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Model-based NH3 Adaptation Method for SCR Control

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Abstract

Selective Catalytic Reduction (SCR) system is widely used for diesel nitrogen oxide (NOx) control, but the closed-loop control and adaptive correction method which based on NOx sensor signal will be affected by the working characteristics of NOx sensor, such as the cross-sensitivity of ammonia (NH3). Based on the highly linear correlation between conversion efficiency and ammonia to NOx ratio (ANR) at insufficient supply level, a model-based adaptive correction method for urea injection quantity is proposed to eliminate this effect, which can effectively correct the deviation caused by multiple sources when using accurate models. The difference between the conversion efficiency of current SCR system and which generated from model is calculated by stopping injection and under injection actions to obtain an accurate adaptation factor, and the basic injection quantity can be modified by this factor. The maximum error of the 18 calculated correction factors from 18 WHTC cycles is only 1.1 % when using standard AdBlue; After urea solution concentration changed, the calculated correction factor error is within 5 % when comparing with the theoretical correction factor after 2 ∼ 3 rounds adaptation function running. The adaptation function keeps the reductant supply to adapt the deviation caused by catalyst aging, reductant concentration drift and supply accuracy variation only with slightly influence of tailpipe NOx emission (less than 2 % in average), which ensure SCR system always stay in appropriate dosing control state, make best for NOx emissions and NH3 emissions control.

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Abbreviations

ConcNoxAscMdlDs:

NOx measurement calculated via sensor model for ASC model outputs (ppm)

ConcNoxScrUs:

NOx concentration upstream SCR (ppm)

ConcNoxScrUsFild:

NOx concentration upstream SCR, lowpass filtered (ppm)

ConcNoxSpecAdvStdy:

NOx concentration upstream SCR catalyst steady state condition (ppm)

ConcNoxStateStdy:

detect NOx concentration steady state (ppm)

CswNAFacNh3lninOfs:

configuration switch for selecting the initial value for the adaptation factor calculation (/)

CswTiSatnUpdTriglnin:

configuration switch to choose the initialization value for the saturation calculation of the adaption function (/)

EffCIcdFac:

value of SCR efficiency calculation (/)

EffCtrEnaSpecAdv_P:

lower DeNOx threshold for enabling timer for triggereing next NH3 adaptation event (/)

EffFacSpecAdv_P:

minimum efficiency for releasing special maneuver (/)

EnaMNh3SpecAdvReq_P:

activate triggering depending on NH3 injected mass (/)

EnaNh3SlipDetn_P:

enable NH3 slip detection function (/)

EnaSpecAdvStateStdy_P:

activate triggering when system is in a steady state (/)

EnaTiSpecAdvReq_P:

activate triggering depending on time (/)

FacNh3CormLimd:

limited value for NH3 correction factor (/)

FacNh3CormLimLowr_P:

limit below status signal for too low NH3 correction factor is set (/)

FacNh3CormLimUppr_P:

maximum NH3 correction factor (/)

FacNh3CormStgy:

special maneuver factor before correction (/)

FacNh3LimDelta_P:

maximum permitted change within one time interval (/)

FacNh3LimnDynMax:

maximum for dynamic limitation of NH3 correction factor (/)

FacNh3LimnDynMin:

minimum for dynamic limitation of NH3 correction factor (/)

FacNh3LimnMax:

maximum for NH3 correction factor limitation (/)

FacNh3LimnMin:

minimum for NH3 correction factor limitation (/)

MfExh:

exhaust mass flow (kg/h)

MfNh3CnvnMdlSpecAdv:

ammonia massflow which was used for the NOx reduction (based on model) (g/s)

MfNh3FbFild:

feedback signal of NH3 massflow demand to (or realized by) the injector, lowpass filtered (mg/s)

MfNh3InjrDmd:

ammonia mass flow final demand (after limitation) from delivery control as feedback value (mg/s)

MfNh3MinFltdSpecAdv_P:

minimum filtered NH3 mass flow for releasing Special Maneuver (kg/h)

