Browse Publications Technical Papers 2000-01-1846

Regulated and Unregulated Emissions Reduction with Retrofit Catalytic After-Treatment on Small Two Stroke S.I. Engine 2000-01-1846

The contribution to environmental pollution due to mopeds and motorcycles equipped with 2-stroke engines is very high. Then European regulations will impose in the next future severe limits on pollutant emissions of such vehicles. Up to 40% of the charge at high load and low speed can be lost during scavenging, therefore exhaust hydrocarbon speciation is similar to fuel composition, i.e. with a comparable content of benzene. The use of rich air-fuel mixtures, necessary to reduce cyclic variations and improve driveability during transients, determines also high carbon monoxide emissions. On the other hand NOx emissions are very low in all operating conditions, due to the rich mixtures and the high residual gas fraction.
An effective solution to reduce emissions from current two-stroke engines for two wheelers in a short time could be retrofitting circulating vehicles with a catalyst for exhaust after-treatment. In fact the technology of catalyst for internal combustion engine exhaust after-treatment is consolidated and, in case of two-stroke engines, a very accurate air-fuel ratio control is not necessary, being a partial CO and HC conversion possible also with rich mixtures because of the presence of oxygen in the exhaust coming from scavenging losses.
On the basis of an experimental activity carried out at Istituto Motori of Italian National Research Council (CNR) with the financial support of the Environment Ministry and the technical support of Piaggio VE, a first evaluation of pollutant emissions has been done. The effect of exhaust after-treatment has been evaluated simulating ECE R40 cycle: HC conversion resulted 25%, CO 85% and NOx 45%. Overheating problems do not suggest the use of air injection upstream the catalyst.
As concern unregulated species, benzene is reduced of about 45% and 1-3 butadiene presents higher conversion efficiency. First results regarding Polycyclic Aromatic Hydrocarbons (PAH) evaluation have been reported.


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