A COMPREHENSIVE SOLUTION FOR EFFICIENT COMBUSTION SIMULATION WITH - PowerPoint PPT Presentation

DARS FUELS – A COMPREHENSIVE SOLUTION FOR EFFICIENT COMBUSTION SIMULATION WITH DETAILED CHEMISTRY FABIAN MAUSS

Demands on kinetic models • Combination of different fuel components  … for most realistic surrogate fuels • Comprehensive mechanisms  …to cover a wide range of conditions • Reliable models  …a user can not test each model • Consistency  …to ensure a predictive chemistry in all sub-models • Fast calculation times  …to work cost and time efficiently • Table approaches  …compatible with CFD software 2

The variable mechanism concept • • Free combination of models Mechanisms for emission • The base chemistry - contains formation fuels from C1 to C6 • All these mechanisms can be • Larger fuel molecules can be combined into a reaction- combined with the base mechanism according to needs. chemistry • • Alcohol 1 Ester 1 • • Ester 2 Alcohol 2 • • Alcohol 3 Ester 3 • Aliphatic Compound 1 • Aliphatic Compound 2 • Aliphatic Compound 3 • Aromatic Fuel 1 • Aromatic Fuel 2 Base Chemistry • Aromatic Fuel 3 NOx Soot PAH 3

Validation Base chemistry I Experimental and simulated laminar flame speed for fuels, toluene, n-heptane, iso-octane, ethanol, methanol, methane, ethane, propene, ethylene, propane, butane, acetylene. Most experiments at 1bar and 300K. All data plotted with an offset for better presentation. Details can be found from Hoyermann et. al. 2004. 4

Validation Base chemistry II Experimental and simulated ignition delay times for: methane, ethylene, ethane, propene, propane, n-butane, iso-octane, methanol, ethanol and hydrogen. Data plotted with an offset for better presentation. Details can be found from Hoyermann et. al. 2004. 5

Validation targets Covering wide ranges: All mechanism are validated • against available experiments Pressure (200mbar – 70bar) in: • Temperature (500K – 2000K) • Shock tube • Mixture fraction (very lean to • Flow reactor rich conditions and pyrolysis) • • Rapid compression Dilution machine • Flames: burner stabilized, Against different targets : freely propagating, • Ignition delay counter flow • Fuel decomposition • Intermediates • Emission • Heat release • Flame speeds 6

Key Features Libraries for CFD software Reduced stiffness • • Pre compiled libraries for direct Using different techniques to use in simulations reduced the stiffness of a mechanism -> short • Compatibility with STAR-CD computational time, even with products detailed models Consistency Compact even in detailed format • Reaction • Only species which are • Names important for the • Thermodynamic data decomposition of the fuel are • Transport properties included Multiple formats • The mechanisms are available in various formats 7

Key Features Good documentation Soot • Integrated modeling of soot Rule based Semi Automatic precursors Generation* Complete solution • Mechanism generation for • From mechanism development larger alkanes based on rules to table generation • Rules tested against several • From detailed reaction schemes alkanes to highly reduced, special • Extrapolation to fuels without purpose mechanisms experimental base • Constant development Automatic graph based generation -> efficient and • Constant improvement and less error prone development of new models *M. Hilbig, L. Seidel, X. Wang, F. Mauss, and T. Zeuch. ´“C omputer aided detailed mechanism generation for large hydrocarbons: n-decane .” 23rd ICDERS, 2011. 8

Example for a complete validation Complete validation for an n-decane reaction mechanism. Validation against all available experiments in literature for: • flames • perfect stirred reactor and • shock tubes Specifications: • Detailed: 374 species ⁻ including detailed NOx, soot formation and all fuels from the base chemistry. • Skeletal: 193 species - including detailed NOx, soot formation and a reduced set of fuels in the base chemistry 9

Example for a complete validation Laminar flame speeds at atmospheric pressure and different temperatures. 10

Example for a complete validation Concentration of major species in a Jet Stirred Reactor at 10 atm. 11

Example for a complete validation Ignition delay times in a shock tube Ignition delay times in a shock tube at Φ =0.25. at Φ =0.5 and Φ =0.67. 12

