Influence of size and temperature on the auto-ignition characteristics of solid beech and spruce wood

The influence of size and temperature on the heating and auto-ignition of beech (fagus sylvatica) and spruce (picea abies) wood cubes were studied. Experiments were conducted in a furnace at five isothermal temperatures (240 degrees C, 270 degrees C, 300 degrees C, 330 degrees C and 360 degrees C) with four cube sizes (5 mm, 10 mm, 15 mm and 20 mm). Tem-peratures inside the cubes were recorded with thermocouples (TC). Arising temperatures from the experiments were compared to mass-losses and exothermic reactions measured with simultaneous thermal analysis (STA). While heating up isothermal phases at approx. 360 degrees C can be seen in the temperature curves due to ongoing pyrolysis. After pyrolysis, a combination of internal heating and heterogenous oxidation reactions on the surface lead to ignition and combustion. Differences in chemical composition between beech and spruce are the cause for exothermic reactions at lower temperatures. Bigger samples tend to ignite at lower temperatures due to lower surface to volume ratio and a larger reactive surface.