The role of smoldering in the ignition of Pinus palustris needles

The pyrolysis process and the critical ignition conditions of dead Pinus palustris needles were studied experimentally to understand the role of smoldering in the onset of flaming combustion. The results obtained show that methane (CH₄), carbon monoxide (CO), carbon dioxide (CO₂), and water vapor (H₂O) are the main constituents of the pyrolysis gases generated. The predominance of these compounds was found to be independent of the external heat flux, while their concentrations were sensitive to it. The heat of combustion of the pyrolysis gas and the pyrolysis reaction rate increased with increasing external heat fluxes. Visual observations and parameter measurements during testing hinted at the significance of smoldering to flaming ignition under forced flow conditions. The contribution of smoldering to flaming ignition was quantitively analyzed by combining the measured parameters during testing with the characterized pyrolysis process. The quantification results suggested a significant contribution of smoldering combustion to the flaming ignition under low heat fluxes and high airflow rate conditions.