Strategies for Optimization of Engines, Fuels, and Aftertreatment

Transcription

1 Strategies for Optimization of Engines, Fuels, and Aftertreatment Bruce G. Bunting senior staff scientist Fuels, Engines, and Emissions Research Center Oak Ridge National Laboratory University of Wisconsin Engine Research Center Symposium: Fuels for Future Internal Combustion Engines June 6-7, 2007

2 What I want to show Fuel plays a role in HCCI engine performance HCCI engines put out pollution, too Some effects same as conventional engines, some different Aftertreatment needs to play a role Fuel economy considerations can drive choices Order of talk: Fuels Engines Aftertreatment Interactions (examples, data) Conclusions

3 Scope of this talk - fuels Liquid fuels Compatible with existing fuels and infrastructure Compatible with current in-use vehicles Meaning: Gasoline Diesel Bio-derived fuels or blend components Allowing for the slow evolution of these fuels as driven by Market requirements Legislation Product differentiation Source and type of raw material oil sands, oil shale, coal, NG, corn, oil crops, cellulose, etc.

4 Why did I set the scope here? If a new fuel requires a new infrastructure, it is going to happen slowly A new fuel type will take time to develop sufficient volume to make a difference Companies, investors, and the public have choices and take time to decide Every possibility for a significant transportation fuels that I see for my lifetime fits into this scope (except maybe electric) But, hey, I am here to learn, too

5 Fuels defined Fuels have specifications Cetane, octane, distillation, vapor pressure, flash point, stability And simple chemistry specifications Sulfur, aromatics And more chemistry, more chemistry And, eventually, individual molecule types How far do you need to go to control manufacturing and quality? How far do you need to go to understand and optimize?

6 Fuels defined OIL SANDS DERIVED DISTILLATE FUELS AND INTERMEDIATE STREAMS F6-483 F6-482 F6-606 F6-530 F6-605 F6-480 F6-607 F6-531 Density ASTM D4052 g/ml, 15 C Viscosity ASTM D445 cst, 40 C Sulfur content ASTM D5623 mg/l Carbon content ASTM D5291M wt% Hydrogen content ASTM D5291M wt% Nitrogen content ASTM D4629 mg/l Saturates SFC ASTM D5186 mass % Total Aromatics SFC ASTM D5186 mass % Mono-Aromatics SFC ASTM D5186 mass % Di-Aromatics SFC ASTM D5186 mass % Poly-Aromatics SFC ASTM D5186 mass % Saturates PIONA+SOAP-SPE mass % Olefins PIONA+SOAP-SPE mass % Aromatics PIONA+SOAP-SPE mass % Polars PIONA+SOAP-SPE mass % Cloud Pt C deg.c < Pour Pt. C deg.c -21 <-60 < < Cetane Index D976 ASTM D Cetane Number na Boiling point curve ASTM D86 Distillation IBP Boiling point curve ASTM D86 Distillation 5% Boiling point curve ASTM D86 Distillation 10% Boiling point curve ASTM D86 Distillation 60 20% Boiling point curve ASTM D86 Distillation 50% Boiling point curve ASTM D86 Distillation 70% Boiling point curve ASTM D86 Distillation 90% Boiling point curve ASTM D86 Distillation 95% Boiling point curve ASTM D86 Distillation FBP % distilled temperature, C DISTILLATION CURVES (#2 SPECS IN RED)

7 Diesel vs. B100 Concentration (a.u.) ECD1 C11 C12 C13 C14 C15 C17 C16 C19 C18 C20 C21 C22 C23 C24 SME B100 Mixed C18 Methyl esters C16 methyl ester C9 C10 C Elution Time Elution Time Biodiesel is far more monolithic than petrodiesel Higher, narrower boiling point distribution Fewer types of molecules No low MW components

8 2D-GCMS provides individual molecular composition of complex fuels (up to ~ 2500 compounds) SR- HGO SR- LGO POLAR AROMATICS CYCLOPARAFFINS OLEFINS PARAFFINS LIGHT.HEAVY NON-POLAR METHYL ESTERS B20- SOY PEAK # COMPOUND % COMPOSITION 85 n-c n-c n-c Hexadecane n-c Cyclotetradecane Pentadecane Cyclodecene, 3-bromo Spiro[2.3]hexan-4-one, 5,5-diethyl Octadecyne, 2-methyl Eicosane Heptadecene, 1-chloro C14-diene Cyclopentane, hexyl Methyl-4-(1-methylethyl)-cyclohexane Tetradecane n-nonylcyclohexane n-c Dodecane Heptadecene, 17-chloro Anthracene-D Cyclopentane, 1-methyl-3-(2-methylpropyl) n-c Naphthalene, C4-decahydro Cyclopentane, hexyl Heptadecane, 2,6,10,14-tetramethyl etc etc etc Search routines identify 1000 s of compounds Fuel issues confound automated identification of HCs Experimental procedures must match analysis goals

