Various mechanisms have been proposed in the literature for the hypergolic reactions of methylhydrazine (MMH) and dinitrogen tetroxide (NTO). Most of these mechanisms involve radical reactions. However, experimental results obtained on the liquid-phase reactions of MMH and NTO by using high-resolution linear quadrupole ion trap/orbitrap mass spectrometry suggest that highly energetic ionic reactions play an important role in the hypergolic reactions of MMH with NTO. The elemental compositions of the detected ions were determined and their structures were explored by using tandem mass spectrometry experiments. Quantum chemical calculations indicate that the reactions of the nitrosonium and/or nitronium cations generated from NTO via the unsymmetrical NTO (UNTO) are important in explaining the hypergolic behavior of NTO with MMH. The most important reactions include the initial generation of the MMH radical cation that then reacts with the nitrate anion or nitrogen dioxide radical to form the final detected product ions.

In this paper, we present the results of the design and testing of two sequential liquid fed coaxial pulsed plasma thrusters (PPT). This work confirmed successful operation of a liquid fed PPT in a magnetoplasmadynamic regime with discharge voltages on the order of 100-200 V with discharge currents of similar to 10 kA. Ion exhaust velocity and cathode erosion rates are reported using ASCENT as a propellant, with ion velocity reported at 30.6 +/- 4.8 km/s, and cathode erosion reported at 15.4 +/- 0.6 mu g/C. Further, long exposure photography and ICCD imaging, with corresponding current and voltage profiles, are reported for our second system. Long exposure and ICCD images show successful consumption of ASCENT as propellant at pressures below 10(-5) torr and indicate minimal cathode spotting. This demonstrates potential of the low cathode erosion and extended operational lifetime of the system.

Aerojet Rocketdyne has discovered a new class of enhanced-performance hydrazine blended monopropellants with 100- to 1000-fold reduced vapor pressure compared to neat hydrazine. Such propellants present a previously-unexplored path to realize the same benefits offered by current high-TRL green ionic liquid propellants while preserving the favorably low operating temperatures and preheat power requirements of heritage monopropellant technologies. Specifically, green hydrazine-based propellants: center dot Can be fired in conventional, low-cost nickel-based super-alloy thrusters center dot Deliver specific impulse equal to hydrazine and 25-35% greater density-specific impulse center dot Do not require higher catalyst bed preheat temperatures than hydrazine center dot Remain liquid below -50 degrees C, potentially obviating the need for feed system heating To date, a baseline formulation under development for in-space propulsion applications has been experimentally verified to exhibit high thermal stability as well as low impact and shock sensitivity. The formulation has also been shown to be nonflammable and non-combustible. Recent hot-fire testing in a standard production 1-N thruster completed at Purdue University Zucrow Laboratories demonstrated excellent operational stability and performance consistent with predictions. Aerojet Rocketdyne is presently on-track to complete Department of Transportation certification and qualification testing of a 1-N thruster operating on the new propellant by the end of the first quarter, 2024.

The purpose of this study is to determine the effect of nitric oxide on the ignition delay of dinitrogen tetroxide (NTO) and monomethylhydrazine (MMH). Nitric oxide is commonly added to NTO to create mixed oxides of nitrogen (MON), which lowers its freezing point and decreases its corrosiveness. However, to the authors’ knowledge, the effect of nitric oxide addition on the ignition delay of MMH with MON has not been reported using a common experimental setup for multiple MON concentrations. To evaluate these effects, an experimental system was designed to perform ignition delay measurements of MMH/MON in an inert, pressure-controlled environment, while controlling the temperatures of the propellants. Tests were conducted with NTO, MON-2.9, MON-10.1, and MON-25.4 at several conditions: a comparison condition where all concentrations were tested at the same temperature and pressure, a condition controlling for vapor pressure where all concentrations were tested at the same temperature and up to 10 psi above their vapor pressures, and at the lowest achievable temperature and pressure for each concentration.

