Premixed charge compression ignition (PCCI) is an interesting
alternative to conventional diesel combustion, as it allows very
low emission levels for part load operation. The difficult control
of the onset of combustion is an obstacle to the implementation of
PCCI. In a recent study, different mixtures of gasoline and diesel
fuel have been used in a modified diesel engine to delay the
ignition and thus to allow for a substantial premixing time. For
these cases, very low levels of particulate emissions have been
reported. However, the emissions of CO and NOx were
considerably high.
In this study, combustion and pollutant formation in the
above-mentioned modified diesel engine are simulated using the
representative interactive flamelet (RIF) approach. A detailed
chemical reaction mechanism for a mixture of n-heptane, iso-octane,
toluene, and ethanol, serving as surrogate fuel for the
diesel-gasoline blend, is used for the simulations. By systematic
comparison of experimental and numerical results, an improved
understanding of PCCI combustion is achieved and the origins of the
CO and NOx emissions are identified. Finally, measures
to reduce these emissions while keeping the low PM levels are
suggested.