Berlin Huang

Optical observation of the impingements of nitrogen tetroxide/ monomethylhydrazine simulants

The spray phenomena of doublet and triplet impingements of nitrogen tetroxide (NTO) and monomethylhydrazine (MMH) simulants were studied by the planar laser induced fluorescence technique. The total flow rates of the simulants were controlled at ∼8.00 g/s to simulate the operations of a 5-lb f rocket, and the ratios of the mass flow rates (O/F) of NTO and MMH simulants were varied from 1.0 to 2.4. Statistical analysis was employed to examine the probability distributions of the mass of individual simulants at 10 mm downstream from the impinging point. The distributions of local mixture ratios and flame temperatures were deduced, and the estimation of characteristic exhaust velocity was performed. The results revealed that the breakup and mixing of the impinging jets were closely related to the momentum flux ratio of the jets and the surface tension of the liquids. The triplet impingement was superior in symmetry and uniformity of the spray than that of the doublet impingement, and its mixing was less sensitive to the momentum flux ratio and showed a better mixing effect than doublet impingement at higher O/F ratio conditions. With the detailed distribution information provided by the optical technique, the optimum C* occurred at O/F = 1.18 with doublet impingements for the operation of a 5-lb f NTO/MMH rocket.

Comparison of Hot-Fire and Cold-Flow Observations of Nitrogen Tetroxide/Monomethylhydrazine Impinging Combustion

The combustion phenomena of doublet impingements of nitrogen tetroxide and monomethylhydrazine were observed in this research. The total flow rates of the propellants were controlled at 8:00 g=s to simulate the operation of a 5 lbf rocket, and the ratios of the mass flow rates (O=F) of nitrogen tetroxide and monomethylhydrazine were varied from 1.0 to 2.5. With a two-axis translation module, a C-type thermocouple was used to measure the two-dimensional temperature distributions of the flames at 20 mm downstream of their impinging points. The observations showed that induction distances always appeared from the positions of propellants’ impingement to ignition, and the ignition was induced by the local concentrations of gaseous monomethylhydrazine.Themaximum flamelengthof80 mmappearedatthebestmixingconditionofO=F 1:2, and diffusion-type flames at higher O=F showed shorter flame lengths for poor mixing after the flames had been ignited. Comparing to the previous cold-flow observations by the planar laser induced fluorescence technique with simulants of water- and chloroform-based solutions to match the densities, viscosities, and surface tensions of monomethylhydrazine and nitrogen tetroxide, the locations of high-temperature zones in hot-fire experiments were adequately described by the calculated two-dimensional temperature distributions from the observed local mixture ratio data at the corresponding ignition positions in the cold-flow experiments. These results inferred that the mixture ratio profile was almost conserved after ignition. That is, by properly analyzing the mass distribution of the cold-flow observation with simulants, the temperature distribution of the impinging combustion of nitrogen tetroxide/monomethylhydrazine can be predicted.

Design, fabrication, and test of a microelectromechanical-system-based millinewton-level hydrazine thruster

T HE miniaturization of space systems, such as microsatellites, has become an important development trend. Using a cluster of microspacecraft with a constellational architecture to replace a traditional spacecraft can greatly reduce the costs of production and launch, increase flexibility, and disperse the risks of a mission. Miniaturized spacecraft are classified based on mass, power, and dimensions. Spacecraft with amass of less than 20 kg are classified as class I microspacecraft [1] and require millinewton-level thrusts for spacecraft control. For microspacecraft, the onboard thrusters must be extremely small and lightweight; microelectromechanical systems (MEMS) are thus employed in microthruster design and fabrication [2]. A number ofmicropropulsion systems have been proposed.Micro cold-gas systems have been constructed and used in practice [3,4]; however, a rather low specific impulse (60–80 s) limits their usage. Micro electric-type thrusters provide a high specific impulse [5], but the requirement of high power for operation limits them to larger spacecraft. Miniaturized solid-propellant thrusters have a simple structure and a high specific impulse [6], but their relatively high thrust level (10–10 mN) and single use restrict their application. Monopropellant thrusters are appropriate for miniaturization due to their simplicity and acceptable working temperatures [7]. The catalytic reaction of monopropellant systems mitigates the constraints of radical quenching and mixing prohibition found in the microcombustion of bipropellant systems. Although hydrogen peroxide/silver systems have been tested and effectively reacted in microreactors, hydrazine is considered a better monopropellant for actual microthruster design and operation [7]. A millinewton hydrazine (N2H4) monopropellant thruster is presented in this work. MEMS technologies are employed in the design. The design considerations and component fabrication are discussed. The vacuum thrust of the designed thruster was measured and its propulsive performance was analyzed.

