Journal of Propulsion and Power

Journal Information
ISSN / EISSN : 0748-4658 / 1533-3876
Total articles ≅ 5,759
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Daisuke Nakata, Kiyoshi Kinefuchi, Hitoshi Sakai, Suyalatu
Journal of Propulsion and Power pp 1-9; https://doi.org/10.2514/1.b38187

Abstract:
A high-efficiency concentric tubular-type resistojet with potential application to short-term orbit-raising maneuvers has been fabricated by 3-D printing and demonstrated. The propellant flows through multiple layers of cylindrical shells, with this structure also functioning as a single-piece heater. A 6-cm-high cylinder was realized with a wall thickness of 0.2 mm, using Inconel 718. A nodal thermal analysis was performed to identify the upper-limit current at a temperature limit of the wall material, and it was revealed that an outlet gas temperature of 871 K can be achieved with 77 A of current at 0.2 g/s of mass flow rate. The designed heater was combined with a boron nitride insulator and a stainless-steel housing, and thrust was measured in a vacuum chamber with nitrogen as the propellant. At a mass flow rate of 0.2 g/s and 75 A of current, an outlet temperature of 747 K, a specific impulse of 108 s, and a heater efficiency of 72% were achieved. These results with nitrogen propellant were used to predict the performance of a tungsten-made resistojet with a hydrogen propellant, and a specific impulse of over 700 s can be expected at a heater temperature of 2000 K.
Simon Peterschmitt, Denis Packan
Journal of Propulsion and Power pp 1-10; https://doi.org/10.2514/1.b38156

Abstract:
The electron-cyclotron resonance thruster with magnetic nozzle relies on two successive energy transfer processes: first from electromagnetic energy to electron thermal energy, facilitated by a coupling structure; and second from electron thermal energy to ion directed kinetic energy, facilitated by a diverging magnetic field. The nature and geometry of the coupling structure are crucial to the first energy transfer process. This paper presents an experimental study of the performance of an electron-cyclotron resonance thruster with magnetic nozzle, equipped either with a waveguide-coupling structure or with a coaxial-coupling structure. The necessity of thrust balance measurements to perform such a comparison is demonstrated. The low coupling efficiency from microwave power to the plasma achieved by waveguide coupling is found to result in very large uncertainty with respect to the deposited power. A method to significantly reduce this uncertainty is proposed and implemented. Thrust balance measurements indicate 500 μN for the coaxial-coupled thruster and 240 μN for the waveguide-coupled thruster, both operated at 25 W of deposited microwave power and a mass flow rate of 98 μg/s of xenon. Electrostatic probe measurements reveal that this difference can be explained by a difference in ion energy. The results emphasize the critical role of the coupling structure, which may have been previously overlooked.
Samith Sirimanna, Balachandran Thanatheepan, Dongsu Lee, Shivang Agrawal, Yangxue Yu, Yuyao Wang, Aaron Anderson, Arijit Banerjee, Kiruba Haran
Journal of Propulsion and Power, Volume 37, pp 733-747; https://doi.org/10.2514/1.b38195

Abstract:
Electric aircraft propulsion is a growing research area that looks into achieving propulsion through fully electric or hybrid electric systems while achieving low CO2 emissions. The system-level benefit gained by different electric and hybrid-electric propulsion schemes depends heavily on the performance of system-level components in the electric drive-train, including the electric motor, gear box, motor drive, protection systems, as well as the thermal management system. When comparing motor topologies, it is important to understand performance measures such as efficiency and specific power on a drive system level. Many different motor types have been qualitatively compared and can be found in the literature. To guide appropriate component selection, this paper presents details of a quantitative study for a given electric propulsion drive system. A Pareto optimal front for a notional drive system of a 1.5 MW electrical propulsor with different motor types is generated and compared. An optimization algorithm coupled with an electromagnetic finite element analysis software tool was used to optimize the induction motor, switched reluctance motor, wound rotor synchronous motor, permanent magnet synchronous motor (PMSM), slotless PMSM, permanent-magnet-assisted synchronous reluctance motor, brushless DC motor, and brushless doubly fed reluctance motor types for efficiency and specific power. Overall advantages considering system-level efficiency, specific power, and a few other key metrics such as origin of losses, cooling complexity, manufacturing tolerance, and fault tolerance are discussed. This gives an indication of the relative performance of different motor types and confirms the overall advantage of PM motor topologies in aircraft propulsion.
Michael R. Natisin, Henry L. Zamora, Zachary A. Holley, N. Ivan Arnold, Will A. McGehee, Michael R. Holmes,
Journal of Propulsion and Power, Volume 37, pp 650-659; https://doi.org/10.2514/1.b38160

