High Efficiency Engines through Dilution Opportunities and Challenges. Dr. Terry Alger Southwest Research Institute

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1 High Efficiency Engines through Dilution Opportunities and Challenges Dr. Terry Alger Southwest Research Institute

2 Efficiency Drivers from the Marketplace and Regulators Oil price volatility CO 2 and CAFE regulations Emissions Standards mg/km NMOG CO Nox PM T2B T2B T2B E5-petrol E5-diesel E6-diesel //2011

3 What Limits the Efficiency of an SI Engine? BSFC [g/kw h] Behavior in this region sets the CR of the engine BMEP [bar] Knock Combustion Phasing Losses Pumping Work Friction Engine Speed [rpm] 3 6//2011

4 Utility of EGR Cooled and/or Uncooled 4 6//2011

5 Improved Cycle Efficiencies Through Knock Reduction Cylinder Pressu ure [bar] % EGR % EGR 15% EGR 20% EGR 25% EGR Cylinder Pressure [bar] Crank Angle [deg atdcf] Modern GDI engine 1500 rpm / 60% load Cylinder Volume [L] 5 6//2011

6 Improved Cycle Efficiencies Through Charge Properties and Pumping Work Cooler combustion improves the ratio of specific heats and reduces HT losses Lean burn results in a slightly larger improvement Cycle-Averaged γ [-] EGR [%] ~ +1 % BTE Use of either internal EGR (through cam phaser) or cooled EGR decreases throttling losses Also not quite as good as lean operation 6 6//2011

7 Emissions Reduction With EGR Cool combustion reduces PM, 25 PN, CO and NOx Lower postflame 20 temperatures 15 lead to small HC increase Stoichiometric exhaust composition yields low-cost, low-emissions x [g/kwh] x ] BSCO, BSHC, BSNOx BSPM [mg/kwh x BSCO BSHC BSNOx BSPM BSPN 5 BSFC [g/kwh] EGR [%] Data from modern GDI 0 rpm / 75% load 0 solution BSPN [#/kwh/1e e12] EGR [%]

8 Exhaust Temperature Reduction With EGR Pre-Turbin ne Temperature [ o C] EGR cools exhaust via: Higher thermal mass Slower reaction rates 4000 RPM 0% EGR (Engine φ shown as label) 15% EGR (Engine φ = 1 at all conditions) More advanced combustion phasing at high load BMEP [bar]

9 EGR Challenges $ 9 6//2011

10 Misfire and Stability Issues Dilution reduces laminar burning velocities Decreases volumetric HR Slows reaction rates Reduces flame temperatures In an engine, slower burn rates can lead to: Unstable operation Full Misfire Primary affect felt on 0-2% MFB Solutions come in two categories Igniter and igniter hardware Fuel and charge enhancement Degrees Crank Angle % MFB duration [deg] 50-90% MFB duration [deg] 2-50% MFB duration [deg] EGR [%] 6//2011

Volumetric ignition Large initial flame area Very fast burn rates 90 0-50% MFB [deg] 80 70 60 50 40 Stock System Multi-strike

11 Ignition System Solutions for Dilute Engines Alternative system approach Long duration, continuous discharge OR Volumetric ignition Continuous discharge Overcomes HT losses to plug and gasses Couples with the flow field Forces flame kernel growth Volumetric ignition Large initial flame area Very fast burn rates % MFB [deg] Stock System Multi-strike system DCO System CoV IMEP [%] High EGR tolerance potential EGR [%] Increasing EGR tolerance of volumetric igniters

Fuel or Charge Enhancement Solutions Fuel-based solutions Pilot ignition using diesel or diesel-like fuel Charge Enhancement Chemical supplementation 220 H 2

12 Fuel or Charge Enhancement Solutions Fuel-based solutions Pilot ignition using diesel or diesel-like fuel Charge Enhancement Chemical supplementation 220 H 2 enhancement 2 2 Engine Design Based High turbulence High CR operation High S/B ratio gisfc (g/kwh) Electrical ignition % EGR Pilot ignition

13 Boosting Challenges for Dilute Engines High EGR rates High MAP and low pre-turbine temperatures H = U + PV & = m corr m& P T High expansion ratio required for turbine power High pre-turbine pressure Low Dilution Low corrected flow rate Low U/C (blade speed ratio) High Dilution Low Turbine Efficiency Turbine is small relative to the compressor Shaft speed will be too low for best efficiency From SAE Paper