MfNh3MinSpecAdv_P:

minimum NH3 mass flow for releasing special maneuver (kg/h)

MMolar:

molar weight of something (g/mol)

MMolarAir:

molar weight of air (g/mol)

MMolarNh3 :

molar weight of NH3 (g/mol)

MNh3Fb:

feedback signal of NH3 massflow realized by the injector (mg/s)

MNh3lnjSpecAdv:

NH3 mass injected (g)

MNh3SpecAdvLimRchd_P:

NH3 mass injected limit (g)

MNh3SpecAdvReq:

minimum NH3 mass to trigger the special maneuver (kg)

MNh3SpecAdvReq_P:

minimum NH3 mass to trigger the special maneuver (kg)

MNh3SpecAdvReqlv_C:

mass NH3 special advanced request initial value (kg)

NAFacNh3lninOfs:

initialization value for the adaptation factor calculation (/)

NEng:

engine speed (rpm)

NEngMinSpecAdv_P:

minimum engine speed. This is the lowest limit to consider a normal operation (rpm)

ReqNh3AdapFctRst:

request signal to reset the adaptation function (/)

ReqSpecAdv:

request signal for the special maneuver (/)

ReqSpecAdvFctRst:

request signal to reset the special maneuver function (/)

RstSpecAdv:

reset signal for the special maneuver (/)

StCombdFildSpecAdvRels:

filtered space velocity and temperature conditions release (/)

StCombdSpecAdvRels:

space velocity and temperature condition release (/)

StEffRchdSpecAdvRels:

DeNOx efficiency minimum limit (/)

StEffRchdSpecAdvRelsRaw:

DeNOx efficiency minimum limit, before turn-off and turn-on delays (/)

StEnaNh3SpecAdv:

enable signal to request a special maneuver (/)

StMfNh3FildSpecAdvRels:

filtered injection NH3 massflow condition release signal (/)

StMfNh3FildSpecAdvRelsRaw:

filtered injection NH3 massflow condition release signal, before turn-off and turn-on delays (/)

StMfNh3SpecAdvRels:

injected NH3 massflow condition release (/)

StMfNh3SpecAdvRelsRaw:

injected NH3 massflow condition release, before turn-off and turn-on delays (/)

StMNh3SpecAdvReq:

request if NH3 massflow conditions are satisfied (/)

StSatnUpdTrig:

saturation update trigger (/)

StSpecAdvFnshd:

SCR discharge finished (/)

StSpecAdvScrDcha:

SCR discharge (/)

StSpecAdvScrDchaFnshd:

SCR discharge finished (/)

StSpecAdvStateStdyRels:

released SCR NOx us concentration steady state signal (/)

StSpecAdvTrig:

release special maneuver trigger signal (/)

StSvFildSpecAdvRels:

filtered space velocity condition release (/)

StTFildSpecAdvRels:

filtered SCR catalyst temperature condition release (/)

StTiSpecAdvReq:

Request if engine speed condition is satisfied (/)

StTrigAdapCormFacStgy:

Trigger state for adaptation of correction factor (/)

StTringAdapSpecAdv:

time that system must be under the lower efficiency limit to perform a new special maneuver (/)

StTSpecAdvRels:

status if SCR catalyst temperature condition is released (/)

SvExh:

exhaust space velocity (1/h)

SvMinFildSpecAdv_P:

minimum filtered space velocity for releasing special maneuver (1/h)

SvMinFildSpecAdv_P:

minimum filtered space velocity for releasing special maneuver (1/h)

SvMinFildSpecAdvRels:

minimum filtered space velocity for releasing special maneuver conditions release (/)

SvMinSpecAdv_P:

minimum space velocity for releasing special maneuver (1/h)

SvSpecAdvRels:

status if space velocity condition is released (/)

TcMfNh3FildSpecAdvReq:

time constant of NH3 flow filter for releasing special maneuver (s)

TcNoxUsSpecAdvStdy_P:

time constant of Nox upstream filter for releasing special maneuver when system is in a steady state (s)

