A computational study of burning of vertically oriented leaves with various fuel moisture contents by upward convective heating. (15th September 2020)

• Record Type: Journal Article
• Authors: Borujerdi, Peyman Rahimi; Shotorban, Babak; Mahalingam, Shankar
• Is Part Of: Fuel. Volume 276(2020)
• Publication Date: 2020-09-15
• Subjects: Pyrolysis -- Combustion -- Moisture content -- Convection -- Live fuel; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2020.118030
• Languages: English
• ISSNs: 0016-2361

Abstract

Abstract: Pyrolysis and combustion of a solid fuel representing a vertically oriented leaf of manzanita (Arctostaphylos glandulosa) were computationally investigated. Various fuel moisture content (FMC) values corresponding to four manzanita leaf treatments studied experimentally by others, were considered. The fuel was exposed to an upward stream of hot gases in a computational configuration resembling the experimental setup where leaves were burned. Time evolution of the normalized mass of the leaves was used to validate the simulations against the experimental data. Examining the time history of heat release rate confirmed that increasing FMC delays ignition time. The ignition times in simulations were in good agreement with those determined by empirical correlations for all FMCs. The burnout times were somewhat shorter in simulations than the empirically-determined ones. Simulations showed that thermal, momentum and concentration boundary layers are formed on the leaf faces. The boundary layers played a significant role in heating, and subsequent moisture evaporation and pyrolysis of the leaves. Within the leaves, an evaporation front propagating inward from the edges, was detected. A considerable amount of liquid moisture remained in the leaf after ignition. Accumulation of water and fuel vapor around the leaf, as a consequence of the leaf moisture evaporation and pyrolysis, displaced oxygen, decreasing the oxygen concentration therein. A post ignition time was characterized by a high temperature zone around the leaf. At such times, oxygen consumption by gas phase combustion resulted in a noticeable decrease in oxygen concentration around the leaf. The flaming pattern after ignition was qualitatively in agreement with previously reported experimental observations.