NEW DIESEL EMISSIONS CONTROL STRATEGY for US TIER 2 Jeffrey A. Leet Shizuo Sasaki, PhD. Yiqun Huang, PhD. Gary Neely Department of Engine and Emissions Research Southwest Research Institute 24 Diesel Engine Emissions Reduction Conference September 2, 24
Outline Emissions Regulations SwRI s Tier 2 Concept Modified Combustion Dual-Loop EGR 4-way Catalyst System Combustion Characteristics Tailpipe Emissions Summary
Emissions Regulations - Light Duty PM (g/km).8.6 Different test cycles apply, no correlations applied, Tier 2 applies at full useful life (12,miles/193,8 km).4 LEV (CARB LEV I) EURO III.2 Tier 2, Bin 5 Japan 25 EURO IV (25) Euro V?...1.2.3.4.5 NOx (g/km)
SwRI s Tier 2 Concept
Modified Combustion Processes: Low Temperature Combustion (LTC) Decreasing A/F and/or increasing EGR eventually reduces combustion temperatures low NOx freezes soot formation reactions low soot Increases HC and CO which is good for regeneration of exhaust treatment devices Smoke(%) Reducer (%) 1 8 6 4 2 2 15 1 5-5 Rich combustion area CO HC Smoke BSFC NOx 12rpm 2Nm 1 8 6 4 2-1 3 1 15 2 25 3 35 4 Air Fuel Ratio Toyota JSAE 23 Potentially no BSFC penalty for lean operation Limited to light-load operation (< 5 bar BMEP) 6 55 5 45 4 35 NOx(ppm) BSFC (g/kwh)
Modified Combustion Processes: Premixed Controlled Compression Ignition (PCCI) Premixing 2-5% of charge followed by main injection Larger pilot quantities than conventional pilot injections Increases amount of fuel undergoing lean combustion to 1 NO x 8 Baseline A subset of HCCI PCCI 6 Useful to stabilize 15 rpm / 2.7 bar BMEP rich combustion 4 under high load 2 conditions by reducing ignition delay -2 Injector Current Used at mid -4 to high loads -4-3 -2-1 1 2 3 4 HRR [J/deg] Crank Angle [deg]
Elements Necessary for LTC: SwRI s Dual-Loop EGR System Intake Manifold P O 2 Sensor Throttle Valve EGR Valve Low Pressure Loop (Mid Load) High EGR Rates Low Engine-out NOx Expand LTC area High Pressure Loop (Low Load) High Intake Temp. Stabilize LTC Low Exhaust Gas Flow Maintain Temp. of EGR Oxicat Intercooler Oxicat EGR Valve Throttle Valve Airflow Meter EGR Cooler
SwRI s Dual-Loop EGR and 4-Way Catalyst System LTC & PCCI O 2 Sensor 4-Way Catalyst Oxicat : Consumes HC, CO, O2 Avoids Deposit (DPF Front) DPF : PM Trap/Oxidation Cleans EGR LNT : NOx Storage/Reduction P P Sensor O 2 Sensor Intercooler Oxicat Oxicat DPF EGR Valve LNT Throttle Valve Airflow Meter EGR Cooler
Exhaust Treatment Example (SwRI IR Project 3.R9467, PSA DW1 2L Engine) Oxidation Catalyst: Pt based, V=1.2L DPF: Catalyzed, SiC, wall-flow, V=2.5L LNT: mass-produced for gasoline DI in Japan, V=1.7L LNT EGR Oxicat DPF Oxicat Gas Flow
5432Test Modes - Analog of US FTP-75 Cycle (ref. SAE Paper 21-1-148) 2 15 1Production full load curve BMEP [bar] 1 5 1 15 2 25 3 35 4 Speed [rpm]
Tier 2 Combustion Strategies
Strategy: Normal Operation BMEP [bar] 2 15 1 5 Mode1 Normal Operation 3 Standard Diesel Combustion 2 4 1 15 2 25 3 35 4 5 LTC (Lean) Speed [rpm] LTC Lean produces: low engine-out NOx (<15 ppm) high HC (~2 ppmc) and CO (~2%) for activating oxidation catalyst and DPF
Strategy: Rich Operation for LNT Regeneration Operate rich (~12.5-14:1 air-fuel ratio) for a few seconds every several minutes Provides reductant to regenerate stored nitrates in the LNT Rich Operation PCCI (Rich) 3 2 Mode1 4 1 15 2 25 3 35 4 5 LTC (Rich) Speed [rpm] 2 15 1 5 BMEP [bar]
