Exhaust gas purification system

Abstract

The invention relates to an exhaust gas purification system for removing carbon monoxide, hydrocarbon and nitrogen oxide from an exhaust gas of an internal combustion engine. This system includes an upstream catalyst containing at least one selected from the group consisting of platinum, palladium and rhodium, and a downstream catalyst that is arranged downstream of the upstream catalyst. This downstream catalyst contains platinum in an amount greater than that of platinum of the upstream catalyst. In the system, a first oxygen excess ratio of an exhaust gas at an inlet of the upstream catalyst may be adjusted to at least 0.9, and a second oxygen excess ratio of an exhaust gas at an outlet of the upstream catalyst and at an inlet of the downstream catalyst may be adjusted to at least 0.1. Alternatively, a first air-fuel ratio of an exhaust gas at an inlet of the upstream catalyst may be adjusted to at least 14.5, and a second air-fuel ratio of an exhaust gas at an outlet of the upstream catalyst and at an inlet of the downstream catalyst may be adjusted to at least 13.3. The system is capable of removing even slightly oxidizable hydrocarbons.

Dependencies are inferred from the claim text.