Effects of the intake air oxygen enrichment (IOE) on the combustion processes and performance of a spark ignition (SI) engine were investigated when the engine was operated under part load conditions both after and during the warm-up period.
The study was performed by comparing the direct measurements of engine performance and emission characteristics with instantaneous digital imaging of in-cylinder reaction processes obtained using our high-speed dual-spectra infrared imaging system developed at Rutgers.
The IOE under the partial load operations of an SI engine produced some comparable improvements in the thermal efficiency and mean effective pressure to those from the full load operations. Although no dramatic reduction of unburned hydrocarbon emissions with the IOE was realized in the present measurement, the insignificant increase of Nox under the same condition is noteworthy.
On the other hand, the reduction of emission and increase in performance by the IOE during the warm up period were as comparably significant as those observed in the full throttle open operations.
The high-speed in-cylinder IR imaging obtained under corresponding conditions exhibits some consistency with the above findings. The instantaneous successive digital IR images did not show an obvious difference between those obtained with and without the IOE in the partial load experiment There was observable difference, however, in the results during the warm-up period: with the IOE, the combustion started earlier and burned stronger, which was followed by a shorter combustion period.