A Representative Interactive Linear Eddy Model

Licentiate thesis, 2015

To further improve the efficiency and emissions profiles of internal combustion engines, 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 the use of high levels of exhaust gas recirculation (EGR) in diesel engines. The typical combustion temperatures in all of these concepts are lower than those in traditional spark ignition or diesel engines. Most of the combustion models that are currently used in computational fluid dynamics (CFD) simulations were developed to describe either premixed or non-premixed combustion under the assumption of fast chemistry. The refinement of existing combustion concepts for highly efficient clean engines and the development of new ones would be greatly facilitated by the introduction of new computational tools and combustion models that are mode- and regime- independent, i.e. capable of modeling both premixed and non- premixed and also fast and non-fast chemistry. Such tools should enable more accurate simulation of combustion under non-standard conditions such as those established during low temperature combustion. This thesis presents a new regime-independent combustion modeling strategy for non-premixed combustion in which the linear eddy model (LEM) is used as a representative interactive regime-independent turbulent combustion model and coupled to a 3D CFD solver. Parameters and boundary conditions that determine the evolution of the LEM are supplied by the 3D CFD calculation and updated at each time step. The LEM is then solved for the corresponding time step, providing the 3D CFD code with an updated composition state.