14 Boosting Solutions Two stage boost systems can achieve very good torque curves More expensive than non- EGR systems Cheaper than a light-duty diesel with aftertreatment Other options Pursue diesel torque curve with high EGR gasoline application Similar efficiency / Lower cost Limit EGR flow at certain portions of the engine map Torqu ue 1.6 L Engine Torque Curves < 235 g/kwh BSFC 2-stage boost (20% EGR) 2-stage boost (25% EGR) Production Gasoline Production Diesel (with overboost) Engine Speed [rpm]

15 EGR Control Challenges Transient control of EGR is vital At high loads and during tip-ins Too little EGR can lead to knock and high pre-turbine temperatures Too much EGR can lead to misfire At low loads and during tip-outs EGR required to improve BSFC Too much EGR can lead to misfire Hardware design and advanced air handling control are vital to EGR control success

16 Materials and Design Requirements Peak Pressure Peak pressure is the key limiting parameter for torque above 2500 rpm in 2-stage TC applications Spark retard to limit PCP leads to instability At least 130 bar will be 40 required in the future Powertrain Architecture EGR system design will be key to control and packaging Heat rejection requirements in LPL EGR mode will need to be accounted for Downspeeding potential offers increased S/B ratio Cylinder Pr ressure [bar] Increasing EGR 0% 25% Crank Angle [CAD]

17 After addressing the challenges, the result is a high-efficiency, ultra-low emissions engine Single-stage boost system BSFC [g/kwh] BSFC [g/kwh] 2-stage boost system BMEP [bar] Engine Speed [rpm] Both engines operate at ~25% EGR 17 6//2011

18 High EGR engines have become a realistic option for Tier 4 (Final) applications Single-stage boost system BSFC [g/kwh] Similar torque as an offroad diesel engine of similar displacement Low-cost, high-power, low-co2 engine for Tier IV Main Fuel: HEEE Gasoline, Ignition: Diesel and/or SI Diesel short-block converted to run as pilotignited gasoline engine TWC compliant for ultralow emissions BMEP (bar) Engine Speed (rpm) 6//2011

19 The future of high EGR engines BS FC (g/kwh ) BMEP - Brake Mean Effective Pressure (bar) 6// BMEP - Brake Mean Effective Pressure (bar) E ng ine S pe ed (RP M) Dual-fuel 13 L on-highway engine (predicted BSFC)

20 Summary High EGR engines allow operation at high CR with low emissions Significant FE improvement potential Challenges remain Ignition Boosting Control Addressing these challenges, and others, will determine the ultimate application potential of the high EGR engine Latest results indicate that the high EGR engine can challenge the LD diesel at much lower cost and tailpipe emissions levels

21 What is next in High Efficiency? The industry needs to continue to address key issues: PM emissions and their effect on operating strategy for high efficiency Lean burn is it or isn t it a realistic option? Limits of downsizing LSPI as a limiting factor New drive cycles Friction improvements Increased requirement for cylinder pressure Knock reduction in SI engines will be a key item for the future

22 Reducing Knock in SI Engines through Oil Properties Altering the lubricant s chemical or physical properties can make it less reactive Lower CN lubricants allow more spark advance or higher boost levels Potentially significant enabler for downsizing / downspeeding W40 High CN Mid CN Low CN 89 ISFC [g g/kwh] W40 Oil Fully-Formulated IQT CN: 62, 91, 78 High CN Oil PAO base-stock IQT CN: 74, 8, 89 Mid CN Oil AN base-stock IQT CN: 49, 77, 64 Low CN Oil Ester base-stock IQT CN: 26, 45, 38 IQT derived Cetane Number W40 fully-formulated PAO base-stock R&D formulation PAO base-stock 64 R&D formulation AN base-stock 38 R&D formulation Ester base-stock Spark Timing [deg btdc] 16 ~ 3.0% 14

Dr. Terry Alger. Southwest Research Institute. Southwest Research Institute. San Antonio, Texas

Dr. Terry Alger. Southwest Research Institute. Southwest Research Institute. San Antonio, Texas Gasoline Engine Technology for High Efficiency Dr. Terry Alger Southwest Research Institute Southwest Research Institute San Antonio, Texas Losses and Opportunities for Improvement in Gasoline Engines