99.5% purity). Type III red fuming nitric acid is an oxidizer consisting of about 84% nitric acid (HNO3), 14% NTO, and 1–2% water by weight. The type III RFNA used in the present study was synthesized in our laboratory using the same Sigma-Aldrich provided NTO, and white fuming nitric acid also acquired from Sigma-Aldrich (PN: 84392, >99% purity). The laboratory synthesized RFNA contains 14 ± 1.7% NTO by weight. MMH, NTO, and RFNA are highly toxic and corrosive and MMH is a known carcinogen, necessitating mandatory safety precautions (e.g. fume hoods, personal protective equipment). The physical properties of nitric acid, RFNA, NTO, and MMH are outlined in Table 1.