Experimental and Numerical Studies on Combustion Model Selection for Split Injection Spray Combustion 2015-01-0374

A wide variety of spray models and their associated sub-models exist to assist with numerical spray development studies in the many applicable areas viz., turbines, internal combustion engines etc. The accuracy of a simulation when compared to the experiments varies, as these models chosen are varied. Also, the computational grid plays a crucial role in model correctness; a grid-converged CFD study is more valuable and assists in proper validation at later stages. Of primary relevance to this paper are the combustion models for a grid-converged Lagrangian spray modeling scenario. CONVERGE CFD code is used for simulation of split injection diesel (n-heptane) sprays and a structured methodology, using RNG k-ε turbulence model, is followed to obtain a grid-converged solution for the key Computational Fluid Dynamics (CFD) parameters viz., grid size, injected parcels and spray break-up time constant. Four combustion models namely the SAGE model, the Representative Interactive Flamelet model, the 3-Zone Extended Coherent Flamelet model, and SHELL+Characteristic Time Combustion model will be examined using the grid-converged CFD settings and validation against experimental flame luminosity data will be conducted with soot (empirical Hiroyasu model) as a key validating parameter. The primary focus of this work is to select a suitable combustion model for split injection combusting sprays, which would not only exercise moderate runtimes but also keep intact the interaction physics and flame characteristics. This is achieved through analysis of flame characteristics like ignition delay, flame lift-off, flame penetration length, global structure of the flame and consequent validations with the experiments.