Method and apparatus for monitoring a reductant injection system in an exhaust aftertreatment system

Method for monitoring a reductant injector of a reductant injection system configured to dispense a reductant into an exhaust gas feedstream upstream of a selective catalytic reduction device, comprising:

• generating injector pulsewidth commands corresponding to a prescribed reductant flowrate;
• monitoring the injector pulsewidth commands;
• monitoring a fluidic pressure in the reductant injection system;
• estimating a first injected quantity of the reductant corresponding to the injector pulsewidth commands;
• estimating a first injected quantity of reductant using a physical relationship between a reductant flowrate {dot over (U)} and the injector pulsewidth commands in accordance with the relationship
• U
• .
• =
• f
• AREA
• 
• (
• PWM
• )
• 
• 2
• 
• P
• RT
• 0
• 
• (
• P
• -
• P
• st
• )
• wherein
• fAREA(PWM) is an equivalent effective open area of a nozzle of the reductant injector corresponding to the injector pulsewidth commands,
• P is the fluidic pressure in the reductant injection system,
• T0 is a temperature of the reductant,
• Pst is an exhaust pressure within an exhaust pipe into which the reductant injector is inserted, and
• R is an ideal gas constant,
• analyzing a variance of the fluidic pressure in the reductant injection system;
• estimating a second injected quantity of reductant corresponding to a magnitude of the variance of the fluidic pressure in the reductant injection system;
• comparing the first and second injected quantities of reductant;
• and
• detecting a fault associated with the reductant injector when a difference between the first and second injected quantities of the reductant exceeds a threshold.

System for dispense a reductant into an exhaust gas feedstream of an internal combustion engine upstream of a selective catalytic reduction device, comprising:

• a source of pressurized reductant;
• a reductant injector configured to receive the pressurized reductant and dispense the reductant into the exhaust gas feedstream;
• a pressure sensor configured to monitor pressure of the pressurized reductant;
• and
• a control module
• providing injector pulsewidth commands corresponding to a prescribed reductant flowrate to the reductant injector,
• monitoring the pressure sensor,
• estimating a first injected quantity of the reductant corresponding to the injector pulsewidth commands,
• estimating a second injected quantity of the reductant corresponding to the pressure of the pressurized reductant,
• comparing the first and second injected quantities of reductant, and
• detecting a fault associated with the reductant injector when a difference between the first and second injected quantities of the reductant exceeds a threshold.