In this paper, we investigate several cold gas thrusters with different nozzles geometries numerically and experimentally in the Purdue Altitude Chamber Facility where we use a diffuser-ejector system to simulate high altitude conditions. Here, the main aim is to study the effects of different thruster nozzle geometries and axial/radial gaps between the thruster nozzle exit and the diffuser inlet on the performance of the diffuser-ejector system. We used a two-stage ejector system to create the desired diffuser back pressure conditions at the exit of a second throat diffuser during the tests. Results to date focus on one of the thrusters having a highly truncated ideal contoured nozzle. While testing that cold gas thruster, we used the mass flow provided by the thruster as the suction load for the ejector system and completed its full performance characterization. We also studied the minimum starting, operating pressure ratios, and hysteresis behavior of the second throat diffuser. We obtained a noticeably small hysteresis region. We also found that the diffuser starting pressure ratio increased with increasing the axial gap between the nozzle exit and the diffuser inlet. Future work will consist of completing the tests for all the thrusters nozzle geometries. Furthermore, as we had used the same diffuser and the ejector system with a hybrid motor at simulated high altitude conditions, we compared the performance of the diffuser – ejector system with both hot and cold gas flows. By doing that, we can explore the effects of the specific heat ratio and the temperature of the exhaust gas flow on the diffuser-ejector system performance.

Knowledge on short-lived reaction intermediates is often essential for mechanistic investigations of organic reactions and for reaction optimization. Unfortunately, most conventional analytical methods are too slow to allow the detection of short-lived reaction intermediates. Herein, a direct laser desorption/ionization method coupled with linear quadrupole ion trap/orbitrap high-resolution tandem mass spectrometry was used for the detection and structural characterization of several previously proposed but undetected reaction intermediates formed during laser-induced UV/H2O2 advanced oxidation of 2-methylbenzoisothiazol-3-one. The elemental compositions of most detected (ionized) compounds were determined. Tandem mass spectrometry experiments based on gas-phase collision-activated dissociation (CAD) were conducted to gain information on the ion structures. The mechanisms of the CAD reactions were explored using high-level quantum chemical calculations to support the structures proposed for the neutral reaction intermediates formed during the laser-induced UV/H2O2 advanced oxidation of 2-methylbenzoisothiazol-3-one. In the negative-ion mode experiments, anions corresponding to three reaction intermediates were detected and structurally characterized: 1-hydroxy-2-methyl-1,2-dihydro-3H-1λ4-benzo[d]isothiazol-3-one, 2-(methylcarbamoyl)benzenesulfinic acid, and 2-(dihydroxy(oxo)-λ6-sulfaneyl)-N-methylbenzamide. One of the final products, 2-(methylcarbamoyl)benzenesulfonic acid, was also detected and characterized. In positive-ion mode experiments, cations corresponding to the reactant, 2-methylbenzoisothiazol-3-one, as well as an intermediate reaction product and the two final reaction products, 2-methylbenzo[d]isothiazol-3(2H)-one 1-oxide, N-methylsaccharine, and 2-(methylcarbamoyl)benzenesulfonic acid, respectively, were detected and identified. This research substantially improved the understanding on the reaction intermediates formed during laser-induced UV/H2O2 advanced oxidation of 2-methylbenzoisothiazol-3-one, which facilitates the delineation of the reaction mechanisms occurring in these processes.

The purpose of the study is to determine the surface tension of commonly used Mixed Oxides of Nitrogen (MON) concentrations as a function of temperature Mixed Oxides of Nitrogen are a mixture of nitrogen tetroxide (NTO) and nitric oxide (NO) that react hypergolically with fuels such as monomethylhydrazine (MMH). While MON has been used in propulsion applications for decades, there is limited up-to-date data on key properties – such as surface tension, speed of sound, and heat capacity. In this work, a custom surface tension test apparatus was developed that uses capillary action to measure surface tension. Two capillary tubes of different inner diameters are used to determine surface tension of a variety of MON concentrations by measuring the height difference between the tube menisci. The test apparatus includes an integrated pressure vessel in order to accommodate the high vapor pressure of high MON concentrations surrounding by a jacket for temperature control between 0°C and 50°C. Initial testing on a simulant fluid with a comparable surface tension, isopropyl alcohol, resulted in measured values within 3% of reported literature data. Results to date include room temperature surface tension values of 21.2 mN/m, 20.5 mN/m, and 24.0 mN/m for NTO, MON-10.18, and MON-25.4 respectively. Testing with MON-3 will be completed in the future.

