The Distribution Pattern of Pyrolysis Products from Thermally Thick PMMA under Constant Thermal Radiation in a Cross Forced Airflow

With the ever-expanding applications of polymers, the issue of polymer fires has garnered increasing attention in academic circles. Compared to the situation in a static air environment, the ignition of polymers in airflow presents a more complex scenario, based on the fact that different air flow velocities alter the accumulation of pyrolysis products of the polymers in space. This study addresses the impact of airflow on PMMA (poly-(methyl methacrylate)) pyrolysis under constant heat flux through experimental, analytical, and numerical methods. Measurements of gas temperature, mass flux, and ignition delay time were performed to evaluate the influence of airflow and heat flux. The findings reveal a dynamic relationship between heat flux and airflow velocity: Increased heat flux enhances pyrolysis gas production, while higher airflow velocity enhances the transport capacity of pyrolysis gas. When gas production lags behind transport capacity, gas phase temperature remains uniform; exceeding transport capacity leads to local high temperature. This phenomenon impacts ignition delay time: At low airflow velocity, the shortest ignition delay time (approximately 0.44 times the maximum value) occurs at the sample's rear edge, whereas at high airflow velocity, it shifts to the sample's center. A condensed phase analytical model and a gas phase numerical model were developed. The distribution trend of the pyrolysis gas was computed using this model. The result validated the conclusion drawn from the measured gas phase temperature. The proposed analytical-numerical model helps to reduce the complexity of the calculation, compared to the traditional solid-gas numerical model. The research results are helpful for predicting the polymer ignition situation under air flow.