DEVICE FOR PURIFYING EXHAUST GAS OF ENGINE

摘要

Disclosed is a device for purifying exhaust gases of engines comprising a reduction catalyst which is arranged in an engine exhaust pipe and reduces nitrogen oxides with a liquid reducing agent and a spray nozzle arranged in the exhaust upstream of the reduction catalyst for supplying the liquid reducing agent as a spray. In this exhaust gas purifying device, a heater is arranged around at least a part of the exhaust pipe including the portion where the liquid reducing agent sprayed from the spray nozzle adheres, and the exhaust pipe is heated by this heater to a temperature not lower than the melting point of the solute of the liquid reducing agent, thereby melting the solute deposited on the exhaust pipe. By injecting a compressed air to the vicinity of the spray orifice from the exhaust upstream or downstream of the spray nozzle, diffusion of the liquid reducing agent can be accelerated. Furthermore, by changing the open area ratio of the exhaust pipe passage in the vicinity of the spray orifice of the spray nozzle according to the exhaust flow rate of the engine, the exhaust flow velocity near the spray orifice of the spray nozzle can be maintained high, thereby accelerating diffusion and mixing of the liquid reducing agent in the exhaust gas.