Combustion modeling in heavy-duty diesels

A focus on the development of a CFD methodology for combustion simulations took two different approaches to model flame propagation, both of which employed detailed chemistry and turbulence chemistry interaction. The first, MRIF, assumed that diesel spray combustion can be represented by a set of laminar diffusion flames, while in the second model the flame structure is described by multiple homogeneous reactors with turbulence-chemistry interaction.

Diesel engines have found their way into most heavy-duty applications in the stationary, construction, industrial, and agriculture industries. They have a high power density and can easily operate on a large range of speeds and loads. However, to meet new emissions standards and reduce fuel consumption, continuous R&D is needed in different areas including combustion, engine turbocharging/downsizing, and aftertreatment systems.

The combustion process will continue to play a central role since it affects both cycle efficiency and the quality of exhaust gases that are later cleaned up by the aftertreatment systems. To this end, both advanced numerical and experimental tools are necessary to investigate how the flame propagates under conventional, advanced combustion modes and at full load conditions when cylinder and injection pressures are very high and a strong interaction between flame and walls is expected. For what concerns numerical models, it is now widely accepted that complex chemistry should be included for a proper prediction of auto-ignition, flame structure evolution, soot, and NOx emissions formation.