Reduction of nitrogen oxide emission from diesel engine with SCR catalytic converter

摘要

When the value of catalytic converter efficiency drops below a predetermined level, the control unit (1) initiates action, as a function of the expected efficiency value. This action varies the engine control parameters to achieve two goals. The NOx concentration in the untreated exhaust gas is reduced and the exhaust temperature is raised. The action retards fuel injection and/or increases engine idling speed. When the diesel engine has a fuel cutout on overrun, the action is to disable the cutout. With engines having exhaust recycle, the action increases the recycle rate. It will be evident that each foregoing action tends to increase exhaust gas and catalytic converter temperature, hence keeping catalyst efficiency high, in situations otherwise tending to cool it. The expected catalyst efficiency is determined from control parameters. These are especially the exhaust gas mass flow rate, and the measured exhaust temperature. Exhaust mass flow rate is deduced from engine speed and air induction-charging pressure.