9 Fuel energy content Virtually all fuels have different energy contents Energy content can be measured on a Volumetric basis (if you are interested in miles per gallon) Weight basis (if you are interested in grams per kw-hr) For HC fuels Higher energy on weight basis favors high H/C, lighter fuels Higher energy on volume basis favors low H/C, heavier fuels Oxygen containing fuels have a lower energy content In fuels and engines research, it is common to zero out energy content by comparing on an energy efficiency basis But, that doesn t get you any farther on a tank of fuel!!! density vs. % aromatics fuel energy content density, gm/cc % aromatics energy content, btu per xx btu/gram 40 btu/cc % aromatics

10 HCCI combustion Defined here as fully premixed combustion with ignition initiated kinetically near top of compression stroke (traditional HCCI) Temperature is main initiator of combustion Intake heating, retained exhaust, higher compression ratio Burning rate must be moderated Lean mixtures excess air Dilute mixtures EGR, retained exhaust, and/or excess air Advantages - potential for more efficient combustion Fast combustion, un-throttled operation (maybe), high compression ratio (maybe), less heat loss to cylinder wall (maybe) Low NOx and low smoke Risks - under development - potential issues include Lower power density, more difficult to control, combustion noise, control compromises leading to reduced fuel efficiency, more sensitive to fuel variations

11 Why focus on this engine type for our fuels research? Easy to build, operate, model, and understand Good for fuels research Don t need much fuel (5 gallons is usually enough) Chemistry happens sequentially Separation of LTHR and HTHR Same processes happen in all engines But more mixed up in time and space

12 By the way, ORNL Fuels, Engines, and Emissions Research Center also has. 35 engineers, scientists, post graduates 6 engine test cells 12 engines currently installed 8 to 600 hp Several advanced PCCI engines Advanced emissions characterization capabilities Research in combustion, controls, fuels, aftertreatment, and emissions characterization DOE funding and private funding Partnerships with industry, universities, other labs Speed ft/s Accel ft/s/s VW Jetta Tailpipe NOx emissions, mg/s NOx mg/s Offsite Projects Simulink Model

13 Two specific research platforms ORNL HCCI engine Converted from small industrial diesel Highly premixed true HCCI Lean, with intake air heating Diesel or gasoline range fuels AVL HCCI engine Located at AVL, used under subcontract Hydraulic variable valve actuation, 60 to 70% retained exhaust Dilute, nominally stoichiometric Highly premixed true HCCI Gasoline range fuels Same fuel effects occur in more complex engines in certain operating modes, certain times, or select regions in combustion chamber

14 ORNL Research Platform ENGINE INTAKE AIR HEATER MODIFIED PISTON WITH SPHERICAL COMBUSTION BOWL BELT DRIVE ATOMIZING INJECTOR Engine Displacement (cc) Bore (cm) Stroke (cm) 7.0 Compression Ratio 10.5:1 Intake Valve Opening (CA deg) 710 CONSTANT SPEED MOTORING DYNO Intake Valve Closing (CA deg) Exhaust Valve Opening (CA deg) Exhaust Valve Closing (CA deg) Intake Air Temperature ( C)

15 AVL single cylinder research engine Capable of HCCI, mixed mode, and conventional operation 500 cc, C/R 2 valves, naturally aspirated Gasoline port fuel injection Spark ignition Fully variable valve actuation HCCI currently initiated by early exhaust valve closing negative overlap Retains heat in cylinder Retains internal EGR Typically operates at > 50% EGR

16 Does an HCCI engine need aftertreatment? Many of the same emission production zones can exist as in a conventional engine Rich, lean, quenched, stoichiometric, dilute R Reitz, 2005 An HCCI engine may need to transition to conventional operation at higher load or other conditions (cold operation, starting, etc.) Generally, HCCI engines are more uniformly lean, but can be stoichiometric with very high levels of EGR Fuel economy considerations may drive emissions characteristics

17 Aftertreatment choices NOx Three way catalyst Lean NOx (SCR, LNT, or other) Smoke, particulate Oxidation cat DPF HC, CO Oxy cat TWC DPF lean NOx

18 Interactions, data, examples Example 1, combustion phasing and fuel specific effects Example 2, oxidation catalyst on HCCI engine Example 3, TWC catalyst potential of HCCI engine

