Journal of Propulsion and Power最新文献

The performance of a magnetically shielded Hall thruster operating on xenon and krypton is characterized at discharge current densities up to 10 times greater than its nominal level. A thrust stand and far-field probe suite are employed to evaluate operation at 300 V discharge voltage and discharge currents from 15 to 125 A (xenon) and from 15 to 150 A (krypton). The thrust, specific impulse, and anode efficiency at the highest currents are found to be $1650\pm 30\mathrm{mN}$, $2309\pm 56\mathrm{s}$, and $52.8\pm 2.0\%$ respectively for xenon, and $1839\pm 18\mathrm{mN}$, $2567\pm 48\mathrm{s}$, and $55.0\pm 1.6\%$ for krypton. The thrust density at the highest conditions are shown to be six (xenon) and eight (krypton) times higher than the lowest current condition. A maximum in anode efficiency as a function of discharge current is observed for both gases. This is attributed to a trade between mass utilization, which increases to unity with current, and beam utilization, which gradually decreases with current. The dependence of these efficiency modes on current is discussed in the context of a series of first-principles scaling laws. The observation that efficiency only moderately decreases with current density is examined in the context of high-power electric propulsion development.

This paper describes an experimental study investigating unsteady combustion regimes in a kerosene-fueled scramjet. The results are obtained under inflow conditions of a 2.9 MPa stagnation pressure, 1900 K stagnation temperature, and a Mach number of 3.0. The air throttling position is 240 mm downstream of the combustor entrance, with an air throttling flow rate (ratio of air throttling mass flux to inflow mass flux) of 38% and a fuel equivalence ratio of 0.37. Combustion is relatively stable when air throttling is applied and is dominated by auto-ignition. When air throttling is turned off, the combustion becomes more unsteady and is dominated by flame propagation. At the same time, the combustion mode changes, and the frequency of the combustion mode transition is 286 Hz. Schlieren images and one-dimension analysis show that the effect of air throttling is the coupling of cold throat (aerodynamic throat) and hot throat (thermal throat). The proper orthogonal decomposition and dynamic mode decomposition analysis present that when air throttling is applied or removed, the frequencies of injector–flame feedback are almost the same, while the frequencies of shock–flame feedback exhibit considerable variation, which is caused by the location of the precombustion shock affected by air throttling.

In this work, we carry out three-dimensional mesoscale simulations of heterogeneous solid propellant combustion. We solve the reactive low-Mach-number equations in the gas phase with complete coupling to the solid phase. The model takes into account thermal expansion and deformation in the solid phase by using a hypoelastic law in the quasi-static limit. To account for morphology, we select two different propellant formulations with different particle size distributions and present the results as a function of pressure. The thermomechanical behavior is accessed by examining quantities such as strain and stress in the propellant as a function of pressure and propellant morphology. We also show that temperature and velocity fluctuations exist in the far field above the propellant surface and that these fluctuations can be significant. To better understand the nature of these fluctuations, we vary the pressure and make relevant plots of normal velocity and temperature probability density functions, as well as time autocorrelations. Such descriptions are necessary to account for the coupling between the mesoscale and the macroscale, where the fluctuations at the mesoscale can affect quantities at the macroscale, such as head-end pressure, trigger parietal vortex shedding, and aeroacoustics.

Hydrogen (${\mathrm{H}}_2$) combustion and solid oxide fuel cells (SOFCs) can potentially reduce aviation-produced greenhouse gas emissions compared to kerosene propulsion. This paper outlines a methodology for evaluating performance and emission tradeoffs when retrofitting conventional kerosene-powered aircraft with lower-emission ${\mathrm{H}}_2$ combustion and SOFC hybrid alternatives. The proposed framework presents a constant-range approach for designing liquid hydrogen fuel tanks, considering insulation, sizing, center of gravity, and power constraints. A lifecycle assessment evaluates greenhouse gas emissions and contrail formation effects for carbon footprint mitigation, while a cost analysis examines retrofit implementation consequences. A Cessna Citation 560XLS+ case study shows a 5% mass decrease for ${\mathrm{H}}_2$ combustion and a 0.4% mass decrease for the SOFC hybrid, at the tradeoff of removing three passengers. The lifecycle analysis of green hydrogen in aviation reveals a significant reduction in ${\mathrm{CO}}_2$ emissions for ${\mathrm{H}}_2$ combustion and SOFC systems, except for natural-gas-produced ${\mathrm{H}}_2$ combustion, when compared to Jet-A fuel. However, this environmental benefit is contrasted by an increase in fuel cost per passenger-km for green ${\mathrm{H}}_2$ combustion and a rise for natural-gas-produced ${\mathrm{H}}_2$ SOFC compared to kerosene. The results suggest that retrofitting aircraft with alternative fuels could lower carbon emissions, noting the economic and passenger capacity tradeoffs.