Timothée L. Pourpoint

High-repetition-rate three-dimensional OH imaging using scanned planar laser-induced fluorescence system for multiphase combustion

Imaging dynamic multiphase combusting events is challenging. Conventional techniques can image only a single plane of an event, capturing limited details. Here, we report on a three-dimensional, time-resolved, OH planar laser-induced fluorescence (3D OH PLIF) technique that was developed to measure the relative OH concentration in multiphase combustion flow fields. To the best of our knowledge, this is the first time a 3D OH PLIF technique has been reported in the open literature. The technique involves rapidly scanning a laser sheet across a flow field of interest. The overall experimental system consists of a 5 kHz OH PLIF system, a high-speed detection system (image intensifier and CMOS camera), and a galvanometric scanning mirror. The scanning mirror was synchronized with a 500 Hz triangular sweep pattern generated using Labview. Images were acquired at 5 kHz corresponding to six images per mirror scan, and 1000 scans per second. The six images obtained in a scan were reconstructed into a volumetric representation. The resulting spatial resolution was 500×500×6 voxels mapped to a field of interest covering 30  mm×30  mm×8  mm. The novel 3D OH PLIF system was applied toward imaging droplet combustion of methanol gelled with hydroxypropyl cellulose (HPC) (3 wt. %, 6 wt. %), as well as solid propellant combustion, and impinging jet spray combustion. The resulting 3D dataset shows a comprehensive view of jetting events in gelled droplet combustion that was not observed with high-speed imaging or 2D OH PLIF. Although the scan is noninstantaneous, the temporal and spatial resolution was sufficient to view the dynamic events in the multiphase combustion flow fields of interest. The system is limited by the repetition rate of the pulsed laser and the step response time of the galvanometric mirror; however, the repetition rates are sufficient to resolve events in the order of 100 Hz. Future upgrade includes 40 kHz pulsed UV laser system, which can reduce the scan time to 125 μs, while keeping the high repetition rate of 1000 Hz.

Amine–Boranes: Green Hypergolic Fuels with Consistently Low Ignition Delays

Complexation of amines with borane converts them to hypergols or decreases their ignition delays (IDs) multifold (with white fuming nitric acid as the oxidant). With consistently low IDs, amine-boranes represent a class of compounds that can be promising alternatives to toxic hydrazine and its derivatives as propellants. A structure-hypergolicity relationship study reveals the necessary features for the low ID.

Investigation into the Hypergolic Ignition Process Initiated by Low Weber Number Collisions

The processes leading to the hypergolic ignition of monomethyl hydrazine and red fuming nitric acid have been the subject of several studies. Whereas drop test experiments provide the scale necessary for detailed observations, they typically rely on the impact of a fuel droplet moving at its terminal velocity and an oxidizer pool contained within a crucible. By controlling the kinetic energy and the size of the fuel droplet, effectively varying the Weber number of the fuel droplet, precise amounts of reactants can be made to react at a defined location, thus, increasing the repeatability of the experiment. With an unrestrained oxidizer pool, the reaction can be made to resemble that occurring in a combustion chamber. In this study, the collisions of fuel droplets, limited to a Weber number below 12, with unrestrained red fuming nitric acid pools within a dry nitrogen environment were observed. The postprocessing of high-speed visible and infrared movies revealed that, under most conditions, explosion even...

