Aluminum combustion in strong convective flows

This paper addresses the behavior of aluminum combustion in high speed flows, typical of choked noz-zles or behind detonation fronts. Numerical simulations are conducted on a single burning droplet with Reynolds numbers Red up to several hundreds. The combustion mass rate is found to increase with Red and is well described by the classical Ranz-Marshall correlation but only provided that Red is estimated at flame conditions. The exponent n , relating combustion time and droplet diameter (tb proportional to dn), is found to decrease from n = 2 at quiescent conditions to n approximate to 1 for the highest Red. This is indicative of a transition from diffusion-limited to kinetic-limited combustion regimes. A Damkohler number Da*-that depends on pressure, oxidizer content, droplet size, and Reynolds number-is proposed and allows to delineate this diffusion/kinetic regime through a unique master curve n = n(Da*). A correction on the burning time accounting for this change of combustion regime is also proposed and depends only on Da*. This work unequivocally confirms the existence of a flow-induced transitional regime for aluminum combustion that has significant implication in the burning time of aluminum droplets in strong convective flows.(c) 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

This paper investigates the behavior of aluminum combustion in high-speed flows and identifies a transition from diffusion-limited to kinetic-limited combustion regimes. The combustion mass rate increases with Reynolds number Red and is accurately described by the Ranz-Marshall correlation when Red is estimated at flame conditions. A Damkohler number Da* is proposed to characterize this diffusion/kinetic regime, and a correction on the burning time is suggested based on Da*. This study confirms the existence of a flow-induced transitional regime for aluminum combustion with significant implications for the burning time of aluminum droplets in strong convective flows.