The frequency of pairwise molecular collisions in supercritical states

The frequency of pairwise molecular collisions in supercritical states was studied using conventional molecular dynamic method. Two relevant systems were considered including both argon and n-octane that covers a wide range of thermodynamic states. We found that the local clustering phenomenon can introduce local fluctuation and lead to a higher collision frequency, and the gain in collision frequency can be as large as a factor of 3 for both supercritical argon and octane. Our finding indicates that the collision frequency is not homogeneous within a supercritical state owing to the clustering phenomenon, and this questions the application of the state-of-art numerical approaches in combustion that are built from the assumption of homogeneous systems.