Development of Reduced Toxicity Hypergolic Propellants

Hypergolic storable high-performance propellants fulfill a wide variety of mission roles in launch vehicle and spacecraft propulsion. The current favored storable hypergolic bipropellant combination of nitrogen tetroxide and monomethylhydrazine has significant handling and environmental issues due to their toxicity. Research into reduced toxicity storable hypergolic fuels has pointed to several types of reduced-toxicity fuel formulations which energetically react with hydrogen peroxide and provide similar performance to the current benchmark propellants. The authors have investigated the feasibility of multiple fuels to achieve adequate performance for bipropellant rocket applications with a hydrogen peroxide oxidizer. Results to date identify four promising candidates as potential competitors for the current benchmark hypergolic propellants. I. Introduction MONG the existing liquid rocket engines, those using liquid oxygen/liquid hydrogen and monomethylhydrazine/nitrogen tetroxide are the best performing propellant combinations in the cryogenic and hypergolic liquid propellant categories, respectively. Specifically among the hypergolic propellants, monomethylhydrazine (MMH) represents the state-of-the-art fuel while Nitrogen Tetroxide (NTO), Mixed Oxides of Nitrogen (MON) & Inhibited Red Fuming Nitric Acid (IRFNA) are the most prevalent oxidizers. The aforementioned propellants have excellent performance characteristics in terms of specific impulse, density impulse, ignition delays and reliability. The MMH/NTO combination has been successfully used in the space shuttle orbital maneuvering systems (OMS) and the Reaction Control Systems (RCS). With the enormous increase in space activities since the 70’s, certain inherent risks with the use of the aforementioned hypergolic propellants have increasingly become matters of concern as the propellants are highly toxic and difficult to handle. Hydrazine based fuels are also identified as carcinogens. Most of the oxidizers mentioned are highly corrosive. Storing highly toxic propellants onboard for long duration space missions poses a major safety hazard. With increased use, ground handling of these propellants creates workplace safety issues. For these reasons, there is a strong research interest in finding hypergolic propellants with far lesser toxicity and comparable performance with the state-of-the-art. The present study focuses primarily on the development and testing of reduced toxicity hypergolic propellants whose performance approaches that of MMH/NTO. Key characteristics of desirable propellants are ease of handling & storability, low ignition delays, restartability and to an extent, low cost. Small ignition delays are likewise an important factor in avoiding hard starts in a hypergolic engine. Several previous efforts in the development of low

HYPERGOLIC REACTION MECHANISMS OF CATALYTICALLY PROMOTED FUELS WITH ROCKET GRADE HYDROGEN PEROXIDE

Abstract The coupling of the physical and chemical processes controlling the ignition delays (τ ign ) of hypergolic propellants complicates the direct analysis of the transient ignition processes. The transport properties of both the propellants and the ambient gas, and the heat of vaporization and reaction affect τ ign and must be considered experimentally. Furthermore, since hypergolic ignition occurs, by definition, on contact, the mechanics of initial contact and subsequent mixing can affect τ ign and must also be considered. Experimental results from a study of the hypergolic ignition of a catalytically promoted fuel with rocket grade hydrogen peroxide (RGHP) are presented. Statistical analysis of the experimental data was conducted to evaluate the relative effects of RGHP concentration, initial ambient pressure, and the ambient gas on τ ign . At RGHP concentrations of less than 92% in water, stable ignition was difficult to achieve. At sufficiently high Lewis number, an oscillatory ignition process is observed. A phenomenological model comprising mixing, RGHP decomposition, fuel heating and vaporization, and auto-ignition is presented and compared to the experimental results.

Characterization of Ethylenediamine Bisborane as a Hypergolic Hybrid Rocket Fuel Additive

A boron-based catalytic and energetic fuel additive is explored as a mechanism to enhance performance of hybrid motors using nitric-acid-based oxidizers. Ethylenediamine bisborane is highly hypergolic with nitric acid, thereby eliminating the need for a separate ignition system and providing the potential for restart. Ignition delays of 2.9±0.3 ms for ethylenediamine bisborane powder and 31.7±19.6  ms for ethylenediamine bisborane/hydroxyl-terminated polybutadiene combinations have been measured using white fuming nitric acid as the oxidizer. Theoretical specific impulse values higher than any other nitric-acid-based hypergolic hybrid combination tested are obtained; in addition, ethylenediamine bisborane is air stable and not toxic. Also presented is a method of manufacturing large quantities of high-purity ethylenediamine bisborane.

