Method and apparatus for monitoring a reductant injection system in an exhaust aftertreatment system
View Patent ↗An internal combustion engine operating at a lean air/fuel ratio includes a reductant injection system configured to dispense reductant into an exhaust gas feedstream upstream of a selective catalytic reduction device. The reductant injection system includes a reductant delivery system fluidly coupled to a reductant dispensing device that is configured to dispense the reductant. A method for monitoring the reductant injection system includes commanding the reductant dispensing device to dispense reductant at a prescribed reductant flowrate, controlling the reductant delivery system to a preferred operating state, monitoring operation of the reductant delivery system and estimating a reductant flowrate as a function of the monitored operation of the reductant delivery system, and diagnosing operation of the reductant injection system as a function of the prescribed reductant flowrate and the estimated reductant flowrate.
1. Method for monitoring a reductant injection system including a reductant delivery system fluidly coupled to a reductant dispensing device configured to dispense reductant into an exhaust gas feedstream of an internal combustion engine upstream of an ammonia-selective catalytic reduction device, comprising:
commanding the reductant dispensing device to dispense reductant at a prescribed reductant flowrate ({dot over (U)} C ) that achieves a stoichiometric ratio of reductant to NOx in the exhaust gas feedstream upstream of the ammonia-selective catalytic reduction device;
controlling the reductant delivery system to achieve a preferred operating state comprising a desired fluidic pressure in the reductant delivery system to dispense the reductant at the prescribed reductant flowrate ({dot over (U)} C );
monitoring fluidic pressure in the reductant delivery system;
determining a ratio of an estimated reductant flowrate out of a reductant pump ( {dot over (U)} a ) and the prescribed reductant flowrate ({dot over (U)} C ) corresponding to the desired fluidic pressure and the monitored fluidic pressure; and
diagnosing operation of the reductant injection system based upon the prescribed reductant flowrate {dot over (U)} C ) and the estimated reductant flowrate out of the reductant pump {dot over (U)} a ).
2. The method of claim 1 , wherein diagnosing operation of the reductant injection system based upon the prescribed reductant flowrate {dot over (U)} C )and the estimated reductant flowrate out of the reductant pump ({dot over (U)} C )comprises identifying a fault associated with the reductant injection system when a difference between the prescribed reductant flowrate ({dot over (U)} C )and the estimated reductant flowrate out of the reductant pump ({dot over (U)} a )exceeds a threshold.
3. The method of claim 1 , comprising determining the ratio of the estimated reductant flowrate out of the reductant pump ({dot over (U)} a ) and the prescribed reductant flowrate ({dot over (U)} C ) corresponding to the desired fluidic pressure and the monitored fluidic pressure in accordance with the following relationship:
U
.
a
U
.
c
=
P
_
(
P
_
-
P
st
)
P
R
(
P
R
-
P
st
)
wherein {dot over (U)} a is the estimated reductant flowrate out of the reductant pump comprising a mass flowrate,
{dot over (U)} C is the prescribed reductant flowrate comprising a mass flowrate,
P is the average value of the measured fluidic pressure in the reductant delivery system,
P R is the measured fluidic pressure in the reductant delivery system, and
P st is pressure in the exhaust gas feedstream.
4. Method for monitoring injection of a reductant into an exhaust gas feedstream upstream of an ammonia-selective catalytic reduction device, comprising:
commanding a reductant dispensing device to dispense reductant at a prescribed reductant flowrate ({dot over (U)} C )from a supply of pressurized reductant to achieve a stoichiometric ratio of reductant to NOx in the exhaust gas feedstream upstream of the selective catalytic reduction device;
providing a control signal to a reductant delivery system to establish the supply of pressurized reductant at a desired pressure;
monitoring fluidic pressure in the reductant delivery system;
determining a ratio of an estimated reductant flowrate out of a reductant pump ( {dot over (U)} a ) of the reductant delivery system and the prescribed reductant flowrate ({dot over (U)} C ) corresponding to the desired fluidic pressure and the monitored fluidic pressure; and
diagnosing operation of the reductant injection system based upon the prescribed reductant flowrate ({dot over (U)} C ) and the estimated reductant flowrate out of the reductant pump ({dot over (U)} a ).
5. The method of claim 4 , comprising determining the ratio of the estimated reductant flowrate out of the reductant pump ({dot over (U)} C ) and the prescribed reductant flowrate ({dot over (U)} C ) corresponding to the desired fluidic pressure and the monitored fluidic pressure in accordance with the following relationship:
U
.
a
U
.
c
=
P
_
(
P
_
-
P
st
)
P
R
(
P
R
-
P
st
)
wherein {dot over (U)} a is the estimated reductant flowrate out of the reductant pump comprising a mass flowrate,
{dot over (U)} C is the prescribed reductant flowrate comprising a mass flowrate,
P is the average value of the measured fluidic pressure in the reductant delivery system,
P R is the measured fluidic pressure in the reductant delivery system, and
P st is pressure in the exhaust gas feedstream.
6. A reductant injection system, comprising:
a reductant dispensing device receiving a supply of pressurized reductant;
a control module commanding the reductant dispensing device to dispense reductant at a prescribed reductant flowrate ({dot over (U)} C )from the supply of pressurized reductant to achieve a stoichiometric ratio of reductant to NOx in the exhaust gas feedstream upstream of an ammonia-selective catalytic reduction device;
a reductant delivery system including a motor driving a reductant pump to establish the supply of pressurized reductant;
a control module providing a control signal to control the motor driving the reductant pump to establish the supply of pressurized reductant at a desired pressure; and
a control module monitoring fluidic pressure in the reductant delivery system, determining a ratio of an estimated reductant flowrate out of the reductant pump ({dot over (U)} a ) and the prescribed reductant flowrate ({dot over (U)} C ) corresponding to the desired fluidic pressure and the monitored fluidic pressure, determining the reductant flowrate out of the reductant pump ({dot over (U)} a ) based upon the prescribed reductant flowrate ({dot over (U)} a ) and the ratio of the estimated reductant flowrate out of the reductant pump ({dot over (U)} a ) and the prescribed reductant flowrate ({dot over (U)} C ), and diagnosing operation of the reductant injection system based upon the prescribed reductant flowrate ({dot over (U)} C ) and the estimated reductant flowrate out of the reductant pump ({dot over (U)} a ).
7. The method of claim 6 , comprising determining the ratio of the estimated reductant flowrate out of the reductant pump ({dot over (U)} a ) and the prescribed reductant flowrate ({dot over (U)} C )corresponding to the desired fluidic pressure and the monitored fluidic pressure in accordance with the following relationship:
U
.
a
U
.
c
=
P
_
(
P
_
-
P
st
)
P
R
(
P
R
-
P
st
)
wherein {dot over (U)} a is the estimated reductant flowrate out of the reductant pump comprising a mass flowrate,
{dot over (U)} C is the prescribed reductant flowrate comprising a mass flowrate,
P is the average value of the measured fluidic pressure in the reductant delivery system,
P R is the measured fluidic pressure in the reductant delivery system, and
P st is pressure in the exhaust gas feedstream.