Importance

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Abstract

An exhaust pipe for an exhaust gas is provided, at its position on upstream side of nitrogen oxides (NOx) catalytic converter, with an internal tubular member disposed to have open opposite ends in a direction along exhaust gas flow while leaving a clearance between internal tubular member and exhaust pipe inner wall. A urea aqueous solution from the storage tank is additively injected by an injection nozzle in a direction of exhaust gas flow within internal tubular member capable of being heated by exhaust gas in exhaust pipe, to thereby shortly bring temperature of internal tubular member to become substantially equal to an exhaust gas temperature. Thus, temperature of urea aqueous solution additively injected into internal tubular member does not decrease when the solution adheres to an inner wall of that tubular member forming liquid droplets, thereby enhancing hydrolysis an inner wall of urea aqueous solution.

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First Claim