Numerical Study of Radiation Effects on Polypropylene Combustion Using High-temperature Oxidizer Diluted with H₂O and CO₂

Abstract

Combustion of polypropylene (PP) in a high-temperature, low-oxygen oxidizer enriched with H₂O and CO₂ in stagnation-point flow was studied numerically to explore fundamental characteristics of polymer incineration under the condition of high-temperature air combustion (HiTAC). The detailed chemistry of propene as a decomposition gas was used for the calculation. Two typical gas radiation models, i.e., the optically thin model (OTM) and the statistical narrow-band (SNB) model, were employed to clarify the effect of gas radiation on PP combustion as well as the validity of the use of these models under HiTAC conditions because the H₂O and CO₂ included in the burnt gas recirculated in HiTAC furnaces are highly radiative species. Results showed that, under HiTAC conditions, calculations using OTM overpredicts regression rates compared with those using SNB, indicating that OTM is not suitable for use with polymer combustion under HiTAC conditions, while the differences of these gas radiation models were slight when ordinary air at high temperature was used as an oxidizer. It was also shown that when SNB was used, CO₂ enrichment in the oxidizer hardly enhanced the regression because CO₂ near the PP surface behaves as a barrier against the radiative heat flux. The most effective condition to increase the regression rate is to maintain a higher concentration of H₂O in the high-temperature oxidizer so as to enhance the gas radiation to the PP surface.