The influence of oxygen concentration on the combustion of a fuel/oxidizer mixture

The aim of the present study is to investigate the influence of the O2 concentration on the combustion behaviour of a fuel/oxidizer mixture. The material tested is a ternary mixture of lactose, starch, and potassium nitrate, which has already been used in an attempt to estimate heat release rate using the FM-Global Fire Propagation Apparatus. It provides a well-controlled combustion chamber to study the evolution of the combustion products when varying the O2 concentration, between air and low oxidizer conditions. Different chemical behaviours have been exhibited. When the O2 concentration was reduced beyond 18%, large variations were observed in the CO2 and CO concentrations. This critical O2 concentration seems to be the limit before which the material only uses its own oxidizer to react. On the other hand, mass loss did not highlight this change in chemical reactions and remained similar whatever the test conditions. This presumes that the oxidation of CO into CO2 are due to reactions occurring in the gas phase especially for large O2 concentrations. This actual behaviour can be verified using a simplified flammability limit model adapted for the current work. Finally, a sensitivity analysis has been carried out to underline the influence of CO concentration in the evaluation of heat release rate using typical calorimetric methods. The results of this study provide a critical basis for the investigation of the combustion of a fuel/oxidizer mixture and for the validation of future numerical models