Abstract:
The overall propulsion efficiency for ion-mode electrospray thrusters has been predicted to be as high as 90%; however, experimental measurements currently fall far short of these predictions. Further complicating this is that for passively fed electrospray thrusters, the mass flow rate, which is required to obtain the propulsion efficiency and specific impulse, is not directly controlled or measured, and so this parameter is typically estimated by assuming all mass loss is due to the emitted ion current. Presented here is a detailed investigation into the efficiencies associated with a porous-media-based electrospray thruster operated in the purely ionic regime using the ionic-liquid propellant 1-ethyl-3-methylimidazolium tetrafluoroborate in both positive and negative ion emission modes. Measurements of performance metrics that affect thruster efficiency are discussed, including the transmission, angular, polydispersive, energy, and mass utilization efficiencies, in order to determine their impact on overall efficiency. The overall propulsion efficiency and specific impulse are also calculated using a variety of methods to better investigate how the assumptions made to estimate the mass flow rate affect these parameters. These results suggest that the efficiency of these devices may primarily be limited by the presence of additional mass loss mechanisms other than ion emission occurring during thruster operation.
V. I. Yazhini, Balusamy Kathiravan, T. M. Muruganandam,
Journal of Propulsion and Power, Volume 37, pp 780-791; https://doi.org/10.2514/1.b38217

Abstract:
Experiments have been carried out to investigate the effect of cowl length variation on performance characteristics of a single expansion ramp nozzle. The performance parameters were estimated for cowl lengths of 0, 25, 50, 75, and 100% with respect to the horizontal length of the ramp. Experiments were conducted for different nozzle pressure ratios ranging between 1.5 and 9. The wall static pressure distribution data were measured from the tests to estimate the various performance parameters, such as axial thrust, normal force, gross thrust, thrust vectoring angle, and coefficient of pitching moment. High-speed schlieren imaging was used to visualize the flow separation and shock patterns and to measure the jet width. The flow was separated from the ramp wall up to a nozzle pressure ratio of 3 for all cowl cases. The shorter cowl length delays the downstream movement of shock-induced boundary separation inside the nozzle as compared to the longer cowl. The cowl trailing-edge flow was more underexpanded than the ramp tip flow. As cowl length increases, the increased restriction results in higher axial thrust and also increases the normal force. The pitching moment and thrust vectoring were dominated by normal force. Overall, as the nozzle pressure ratio increases, the axial force and jet width increase, whereas the normal force and the pitching moment increase up to a certain level and then decrease. As the cowl length increases, the axial thrust, normal thrust, pitching moment, and thrust vector angle increase, while the jet width decreases.
Alexis J. Harroun, Stephen D. Heister, Joseph H. Ruf
Journal of Propulsion and Power, Volume 37, pp 660-673; https://doi.org/10.2514/1.b38244

