Particulate and gaseous emissions during combustion of wood pellets under high heating rates in a drop tube furnace

To better understand pollutant formation during wood pellet combustion under conditions representative of domestic stoves and industrial boilers, single-pellet experiments were carried out in a drop tube furnace operated at high heating rates (400-900 °C s −1 ). A commercial wood pellet was dropped into the furnace preheated between 400 and 900 °C. Time-resolved gaseous emissions (CO, CO 2 , O 2 ) and particulate emissions (PM 0.1 to PM 2.5 ) were continuously monitored using gas analyzers and an Electrical Low-Pressure Impactor (ELPI), respectively. Two combustion regimes were identified. At 400 °C, no visible flame developed and combustion mainly proceeded through glowing oxidation, leading to low O 2 depletion and high particulate emissions. Above 500 °C, the appearance of a transient flame significantly enhanced oxidation, resulting in higher CO 2 production, stronger O 2 depletion and improved combustion efficiency. PM 2.5 emissions decreased drastically with increasing temperature and became extremely low above 700 °C. An empirical exponential correlation was established to describe PM 2.5 concentrations as a function of furnace temperature, providing a quantitative basis for temperature-drive mitigation strategies. Regardless of temperature, particle number emissions were dominated by ultrafine PM 0.1 , with aerodynamic geometric mean diameters between 25 and 40 nm, indicating nucleation-driven formation. Overall, coupling real-time gas and particle measurements enable stage-resolved interpretation of devolatilization and char oxidation under high heating rates and highlights the strong benefit of high-temperature operation to reduce particulate emissions from pellet combustion.