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The development of a leanburn engine is described, in which optimized engine design, innovative engine management and exhaust gas aftertreatment using a special NOx-storage catalyst were combined to yield a significant improvement in fuel economy with reduced NOx emissions. To achieve stable combustion near the lean limit a swirl system was used and the appropriate parameters of the 2.2 I 4-cyIinder 4-valve SI engine were optimized. As a result, the mixture formation was improved and the lean limit was extended to higher air-fuel ratios. An adaptive lambda controller which was based on the evaluation of engine-smoothness calculated from the RPM-sensor was implemented to control each cylinder individually close to the lean limit. A model-based control system was developed to achieve extremely accurate air-fuel ratio control during transients.

The effect of fuel additives based on the alkali metals sodium and lithium on the regeneration behaviour of diesel particulate filters was studied. For this purpose the diesel fuel was doped with the lithium and sodium salts of an aliphatic alcohol. The efficiency of these additives was assessed by comparing it to ferrocene, which is, at present, the best studied additive for particulate filter regeneration. The additives were tested on an engine test bench under steady state conditions, on a transient dynamometer and finally in a real driving test. As a result of the addition of the alkali metal salts, the ignition temperature of the soot trapped in the particulate filter is considerably lower than the ignition temperature without additives. The results with the alkali metal additives are similar to those of ferrocene or other additives with transition metals like manganese or copper.