The Legion version runs inside of the original Fortran+message passing interface version, offloading the main simulation loop but using the existing Fortran code for everything else. The S3D-Legion code was used to simulate two separate scientific problems that are described below. The first scientific problem was the simulation of reactivity controlled compression ignition that was performed using all periodic boundaries and therefore did not require any special boundary condition (BC). The second scientific problem simulated using the S3D-Legion is the temporal evolution of a nonpremixed jet mixing layer, which required the application of outflow BCs and nonuniform mesh spacing through algebraic stretching. Singe takes as input a standard description of a chemical mechanism along with tables describing the transport and thermodynamic properties of chemical species. Legion isolates the specification of a program in the form of tasks and logical regions from how mapping decisions are made through the mapping interface.