Profiles of the Power Density and Other Properties of Hydrogen Magnetohydrodynamic Generators at Conditions

TL;DR

This study explores the electric conductivity and power density of hydrogen-based magnetohydrodynamic generators under various conditions, highlighting potential for high power output at low pressures with cesium seeding.

Contribution

It provides a quantitative analysis of power density in hydrogen MHD generators, identifying optimal conditions for maximum output and comparing seed and oxidizer types.

Findings

Power density can exceed 1000 MW/m3 at 0.1 atm with cesium seeding.

Cesium as seed material yields higher power density than potassium.

Lowering pressure to about 0.1 atm enhances power output significantly.

Abstract

Hydrogen and some of its derivatives (such as e-methanol, e-methane, and e-ammonia) are promising energy carriers that have the potential to replace conventional fuels, thereby eliminating their harmful environmental impacts. An innovative use of hydrogen as a zero-emission fuel is forming weakly ionized plasma by seeding the combustion products of hydrogen with a small amount of an alkali metal vapor (cesium or potassium). This formed plasma can be used as a working fluid in supersonic open-cycle magnetohydrodynamic (OCMHD) power generators. In these OCMHD generators, direct-current (DC) electricity is generated straightforwardly without rotary turbogenerators. In the current study, we quantitatively and qualitatively explore the levels of electric conductivity and the resultant volumetric electric output power density in a typical OCMHD supersonic channel, where thermal equilibrium plasma is accelerated at a Mach number of two (Mach 2) while being subject to a strong applied magnetic field (applied magnetic-field flux density) of five teslas (5 T), and a temperature of 2300 K (2026.85 {\deg}C). We varied the total pressure of the pre-ionization seeded gas mixture between 1/16 atm and 16 atm. We also varied the seed level between 0.0625% and 16% (pre-ionization mole fraction). We also varied the seed type between cesium and potassium. We also varied the oxidizer type between air (oxygen-nitrogen mixture, 21-79% by mole) and pure oxygen. Our results suggest that the ideal power density can reach exceptional levels beyond 1000 MW/m3 (or 1 kW/cm3) provided that the total absolute pressure can be reduced to about 0.1 atm only and cesium is used for seeding rather than potassium.