Fuel Effects in Advanced Combustion -Partially Premixed Combustion (PPC) with Gasoline-Type Fuels William Cannella Chevron
Acknowledgement Work Done In Collaboration With: Vittorio Manente, Prof. Bengt Johansson, Prof. Per Tunestal Lund Institute of Technology Department of Energy Sciences Division of Combustion Engines Lund, Sweden SAE Publications: 2009-01-2668 2010-01-0871 2010-01-1471 2010-01-2198
Goals for Advanced Combustion Systems Improve engine efficiency/fuel economy and meet CO 2 emissions regulations Lower engine-out NOx and PM/soot emissions to meet stricter regulations Reduce size, costs, and fuel consumption penalties of aftertreatment systems (especially NOx) Operate effectively over wide speed/load range In Europe: Options for mitigating diesel/gasoline supply/demand imbalance
Partially Premixed Combustion Characteristics: Avoid conditions that cause NOx & soot formation in conventional diesel CI combustion -- form of PCCI Fuel/air mixing intermediate between HCCI & conventional CI combustion ( partial premix ) Better performance than HCCI due to some fuel/air stratification Approach: One or two fuel injections When used, first one placed @ -60 TDC to create homogeneous mixture (Similar to Toyota Unibus approach) Last injection around TDC (to achieve CA50 @ MBT ~5-10 ATDC) - Stratification created by this injection triggers combustion. Same energy content injected per fuel EGR used to prevent early reaction during compression stroke [a.u.] 1 0.8 0.6 0.4 0.2 0 Const. Load & CA50 Pilot quantity function of: -Fuel properties -Operating conditions -60-50 -40-30 -20-10 0 10 CAD [TDC]
Study Objectives Test effects of properties of different gasoline range blends in HD CI engine operated under Partially Premixed Combustion Mode Different fuel properties/composition Different reactivity Different ignition and combustion characteristics Different effective speed/load operating ranges
Fuel Selection Gasoline-type fuels selected based on prior results which suggest gasoline may better achieve goals than diesel fuel in PPC due to higher volatility and longer ignition delay (SAE2006-04-3385, SAE2007-01-0006, SIAT 2009) Blends of refinery gasoline range components: Studied fuel property effects by blending streams with different compositions and RON s RON s ranging from 69-99 also tested Gasoline Fuel RON MON C H/C LHV [MJ/kg] A/F stoich 99.00 96.90 7.04 2.28 44.30 15.10 92.90 84.70 6.90 1.99 41.60 14.02 88.60 79.50 7.21 1.88 43.50 14.53 87.10 80.50 7.20 1.92 43.50 14.60 80.00 75.00 7.16 1.97 43.70 14.65 70.30 65.90 7.10 2.08 43.80 14.83 69.40 66.10 7.11 1.98 43.80 14.68 107.00 89.00 2.00 3.00 26.90 9.00
Typical Refinery Streams 50 < ON < 75 90 < ON < 99 Gasoline-range streams having octane numbers as low as ~50 exist in refineries and are used to make gasoline blends
Engine Characteristics Scania D12 Heavy Duty Diesel Engine Single Cylinder Bosch Common Rail Prail 1600 [bar] Orifices 8 [-] Orifice Diameter 0.18 [mm] Umbrella Angle 120 [deg] Engine / Dyno Spec rc geometric 14.3* [-] BMEPmax 15 [bar] Vd 1951 [cm3] Swirl ratio 2.9 [-] * - Standard rc geometric = 17.1 Issue: Old, first generation Bosch injector impacts soot emissions
Achieving low CO, HC, NOx & soot: -Controlling T through EGR & λ Temperature [K] 2400 2200 2000 1800 1600 1400 Adiabatic Flame Temperature λ=1 λ=1.1 λ=1.2 λ=1.3 λ=1.4 λ=1.5 λ=1.6 λ=1.7 λ=1.8 λ=2 λ=2.5 λ=3 λ=3.5 λ=4 1200 1000 30 35 40 45 50 55 60 65 70 EGR Ratio [%] Preferred PPC operating region: If lambda is ~ 1.5 and EGR between 45 55 %, combustion should occur in the desired temperature range Low NOx and low HC & CO!!! In addition, should still be enough O2 to limit soot production.