TcSvFildSpecAdv_P:

time constant of space velocity filter for releasing special maneuver (s)

TdEffFacSpecAdv_P:

delay to activate minimum efficiency release condition (s)

TdMfNh3FildOffSpecAdv_P:

delay to activate filtered NH3 mass flow release condition. transition on to off (s)

TdMfNh3HldOffSpecAdv_P:

hold special maneuver if NH3 massflow is under a threshold. transition on to off (s)

TdMfNh3HldOnSpecAdv_P:

hold special maneuver if NH3 massflow is under a threshold. transition off to on (s)

TdMfNh3OffSpecAdv_P:

delay to activate NH3 mass flow release condition. transition on to off (s)

TdMfNh3OnSpecAdv_P:

delay to activate NH3 mass flow release condition. transition off to on (s)

TdStdyOffSpecAdv_P:

delay to activate steady state release condition. transition on to off (s)

TdStdyOnSpecAdv_P:

delay to activate steady state release condition. transition off to on (s)

TdTFildOffSpecAdv_P:

delay to activate filtered temperature release condition, transition on to off (s)

TdTFildOnSpecAdv_P:

delay to activate filtered temperature release condition, transition off to on (s)

TdTOffAdvReqlv_P:

delay to activate temperature release condition. transition on to off (s)

TdTOnAdvReqlv_P:

delay to activate temperature release condition. transition off to On (s)

TFildSpecAdvRels:

filtered SCR catalyst mean temperature (°C)

TiNh3SatnUpdTrig:

interval time for calculation of new saturation limits (h)

TiSatnUpdTriglnin:

initialization time of the saturation update trigger (h)

TiSpecAdvReq_P:

request activation timer (working hours) (h)

TiSpecAdvReqlv_C:

time special advanced request initial value (h)

TiSpecAdvReqlv_P:

request activation timer (working hours) (h)

TiSpecAdvScrStbl:

stabilization time (s)

TiSpecAdvScrStbl_z:

stabilization time (s)

TMinFildSpecAdv_P:

minimum filtered temperature for releasing special maneuver (°C)

TMinFltdSpecAdv_P:

minimum filtered temperature for releasing special maneuver (°C)

TMinSpecAdv_P:

minimum temperature for releasing special maneuver (°C)

Ts_C:

sample time for the SCR adaption manager (s)

TScrMean:

mean temperature SCR monolith (°C)

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Acknowledgement

This work was supported by the co-founding of China Postdoctoral Science Foundation (2022M711353) “Study on urea deposition on-line prediction method for SDPF system” and Jiangxi Provincial Natural Science Foundation (20202BABL314037) “Research on Modeling and urea injection control strategy of copper based SCR + ASC system for ultra-low emission target” The authors are very grateful for the ECU/DCU controller and test bench provided by Jiangling Motors Corporation, Ltd and Key Laboratory of Conveyance and Equipment of East China Jiaotong University respectively.

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Authors and Affiliations

  1. Key Laboratory of Conveyance and Equipment, Ministry of Education, East China Jiaotong University, Nanchang, 330013, China

    Tiantian Wang & Zhichao Huang

  2. Power Transmission Development Department, Jiangling Automobile Co., Ltd., 2111 Yingbinzhong Avenue, Nanchang County, Nanchang, 330100, China

    Tiantian Wang & Xuwei Luo

  3. School of Automotive Engineering, Wuhan University of Technology, Wuhan, 430070, China

    Jie Hu & Yayu Cheng

  4. AVL List Technical Center (Shanghai) Co., Ltd., 327 Rong Qiao Road, Junqiao Export and Development Zone, PuDong New District, Shanghai, 201206, China

    Zhi Wang

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  1. Tiantian Wang
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  2. Zhichao Huang
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  3. Xuwei Luo
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  4. Jie Hu
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Correspondence to Tiantian Wang.

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Wang, T., Huang, Z., Luo, X. et al. Model-based NH3 Adaptation Method for SCR Control. Int.J Automot. Technol. 23, 1621–1637 (2022). https://doi.org/10.1007/s12239-022-0141-8

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