Effect of Water and Humidity on Hypergolic Propellant Ignition Delay
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| D. Water Content in Propellants Typically, water is considered a diluent in rocket propellants resulting in reduced I sp values. However, Baker determined that the characteristic velocity (c) increased 12% in his engine setup for hydrazine/RFNA when water was added to either the fuel (8% water) or the oxidizer (4% water He explains that this substantial increase inc is likely due to the increased reaction rates of liquid phase reactions. Baker suggests that water changes the chemical equilibrium state of hydrazine to increase the concentration of hydrazinium hydroxide or hydroxyl radicals that may allow neutralization reactions to proceed faster. Equation 1 shows his suggested equilibrium reactions for hydrazine and water. Alternatively, he offers that the water may allow the fuel and oxidizer to mix longer in the liquid phase before vaporizing. This improved liquid-liquid reaction can serve to better atomize the propellants 𝑁 2 𝐻 4 + 𝐻 2 𝑂 ↔ 𝑁 2 𝐻 5 𝑂𝐻 ↔ 𝑁 2 𝐻 5 + + 𝑂𝐻 − (1) Schalla and Fletcher extensively studied the behavior of triethylamine with WFNA. They observed that the IDT increased significantly, from 4 ms toms, as the WFNA water concentration increased from 1.6% to 10.4%. With 15% water by weight in WFNA, triethylamine did not ignite Miller determined that mixing water with WFNA and RFNA can yield significantly lower freezing points. The eutectic composition of WFNA-water is at 10% water by weight and freezes at -F rather than -F with neat WFNA, as shown in Figure 2. The eutectic composition of the RFNA-water system occurs at 5% water and 17% NTO, freezing at -F. Maintaining the same NTO content, but replacing the water for nitric acid would yield a freezing point of -60°F. 18 Downloaded by PURDUE UNIVERSITY on July 21, 2017 | http://arc.aiaa.org | DOI: 10.2514/6.2015-3867 |