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Droplet size measurements were performed on the spray from a pintle-type gasoline injector. These quantified the influence of the fuel properties, relative fuel/air velocity and manifold air density upon the droplet sizes. Dimensional analysis and knowledge of the atomization process was used to derive equations predicting mean droplet diameters. Constants and exponents used in these equations were evaluated by correlation with the measured data. The equations were used to predict the individual or combined influence of the above variables. It is concluded that the influence of variations in properties between production gasolines on atomization is likely to be small.

The effects of catalyst and fuel formulation changes were investigated on vehicles meeting European Stage II (94/12/EC) emission limits when tested over the modified European test cycle. The OEM standard Pt/Rh catalyst formulation was compared with advanced Pd/Rh catalysts, at nominally the same PGM cost, and with Pd/Rh catalysts at increased PGM loadings. No other changes were made to the vehicles. The largest relative emissions benefits for the advanced Pd/Rh catalysts at equivalent PGM cost were 28% for THC, 30% for CO and 22% for NOx. Pd/Rh catalysts with higher PGM loadings gave further improvements in emissions, with total reductions of 38% for THC, 40% for CO and 31% for NOx compared to the standard OEM catalyst. In addition, one of the vehicles was tested with a Pt/Pd/Rh catalyst formulation. The performance of this catalyst was comparable with the Pd/Rh catalyst at similar PGM loading.