Example for a complete validation Ignition delay times in a shock tube Ignition delay times in a shock tube at Φ =1.0. at Φ =2.0. 13

Example for a complete validation Species concentration over the hight of the burner in a (disturbed) burner stabilized flame at 1 atm. 14

Available mechanisms Group Chemistry Reference fuel for Oxygenated methanol, ethanol, propanol Gasoline, Bio fuels Mono aromats toluene, m-xylene Gasoline, Diesel, Jet a -methylnaphalene Larger aromats Diesel, Jet Linear alkanes n-heptane, n-decane Gasoline, Diesel, Jet Branched alkanes iso-butane, iso-butane, iso-pentane, iso- Gasoline, Diesel, Jet octane, iso-dodecane Ester methyldecanoate Biodiesel Additives DME Gasoline Other methane, ethane, propane, butane, Natural gas, Biomass to pentane, neo-Pentane, ethylene, acetylene, gas / liquid, turbines propene, hydrogen and others Emission NOx, soot, formaldehyde, unburnt HC and Combinable with all fuels other 15

Multi-component Fuels example Ignition dealy times for a mixture of 56% iso-octane, Ignition dealy times for a mixture of 62% iso-octane, 17% n-heptane and 28% toluene at 50bar. 18% n-heptane and 20% toluene at Φ =1.0. Variation of Φ =0.5, 1.0, 2.0 Variation of pressure: 30bar, 50bar 16

Reference Fuels Properties Euro 4* USA Japan** ROZ (Regular) min. 95 min. 90 min. 89 typical around 92 ROZ (Premium) min. 98 min. 95 min. 96 typical around 100 Ethanol up to 10% in regular up to 3% Aromat content (vol max. 35 max. 22 (California) No regulation - %) typical around 22% (Regular) to 37% (Premium) Ethanol Fuels max. 10% in Regular E10 / E85 / E95 - E5 / E10 / E75 / E85 Gasoline specifications in different * DIN EN 228 countries ** JSAE Review 21 (2000) 457-462 17

Reference Fuels Development of reference fuels based on different criteria: • • Combustion Behavior Physical Properties – Ignition delay time – Density – Octane / Cetane Number – Lower Heating Value – Emission formation • Chemical Properties • – Fraction of chemicals in the Direct testing in engine models fuel, such as aromatics, alkanes, ester… – Ignition behavior – Boiling line 18

EURO 4 - E5 Reference Fuel 4 Component E5 reference fuel Properties Target Mixture ROZ 95 95 LHV [MJ/kg] 40,1 – 41,8 41,0 Ethanol [vol %] 5 5 Aromatic [vol %] 35 35 Density [kg/L] 0,72 – 0,775 0,74 Reference fuel (mole fraction): • ethanol: 0.11 • toluene: 0.405 • iso-octane: 0.354 • n-heptane: 0.131 19

Reduction / Tables – ECFM Reduction of reaction schemes size using: – Flamelet Soot – Horizontal lumping* • Soot source term library – Chemical guided – Flamelet NOx reduction* • NOx source term library – Flame Speed Various table solutions • Laminar flame speed, used – Can be used with STAR-CD, by e.g. Level-Set and ECFM STAR-CCM+ models – Precompiled from detailed – PVM reaction schemes, ready to • Progress variable auto- use ignition and thermodynamics – Covering a wide range of library engine conditions *S. Ahmed, F. Mauss, and T. Zeuch.“ The generation of a compact n-heptane/toluene reaction mechanism using the chemistry guided reduction (CGR) technique .” Z. Phys. Chem., 223:551{563, 2009 20

DARS Fuel • • Accurate reaction schemes – Free basic mechanism for ready to use! TIF/PVM – Plug in to STAR-CD, STAR- – Diesel CCM+, DARS-TIF – Gasoline – No additional work needed – Requires a DARS license • Free basic libraries for ECFM • Other fuels are available as – Diesel library on license base – Gasoline – Pure components – Multicomponent mixture – Dual fuel libraries 21

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