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Previous experiments using an air-assisted spray in a two-stroke direct-injected engine demonstrated a significant improvement in combustion stability at part-load conditions when a wide injection spray was used. It was hypothesized that the decrease in variability was due to the spray following the combustion chamber wall, making it less affected by variations in the in-cylinder gas flows. For this study, experiments were conducted to investigate engine spray combustion for cases where engine performance was not dominated by cyclic variation. Combustion and emission performance data was collected for a wide range of injection timings at several speed/load conditions. Experimental data for combustion shows that combustion stability is relatively unaffected by injection timing changes over a 40 to 100 degree window, and tolerant to spark gap projections over a range of 0.7 to 5.2 mm, depending on operating conditions.

Ceria has become an increasingly important component in automotive exhaust catalysts over the past decade. Recently, with the proposal that measurements of oxygen storage be used for the on-board evaluation of catalyst performance for both low emission vehicles (LEV) and non-LEV vehicles, understanding the role of ceria and its deterioration with catalyst aging has become even more important. It is well established that ceria in an alumina support promotes oxygen storage/release by automotive catalysts under cycled air/fuel conditions, which in turn promotes the catalyst's conversion performance under those conditions. Another benefit of ceria is its enhancement of the catalytic activity for other reactions, such as the water-gas shift reaction under rich conditions. In addition, ceria may help catalyst durability by promoting precious metal dispersion and playing some role as a stabilizer of the support.