Two-stroke, spark ignited, direct-injection combustion differs from conventional premixed spark ignited combustion in that the cylinder contents are intended to be stratified in mixture composition. To try to understand the sources of emissions with this combustion system, separate models were created to examine unburned hydrocarbon emissions and NOx emissions. Hydrocarbon emissions mechanisms identified and modeled are primarily non-burning zone effects. The purpose of the hydrocarbon model was to provide a representation of the influence of known emissions mechanisms, and highlight the experimental results, which could not be accounted for by these mechanisms. The mechanisms included were short-circuiting, over-mixing of fuel and air, misfire and poor combustion, and stray pre- and post-main-injection spray droplets. An empirical equation was created based on the physical mechanisms and, when refined, represented most of the effects seen in the experimental data.
展开▼
