Chemkin_内燃机仿真

● Knock reduction ● Emissions control
lexibility ● Exhaust-gas recirculation ● System control
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Challenges for using detailed kinetics
TDC
20º ATDC
20º ATDC
STAR-CD simulations with simplified chemistry
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An engine system is a chemical plant
Fuel
Air (O2 + N2) Horsepower CO2 + H2O CO, NOX ,PM Unburned HC Pt / Rh CO2 + H2O
Air (O2+N2)
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There is a gap between CFD simulation and testing requirements
Goal: Minimize emissions while maximizing efficiency
10º BTDC
Workflow is incomplete CFD users cannot predict chemistry effects adequately
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Real fuel components can be categorized
50 40 30 20 10 0 alkanes alkenes isoalkanes aromatics miscellaneous cycloalkanes cycloalkenes
Example: Gasoline*
*Reported by: C. V. Naik, et al SAE 2005-01-3742
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With a database of molecules, we can assemble an appropriate surrogate
Real Fuel Characteristics • Class composition • Heat-release rate • Octane / Cetane # • H/C ratio, O content
● Detailed chemistry models are built for each molecule
– Use elementary reactions – Allow merging to form mixtures
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Different model fuels can be assembled for different applications
Strategies for Using Detailed Kinetics in Engine Simulations
Ellen Meeks ERC Symposium: Fuels for Future IC Engines June 6-7, 2007 Madison, Wisconsin
Outline
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Addressing the challenges…
● Real fuels are too complex ● Validated detailed mechanisms are scarce ● Simulations are too time-consuming ● Companies often lack chemistry expertise
● Tailor to prediction of desired combustion and physical properties:
– – – – – Ignition delay Knocking tendency Flame speeds Pollutant emissions Sooting tendency & particle size distributions
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How effective can simulation be?
● According to our customers, it depends on the accuracy:
– Needs to be predictive to
Allow exploration and discovery Guide design and testing
CFD Simulation: Determine effects of port flow distribution, injector design, injector timing, piston bowl geometry
TDC
20º ATDC
Ignition delay, CO, UH, PM, etc.
Real Fuel Component iso-paraffins normal paraffins single ring aromatics cyclo-paraffins olefinic species multi-ring aromatics oxygenates Surrogate Fuel Candidate iso-octane, hepta-methyl nonane n-heptane, n-hexadecane toluene methylcyclohexane 1-pentene alpha-methyl napthalene methyl stearate, methyl linoleate
No
aromatics
Group Contribution
Surrogate Fuel & Oxidizer
Properties
Stored Data
Groups
Quantum Chemistry
Experimental Data
Kinetic Rates
OK?
Yes
e n-h
olefins
xad eca ne
● Real fuels are too complex ● Validated detailed mechanisms are scarce ● Simulations are too time-consuming ● Companies often lack chemistry expertise
– Methyl-ester structures – Contain oxygen
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Surrogate fuel mixtures can be used to represent real fuels in simulations
● 1 or 2 molecules represent each significant chemical class, e.g.:
Geometry A
Example Goal: Maximize uniformity in piston bowl
Geometry B
10º BTDC
10º BTDC
TDC
CFD Simulation: Determine effects of port flow distribution, injector design, injector timing, piston bowl geometry
*/toxprofiles/tp72-c3.pdf
● Classes of chemical compounds have
– Common molecular structures – Similar chemical behavior
● Biofuels have different compositions
– Must provide deep understanding of dependencies to
Manage complexity of tradeoffs Facilitate innovative solutions
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Computational fluid dynamics (CFD) is already widely used for engine design
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Test: Determine emissions, efficiency, performance
Detailed chemistry is required to address many important issues
● Ignition timing
– Diesel – HCCI/CAI
● Role of simulation in design ● Importance of chemical kinetics ● Challenges of using detailed kinetics ● Strategies that bridge the gap between design simulation and kinetics
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Simulation reduces cost of development
Cost Testing
● There is a growing opportunity to:
Simulation Complexity, Capability, Time
– – – –
Reduce risk Improve use of testing Speed development Facilitate innovation
c-paraffins i-paraffins
Based on work in collaboration with the Dow Chemical Company
n-paraffins
Chemical Chemical Mechanism Mechanism
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Validation focused on mechanismgeneration rules is key to building database
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Example shows prediction of ignition delay with 5-component mixture
● Surrogate mixture compositions defined to match class composition or RON #*
– All do reasonably well in capturing ignition behavior with idealized model of engine, detailed kinetics
n-heptane Iso-octane 19% 1-pentene mchexane 45% m-xylene
e an pt he n-
15% 3% 1% 15%
ethanol
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Addressing the challenges…
● Real fuels are too complex ● Validated detailed mechanisms are scarce ● Simulations are too time-consuming ● Companies often lack chemistry expertise
aromatics olefins c-paraffins i-paraffins n-paraffins
U.S. E15 Gasoline
Match Properties • Select Molecules • Set Composition Merge Mechanisms • Species • Reactions Surrogate Fuel Composition Chemical Model for Simulation
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Mechanism generation for a molecule can be fully automated
Reaction Patterns Determine Reactions and Molecules Determine Properties of Molecules Determine Kinetic Rate Parameters Simulate Target Experiments Rules