Three Way Catalyst and Lean NO x Trap Modeling for a Lean Burn SIDI Gasoline engine

Transcription

1 Three Way Catalyst and Lean NO x Trap Modeling for a Lean Burn SIDI Gasoline engine Jian Gong, Christopher J. Rutland Presented at CLEERS on April 12 th, 213 Engine Research Center University of Wisconsin-Madison

2 Outline Background and objectives DeNO x modeling Three way catalyst (TWC) Lean NO x trap (LNT) erimental setup ulation results Summary 2

3 3 Background Lean-burned SIDI engines show great benefit on fuel efficiency and CO 2 reduction Relatively higher nitrogen oxides (NO x ) Reduce dependency on conventional fuels Flexible fuel (fuel neutral) engines (e.g. gasoline & ethanol blends) Worldwide tightening emission regulations for light duty vehicles NO x : Tier 2 Bin 5: 7 mg/mile; LEV III: (NO x +NMOG) 3 mg/mile in 225; Euro 5+: 96 mg/mile Passive ammonia SCR system TWC SCR NH 3

4 Objectives: Fuel-neutral AT Modeling Development of DeNO x models with global kinetics Reasonable accuracy over a wide range of (fuel neutral) engine exhaust conditions NH 3 kinetics (global) Study the overall engine aftertreatment system (e.g. DeNO x + DeSoot) Interactions among different AT devices Feedback to the engine performance 4

5 TWC Reaction Kinetics A single-channel, one-dimensional model Using GT-Power to solve conservation equations and chemistry 2 surface reactions (Ramanathan et al. 211) ( in Langmuir-Hinshelwood structure) Include kinetics for oxidation of CO, HC, and NO to CO 2, H 2 O and NO 2 NO x reduction reactions Water-gas shift and steam reforming reactions Oxygen storage reactions NH 3 kinetics Proposed N 2 O kinetics The detail of the TWC kinetics is reported in SAE paper

6 Inhibition Function of N 2 O [-] NH 3 N 2 O NH 3 and N 2 O Commonly formed during the rich operation of.8 TWC/LNT.7.6 Global mechanism (Ramanathan et al. 212).5 NO+2.5H 2 NH 3 +H 2 O.4 NH O 2 NO+1.5H 2 O.3 NH NO 1.25N H 2 O Temperature [ Predominantly formed during cold start and transient o C] operations A byproduct of NO x reduction by HCs during light-off Global mechanism NO+1/18C 3 H 6.5N 2 O+1/6CO 2 +1/6H 2 O N 2 O+1/9C 3 H 6 N 2 +1/3CO 2 +1/3H 2 O Temperature [ o C] peaks at 225 o C appears at 15 o C very little (T> 4 o C) 6

7 erimental Setup Lean gasoline vehicle (BMW12i 2.L L4) on a chassis dynamometer at ORNL (Parks et al. 211) Three different types of data for model validations Time-resolved (transient lean/rich cycle) Time-averaged (steady state lean/rich cycle) Transient driving cycle 7

8 Wall Temperatures [ o C] CO [ppm] Gas Temperature [ O 2 [g/s] o C] Time-resolved Data: 35 rpm 3% 4 In_exp 3 Out_sim Out_exp Gas Temperature Catalyst Temperature Tw_sim Tw_exp Gas & Catalyst temperatures match data O 2 and CO predictions are good Lean Rich O 2 In_exp Out_sim Out_exp x In_exp Out_sim Out_exp CO

9 N 2 O [ppm] Cumulative NO x [g] THC [ppm] NO x [ppm] rpm 3%: THC/NO x /N 2 O In_exp Out_sim Out_exp THC N 2 O In_exp Out_sim Out_exp NO x sim =13.576% exp = % Good predictions of THC Transient N 2 O is captured Instantaneous NO x and accumulative NO x are very comparable.5 Cumulative NO x

10 Cumulative H 2 [g] Cumulative NH 3 [g] H 2 [ppm] NH 3 [ppm] 35 rpm 3%: H 2 & NH 3 5 x 14 4 H NH Cumulative H Cumulative NH Slightly high H 2 peak; enough H 2 compared to NO x Instantaneous NH 3 and accumulative NH 3 are very comparable NH 3 /inlet NO x =.72/2.4 ~ 3%

