14th Diesel Engine-Efficiency and Emissions Research (DEER) Conference BenefitsBenefits andand drawbacksdrawbacks ofof compressioncompression ratioratio reductionreduction inin PCCIPCCI combustioncombustion applicationapplication inin anan advancedadvanced LDLD dieseldiesel engineengine Carlo Beatrice and Chiara Guido Istituto Motori, Consiglio Nazionale delle Ricerche Naples , ITALY Contacts: [email protected] [email protected] DEER 2008, Dearborn MI, 4-7° August 2008 1 Future Targets and Technology Pathways for PC Diesel Engines 0.08 0.07 Tier 2, Bin 10 EURO 3 (2007-2010) (2000) 0.06 •Advanced combustions 0.05 (PCCI/LTC etc.); 0.04 •New CRS with Inj. Rate Shaping; EURO 4 •Cold LP EGR + HP EGR; PM [g/mi] PM [g/mi] 0.03 •Closed-Coupled DPF; (2005) T2, Bin 8 •VVA System; 0.02 EURO 5 •Closed-Loop Combustion Control; EURO 6 prop •SCR/LNT 0.01 T2, Bin 5 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 NOx [g/mi] DEER 2008, Dearborn MI, 4-7° August 2008 2 PCCIPCCI (or(or LTC/HCCI)LTC/HCCI) potentialpotential forfor NOxNOx && PMPM reductionreduction Source M. Lisbona, FPT, ATA2006 In the transition from conventional combustion to PCCI mode the fuel/air mix change from orange to light-blue pathway Source M. Potter, GM, DEER2006 Compression Ratio appears a key parameter to improve PCCI combustion performance in partial load range Source M. Potter, GM, DEER2006 DEER 2008, Dearborn MI, 4-7° August 2008 3 IM-CRF Research Project on CR influence on PCCI performance Starting from an Eu4 Reference Engine (FIAT 1.9 MultiJet) An advanced low NOx calibration was applied (PCCI calib. with single shot inj. and high EGR/pressure inj.) FIAT M741 MultiJet engine Three CR values were selected for the tests Engine 4 cyl, 1.9L (16.5:1 → 15.5:1 → 14.5:1) Bore x Stroke 82 x 90 The 3 engine configurations were run in [mm] several test points typical of NEDC engine Stroke [mm] 90.0 operating area. Aim of the project was to Compr. Ratio 17.5 characterize the influence of CR reduction Turbo VGT on PCCI application in the largest NEDC area with NOx near Eu6 targets DEER 2008, Dearborn MI, 4-7° August 2008 4 CRCR selectionselection andand PistonPiston DesignDesign Starting from the commercial Eu4 piston geometry, 3 guidelines were followed: ¾Same air flow structure at TDC (same swirl and turbulence charac. vs CR); ¾Same squish height and internal lip diameter (similar squish flow in the bowl); ¾Same lip profile of the bowl (same structural robustness at rated power). Parameter Formula CR 16.5 CR 15.5 CR 14.5 K-factor [%] Bowl volume/Comb. 75.2 76.8 78.4 chamber volume Reentrant Ratio [%] (Dext-Dint)/Dint 9.3 10.9 13.5 Aspect Ratio [%] Hmax/Dext 33.0 34.0 35.2 DEER 2008, Dearborn MI, 4-7° August 2008 5 InIn--bowlbowl flowflow characteristicscharacteristics vsvs CRCR •The main air flow patterns appear very similar; RC 16.5 •The main differences are in the central part of the bowl. 5 RC 16.5 RC 15.5 RC 15.5 RC 14.5 4 RC 14.5 3 Swirl Ratio [a.u.] SR@ -180 c.a. [°] = 2.7 Slight increase of swirl ratio vs CR 2 decrease -50 0 50 crank angle [°] Friction loss reduction due to the surface/volume reduction and The CR influence on engine can be increment of moment of inertia ascribed mainly to different fuel DEER 2008, Dearborn MI, 4-7° August 2008 vaporization and thermodynamic effects 6 TestTest MethodologyMethodology 12 Starting from a prototype “near NOx Steady state test points with PCCI combustion Euro6” engine calibration for a CR=16.5 10 8 All CRs were tested in different 6 operating points typical of NEDC area 4 Engine load - BMEP [bar] - BMEP load Engine In the engine speed range, the load was 2 increased until one of the following NEDC operating area for FIAT MultiJet Engine limits were reached: 0 0 1000 2000 3000 4000 •+5% of FC w resp to Eu4 calib.; Engine speed [rpm] •80 bar/ms of the dp/dtmax ; In this way all CRs can be •1.5 FSN of smoke as limit for DPF. compared with optimized combustion timing and intake MBF50% and boost pressure were optimized airflow conditions vs CR varying SOI and VGT nozzle. The fuel is a commercial Low Sulfur DEER 2008, Dearborn MI, 4-7° August 2008 respecting the EN 590 standards 7 CR influence on max PCCI torque: max torque, FC & smoke FC & dp/dtmax limiting factors 5 Smoke limiting factor 4 Reducing CR only small increments in maximum engine torque are possible 3 within the limits and without changing RC 16.5 the engine technology (Euro4) 2 RC 15.5 RC 14.5 Engine load [bar] - BMEP 1 ] 10 2.5 Constant engine calibration CR 16.5 0 CR 15.5 500 1000 1500 2000 2500 3000 3500 8 2 CR 14.5 Engine speed [rpm] Reducing CR the τid increases 6 1.5 lowering the smoke in the whole 4 1 range. [FSN] Smoke dp/dtmax limits the MBF50% that 2 0.5 controls