Estimation of Air Motion Kinetic Energy Dissipation Rates in a D.I. Diesel Combustion System

This paper sets out to investigate the relationship between air-motion kinetic energy and mixing rates in D.I. diesel engines, without resort to computational fluid dynamics (CFD). Particular attention is focused on the rate at which bulk flow kinetic energy decays into turbulence.

A relatively simple phenomenological model of in-cylinder air motion is used. Turbulence production and decay associated with intake flows, with compression, with inward and outward squish, and with decay of swirl are considered. In the latter case, the effects of wall friction and of the “braking” or drag caused by radially-injected fuel sprays are considered.

The results of these calculations are compared with heat release rates derived from experimental cylinder pressure data, and provide some modest theoretical support for a novel interpretation of the observed trends.