Method for exhaust gas purification and system for exhaust gas purification used therein

A method for exhaust gas purification by the use of a system for exhaust gas purification, which system comprises:

• (a) an adsorbent containing an adsorbent component capable of adsorbing hydrocarbons present in the exhaust gas emitted from an internal combustion engine, provided in the exhaust pipe of the engine,
• (b) at least one catalyst containing a catalyst component capable of reducing harmful substances present in the exhaust gas, provided in the exhaust pipe at a site upstream of the adsorbent in the flow direction of the exhaust gas,
• (c) at least one catalyst containing a catalyst component capable of reducing harmful substances present in the exhaust gas, provided in the exhaust pipe at a site downstream of the adsorbent in the flow direction of the exhaust gas,
• (d) a first inlet for introduction of secondary air into exhaust gas, formed in the exhaust pipe at a site upstream of the most downstream catalyst of the catalyst (b), and
• (e) a second inlet for introduction of secondary air into exhaust gas, formed in the exhaust pipe at a site between the catalyst (b) and the moat downstream catalyst of the catalyst (c), which method comprises
• introducing secondary air from the first inlet for a period from engine start to the activation of the catalyst (b) provided upstream of the adsorbent;
• at the timing when the catalyst (b) has been activated, stopping the introduction of secondary air from the first inlet;
• and
• introducing secondary air from the second inlet while the hydrocarbons of exhaust gas adsorbed, by the adsorbent (a) are desorbed from the adsorbent (a) with the temperature rise of the adsorbent (a) brought about by the hat of the exhaust gas, wherein the stopping of the introduction of secondary air from the first inlet is earlier than the starting of the introduction of secondary air from the second inlet.

A method for exhaust gas purification by the use of a system for exhaust gas purification, which system comprises:

• (a) an adsorbent containing an adsorbent component capable of adsorbing hydrocarbons present in the exhaust gas emitted from an internal combustion engine, provided in the exhaust pipe of the engine,
• (b) at least one catalyst containing a catalyst component capable of reducing harmful substances present in the exhaust gas, provided in the exhaust pipe at a site upstream of the adsorbent in the flow direction of the exhaust gas,
• (c) at least one catalyst containing a catalyst component capable of reducing harmful substances present in the exhaust gas, provided in the exhaust pipe at a site downstream of the adsorbent in the flow direction of the exhaust gas,
• (d) a first inlet for introduction of secondary air into exhaust gas, formed in the exhaust pipe at a site upstream of the must downstream catalyst of the catalyst (b), and
• (e) a second inlet for introduction of secondary air into exhaust gas, formed in the exhaust pipe a site between the catalyst (b) and the most downstream catalyst of the catalyst (c), which method comprises
• introducing secondary air from the first inlet for a period from engine start to the activation of the catalyst (b) provided upstream of the adsorbent;
• at the timing when the catalyst (b) has been activated, stopping the introduction of secondary air from the first inlet;
• and
• introducing secondary air from the second inlet while hydrocarbons of exhaust gas adsorbed by the adsorbent (a) are desorbed from the adsorbent (a) with the temperature rise of the adsorbent (a) brought about by the hat of the exhaust gas, wherein the stopping of the introduction of secondary air from the first inlet is later than the starting of the introduction of secondary air from the second inlet.

A system for exhaust gas purification, comprising:

• (a) an adsorbent containing an adsorbent component capable of adsorbing hydrocarbons present in the exhaust gas emitted from an internal combustion engine, provided in the exhaust pipe of the engine,
• (b) at least one catalyst containing a catalyst component capable of reducing harmful substances present in the exhaust gas, provided in the exhaust pipe at a site upstream of the adsorbent in the flow direction of the exhaust gas,
• (c) at least one catalyst containing a catalyst component capable of reducing harmful substances present in the exhaust gas, provided in the exhaust pipe at a site downstream of the adsorbent in the flow direction of the exhaust gas,
• (d) a first inlet for introduction of secondary air into exhaust gas, formed in the exhaust pipe at a site upstream of the most downstream catalyst of the catalyst (b),
• (e) a second inlet for introduction of secondary air into exhaust gas, formed in the exhaust pipe at a site between the catalyst (b) and the most downstream catalyst of the catalyst (c), and
• (f) detecting means for judging the stoppage of the introduction of secondary air from said first inlet located downstream of the most upstream catalyst.