Oxy-fuel based pulse detonation combined with a magnetohydrodynamic system (MHD) has the potential to improve efficiency of thermal power plants. The MHD system facilitates direct power extraction through a magnetohydrodynamic generator, working on Faraday's law of induction.  The power \\textit{(P)} extracted from MHD systems is proportional to the electrical conductivity of the fluid \\textit{(\$\\sigma\$)}, the square of the velocity of the flow \\textit{(V)} and the square of the magnetic field strength \\textit{(B)}

Prior research focus on using MHD systems for power extraction has involved usage of exhaust gases as working fluid from low speed combustion. However, an inherent challenge is that combustion gases must be accelerated to enable power extraction. On the other hand, pulsed detonations, which result in pressure gain combustion, release chemical energy at supersonic speeds. The high velocities of detonations (e.g. Ma \> 2) can enable greater extraction of power without the need for additional pressure drops to accelerate the working fluid. Another significant advantage is that the higher temperatures of detonation waves from oxy-combustion (T \> 3000K) can increase electrical conductivity of the working fluid resulting in higher power extraction by the MHD system When such an MHD system is used as a topping cycle unit in a combined-cycle power plant, the thermal efficiency of the plant can be expected to be close to 60%.

A space-time conservation element solution element (CE/SE) method is used to investigate the operational envelope of oxy-coal detonations with gaseous methane as a surrogate fuel. The CE/SE method results in a consistent multi-dimensional formulation for structured/unstructured meshes by providing flux conservation in space and time without the need for complex Riemann solvers to capture solution discontinuities. 

A modified revised Jones-Lindstedt (JL-R) reaction mechanism accounting for radicals such as O, OH, and H was used as a reduced mechanism to simulate detonation waves from \\ce{CH4-O2} combustion. The numerical scheme is first verified by comparing predictions with the ZND theory and other published data to show excellent agreement. For shock-induced detonation, the effect of driver shock temperature, pressure, stoichiometric ratio (\$\\phi\$) and initial driver shock length, on detonation initiation and propagation was investigated. The simulations accurately predicted detonation velocities, at various \$\\phi\$ values, compared with available experimental data. The results show that higher gas temperatures and velocities are achieved through oxy-detonations compared to air. The chosen reduced chemical kinetic mechanism, that accounts for radical disassociation, is found to be critical in appropriately limiting heat release during oxy-combustion, thereby predicting detonation temperature and velocity accurately. 


Numerical Investigation of High-Speed Oxy-Fuel Pulsed Detonation for Direct Power Extraction

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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