Abstract:
A computational and experimental study was conducted on nozzle geometries for rocket application rotating detonation engines (RDEs). Three geometries, including a nozzleless blunt body typically employed in RDE combustor hot-fire testing and two aerospike nozzles, were investigated. Simulations of the exhaust flow of a rotating high-frequency, high-pressure ratio wave based on rocket RDE test results were related to comparable constant-pressure conditions. Computational and experimental results showed the high momentum added by the highest-pressure detonation products influences the exhaust plume differently than a comparable steady flowfield fed by the same average product gas flow rate. In particular, the RDE exhaust flow tended to enhance entrainment on the nozzleless blunt body recirculation region and delay flow separation on nozzle expansion surfaces due to overexpansion compared to a constant-pressure engine. Results have important ramifications for isolating RDE combustor performance from nozzle effects and must be considered for future design of nozzle geometries to exploit the high-frequency, high-pressure ratio outflow of an RDE.
Ewan Fonda-Marsland, Graham T. Roberts, Charles N. Ryan, David Gibbon
Journal of Propulsion and Power, Volume 37, pp 713-724; https://doi.org/10.2514/1.b38083

Abstract:
Experimental testing of a number of novel additively manufactured monopropellant microthrusters was conducted under atmospheric conditions using 87.5% concentration hydrogen peroxide. The aim of this work was to select a specific catalyst bed geometry for the thruster system and to investigate more general methodologies for monopropellant packed catalyst bed optimization. Characteristic velocity efficiencies approaching 0.98 were demonstrated, and performance improved for smaller beds with low aspect ratios; although, these beds flooded at lower propellant flow rates. The onset of bed flooding was used to identify physical limits of propellant flow rate supported by the catalyst. The particular propellant–catalyst pairing limit was defined by a Damköhler number of 56, independent of the bed geometry, with thermal performance peaking for the high flow rates just before flooding occurred. It is suggested that this method is extensible to other monopropellant systems, although with further work required to confirm it is a more general effect beyond thrusters using hydrogen peroxide.
Darren C. Tinker, Marsalis P. Pullen, Robin J. Osborne, Robert W. Pitz
Journal of Propulsion and Power, Volume 37, pp 748-758; https://doi.org/10.2514/1.b38303

Abstract:
Spark discharges were parametrically examined for a cylindrical air-gap electrode configuration. The aim of this study was to elucidate spark discharge characteristics, arc penetration, and exhaust plume development to guide designers of relevant ignition devices. Spark gaps ranged from 0.5 to 2.3 mm, nominal pressures ranged from 150 to 2200 kPa, and two exciter types (bipolar and unipolar) were tested. Positive correlations were observed between the pressure–distance product and multiple dependent variables: breakdown voltage, energy discharged, and percentage of sparks quenched. Positive correlations were observed between the pressure–distance quotient and various other dependent variables: spark duration, channel resistance, and plume velocity. This study also discusses the effects of quenching on electrical measurements, how these effects are nontrivial, and the subtle irregularities in electrical results that are indicative of quenching.
Yujun Leng, Nicole L. Key
Journal of Propulsion and Power, Volume 37, pp 682-692; https://doi.org/10.2514/1.b37765

Abstract:
A generalized flat plate cascade model is used in this study to predict the unsteady aerodynamics of a vibrating blade row with nonuniform blade spacing in subsonic compressible flow. The blade row is assumed to vibrate in an isolated family of blade-dominated modes. The effect of nonuniform blade spacing on compressor rotor flutter stability is demonstrated by case studies based on the geometric and flow conditions of a high-speed three-stage axial research compressor. The results show that nonuniform blade spacing can greatly alter the blades’ aerodynamic damping. At certain vibrational nodal diameters, some blades are destabilized so much that their aerodamping becomes negative. However, negative aerodamping of some blades do not necessarily lead to the instability of the whole blade row. A general multibladed system aeroelastic model is derived to study the effects of the nonuniform blade spacing on rotor stability through an eigenvalue approach. The aerodynamic influence coefficients matrix can be calculated using the generalized flat plate cascade model for a blade row with any user-specified blade spacing patterns. The case studies investigated in this paper show that alternating blade spacing and shifting only one blade position can slightly increase the stability of the least-stable eigenmode, whereas sinusoidal blade spacing has a slightly destabilizing effect. On the other hand, the eigenvectors of the least-stable mode for the nonuniformly spaced blade rows can be significantly different from the uniform blade spacing case.
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