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Analysis of non-legislated engine-emission components, with different exhaust-gas after-treatment techniques, is an important air quality objective. This paper reports the results for various nitrogen oxides, ammonia and differentiated hydrocarbons emitted at part load from a small 4-S SI engine. It was operated with gasoline, with CNG and with two different three-way catalytic converters. CNG produces less HC and less aromatics. But the HC conversion rate is insufficient. This is due to the lower exhaust gas temperatures, at part load with CNG, and due to the higher stability of light HCs. CNG affects the λ-regulation window, of the investigated system, such that the NOx conversion rate is lowered. In the rich domain of the λ-regulation window, the NO & NOx emissions after catalyst were lowest, while the NH₃ formation was most intense, and vice versa.

In this study, the combustion of butanol, neat and mixed with gasoline, was investigated on a 0.6 liter two-cylinder spark ignition engine with fully adjustable fuel injection and spark timing, coupled with an eddy current dynamometer. Two isomers of butanol, n-butanol and iso-butanol, were examined. This basic parameter study gives information about potential requirements of engine control systems for butanol FFV. Compared to the traditionally used ethanol, butanol does not exhibit hygroscopic behaviour, is chemically less aggressive and has higher energy density. On other hand, different laminar burning velocity and higher boiling temperature of butanol, compared to gasoline, requires some countermeasures to keep the engine operation reliable and efficient.