Importance

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Abstract

Exhaust gas due to combustion is discharged into the atmosphere through a combined catalytic-hydrocarbon adsorbent 20. The combined catalytic-hydrocarbon adsorbent consists of a hydrocarbon adsorbent layer 20A and a three-way catalytic layer 20B. The hydrocarbon adsorbent layer 20A adsorbs hydrocarbons at a lower temperature, and desorbs hydrocarbons at a higher temperature. The three-way catalytic layer 20B purifies hydrocarbons desorbed from the hydrocarbon adsorbent layer 20A. To reduce the amount of hydrocarbons discharged to atmosphere, when the running condition of the engine is in the idling region, the ignition timing is retarded. This retarding of the ignition timing is limited to the time period after the hydrocarbon adsorbent layer 20A begins desorbing hydrocarbons until three-way catalytic layer 20B activates. With this design, the temperature of the combined catalyst-hydrocarbon adsorbent rises rapidly and the amount of hydrocarbon emission is controlled to be minimum.

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First Claim