초록 ▼

A safe, reliable SCR system for reducing NO.sub.x emissions from a lean-burn internal combustion engine utilizes urea in aqueous solution. Overheating and hydrolysis of the solution are prevented by maintaining the temperature of the urea solution sufficiently low that it is not permitted sufficient

A safe, reliable SCR system for reducing NO.sub.x emissions from a lean-burn internal combustion engine utilizes urea in aqueous solution. Overheating and hydrolysis of the solution are prevented by maintaining the temperature of the urea solution sufficiently low that it is not permitted sufficient time at elevated temperature to hydrolyze the urea to such an extent that solids precipitate. In a preferred embodiment, an injector system similar to those used for fuel injection provides a constant feed to injectors and a return line. The feed and injection can be controlled to provide sufficient urea for NO.sub.x reduction and sufficient cooling capacity for the feed and injection system to avoid hydrolysis and deposits of hydrolysis products.

대표청구항 ▼

[ We claim:] [1.] A method for reducing the emissions of NO.sub.x from a lean-burn engine having associated therewith an exhaust system having an exhaust passage for carrying exhaust gases containing NO.sub.x to a reactor effective for selective catalytic NO.sub.x reduction, comprising:feeding an aq

[ We claim:] [1.] A method for reducing the emissions of NO.sub.x from a lean-burn engine having associated therewith an exhaust system having an exhaust passage for carrying exhaust gases containing NO.sub.x to a reactor effective for selective catalytic NO.sub.x reduction, comprising:feeding an aqueous urea solution from a storage vessel through a line to an injector;returning urea solution from the injector to the storage vessel, the rates of feed and return being sufficient to supply urea as needed to the exhaust gases for NO.sub.x reduction and maintain the temperature of the urea solution sufficiently low that it is not permitted sufficient time to hydrolyze the urea to such an extent that solids precipitate prior to injection of the urea solution into the exhaust gases;injecting urea solution into the exhaust gases at an exhaust gas temperature sufficient for SCR; andpassing the exhaust gas through an SCR reactor.