19 Example 1 Combustion phasing, efficiency, and fuel effects Diesel HCCI engine 17 fuels and blend streams derived from oil sands crude 34 to 60 cetane 196 to 336 C T50 16 to 41% aromatics, ~50% cyclo-paraffinic Identified optimum combustion behavior and fuel specific effects

20 Fuel efficiency shows both engine specific and fuel specific trends 10.5 gm/min fuel rate f f439 f440 FUEL SPECIFIC 340 f441 f444 ENGINE SPECIFIC ISFC, ISFC, gm/kwhr gm/kw-hr f445 f446 f447 f480 f481 f482 f483 f530 f TDC -> f605 f606 f COMBUSTION MFB50, PHASING, deg.ca MFB50

21 Ability to advance timing limited by NOx, dp/dca, peak pressure, noise, etc. NOx at 10.5 gm/min fuel rate 250 NOx, ppm NOx ppm f438 f439 f440 f441 f444 f445 f446 f447 f480 f481 f482 f483 f530 f531 f605 f606 f MFB50, deg.ca COMBUSTION PHASING, MFB50

22 Ability to retard timing limited by incomplete burning, high CO CO ppm vs. MFB50 at 10.5 gm/min fuel rate 2500 CO, ppm ppm f438 f439 f440 f441 f444 f445 f446 f447 f480 f481 f482 f483 f530 f531 f605 f606 f607 bp MFB50 COMBUSTION PHASING, MFB50

23 And high HC HC ppm at 10.5 gm/min fuel rate 4500 HC, ppm HC ppm f438 f439 f440 f441 f444 f445 f446 f447 f480 f481 f482 f483 f530 f531 f605 f606 f607 bp COMBUSTION MFB50 PHASING, MFB50

24 Best achievable ISFC correlates to cetane and T50 best ISFC vs. cetane Best ISFC vs. T R 2 = R 2 = best ISFC best ISFC cetane number T50 distillation temperature, deg.c Don t forget, cetane and T50 also correlate to energy content and % aromatics and % heavy aromatics

25 Variations on 2D-GCMS spectra FUEL 606 GOOD ISFC LOW CETANE LOW T50 FUEL 444 GOOD ISFC MID CETANE HIGH T50 POLAR AROMATICS CYCLOPARAFFINS OLEFINS PARAFFINS LIGHT.HEAVY FUEL 530 POOR ISFC HIGH CETANE LOW T50 NON-POLAR FUEL 438 POOR ISFC LOW CETANE HIGH T50

26 Example 2 Diesel HCCI engine Temperature (load) specific emissions behavior Performance of two different oxy cat formulations

27 Diesel HCCI engine, lean, shows increasing CO and HC at low exhaust temperatures, increasing NOx at high exhaust temperatures (load) Diesel HCCI engine emissions vs. exhaust temperature HC CO NOx CO, HC, ppm NOx, ppm exhaust temperature, C

28 Low temperature light-off for CO and HC are important due to low exhaust temperatures of dilute-operation engines, not all catalysts perform the same Oxidation catalyst performance vs. exhaust temperature % HC or CO reduction cat 1 HC cat 1 CO cat 2 HC cat 2 CO exhaust temperature, C

29 Example 3 Stoichiometric gasoline HCCI engine Early exhaust valve closing used to control HCCI ignition Emissions characteristics vs. lambda Fuel efficiency characteristics vs. lambda Stoichiometric operation for TWC may not match optimum fuel efficiency

30 NOx ppm NOx, ppm Stoichiometric HCCI engine looks like a conventional gasoline engine (AVL VVA) HC, ppm lambda HC ppm lambda CO, ppm CO, ppm lambda FUEL ON TIME, μs IMEP=2 to 5 bar ON 3650 ON 4200 ON 4650 ON 6250 ON 6450

31 If engine is run stoichiometric, a TWC should work, but fuel economy favors lean operation 280 FUEL ON TIME, μs ISFC, gm/kwhr lambda ON 3650 ON 4200 ON 4650 ON 6250 ON 6450 We are returning to AVL to Map engine for wider lambda range (0.9 to 1.5) Operation and fuel economy Including a TWC to map catalyst operation and performance

32 Conclusions Fuel characterization can be carried down to individual molecules Refiners and researchers generally work with simpler data sets How far do you need to go Fuel properties and chemistry do affect HCCI engine performance and optimization HCCI engines put out pollutants, too Aftertreatment will be required Fuel economy considerations can drive choices THANK YOU FOR YOUR TIME!