Approaches shown: Comments capitalize on inherently low engine-out NOx and smoke emissions at low load use airflow control and minor in-cylinder fuel increases to run rich temporarily Control strategies depend upon the formulation of the LNT and orientation of the exhaust treatment components
Combustion Characteristics
Cylinder Pressure [bar] HRR [J/ o CA] 32 33 34 35 36 37 38 39 4 6 6 5 4 3 2 1 3 2 1-1 Combustion Characteristics - Mode 1 Lean A/F Ratio = 16.5:1 Rich A/F Ratio = 13.6:1 LTC-Lean LTC-Rich (12rpm,.8bar BMEP, PSA DW1) LTC-Lean 32 33 34 35 36 37 38 39 4 Crank Angle [deg] LTC-Lean LTC-Rich 5 4 3 2 1 Injector Current Single injection, advanced from standard diesel Hot, high pressure EGR (>6%) Smooth combustion 3 C LNT bed temperature for steady-state lean LTC Rich used for LNT regeneration no post no exhaust port injection
Approach to Stabilize Combustion at Light Load - Mode 1 6-7% EGR causes instability Use of higher temperature EGR stabilizes combustion High- pressure EGR loop used Timing advance required IMEP Std Dev (kpa) 3 25 2 15 1 5 Target Hot EGR, T1=25degBTDC Hot EGR, T2=2degBTDC Cooled EGR, T1=25degBTDC Achieved by hot EGR and advanced single injection 12 14 16 18 2 22 24 26 28 3 32 Air/Fuel Ratio (Sensor)
Cylinder Pressure [bar] HRR [J/ o CA] Combustion Characteristics - Mode 5 12 8 4 (26rpm, 8.2bar BMEP, PSA DW1) 32 34 36 38 4 42 12 12 1 8 6 4 2 PCCI-Rich Standard PCCI-Rich AFR=14:1 Standard -4 Standard PCCI-Rich 32 34 36 38 4 42 Crank Angle [deg] Standard PCCI-Rich 1 8 6 4 2 Injector Current No post injection < 3% peak opacity with 135 bar peak injection pressure Main timing for PCCI-rich is 8 ATDC - smoke control
Peak Opacity vs. A/F Ratio and Rail Pressure: PCCI - Mode 5 5 45 4 Opacity vs. A/F Ratio with Different Rail Pressure Rail Pressure: 115 bar 35 Opacity, -1% 3 25 2 15 Target Rail Pressure: 135 bar 1 5 Increased injection pressure, combustion system tuning 13 14 15 16 17 18 A/F ratio
Constant Torque during Rich-Lean Switching (Mode 4) MAF Torque 2 15 1 5 3:1 13:1 MAF Torque AF engine-out 4 8 12 16 4 8 12 16 Time, s A/F ratio Airflow- based control Over- shooting of the throttle results in rapid A/F change Minimal torque fluctuations
Tailpipe Emissions with Four-Way Catalyst System
NO x Emissions over 5 Test Modes NOx [g/hr] 1 8 6 4 2 4 3 2 1 Engine Out Tailpipe LNT NOx Conv. efficiency 9% 94% 96% 1 2 3 4 5 Mode 91% 75% NOx conversion efficiencies for a given LNT regeneration strategy Modes 1-3 have very low engine-out NO x due to LTC. LNT will store the remainder. Mode 5 has a low conversion eff.. due to high exhaust temperatures
Estimated Cycle NOx Results Weighted NOx [g/cycle] 2.5 2. 1.5 1..5.2.15.1.5. Tailpipe Engine Out 1 2 3 4 5 Mode Weighted engine-out NOx over cycle =.287 g/mile Weighted tailpipe NOx =.35 g/mile Tier 2, Bin 5 limit is.7 g/mile Average weighted NOx reduction = 88% Initial results done with open-loop fuel control airflow based control will reduce BSFC penalty
Summary SwRI SwRI has developed a combustion control concept capable of achieving US Tier 2, Bin 5 for light-duty diesels with a 4-way catalyst system Issues: Issues: control control algorithms for rich-lean switching control control algorithms for mode switching avoiding uncontrolled exotherms in LNT during de-sulfation DPF DPF regeneration minimizing fuel consumption/co 2 penalties over transient cycles high high load operation (e.g., US 6 cycle)
THANK YOU! Jeffrey Leet jeffrey.leet@swri.org