Advantages and Challenges of Lean Combustion in Automotive IC ...

Opportunities and Challenges of LeanCombustion in Automotive IC EnginesRuss DurrettGM Global R&D1

Intro – Diesel Advantage Over Gasoline Data from EPA show approximately30% reduction in gallons/100 miles fordiesel (approx. 40% higher MPG) Why is a diesel engine more efficientthat a conventional gasoline engine? Common answers: No throttling losses Higher compression ratio These are contributors, but the leancombustion process of the dieselengine is the main factor leading tothe efficiency gainLaboratory 55/45 Fuel Consumptionvs. Vehicle Weightapprox.30% red.Source: Light-Duty Automotive Technology,Carbon Dioxide Emissions, and Fuel EconomyTrends: 1975 Through 2012, EPA, 20132

Intro – Diesel Advantage Over Gasoline Use cycle simulation to look at the independent effects of: Throttling Compression ratio Lean combustion Engine configuration: 2 liter, in-line 4 cylinder CR = 9.5 Port fuel injected Wiebe heat release Woschni heat transfer Chen-Flynn friction 98% Comb. Efficiency 2000 RPM / 5 bar BMEPoperating condition3

Intro – Diesel Advantage Over Gasoline Four cases modeled1. Baseline case – throttled, stoichiometric, CR = 9.52. Un-throttled case - use EIVC to un-throttle the engine3. High CR case - increase CR from 9.5 to 16.04. Lean case - increase lambda from 1.0 to 2.04

Percent of Fuel EnergyIntro – Diesel Advantage Over Gasoline Four cases modeled1. Baseline case – throttled, stoichiometric, CR = 9.52. Un-throttled case - use EIVC to un-throttle the engine3. High CR case - increase CR from 9.5 to 16.04. Lean case - increase lambda from 1.0 to 2.0 Effects are cumulativefor the 4 cases100%90% Bars show percentage of fuelenergy going to:80%70% Brake work Friction losses Heat transfer losses (coolant) Exhaust thermal losses Exhaust chemical losses60%50%40%30%20%10%29.0 %30.7 %32.7 %37.0 %Exh Chem.Exh ThermalHeat TransferFrictionBrake0%throttstoichCR = 9.5EIVCstoichCR = 9.5EIVCstoichCR = 16EIVCleanCR = 165

Percent of Baseline Fuel EnergyIntro – Diesel Advantage Over Gasoline Four cases modeled1. Baseline case – throttled, stoichiometric, CR = 9.52. Un-throttled case - use EIVC to un-throttle the engine3. High CR case - increase CR from 9.5 to 16.04. Lean case - increase lambda from 1.0 to 2.0 Effects are cumulativefor the 4 cases100%90%94.5 %88.8 % Bars re-scaled to show equalbrake work for all cases80%70%78.6 % This reflects the actual fuelenergy used in the 4 cases60%50%Exh Chem.Exh Thermal40%30%Heat TransferFrictionBrake20%10%0%throttstoichCR = 9.5EIVCstoichCR = 9.5EIVCstoichCR = 16EIVCleanCR = 166

Percent of Baseline Fuel EnergyIntro – Diesel Advantage Over Gasoline Four cases modeled1. Baseline case – throttled, stoichiometric, CR = 9.52. Un-throttled case - use EIVC to un-throttle the engine3. High CR case - increase CR from 9.5 to 16.04. Lean case - increase lambda from 1.0 to 2.0 Effects are cumulativefor the 4 cases100%90%94.5 %88.8 % Bars re-scaled to show equalbrake work for all cases80%70%78.6 % This reflects the actual fuelenergy used in the 4 cases60%50%Exh Chem.Exh Thermal40%30%Heat TransferFrictionBrake20%10%0%throttstoichCR = 9.5EIVCstoichCR = 9.5EIVCstoichCR = 16EIVCleanCR = 167

Percent of Baseline Fuel EnergyBTE ImprovementOver BaselineIntro – Diesel Advantage Over Gasoline Cumulative gains in brakethermal efficiency: 6% from un-throttling 7% from increased CR 15% from lean combustion Total gain of 27%100%0.0%5.8%12.6%27.3%30%25%20%15%10%5%0% Over half of the gain comes fromthe lean combustion process90%80%70%60%50%40%30%Exh Chem.Exh ThermalHeat TransferFrictionBrake20%10%0%throttstoichCR = 9.5EIVCstoichCR = 9.5EIVCstoichCR = 16EIVCleanCR = 168

Why Lean Combustion Increased dilution improvesisentropic efficiency by loweringtemperatures and increasinggamma Switching from exhaust dilutionto air dilution improves isentropicefficiency by increasing gamma Increased dilution improves theindicated efficiency by loweringtemperatures and decreasingheat lossesSource: FosterCombustion Engine Efficiency ColloquiumDOE, 20109

