The emission characteristics of hydrocarbons during the cold start and the warm-up have been investigated with a timed gas sampling technique. The experimental results show that the emission characteristics of hydrocarbons are influenced by both the engine operating conditions and the heating characteristics of catalytic converters. The formation routes of engine-out hydrocarbons are estimated on the basis of the experimental results.
In the case of engine-out hydrocarbons, about 60% of them are unburned fuel components and the percentage contribution of C2-C4 olefins to the engine-out hydrocarbons increases as the warm-up proceeds.
The adsorption and desorption processes of the engine-out alkylbenzenes on the catalyst occur before the catalyst light-off. The catalyst conversion efficiencies after the catalyst light-off observed for various classes of hydrocarbons are in the order of C2-C4 olefins, alkylbenzenes and paraffins. Before the catalyst light-off, the C2-C4 olefins and unburned fuel components are dominant for the specific reactivity ( SR ). After the catalyst light-off, on the other hand, the unburned fuel components are dominant for the SR.
Based on these characteristics, it has been clarified that the total hydrocarbons and the SR are greatly affected by engine operating conditions, the fuel composition and the structure of a catalytic converter.