Performance of Dicyclopentadiene/H2O2-Based Hybrid Rocket Motors with Metal Hydride Additives

An experimental performance evaluation of metal hydride fuel additives for hybrid rocket motor propulsion systems is examined in this paper. Some metal hydride additives offer improved performance, but a common issue is material aging. An accelerated aging study revealed that dicyclopentadiene can protect sodium borohydride (NaBH4) particles from exposure to air and water vapor much better than conventional hydroxyl-terminated polybutadiene. Static hybrid rocket motor experiments were conducted using dicyclopentadiene as the fuel. Sodium borohydride and aluminum hydride (AlH3) were examined as fuel additives. Ninety percent rocket-grade hydrogen peroxide was used as the oxidizer. In this paper, the sensitivity of solid fuel regression rate and characteristic velocity efficiency to total fuel grain port mass flux and particle loading is examined. Chamber pressure histories revealed steady motor operation in most tests, with reduced ignition delays when using the NaBH4 fuel additive. The addition of NaBH4 a...

Ignition of Advanced Hypergolic Propellants

The hypergolic ignition of droplets of monomethyl hydrazine, 2-Azido-N,Ndimethylethanamine, N,N,N’N’-Tetramethylethylene-1,2-diamine, a blend of 2-Azido-N,Ndimethylethanamine and N,N,N’N’-Tetramethylethylene-1,2-diamine, 1-Butyl-3-methylimidazolium dicyanamide, and Fuel A with red fuming nitric acid were investigated using a controlled descent under a nitrogen environment and via standard drop tests under a fume hood. For the controlled-descent experiments, ignition was only observed for monomethyl hydrazine and Fuel A. Ignition was achieved with monomethyl hydrazine, Fuel A, N,N,N’N’Tetramethylethylene-1,2-diamine, and a blend of 2-Azido-N,N-dimethylethanamine and N,N,N’N’-Tetramethylethylene-1,2-diamine for the drop tests. The controlled-descent, inert atmosphere tests provided some insight into the importance of liquid-liquid reactions on hypergolic ignition.

Aluminum-Ice (ALICE) Propellants for Hydrogen Generation and Propulsion

An experimental investigation was conducted to determine the relative propulsive performance and viability of novel solid propellants comprised of ALICE using fundamental techniques such as steady-state strand experiments and applied experimentation such as labscale static fire rocket tests. Burning rates, slag accumulation, thrust, and pressure are some of the experimental parameters obtained. System scaling has been performed to examine the effect of larger systems on slag accumulation and performance parameters. The effect of pressure on the linear burning rate was examined and correlated using a Saint Roberts’s law fit. The pressure exponent for ALICE was 0.73, which is approximately a factor of two larger than Al/water mixtures. Three sizes rocket motors ranging from internal diameters of 0.75 to 3-in. Nozzle throat diameter and igniter strength were varied. It was found that ALICE propellants successfully ignited and combusted in each lab-scale rocket motor, generating thrust levels above 223 lbf for expansion ratios of 10 and center-perforated grain configurations (3-in length). For the 3-in motor, combustion efficiency was around 70%, while the specific impulse efficiency was 64%.

Rheological Characterization of Monomethylhydrazine Gels

In this paper, viscometry, yield stress, and small shear strain oscillation experiments on monomethylhydrazine gels are presented. The goal is to define a gel formulation with a measurable yield stress under low-shear conditions and shear-thinning behavior at shear rates representative of typical rocket injectors. Hydroxypropylcellulose, fumed silica, and a hybrid of the two materials are investigated as gelling agents for monomethylhydrazine. The two gel formulations that included hydroxypropylcellulose exhibited similar shear-thinning behavior with power-law flow indices of ∼0.1 to 0.2. The pure fumed silica gel samples exhibited highly shear-thinning behavior with negative power-law flow indices indicative of thixotropic behavior. Tests performed after a preshear cycle showed shear-thinning power-law flow indices of ∼0.3. Unlike the pure hydroxypropylcellulose and hybrid gels, the fumed silica gel exhibited a well-defined, measureable yield stress. Small-strain oscillatory experiments showed that hydro...