Speciated Hydrocarbon Emissions of SI Engine During Cold Start and Warm-up 932706
The emission characteristics of hydrocarbons during the cold start and the warm-up have been investigated. Timed sampling of hydrocarbon emissions upstream and downstream of a close-coupled catalytic converter have been carried out. The experimental results show that the emission characteristics of hydrocarbons are influenced by both the engine operating conditions and the heating characteristics of the catalytic converter.
In the case of engine-out hydrocarbons, the total amount of hydrocarbons drastically decreases but the percentage contribution of the C2-C4 olefins to the engine-out hydrocarbons increases as the warm-up proceeds. Since these olefins have relatively high maximum incremental reactivity (MIR) factors, the specific reactivity (SR) of the engine-out hydrocarbons gradually increases during the warm-up.
The adsorption and desorption processes of the engine-out hydrocarbons on the catalyst occur before the catalyst light-off. These phenomena are significantly observed for the alkylbenzenes, which have the high boiling points and relatively high MIR factors. The catalyst conversion efficiencies after the catalyst light-off observed for the various classes of hydrocarbons are in the order of C2-C4 olefins > alkylbenzenes >> paraffins. Hydrocarbons which have relatively high MIR factors are much easy to oxidize over the catalyst. Before the catalyst light-off, the C2-C4 olefins are dominant for the SR but after the catalyst light-off, the unburned fuel species contributing 79.2% are dominant for the SR.
On the basis of these characteristics, it has been clarified that the total hydrocarbons and the SR are affected greatly by the engine operating conditions, the fuel composition and the type of the catalytic converter.