Why Lean Combustion Increased dilution improvesisentropic efficiency by loweringtemperatures and increasinggamma Switching from exhaust dilutionto air dilution improves isentropicefficiency by increasing gamma Increased dilution improves theindicated efficiency by loweringtemperatures and decreasingheat losses Ignition and flame propagationlimit the potential of traditionalhomogeneous, flame propagationbased combustion systems Operating lean with high levels ofdilution can improve vehicle-levelefficiency by about 15%Lean w/o EGRLean w/ EGRStoichiometricw/ EGRSource: FosterCombustion Engine Efficiency ColloquiumDOE, 2010Stoichiometricw/o EGR10

Why Lean Combustion To maximize efficiency we must migrate to air dilution and use levels ofdilution beyond the limits of traditional homogeneous ignition and flamepropagation Operating lean with high levels of dilution can improve vehicle-levelefficiency by about 15%Leanw/ EGRIsentropicStoichiometricw/ EGRIndicatedStoichiometricw/o EGR13%3%11

Challenges of Lean Combustion Lean combustion offers a significant efficiency advantage as described However, there are also several challenges associated with implementingthe technology in a practical light duty automotive application: Combustion stability and robustness over a wide operating range Boosting system requirements Controls requirements (including sensors & actuators) Low exhaust temperature Advanced lean aftertreatment Cold start and transient operation12

Lean Combustion Alternatives To maximize ICE efficiency it is necessary to operate lean (air dilution)with overall dilution levels beyond the limits of traditional homogeneousflame propagation combustion modesCombustionTechnologyLean SI – GasolineLean SI Stratified Charge –GasolineSI-HCCI – GasolineGasoline CIDIRCCI CIDIPCCI / LTC Diesel CIDITraditional Diesel CIDIKey ChallengesIgnition and flame propagation limits along withemission challengesCombustion robustness and emission challengesCombustion control and NVH challengesCombustion control and NVH challengesMulti-fuel requirement and emission challengesEmission and NVH challengesEmissions challenges13

Equivalence Ratio (phi)The Combustion Control Challenge To maximize the fuel economypotential of the ICE whileminimizing emissions we mustoperate in a narrow range ofequivalence ratios andtemperatures We must avoid rich diffusionflames We must avoid high temperaturehomogeneous propagating flames We must maintain sufficienttemperature for completeoxidations We must maintain these idealconditions over all operatingconditions654321Soot reductionvia increasedmixingCO / UHCoxidationlimitSoot formationzoneNOx reductionvia dilutionNOxzone0500 1000 1500 2000 2500 3000Temperature (K)Source: Kamimoto and Bae– SAE 88042314

The Lean Combustion NVH Challenge To meet the goals of advancedlean combustion , the globalcommunity is exploring a range ofLTC concepts – SI-HCCI, GasolineCIDI, PCCI, RCCI All these concepts are challengedby operating domain constraints –combustion issues at low loads &temperatures and dilution/noiseissues at high loads All these concepts requiresophisticated injection and controlsystems to regulate in-cylinderconditions All these concepts are sensitive toambient conditions and fuelpropertiesRCCI Mapping, Curran, Gao, Wagner,Oak Ridge National Labs15

The Exhaust Temperature Challenge Increasing the fraction of fuel energy that does useful work meansreducing the energy in the exhaust and this poses aftertreatmentperformance challenges16

Fuel EfficiencyThe Exhaust Oxygen Challenge Increasing the extent of lean operation to enhance fuel economy posessignificant aftertreatment cost and robustness challengesLean NO x TrapHigh PGM costSulfur poisoningDesulfation requiredNarrow temperaturewindowConventional TWCPoor NO x efficiency withDFCO/Lean-idleUrea-Free SCRLow PGM costNo sulfur poisoningNo secondary tankUrea-SCRSecondary urea tank withinjection system; high ureaconsumption for gasolineUrea solution freezingExhaust Oxygen Content17

Conclusions and Future Research Needs Developing robust, cost-effective, lean combustion technologies forautomotive gasoline engines will be challenging but the fuel economybenefits are significant In-cylinder emissions control is important Challenges for engine optimization: Robust combustion control over all operating conditions Robust emissions control over all operating conditions Good fuel consumption under real world driving conditions Low combustion noise Exhaust temperature This will require a coordinated effort between air handling, combustion,aftertreatment and controls – a system optimization approach In order to do this work effectively it is important to focus research onfundamental insights that have long-term value critical to achievingupper-bound efficiency and lower-bound emissions18

Questions?19