Comparison of a Representative Linear Eddy Model with a Representative Interactive Flamelet Model for Spray Combustion Processes

Paper in proceeding, 2015

To further improve engines in terms of both efficiency and emissions many new combustion concepts are currently being investigated. Examples include homogeneous charge compression ignition (HCCI), stratified charge compression ignition (SCCI), lean stratified premixed combustion, and high levels of exhaust gas recirculation (EGR) in diesel engines. All of these combustion concepts have in common that the typical combustion temperatures are lower than in traditional spark ignition or diesel engines. To further improve and develop combustion concepts for clean and highly efficient engines, it is necessary to develop new computational tools that can be used to describe and optimize processes in nonstandard conditions, such as low temperature combustion. Thus, in the presented study a recently developed model (RILEM: Representative Interactive Linear Eddy Model) for modeling non-premixed combustion, regime-independently, was used to simulate a spray combustion process. RILEM consists of a single representative linear eddy model (LEM) coupled to a 3D CFD solver. All fluid dynamics and scalar field equations are solved in the CFD code, while the turbulent combustion is solved simultaneously in a separate, representative one-dimensional LEM. Parameters and boundary conditions that determine the evolution of the LEM are supplied from the 3D calculation at each time step. The LEM code is then solved for the same time step, providing the 3D CFD code with an update of the composition state. In addition to the modelling strategy, a numerical simulation of a n-heptane spray is presented here. The RILEM output is also compared to calculations for the same case by the RIF (representative interactive flamelet) model.