Comparison of pyrolysis of live wildland fuels heated by radiation vs. convection

During wildland fires, which include both planned (prescribed fire) and unplanned (wildfire) fires, live and dead plants may be subject to both radiative and convective heat transfer mechanisms. In this study, the pyrolysis of 14 live plant species native to the forests of the southern United States was investigated using a flat-flame burner (FFB) apparatus under three heating modes in order to mimic pyrolysis of plants during wildland fires. The heating modes were: (1) radiation-only, where the plants were pyrolyzed under a moderate heating rate of 4 degrees C s(-1) (radiative flux of 50 kW m(-2)); (2) convection-only, where the FFB apparatus was operated at a high heating rate of 180 degrees C s(-1) (convective heat flux of 100 kW m(-2)); and (3) a combination of convection and radiation, where the plants were exposed to both convective and radiative heat transfer mechanisms. Data were also compared with slow heating experiments (0.5 degrees C s(-1)). During the experiments, the pyrolysis products were collected and analyzed using GC-MS for the analysis of tars and GC-TCD for the analysis of light gases. The results indicate that the highest light gas and tar yields were obtained from the combined mode, which was performed at a higher pyrolysis temperature and heating rate. CO, CO2, CH4, and H-2 were the major light gas species in all three heating modes. The radiation-only mode led to formation of primary tars and a few secondary tars consisting of aliphatic and 1-2 ring aromatic compounds with 1 to 3 attachments, including alkyl, hydroxyl, and methoxy groups.