Quantifying downstream proximity effects on the thermal and combustion dynamics of cellulosic leaves in a convective flow

Abstract

This study investigates how the dynamics of drying process, pyrolysis and combustion behaviour of a cellulosic leaf in a hot convective flow is influenced by the presence of a secondary leaf located downstream of the heat flow. The influence of the secondary leaf is introduced as the Downstream Proximity Effect (DPE) in this work.

Specifically, the research examines the drying progression, pyrolysis dynamics, flame formation, and thermal behaviour of an idealized moisturized leaf subjected to a convective heat source, with and without another leaf behind the primary leaf (downstream of the flow), at varying distances. Four separation distances of 5, 10, 15, and 20 mm are assessed under two fuel moisture contents (FMC) levels of 4 % and 34 %. Simulations are conducted using FireFOAM with a Large Eddy Simulation (LES) approach, comparing isolated single-leaf scenarios with those involving the downstream proximity effect. Results show that smaller separation distances (closer downstream proximity) restrain the rate of thermal processes due to limited heat transfer, highlighting the importance of spatial configuration on combustion behaviour and the thermal interference caused by downstream proximity. In contrast, the single-leaf scenario shows the fastest drying and highest pyrolysis rates. The dimensionless Downstream Proximity Effect (DPE) number is proposed to quantify the impact of downstream proximity on different thermal processes, enabling systematic comparisons across varying configurations. This research provides novel insights into the interplay between spatial configuration, pyrolysis dynamics, and fluid-thermal processes.