cimac congress bergen 2010 s ox
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CIMAC Congress Bergen 2010Paper no. 39
16.6.2010© MAN Diesel & Turbo < 1 >
Anders Andreasen & Stefan MayerBasic Research
Process Development R&D / Marine Low Speed
Modelling fuel sulfur oxidation in low speed two-stroke diesel engines
§ Background and motivation
§ Review of current models for S oxidation
§Model description and calculational setup
§ Results
Presentation outline
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§ Proposed model simplifications
§ Summary & Outlook
< 2 >Modelling fuel sulfur oxidation in low speed two-stroke diesel engines
Objective:Provide a realistic, applicable model capturing the essential physics of SO2oxidation in large two-stroke diesel engines for in-house 0D to 3D computationalcodes. Obtain a better understanding of the main mechanisms involved in corrosionalwear of the cylinder liner
§ HFO average Sulfur content ~ 2.5 wt. % (4.5 % max.)
Background & motivation
Source: MEPC 57/4/24
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§ Sulfur oxidised during combustion
Background & motivation
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Background & motivation
Schramm et al. SAE paper, 940818§ Acidic species transported to cylinder liner
§ Acidic species cause (un)desirable corrosion
§ Corrosion controlled trough TBN of lube
§ Challenge: Low sulfur fuel & predicting scuffing
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Background & motivation
Lube base deposits may result
§ Acidic species transported to cylinder liner
§ Acidic species cause (un)desirable corrosion
§ Corrosion controlled trough TBN of lube
§ Challenge: Low sulfur fuel & predicting scuffing
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Lube base deposits may result in bore polish and scuffing
Required knowledge§ Acidic species formed: How, when and how much?§ Transport mechanism of acidic species to lube oil film§ Lifetime and behaviour of acidic species in lube oil (Ostwald ripening?)
§ Lube oxidation behaviour (depleting neutralising agents)
Background & motivation
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Oxidation
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Oil oxidation
Neutralization
Wetting corrosion
SO3/H2SO4 SO2/H2SO3 CO2/H2CO3
Neutralisation (wasteful)Base
Oil film surface
Cylinder liner
Lube
oil
film
After van Helden, CIMAC 1987
§ Frozen equilibrium approach§ A fixed user-defined conversion§ Detailed kinetic mechanism
Review of current models
Conversion, εεεε Ref.
Frozen eq. ~20% Teetz, VDI, No. 626/1984
Mod
el
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Frozen eq. ~20% Teetz, VDI, No. 626/1984
Fixed conversion 3-5% (user defined) Schramm, SAE 940818van Helden, CIMAC 1987
2 stroke Diesel ~4-4.5 J. J. Valente, J. F. Pessoa Amorim, CEM, Macau, June 2006
4 stroke Diesel 2-8% Engel et al., J. Eng. Power, vol. 101 (1979) pp. 598
Boilers 0.2-7% Hunter et al. Contract no. ARB 4-421
Mod
elE
xper
imen
t
§ Sulfur oxidation mechanism from Glarborg et al. § H/O subset. 28 elementary reactions§ S subset. 97 elementary reactions§ Species thermodynamic parameters from NASA polynomials§ Cantera (http://code.google.com/p/cantera/) used to handle
calculation of thermodynamics and integration of kinetic rate equations
Model description
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species(name = "SO3",atoms = " S:1 O:3 ",thermo = (
NASA( [ 1000.00, 5000.00], [ 7.075737600E+00, 3.176338700E-03, -1.353576000E-06, 2.563091200E-10, -1.793604400E-14,-5.021137600E+04, -1.118751760E+01] )
),note = "BUR0302 J 9/65“)
# Reaction 92reaction( "SO3 + O <=> SO2 + O2", [2.80000E+04, 2.57, 29200])# Reaction 88falloff_reaction( "SO2 + OH (+ M) <=> HOSO2 (+ M)",
kf = [5.70000E+12, -0.27, 0],kf0 = [1.70000E+27, -4.09, 0],falloff = Troe(A=0.1, T3=1e-30, T1=1e+30),efficiencies = " H2O:5 N2:1 SO2:5 ")
§ Detailed kinetic mechanism coupled to multi-zone approach§ Post-processing of measured cylinder pressure§ Differential fuel amount from calc. intgr. heat release (1 CAD)
Model description
ParcelAir@ λ =1 EVO∆Fuel
Hea
t rel
ease
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Equilibrate (HP)
Mix air @ Mix air @ airmixm&
Integrate rate eq.Sulfur
NOx (Zeldovich)
For
eac
h C
AD
rep
eat
1 2
1
3
2
1
n
n-1
2
1
∆CAD=1º
SOIH
eat r
elea
se
CAD
§ Tuning the mixing rate parameter (75% load)§ Matching calculated NO with measured§ Finding corresponding mixing rate and ε
Results: Tuning
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Measured NOx
Mix rate 3.29ε = 4.43
Results: Details @ 75 % load (MCR)
Main sulfur speciesconcentrations
NO concentration
SO2
SO3
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Temperature
SO2 Conversion, ε
SO3
§ Range of ε§ Variation in fuel S content
Results: Summary and quasi-validation
Load (%) Epsilon (%)
100 2.59
75 4.43
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50 4.25
25 6.72
Experiments on 4-stroke heavy duty diesel enginesSource: Engel et al., J. Eng. Power, vol. 101 (1979) pp. 598
§ Range ε =1.8-7.7 % (0.2-7% for boilers, Hunter et al. Contract no. ARB 4-421)§ Decreasing ε with increasing S content § Decreasing ε with increasing load (and decreasing exhaust oxygen conc.)
Good agreement with experiments!
§ CycSim: In-house C++ (Object Oriented) Cycle-simulator
§ Zone number reduced from ~50 to 1-2§ Computational effort reduced§ Model concept upgraded from post-processing to
prediction also
Results: applications to two-zone combustion in cyclic simulation
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Slightly different, but general trends are preserved!
§ Current detailed model computational demanding§ Decrease calculation time by model reduction
Step 1: SO2 + OH (+M) = HOSO2 (+M)Step 2: HOSO2 + O2 = SO3 + HO2
Step 3: SO2 + O (+M) = SO3 (+M)Step 4: SO + OH = SO + H
Model simplifications
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Step 4: SO2 + OH = SO3 + HStep 5: SO3 + H2O = H2SO4
< 15 >Modelling fuel sulfur oxidation in low speed two-stroke diesel enginesReaction flow analysis
97 rate equationsreduced to 5!No loss in predictions!
Conclusions§ Detailed model applied with success§ Qualitative agreement between calculations and experimental findings§ Model simplifications possible (reduction in steps, zone no.’s)
Future work
Summary & Outlook
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§ Apply reduced model in CFD code for spatial investigations§ Couple results with mass transport model for lube oil film
Other remaining issues§ Rate of SO3 to H2SO4 from atmospheric chemistry§ Influence of Vanadium in fuel oil (catalytic)§ Influence of N-chemistry on SO2 oxidation§ Measurements of SO3/SO2 in exhaust from large two-stroke engines
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Thank you for your attention. Questions?
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