Variable engine out emission control roadmap
A method for operating an internal combustion engine for variable engine out NOx control talking into account the age of the SCR.
1. A method to operate an internal combustion engine equipped with an electronic control system (ECS) having memory, and an exhaust system including a diesel particulate filter (DPF) and a Selective Catalytic Reducer (SCR) for NOx emission reduction over all ages of said SCR, comprising:
determining the age of the SCR with an age factor;
determining SCR efficiency using SCR age as a factor of SCR efficiency;
determining desired tailpipe NOx emissions as setpoints to control engine out NOx emissions;
determining desired engine out NOx emission by using current SCR efficiency and desired tailpipe NOx emissions;
using fuzzy logic to manage engine control setpoints which forms a forward control portion of the said ECS; and
using closed loop engine out NOx sensor feedback control to accurately control engine out NOx emissions.
2. The method of claim 1 , wherein said engine control setpoints include beginning of injection (BOI) exhaust gas recirculation valve (EGR), and nozzle opening pressure (NOP).
3. The method of claim 1 , wherein said NOx setpoints are determined from a 3D table in memory with engine load and engine rpm as inputs.
4. The method of claim 1 , wherein controlling engine out NOx according to SCR deterioration age includes determining the efficiency of the SCR and the amount of NOx engine out emission produced in a predetermined time period, reducing engine fuel consumption based upon said SCR efficiency and NOx engine out and maximize DPF regeneration, extending the DPF active regeneration interval.
5. The method of claim 1 , wherein said SCR aging factor is determined according to the formula
Age SCR =Σfactor age ×t step
Wherein t is time.
6. The method of claim 1 , wherein said desired engine out NOx is determined based upon desired tailpipe NOx setpoint value and SCR NOx reduction efficiency according to the formula
NOx
de
-
engine
out
=
NOx
des
-
tailpipe
-
out
1
-
η
scr
Wherein
η is an efficiency factor of the SCR.
7. The method of claim 1 , wherein said fuzzy logic based setpoint management is determined according to the formula
des Γrate= des Γrate fresh — SCR ×Y fresh — SCR — membership +desΓ _rate aged — SCR ×Y aged — SCR — membership
wherein:
Y is the SCR efficiency value and
Γ is an engine operating parameter.
8. The method of claim 7 , wherein with engine load, engine rpm and desired engine out NOx as inputs, EGR, BOI and NOP relations at conditions of minimum BSFC, given exhaust temperature and acceptable particulate matter (PM) rate are defined.
9. The method of claim 7 , wherein said fuzzy logic membership function is performed according to the formula:
a ( x 3− x )+ b ( x 2− x )− x+ 1
wherein a and b are 3D tables with engine rpm and load as inputs,
a
=
f
a
(
rpm
,
load
)
b
=
f
b
(
rpm
,
load
)
and
des
NOx
normalized
=
des
NOx
current
-
des
NOx
fresh_SCR
des
NOx
aged_SCR
-
des
NOX
fresh_SCR
.
10. The method of claim 9 , wherein when a and b are zero, the fuzzy logic become linear interpolation.
11. The method of claim 9 , wherein when determining fresh and aged SCR engine setpoints, table for EGR, BOI and NOP, for each operation point choosing between 5 and 6 EGR rate between fresh and aged SCR EGR rates; conducting engine tests at each EGR rate varying BOI and NOP; recording NOx, PM and BSFC at each combination of EGR, BOI and NOP; combining EGR, BOI and NOP at a given NOx with minimum BSFC and accepted PM, and determining a membership function constant a and b for EGR, BOI and NOP.
12. The method of claim 1 , further including using closed loop control to commensurate for engine to engine variation and reduce calibration effort.
13. The method of claim 1 , further including adaptive logic to address any conflict between PID control stability and response.