Widely used since the 1960s, Mixed Oxides of Nitrogen (MON) react hypergolically with monomethylhydrazine (MMH). Despite their prominence in liquid propulsion systems, the properties of MON as a function of temperature have not been well characterized. The MON concentration is determined by the weight percentage of nitric oxide (NO) in the mixture, e.g. MON-3 referring to a 3 wt.% NO mixture, and MON-25 referring to a 25 wt.% NO mixture. There is a strong interest in using high NO concentrations MON, such as MON-25, due to their low freezing points, and as such there is a renewed incentive in carefully documenting the properties of MON relative to temperature. The main objective of this study is to modify a commercial sonic velocimeter to determine the speed of sound of various MON concentrations from NTO to MON-25. Deionized water and isopropyl alcohol, both of which have well documented speed of sounds, were used to validate the measurement method. These calibration tests resulted in sound speeds with a relative uncertainty of 0.7% from the literature at most. This paper details the modifications made to an Anton Paar L-Sonic 5100 sonic velocimeter for use with NTO and MON, and will further present the speed of sound results for NTO and MON-25.17 from -10°C to 50°C in comparison to existing literature data sets. Future work will include testing additional MON grades in order to better document the speed of sound in the oxidizer to improve industry understanding of the oxidizer.

Additive manufacturing of ceramics allows for monolithic catalyst beds with a much wider range of geometries than was previously possible, potentially allowing for higher performance on multiple metrics. Achieving these gains requires a consistent, even, and well-adhering washcoating procedure for the additively manufactured supports, which works well on varied geometry and on support materials that can be readily printed. In this work we present improved methods for surface preparation and coating of additively manufactured alumina catalyst supports intended for use with rocket grade hydrogen peroxide or other monopropellants with similar operating temperatures. Initial methods based on previously published work resulted in uneven coating and poor adhesion on sintered alumina substrates. The current work demonstrates that the surface roughness plays a critical role in both coating distribution and adhesion. We also present a method of controlled thermochemical etching that results in a consistent and desirable surface roughness starting from a variety of surface morphologies. The micro-roughened surface leads to even wetting of the coating solution on the part, and strong mechanical adhesion of the dry coating to the substrate.

Combined with a common fuel binder, solid hypergols can simplify the overall complexity of hybrid rocket engines, as the fuel grain can be ignited and reignited without any external power source or external fluid. Also, with the hypergolic additive embedded in the binder, the flame zone could be placed at the surface of the grain itself, thereby providing heat to the grain to maximize regression rate and promote combustion sustainability. The objective of this study was to demonstrate hypergolic ignition and successive relights of a 2-in motor grain configuration, with a paraffin-based fuel and MON-3 (3 wt % nitric oxide in nitrogen tetroxide) as the oxidizer. With sodium amide and potassium bis(trimethylsilyl)amide as solid hypergolic additives, the study focused on the influence of the additive type, loading, location, and format on the grain ignition delay and combustion sustainability. Hypergolic ignition was achieved with grain configurations composed of a front segment with 90 wt % additive and the main grain with loadings of additive from 40 down to 0 wt %. Two-s single burn tests provided regression rate estimates for the different grain combinations. Grain ignition delays varied between similar to 20 and similar to 250ms, depending on the grain configuration, with C* efficiencies between 64% and 98%.

Carbonaceous deposits formed in fuel-film cooling act as a thermally insulating barrier, but the mechanisms for their formation at the high enthalpies and pressures of rocket engines are not well studied. Various spectroscopic techniques were used to investigate the microscopic chemical and physical structure of carbonaceous deposits formed in a small-scale H2O2-kerosene rocket combustor. Where possible, spectra were measured as a function of axial distance from the fuel-film injector to identify changes in deposit structure as the fuel-film boundary layer vaporized and mixed with the hot core flow. Two carbon layers were found, a tenacious dense layer beneath a porous soot layer. Gas chromatography mass spectrometry was used to determine condensable polycyclic aromatic hydrocarbon (PAH) concentrations in the dense and soot deposits. Raman spectroscopy measured planar coherence length and other indicators of structural order while x-ray photoelectron spectroscopy determined carbon hybridization, surface oxidation, and deposit impurities. All three of these spectroscopy techniques showed independent signs of the dense layer forming via heterogeneous condensation of heavy PAHs, whereas the soot layer deposited via thermophoresis.