A cold-flow experimental observation of the two-stage impinging type injector for rocket propulsion

Green (low toxicity) liquid rocket propellants have become attractive in recent years due to the features of the low cost and less environmental impact. However, the green propellants, such as kerosene/H2O2, usually have different operational conditions (i.e. relatively high O/F ratio) compared to conventional propellants because of their chemical properties. In this research, a new concept of the two-stage impinging type injector (O-F-F-O) is adopted for investigating the spray mixing at high O/F ratios between 3.75 and 6.25. The impinging distance, jet velocity and impinging angle for the two-stage impinging type injector are design parameters examined, where the impinging angle is more effective at spray atomization and droplet distribution. The PLIF technique is used to measure the droplet distribution so as to identify the spray characteristics. In order to simplify the development process of the injector, the predicted mixture ratio distribution from the individual fuel (F-F) and oxidizer (O-O) sprays by overlapping their averaged images is used to compare with the actual distribution from the two-stage impinging spray (O-F-F-O). At a constant total mass flow rate, results indicate that tendencies towards the variations of the average characteristic velocity (C) with increasing O/F ratios are similar for outcomes of the prediction and actual measurement. Also, there is obvious flow fields interaction between the fuel and oxidizer sprays and coordinating their relative intensities of sprays well can optimize the mixture ratio distribution of the two-stage impinging spray. Better mixing occurs when the fuel and oxidizer sprays have more similar and uniform distributions.

The impinging-type injector design of MMH/NTO liquid rocket engine

By the PLIF optical technique, this study focused on the development of the impinging type injector design of the 100-lbf level monomethylhydrazine/nitrogen tetroxide liquid rocket. The design of the multi-pair impinging injector plate is based on the cold flow and hot fire observations of unlike-doublet impinging jets of monomethylhydrazine/nitrogen tetroxide and their simulants. The mass distributions of the impinging jets from the cold flow observations are used to arrange the paired orifices of the impinging unit on the injector plate through a image projection method. For the most uniform distribution and the best overall estimated C* of the overall spray, the orifice size of the impinging element and the configuration of the paired orifices of an injector plate was determined for the prototype injector plate design. Static tests of the ground-test liquid rocket engine with the designed injector plate are performed. The measured sea-level thrust of the engine was 62.1 lb, and the characteristic exhaust velocity reached 1429.2 m/s at a total propellant mass flow rate of 153.4 g/s. The estimated vacuum thrust was 99.8 lb, and the vacuum Isp was 295.8 s as well. The combustor pressure of the liquid rocket engine was 153.2 psi and remained stable during operation. During the 17 seconds of the hot fire test, the highest wall temperature was measured at the nozzle throat, which was about 1000K.

The Integration and Test of a 5-N Hydrazine Propulsion System

As a payload of a sounding rocket mission, this research designed a 5-N hydrazine propulsion system and tested it at high altitude environment. In this system, none of the component used was space-qualified. A piston-type tank was used for propellant storage, a pyrotechnical valve was used to replace the latch valve, single-coil solenoid valves were used as thruster valves. The self-designed hydrazine thruster was equipped with a single-tube radial-type injector and a conical C-D nozzle with an expansion ratio of 81. Two different sizes of Shell 405 catalyst (14~18 meshes and 20~25 meshes) were packed and separated by porous plates connected to a supporting spring in the reactor. The amount of packed catalyst achieved proper hydrazine dissociation with ammonia dissociation near 0.5 in the exhaust at the design hydrazine inlet flow rate (2.1 g/sec). The system had passed a series of environmental tests including thermal, vibration, shock, EMI, and vacuum tests, and produced an vacuum (~2 torrs) thrust of 4.69 N at hydrazine flow rate of 1.97 g/sec, where the chamber pressure was 13.7 bar, and the specific impulse (Isp), characteristic velocity (C(superscript *)) and thrust coefficient (C(subscript f)) were evaluated to be 242.8 sec, 1246.2 m/sec and 1.91, respectively. In pulse operations, the system produced stable impulses of 1.18±0.12 N‧sec for 250 ms pulse duration and 2.07±0.15 N‧sec for 500 ms pulse duration measured in 15-bit cycles. Noticeable pressure oscillations (~30Hz) of a low-amplitude stage followed by a high-amplitude stage in the reactor were observed during hot firing of the system. Analyses revealed that the pressure oscillation was inevitably from the violent catalytic hydrazine dissociation reactions. With an isolation orifice to prevent the pressure wave propagating to the feed line, the pressure oscillation can be effectively suppressed. In addition, the spring of the catalyst supporting assembly was also shown to be an effective damper to the pressure oscillation. By analysis, the second-stage high-amplitude oscillation was induced by the dysfunction of the spring damper for the thermal expansion of the reactor chamber and the catalysts.

The comparison of the hot-fire and cold-flow observations of NTO/MMH impinging combustion

[Abstract] The combustion phenomena of doublet impingements of nitrogen tetroxide (NTO) and monomethylhydrazine (MMH) were studied in this research. The total flow rates of the propellants were controlled at ~8.00 g/s to simulate the operation of a 5-lbf rocket, and the ratios of the mass flow rates (O/F) of NTO and MMH were varied from 1.0 to 2.4. With a 2-axis translation module, the thermocouple array measured the 2-D temperature distributions in the hot-fire experiments at the 20mm downstream of the impinging point. The results showed that the temperature distribution was strongly affected by O/F and mixing effect. Comparing to the previous PLIF cold-flow studies in the same conditions, the results demonstrated that the cold-flow analyses could adequately predict the position and shape of the high temperature zone in hot-fire situation. In views of the combustion phenomena, an induction period (length) to reach intensive reactions always exists, and it can be correlated to the MMH droplet size distribution or the uniformity of the MMH spray. And, a maximum length of ∼80mm of the intensive reaction zone was shown for the conditions investigated. This may be caused by the diffusion-controlled combustion in the downstream reactions.