Chemical reactions during rapid quenching of oxygen‐nitrogen mixtures from very high temperatures

A model has been developed to study chemical reactions which occur in oxygen‐nitrogen mixtures during very rapid cooling in small‐diameter tubes. The system considers both homogeneous gas phase reactions and surface reactions based upon a simplified mass transfer mechanism. With an energy balance used to determine the rate of quenching, the mole fractions of nitrogen, oxygen, nitric oxide, atomic nitrogen, and atomic oxygen were calculated as a function of temperature. In these studies, air and an equimolal oxygen‐nitrogen mixture were cooled from temperatures which ranged between 3,000° and 7,000°K. The calculations showed that when the gases were cooled at rates exceeding ten million degrees per second, the species did not follow a chemical equilibrium path during the quenching process. In cooling from 4,000° to 7,000°K. the computations show that consideration of surface reactions predicts greater nitric oxide yields in the quenched gas than for homogeneous reactions alone. In fact, the heterogeneous reactions must contribute to the overall chemistry of quenching air. The composition of the quenched gas is strongly dependent upon the temperature‐time history of the gas in the probe and upon the composition of the hot gas before it is quenched.