Understanding the fundamental mechanisms of chemical reactions is of great interest to scientists working in many fields as it enables the rationalization, prediction, and design of reactions. Many chemical processes involve the formation of short-lived reaction intermediates, most of which cannot be isolated and are challenging to detect. One such intermediate is the tetrahedral intermediate often proposed to be generated upon the reactions of acetyl chlorides with simple alcohols via an addition/elimination mechanism. However, the formation of this tetrahedral intermediate is a subject of controversy as it has not been detected. Furthermore, some kinetic evidence suggests the SN2 mechanism for this reaction. In the present investigation, a 266 nm pulsed Nd:YAG laser was used to evaporate and ionize reactants, reaction intermediates, and products in microdroplets of acetyl chloride and ethanol. A linear quadrupole ion trap mass spectrometer was used to detect the ions and collision-activated dissociation (CAD) experiments were employed for their structural characterization. The results demonstrate the formation of the protonated tetrahedral intermediate of the addition/elimination reaction. The protonated reaction intermediate was isolated and subjected to CAD, which resulted in the loss of water and ethylene, thus confirming its structure. These results demonstrate that the ethanolysis of acetyl chloride proceeds via an addition/elimination mechanism involving a tetrahedral reaction intermediate. However, the parallel occurrence of the SN2 mechanism cannot be ruled out.

View Video Presentation: https://doi.org/10.2514/6.2022-1859.vid The latent heat storage capacity of phase change materials is frequently used for transient thermal energy storage in high heat flux environments. However, direct measurement of heat fluxes or surface temperatures on the heated surface is difficult in high temperature experimental setups. Instead, thermocouples can be immersed in the phase change material and unknown heat transfer properties, such as flame temperature and the heat transfer coefficients, are approximated using an inverse heat transfer algorithm. In this work, a two model inverse heat transfer algorithm is implemented, where a low temperature model without phase changes is used to approximate a subset of the unknown heat transfer properties. These results are then fed as initial conditions to a high temperature phase change model for the entire experimental duration for determination of the unknown heat transfer properties across the entire temperature range. The two model approach reduces the effective dimensionality of the solution space, improving convergence radius and speed.

Y Carbonaceous deposits can reduce heat flux in fuel-film-cooled kerosene rocket engines, but the deposition process at rocket conditions is poorly understood. Heat flux was measured in a 4.8 MPa (700 psia) fuel-film-cooled kerosene-hydrogen peroxide axisymmetric rocket combustor using 50 null point calorimeters and the Gauss-Newton algorithm with a constant Jacobian matrix. Carbon deposition caused a reduction in heat flux at axial positions furthest from the fuel-film injector, where deposits were later measured as thickest. Heat flux was reduced by a smaller amount in low-thermal-conductivity chamber liners when compared with high-thermal-conductivity copper liners. The roughness of the chamber-liner surface had little effect on quasi-steady-state heat flux but may have affected heat flux and carbon deposition during startup transients.

Mixed Oxides of Nitrogen (MON) are made by mixing nitrogen tetroxide (NTO) with nitric oxide (NO). Nitric oxide reacts with nitrogen tetroxide to form nitrogen trioxide, creating a mixture of oxides of nitrogen, with species the concentration of which is pressure and temperature dependent. Knowledge of the chemical composition of MONs is essential to understanding their physical and thermodynamic properties, and therefore behavior in fluid systems. The main objective of this study was to design a constant pressure feed system to get Raman spectroscopy data of different MON mixtures, from -10 to 50°C, and as a function of pressure. Using samples of known initial composition, we calibrated for N2O4 and N2O3, the major constituents in MON mixtures, to, ultimately, determine the chemical composition of any given MON. Our results include calibration for N2O4 in N2O4/NO2 mixtures and calibration curves relating the amount of N2O3 and N2O4 in various MONs. Finally, a sensitivity analysis was completed based on our results, to determine the smallest change in initial NO wt.% we can detect in unknown MON mixtures.

Mixed Oxides of Nitrogen (MON) are a mixture of nitrogen tetroxide (NTO) and nitric oxide (NO). The addition of nitric oxide to nitrogen tetroxide depresses the freezing point of the mixture, making this oxidizer advantageous for low temperature applications. The renewed interest in higher NO concentrations (MON-25 to MON-30) has made up to date characterization of this propellant critical to future mission sizing. Understanding the quantity of inert pressurant gases that are dissolved in propellants is the first step in determining their characteristics, and is essential to mission design. The main objective of this study was to design and build a feed system that would allow us to determine the mass of helium dissolved in MON, for a given initial pressure and temperature, by tracking the pressure drop due to the dissolution process. With this technique, we were able to estimate helium solubilities for both NTO and MON-25.5. These estimates are currently reported as ranges, since we observed potential species dissociation due to the dissolution process. Additional testing will be needed to deconvolute dissociation from dissolution, and accurately determine the helium solubility in both NTO and MON-25.

