Combustion characteristics of a hydroxylammonium nitrate based liquid propellant. Combustion mechanism and application to thrusters

Abstract

A new composition of hydroxylammonium nitrate based solution containing ammonium nitrate, methanol, and water was developed for monopropellant in a reaction control system (RCS) as an alternative to conventional hydrazine. In comparison with hydrazine, this solution has a 20% higher specific impulse, 1.4 times higher density, and lower freezing point and toxicity. The linear burning rate of the solution is moderate at the operating pressures of RCS thrusters. It was found that the linear burning rate had some characteristics whose mechanisms had not been understood. The combustion mechanism of this solution was investigated. The burning behavior was observed using a medium speed camera, and a temperature profile for the combustion wave was measured with a 2.5 µm diameter thermocouple. From these results, the instability of the liquid-gas interface may trigger a sudden increase in the burning rate, and methanol was found to be effective in reducing the bubble growth rate in the solution. The reactivity of several catalysts was evaluated in an opencup test, and the S405 catalyst for hydrazine showed the best performance among them. Thruster tests were conducted using the S405 catalyst with variation in the propellant mass flow rate, catalyst bed configuration, and length-to-diameter ratio of the combustor. As a result, parameters were determined that ensured long operating time. The model thruster operated stably for up to 100 sec with a specific impulse I sp = 240 sec, which corresponds to a 90% efficiency.

Decomposition Pathways for Aqueous Hydroxylammonium Nitrate Solutions: a DFT Study

“…Because both energy barrier heights of the R4 and R5 pathways are much lower than that for R3, the rate determining step is believed to be R3. Although the energy barrier values determined for this neutral-neutral bimolecular reaction are lower than that for HNO 3 cleavage, these values are still much higher than those associated with other mechanisms, as discussed later. …”

“…The energy barrier was found to be 88.6 kJ/mol, so R6 is considered to be the rate determining step. The maximum energy barrier of the pathway involving NH 3 O is the lowest of all of the neutral-neutral bimolecular pathways shown above, indicating that NH 3 O plays an important role in HAN decomposition. …”

“…The energy barrier for this process was calculated to be 186.5 kJ/mol at the CBS-QB3//ωB97XD/6-311++G(d,p)/SCRF = (solvent = water) level of theory. In the mechanism that proceeds via TS2, decomposition also begins with cleavage of the N-OH bond in HNO 3 , such that the HNO 3 decomposes to OH and NO 2 . The OH subsequently subtracts H from NH 2 OH to form TS2, while the dissociated NO 2 combines with the −NH 2 group in the dehydrogenated NH 2 O to form NH 2 (O)NO 2 .…”

“…-, is one of the most promising candidates as a replacement for commonly used liquid mono-propellants such as hydrazine [1][2][3]. As such, there have been many experimental and theoretical studies concerning the combustion behaviour of the so-called next generation HAN-based propellants [4][5][6][7][8][9][10][11].…”

“…As such, there have been many experimental and theoretical studies concerning the combustion behaviour of the so-called next generation HAN-based propellants [4][5][6][7][8][9][10][11]. Previous research has demonstrated that some HAN-based solutions exhibit extremely high burning rates, and this property has limited the usefulness of such solutions in certain applications [3][4][5][6] because overly high burning rates can sometimes lead to serious accidents [12][13][14]. Therefore, the development of advanced techniques to control the combustion of HAN-based propellants is essential.…”