11 O 2 [g/s] Time-averaged Data Speed: 15 to 45, Load: ~12 N m Total # of steady state operating conditions: 155 (lean+rich) Exhaust Lean Rich Mass flow rate [g/s] 6.7 ~ ~ 46.8 Space velocity [1/s] ~ ~ Exhaust temp [ C] ~ ~ Engine equiratio [-].46 ~ ~ 1.25 NO x [ppm] 156 ~ ~ CO [ppm] ~ ~ 3468 HC [ppm] 19.4 ~ ~ Lean period Rich period Inlet_ss_exp Outlet_sim Outlet_ss_lean_exp Outlet_ss_rich_exp.5 time-averaging during rich period No detailed instantaneous species concentrations Examining the kinetics in a wide window of exhaust conditions

12 CO_sim [g/s] T_wall_sim [ C] NO x _sim [g/s] Time-averaged Data 8 Lean Rich.15 Lean Rich T_wall_exp [ C] Lean Rich Catalyst Temp CO CO_exp [g/s].6.3 NO x NO x _exp [g/s] Good agreement of temperatures and NO x emissions at lean & rich Some discrepancy in CO Consistent with underpredictions of temperatures 12

13 Load [N-m] Load [N-m] Load [N-m] Load [N-m] Phasing Comparisons 12 Catalyst wall temp (rich) 12 8 A good agreement between predicted catalyst temperature, NO x and experimental data Speed [rpm] Speed [rpm] TWC out NO x (lean) Speed [rpm] Speed [rpm]

14 Yield N 2 O/Eng NO x [%] Yield N 2 O/Eng NO x [%] Yield NH 3 /Eng NO x [%] Yield NH 3 /Eng NO x [%] NH 3 & N 2 O kinetics lean rich Eng Out Temp [ o C] Eng Out Temp [ o C] yield NH or N O 3 2 = 1% engine out NO lean rich lean rich Eng Out Temp [ o C] x lean rich Eng Out Temp [ o C] NH 3 mainly formed at rich Some discrepancy at low exhaust temperatures (<4 C) Over-predicted at lean N 2 O Independent of AFR Significantly depends on exhaust temperature Favors at low temp

15 NH 3 [ppm] Wall Temperatures [ o C] NO x [ppm] FTP Cycle (cold start) Tw_sim Tw_exp NOx =4.8% exp =32.3% Inlet_exp Outlet_sim Outlet_exp Model captures the trends of catalyst temp, NO x and NH 3 Higher NO x and NH 3 in the first 2 seconds Might be some NOx storage functionality in the TWC (not in the model)

16 LNT Kinetics LNT kinetics 1 CO+.5O 2 CO 2 2 C 3 H O 2 3CO 2 + 3H 2 O Oxidation reactions 3 C 3 H 8 + 5O 2 3CO 2 + 4H 2 O 4 H 2 +.5O 2 H 2 O 5 NO+.5 O 2 NO 2 NO NO 2 transition 6 CO + NO CO 2 +.5N 2 7 1/9C 3 H 6 +NO 1/3CO 2 +1/3H 2 O+1/2N 2 8.5BaCO 3 +NO+.75O 2.5Ba(NO 3 ) 2 +.5CO 2 9.5BaCO 3 +NO O 2.5Ba(NO 3 ) 2 +.5CO 2 NO reduction NO x adsorption 1.5Ba(NO 3 ) CO.5BaCO 3 +NO+CO 2 11 Ba(NO 3 ) 2 +1/3C 3 H 6 +CO 2 BaCO 3 +2NO+H 2 O NO x desorption 12 Ba(NO 3 ) 2 +8H 2 +CO 2 2NH 3 +BaCO 3 +5H 2 O NH 3 formation from nitrates 13 NH 3 +.5Ba(NO 3 ) 2 +.5CO 2 N 2 O+.5BaCO H 2 O N 2 O formation from nitrates 14 NH 3 +4NO 2.5N 2 O+1.5H 2 O N 2 O formation 15 NO+2.5H 2 NH 3 +H 2 O NH 3 formation 16 NH O 2 NO+1.5H 2 O NH 3 oxidation 17 NH NO 1.25N H 2 O NH 3 and NO Total 17 reactions (Olsson et al. 25) 16

