Cold start-compatible urea scr system

A cold start-compatible urea SCR system, comprising:

• an exhaust gas purification device,
• wherein the exhaust gas purification device comprises:
• a diesel fuel injection means that injects diesel fuel into a diesel engine cylinder or an exhaust manifold to increase an exhaust temperature,
• an oxidation catalyst that oxidizes carbon monoxide, hydrocarbons, and nitrogen monoxide in exhaust gas,
• a lean NOx trap release material that adsorbs nitrogen oxide,
• a urea water injection means for reduction of nitrogen oxide,
• a catalyst of selective catalytic reduction that allows nitrogen oxide to come into contact with ammonia generated by hydrolysis of urea water to reductively remove the nitrogen oxide, and
• a measurement and control means,
• wherein
• satisfactory nitrogen oxide reduction performance is exhibited even at a time of engine start when exhaust gas temperature is too low for urea water injection by:
• using the oxidation catalyst and the lean NOx trap release material, wherein the oxidation catalyst and the lean NOx trap release material are supported on the same integral structure type support or different integral structure type supports in an upper-lower divided manner or a front-rear divided manner, at least the oxidation catalyst being located in an upper layer, a lower layer, or on a front side;
• adsorbing emitted nitrogen oxide onto the lean NOx trap release material under continuous detection of an intake port temperature of the catalyst of selective catalytic reduction from a time of engine start;
• injecting diesel fuel in a pulse form from the diesel fuel injection means at a time when the SCR intake port temperature reaches a temperature suitable for denitrification;
• combusting the injected diesel fuel on the oxidation catalyst to raise an exhaust gas temperature, thereby moderately releasing the nitrogen oxide from the NOx trap release material;
• and
• injecting urea water in a pulse form from the urea water injection means to bring ammonia generated by hydrolysis into contact with released nitrogen oxide on the catalyst of selective catalytic reduction.