Advances in additive manufacturing are allowing complex custom geometries in new catalyst bed designs for monopropellant thrusters. The variety of new geometries that are now possible create a need for improved pressure drop models to inform accurate performance predictions during design. The present study focuses on preparation for a parametric investigation measuring the pressure drop across monolithic catalyst beds for 90% and 98% hydrogen peroxide. Pressure drop needs to be measured as a function of catalyst bed size and geometry, catalyst material, propellant flow rate, and downstream pressure. We have demonstrated a test facility with a modular catalyst bed system for measuring the pressure drop under a variety of flow conditions. We have also explored several materials and techniques for each phase of the monolithic catalyst bed fabrication process, attempting to combine and refine improvements to the state of the art that have not been employed together before. The pressure drop data we are preparing to collect is intended to be used for development of a reduced order model to predict pressure drop that can be used for future design of catalyst beds for both monopropellant and bi-propellant thrusters.

In this paper, we investigate several diffuser-ejector system configurations using cold gas thrusters with conical and bell nozzles numerically and experimentally. Here, the main aim is to study the effects of different thruster nozzle geometries, diffuser geometries, and thruster/ejector operational parameters on the performance of a diffuser-ejector system. A single-stage ejector attached to the exit of a diffuser was used to create the desired diffuser back pressure conditions. We created intentional diffuser start/unstart conditions by regulating the thruster and ejector motive pressure. Different thruster gases such as nitrogen, carbon dioxide, and argon were used to investigate the effects of the specific heat ratio on the system performance. We used the same diffuser configurations with different thruster nozzles to analyze the effects of nozzle geometry on the starting performance of the diffuser-ejector system. We used bell nozzles with two different initial expansion angles to determine their effects on the diffuser performance. Test cases using bell nozzles with θ_n=38° required the highest values for α_s among the other nozzles for the same experimental test case. The hysteresis region for those nozzles was also found to be the largest among the other nozzles. In addition, we compared configurations with conical and bell nozzles with each other in terms of diffuser starting/operation pressure ratios, hysteresis behavior, and normal shock theory correction factors. We re-created the test conditions for several test cases and evaluated them numerically using CFD. Overall, the diffuser wall pressures predicted matched reasonably with the measured diffuser wall pressures.

Detonation of explosive devices produces extremely hazardous fragments and hot, luminous fireballs. Prior experimental investigations of these post-detonation environments have primarily considered devices containing hundreds of grams of explosives. While relevant to many applications, such large- scale testing also significantly restricts experimental diagnostics and provides limited data for model validation. As an alternative, the current work proposes experiments and simulations of the fragmentation and fireballs from commercial detonators with less than a gram of high explosive. As demonstrated here, reduced experimental hazards and increased optical access significantly expand the viability of advanced imaging and laser diagnostics. Notable developments include the first known validation of MHz-rate optical fragment tracking and the first ever Coherent Anti-Stokes Raman Scattering (CARS) measures of post-detonation fireball temperatures. While certainly not replacing the need for full-scale verification testing, this work demonstrates new opportunities to accelerate developments of diagnostics and predictive models of post-detonation environments.

This work reports the design, implementation, and testing of an apparatus that allows for mixing of dinitrogen tetroxide (NTO) with nitric oxide (NO) to synthesize mixed oxides of nitrogen (MON). The apparatus was developed to facilitate a series of experiments which will measure various properties of MON that have either not been reported, or have been reported without an accompanying uncertainty analysis. The apparatus presented in this paper allows for preparation of relatively small batches of MON (< 50 mL) with NO added to the system and allowed to react with mass concentrations between 0 and 30 percent. The final NO composition of samples prepared using this setup are confirmed by observing the mass change of the sample following oxidation of the NO in the system, as outlined in the military specification pertaining to analysis of MON samples. A description of the test stand as well as a high level overview of procedures for MON synthesis are presented. Preliminary freezing point and vapor pressure measurements are reported with comparisons to literature.