17 Wall Temperatures [ Gas Temperature [ NO x [ppm] o C] Cumulative NOx [g] LNT Validation: 35 rpm 3% Gas Temperature In_exp Out_sim Out_exp NO x store NO x o C] 3 In_exp Out_sim Out_exp Catalyst Temperature Inlet NOx =52.545% exp =52.16% Temperatures match data NO x adsorption & desorption & reduction are well captured 1 17

18 Cumulative CO [g] Cumulative HC [g] CO [ppm] THC [ppm] 2 x In_exp Out_sim Out_exp LNT Validation: CO & THC CO In_exp Out_sim Out_exp THC CO = % exp = % Inlet Inlet Slightly lower CO but with reasonable overall conversion rate Both instantaneous and accumulative HCs are good HC =4.9594% exp =31.938% 18

19 H 2 [ppm] NH 3 [ppm] Cumulative NH 3 [g] LNT Validation: H 2 & NH 3 4 x H 2 NH 3 In_exp Out_sim A large amount of H 2 from TWC Peak NH 3 is higher than NO x (6 vs. 5) Generated from nitrates (different from TWC) NH 3 /inlet NO x =.8/4.2 ~ 2% 19

20 Summary A TWC and a LNT model were developed with global kinetics and validated using experimental data from a lean burn DISI engine TWC Validated over a wide range of exhaust conditions Temperature dependences of the conversion rate of NH 3 and N 2 O from NO x were examined LNT NO x adsorption, desorption and reduction were well captured NH 3 formation from LNT could be much more than TWC Need NH 3 kinetics from nitrates The DeNO x models are able to predict the temperatures as well as species concentration with a good accuracy. 2

21 Acknowledgment This project is supported by General Motors as UW-GM Collaborative Research Laboratory (UW-CRL) GM: Kushal Narayanaswamy ORNL: Emissions & Catalysis Research Group Monthly teleconferences Todd Toops, James Parks, Stuart Daw, Vitaly Prikhodko, Zhiming Gao, Josh Pihl 21

22 Reference 1. Li, W., Perry, K., Narayanaswamy, K., Kim, C. et al., "Passive Ammonia SCR System for Lean-burn SIDI Engines," SAE Int. J. Fuels Lubr. 3(1):99-16, 21, doi:1.4271/ Kim, C., Perry, K., Viola, M., Li, W. et al., "Three-Way Catalyst Design for Urealess Passive Ammonia SCR: Lean-Burn SIDI Aftertreatment System," SAE Technical Paper , 211, doi:1.4271/ Ramanathan K. and Sharma C. S., Kinetic Parameters Estimation for Three Way Catalyst Modeling, Industrial & Engineering Chemistry Research, 5 (17), p. 996:9979, Ramanathan K., Sharma C. S., and Kim C. H., Global Kinetics for Ammonia Formation and Oxidation Reactions in a Commercial Three-Way Catalyst, Industrial & Engineering Chemistry Research, 51, pp , Parks, J., Prikhodko, V., Partridge, W., Choi, J. et al., "Lean Gasoline Engine Reductant Chemistry During Lean NOx Trap Regeneration," SAE Int. J. Fuels Lubr. 3(2): , 21, doi:1.4271/ Parks J., et. al. CLEERS Teleconference, March 31, Toops, Todd J., Parks, James E., Pihl, Josh A., DiGiulio, Christopher D., Amiridis, Michael D. DEER Conference, October 18, Olsson L., Blint R. J., and Fridell E., Global Kinetic Model for Lean NOx Traps, Ind. Eng. Chem. Res., (44), pp , Olsson L., Monroe D., and Blint R. J., Global Kinetic Modelling of a Supplier Barium- and Potassium- Containing Lean NOx Trap, Ind. Eng. Chem. Res., (45), pp , 26.

23 Thank You! For further questions, please contact: Jian Gong Mechanical Engineering Department University of Wisconsin-Madison 18 Engineering Research Building 15 Engineering Drive, Madison, WI 5376