The innovation proposed here is a high-performance, high-fidelity simulation capability for simulating liquid rocket spray combustion based on a novel spray-flamelet methodology which will be integrated into Loci-STREAM which is a CFD solver developed by the proposing personnel under funding from NASA over the last several years. A new spray-flamelet formulation will be incorporated into Loci-STREAM. The particular advantages of this formulation are (i) its consistency with the single-phase flamelet-formulation (already available in Loci-STREAM), (ii) its formulation in mixture-fraction space, overcoming the non-uniqueness of the classical mixture-fraction parameterization, and (iii) its applicability to finite Stokes-number, thereby accounting for particle evaporation, slip-velocity, and poly-dispersed spray-phase. The flamelet methodology already available in Loci-STREAM in conjunction with Hybrid RANS-LES (HRLES) methodology has facilitated an order of magnitude improvement in simulation turnaround times for NASA applications involving complex physics in 3D geometries. This project is aimed at extending this flamelet methodology to spray combustion resulting in a state-of-the-art design and analysis tool to enable accurate, fast and robust simulations of multiphase combustion in liquid rocket engines (involving liquid propellants such as LOX and LH2/LCH4/RP-1/RP-2), combustion stability analysis, etc. which constitute critical components of NASA's upper stage launch propulsion systems.