Impact of Radiative Losses on Flame Acceleration and Deflagration to Detonation Transition of Lean Hydrogen-Air Mixtures in a Macro-Channel with Obstacles

Abstract

While there has been some recognition regarding the impact of thermal boundary conditions (adiabatic versus isothermal) on premixed flame propagation mechanisms in micro-channels (hydraulic diameters <10 mm), their impact in macro-channels has often been overlooked due to small surface-area-to-volume ratios of the propagating combustion wave. Further, the impact of radiative losses has also been neglected due to its anticipated insignificance based on scaling analysis and the high computational cost associated with resolving it’s spatial, temporal, directional, and wavelength dependencies. However, when channel conditions promote flame acceleration and deflagration-to-detonation transitions (DDT), large pressures are encountered in the vicinity of the combustion wave, thereby increasing the magnitude of radiative losses which in turn can impact the strength and velocity of the combustion wave. This is demonstrated for the first time through simulations of lean (equivalence ratio: 0.5) hydrogen-air mixtures in a macro-channel (hydraulic diameter: 174 mm) with obstacles (Blockage ratio: 0.51). By employing Planck mean absorption coefficients in conjunction with the P-1 radiation model, radiative losses are shown to affect the run-up distances to DDT in a long channel (length: 11.878 m). As anticipated, the differences in run-up distances resulting from radiative losses only increased with system pressure.

Effect of Obstacle Gradient on the Deflagration Characteristics of Hydrogen/Air Premixed Flame in a Closed Chamber

“…The explosion of premixed gas is essentially a rapid chemical reaction process, so the following basic assumptions are made in this study [21,30]:…”

A Review on Microchannel Fabrication Methods and Applications in Large-Scale and Prospective Industries

“…To maintain the flow rate, velocity, pressure, dosing precision, material selection, ease of fabrication, fabrication technique, reliability, and durability at the lowest scale in microfluidic devices, the parameters must be precisely met. Other important factors, however, include low manufacturing costs, biocompatibility, the right channel type for a given application, the right length and diameter of the channel, flow pattern, flow boiling characteristics, and heat transfer characteristics 62,410) . Before applying a specific fabrication or design principle, experimental analysis at the prototype level or simulation with an in-house or commercial solver or analyzer is required.…”