the engine efficiency. FC increment w respect to E4 level [% FC was similar for all CRs, no fuel 0 0 500 1000 1500 2000 2500 3000 3500 penalty was evidenced reducing CR Engine speed [rpm] DEER 2008, Dearborn MI, 4-7° August 2008 8 CRCR influenceinfluence onon maxmax PCCIPCCI torque:torque: NOxNOx,, HCHC && COCO 4 RC 16.5 NOx emissions are mainly driven by RC 15.5 EGR. 3 RC 14.5 Under PCCI mode, the already very EURO 4 level 2 low NOx concentrations are poorly influenced by CR NOx [g/kWh] NOx 1 0 500 1000 1500 2000 2500 3000 3500 25 12 Engine speed [rpm] RC 16.5 10 20 RC 15.5 RC 14.5 8 HC & CO emissions tend to 15 increase reducing CR. 6 10 HC raw [g/kWh] 4 [g/kWh] raw CO Premixing time and spray wall 5 interaction have effect on unburned 2 compound emissions 0 0 500 1000 1500 2000 2500 3000 3500 DEER 2008, Dearborn MI, 4-7° August 2008 Engine speed [rpm] 9 CRCR influenceinfluence onon maxmax PCCIPCCI torque:torque: Ind.Ind. engineengine cyclecycle 70 140 From CR 15.5 to 14.5 the τid increase PCCI mode - 1800 rpm @ 4 bar BMEP was lower than from 16.5 to 15.5. 60 120 Apart that τid is not linear with temp., . 50 100 possible cause is also the fall of τid in 40 80 the NTC range (1050÷900K) in some conditions. 30 60 CR 16.5 25 Cylinder pressure[bar] 20 CR 15.5 40 PCCI mode - 1800 rpm @ 4 bar BMEP CR 14.5 [A] current energizing Injector 10 20 20 0 0 15 -20-100 10203040 CR 16.5 C.A.[°] CR 15.5 10 CR 14.5 ROHR curves confirm that small °] [%/c.a. ROHR changes were detected varying CR 5 in terms of “thermodynamic” 0 combustion evolution -5 -10 0 10 20 30 40 C.A.[°] DEER 2008, Dearborn MI, 4-7° August 2008 10 EngineEngine OptimizationOptimization vsvs CRCR ] 10 2.5 CR 16.5 EGR has to be kept quite constant in CR 15.5 order to have same NOx. 8 2 CR 14.5 Two ECU parameters affect in opposite way both engine efficiency 6 1.5 and smoke: 4 1 • Rail pressure (friction loss / Smoke [FSN] Smoke atomization); 2 0.5 • Swirl valve position (pumping loss, FC increment w respect to E4 level [% intake valve permeability and heat loss 0 0 500 1000 1500 2000 2500 3000 3500 / fuel premixing level); Engine speed [rpm] These parameters can be optimized in order to exploit the very low smoke of the lowest CRs. Optimization work was done respecting the limits on max Injection strategy optimization was not pressure rise, exhaust smoke considered in this project but it is and max FC increment another key factor DEER 2008, Dearborn MI, 4-7° August 2008 11 EngineEngine OptimizationOptimization vsvs CRCR:: Ind.Ind. engineengine cyclecycle 70 140 PCCI mode - 2200 rpm @ 4.5 bar BMEP 60 120 Reducing Rail Pressure: . 50 100 • Less parasitic and friction losses; 40 80 • Less premixed fuel→ Lower dp/dtmax→ Early SOImain→ MBF50% 30 60 closer to TDC; Cylinder pressure [bar] reference calibration 20 40 optimized calibration Injector energizing current [A] • Less HCs&CO → Higher ηcomb 10 20 Particularly important at high speed and 0 0 medium load (late combustion) -20-100 10203040 C.A.[°] 25 PCCI mode - 2200 rpm @ 4.5 bar BMEP Reducing SW ratio: 20 reference calibration • Less pumping losses; optimized calibration 15 • Less premixed fuel→ etc…..; Diffusive combustion • Higher valve permeability→Higher 10 + Soot trapped gas mass ; ROHR [%/c.a. °] [%/c.a. ROHR 5 • Less heat losses; 0 • Less overleaning A/F zones→Less HCs & CO -5 -10 0 10 20 30 40 C.A.[°] DEER 2008, Dearborn MI, 4-7° August 2008 12 EngineEngine OptimizationOptimization vsvs CRCR:: FCFC && EmissionsEmissions Engine speed 2200 rpm Engine speed 2200 rpm ] 20 1.5 6 bar of BMEP 4 bar of BMEP 4.5 bar of BMEP 6 bar of BMEP 4 bar of BMEP 4.5 bar of BMEP 16 1 12 8 Smoke [FSN] Smoke 0.5 4 BSFC increment w respect to E4 standard [% E4 standard to wrespect BSFCincrement 0 0 reference optimized reference optimized reference optimized reference optimized reference optimized reference optimized calibration calibration calibration calibration calibration calibration Engine speed 2200 rpm Engine speed 2200 rpm 2 12 4 bar of BMEP 4.5 bar of BMEP 6 bar of BMEP 4 bar of BMEP 4.5 bar of BMEP 6 bar of BMEP 10 1.6 Increase of Stoichiometric Zones ] 8 1.2 6 0.8 4 NOx emission [g/kWh NOx HC+CO emission [g/kWh] emission HC+CO 0.4 2 0 0 reference optimized reference optimized reference optimized reference optimized reference optimized reference optimized calibration calibration calibration calibration calibration calibration FC reduction at same dp/dtmax permits the increment of Torque limit DEER 2008, Dearborn MI, 4-7° August 2008 13 EngineEngine OptimizationOptimization vsvs CR:CR: ConditionsConditions @@ 30003000 rpmrpm 70 24 PCCI mode - 3000 rpm @ 3.8 bar BMEP 60 18 50 At high speed the available premixing 40 time is low also at the lowest CR.