Base Test Conditions Dyno LIMIT
Injection Parameters Higher ON gasolines & ethanol required significant amount fuel in pilot Higher ON gasolines & ethanol required high Tin to run lower loads T inlet vs. Load Inlet Temperature [K] 440 420 400 380 360 340 320 300 2 4 6 8 10 12 14 16 18 20 Pilot Ratio [%] 100 90 80 70 60 50 40 30 20 10 Pilot Ratio vs. Load 0 4 6 8 10 12 14 16 18 20 11 Lower ON gasolines performed best with no pilot
Engine-Out NOx and Soot Emissions NOx [g/kwh] 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 NOx vs. Load NOx below US10 limit for most fuels/conditions (little to no aftertreatment needed!) No correlation with RON/MON Soot [FSN] 0.1 0.05 0 2 4 6 8 10 12 14 16 18 20 2.5 2 1.5 1 0.5 Soot vs. Load Low RON Soot [FSN] 3 2.5 2 1.5 1 0.5 Significant improvement in soot when modern injection system used (but DPF still needed for gasolines) G. ON 99/97 G. ON 98/88 G. ON 97/86 G. ON 93/85 G. ON 89/80 G. ON 87/81 G. ON 80/75 G. ON 70/66 G. ON 69/66 D. CN 52 PRF20 Diesel Fuel (CN=52) 0 2 4 6 8 10 12 14 16 18 20 EtOH 0 0 5 10 15 20 25 30
Efficiencies 100 Combustion Efficiency vs. Load Combustion Efficiency [%] Gross Indicated Specific Fuel Consumption [g/kwh] 99.5 99 98.5 98 97.5 97 96.5 96 95.5 95 2 4 6 8 10 12 14 16 18 20 Gross Indicated Phase Specific 4, 1300 [rpm] Fuel Consumption 180 175 170 165 160 155 150 145 140 4 6 8 10 12 14 16 18 20 Gross Indicated Efficiency [%] 60 58 56 54 52 50 48 46 44 42 down to 150g/kwhr! Very high combustion and gross indicated efficiencies over entire load range Approaching 56%! Gross Indicated Efficiency vs. Load 40 2 4 6 8 10 12 14 16 18 20
Maximum Pressure Rise Rate (MPRR) Max Pressure Rise Rate [bar/cad] 25 20 15 10 5 Lower ON fuels had lower MPRR s at high loads 0 2 4 6 8 10 12 14 16 18 20
Load Operating Area Inlet Temperature [K] 440 420 400 380 360 340 T intake vs. Load If T intake limited to ~330 K: 320 300 2 4 6 8 10 12 14 16 18 20 o With no T intake constraints, all fuels tested able to operate at all loads o With reasonable T intake constraints: all fuels tested able to operate at the higher loads only the lowest RON fuels able to operate at the lowest loads
CA50 Sweep: NOx soot-efficiency 0.5 NOx vs. CA50 4.5 Soot vs. CA50 Indicated NOx [g/kwh] 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 US 2010 Limits 0-5 0 5 10 15 20 25 Combustion Phasing, CA50, [TDC] Gross Indicated Efficiency vs. CA50 Soot [FSN] 4 3.5 3 2.5 2 1.5 1 0.5 0-5 0 5 10 15 20 25 Combustion Phasing, CA50, [TDC] Nissan MK type combustion, easier to achieve with fuels with high octane number. For this engine system and mode of operation, optimal timing appears to be ~5-10 ATDC
Summary Gasoline PPC enabled simultaneous achievement of high efficiency, low emissions and acceptable MPRR s at all loads tested (5-18 bar gross IMEP) in heavy duty CI engine with EGR~50%, λ =1.5, & CA50=5-10 ATDC Able to run all gasoline fuels and ethanol at all loads tested Lower ON fuels could be run with reasonable intake T s & 0% pilot Higher ON fuels (incl. ethanol) required high intake T s & significant % fuel in pilot to run @ lower loads Gross indicated efficiency between 52-56% attained for loads higher than 6 bar gross IMEP. (Gross ISFC s down to 150 g/kwhr) Engine-out NOx below US2010 limits without aftertreatment At highest load soot was between 0.2-2 FSN. (<0.5 FSN with modern injection system). Acceptable level with DPF s At high loads, Maximum Pressure Rise Rates (MPRR) were best for the lower ON fuels, with values of ~12 bar/cad 17