Investigation of Systematic Discrepancies Between MCC and TGA Measurements Affecting the Determination of Heat of Combustion

The determination of step‐resolved effective heats of combustion is essential for detailed pyrolysis modelling in fire growth and flame spread predictions, especially in multi‐step processes where the heat of combustion can differ between reaction steps. Typically, the effective heat of combustion is determined from the ratio of heat release rate to mass loss rate, measured for example by microscale combustion calorimetry (MCC) and thermogravimetric analysis (TGA). However, reliable determination requires precise agreement between the experimental boundary conditions of both methods, a requirement systematically compromised by inherent deviations in MCC measurements compared to TGA. The literature attributes this limitation to various causes, yet a comprehensive investigation of their origins and combined impact has been absent. A systematic investigation reveals several key causes of these discrepancies. Non‐constant heating rates in MCC render mass loss and heat release events below 170°C invalid for analysis. A temperature gradient within the pyrolysis chamber, revealed through dedicated measurements using an additional thermocouple inserted into the pyrolyser, induces temperature shifts and apparent heating rate deviations. Additionally, baseline correction problems arise at low initial sample masses when using an electrochemical oxygen sensor, which is often implemented in MCC devices. Based on these findings, compensation strategies are developed, evaluated and assessed with respect to their consequences on the resulting effective heat of combustion.