1. Real experimental evidence of the conversion fraction in large two-stroke diesel engines is severely lacking. In order to improve the confidence in the

model the conversion fraction must be measured and compared with model predictions.  2. In this study we have relied on the kinetic parameters for conversion of SO3 to H2SO4 as reported by Reiner and Arnold [31]. Several other studies exists e.g. [42, 43, 44, 45] signalling both the complexity of the reaction as well as its importance in relation to acid rain.Unfortunately the studies are limited to low pressure and close to ambient temperature. Thus reliable kinetic parameters at elevated temperature and pressure are needed.

3. Until now only the time until exhaust valve opening has been considered. It should also be investigated further what happens after the exhaust valve opens (decrease in temperature and pressure), during the scavenging process and in the exhaust receiver. It should be expected that significantly more SO3 is converted to H2SO4 during these processes.

4. It is well known that vanadium oxide catalyse the oxidation of SO2 to SO3 [46, 47]. Since the fuel used for large twostroke engines may contain significant levels of vanadium, the catalysed oxidation may contribute significantly to the overall conversion fraction. Future

analysis should take this possibility into account.

NOMENCLATURE

cp Specific heat capacity at constant

pressure, J/(mol K)

Crad Heat radiation constant, J/(mol K4)

Conversion fraction of S to SO3 and

H2SO4

ΔH298  Standard formation enthalpy at 298 K

λ Air excess ratio

MCR Maximum continous rating

MEP Mean effective pressure, bar

Tad Adiabatic flame temperature, K

Trad Temperature drop due to radiation

w/w Weight fraction

ACKNOWLEDGEMENTS

We would like to thank our colleagues Mrs.Charlotte B. Røjgaard, Mr. Kjeld Aabo, Mr.Michael F. Pedersen, and Mr. Svend Eskildsen for invaluable discussions during the making of this manuscript. Further we would like to express our deepest gratitude to Prof. Peter Glarborg, Department of Chemical and Biochemical Engineering, CHEC Research Centre, Technical University of Denmark, for many enlightening discussions and, in particular, for commenting on the manuscript.

REFERENCES

[1] Cullis, C. F., and Mulcahy, M. F. R., ―The kinetics of combustion of gaseous sulphur

compounds‖. Combust. Flame, Vol. 18, 1972, pp. 225–292.

[2] Turns, S. R., ―An Introduction to Combustion‖. McGraw-Hill, 1996. [3] Andreasen, A., and Mayer, S., ―Use of seawater scrubbing for SO2 removal from marine engine exhaust gas‖. Energy Fuels, Vol. 21(6), 1996, pp. 3274–3279. [4] Engel, P. K., Thompson, R. E., and Silvestrini, R., ―Corrosion and fouling potential in diesel exhausts‖ Trans. ASME

Journal of Engineering for Power, Vol. 101, 1979, pp. 598–607. [5] McKinley, T. L., ―Modeling sulfuric acid condensation in diesel engine EGR coolers‖. Engine modelling, Vol. 1255, 1997, pp. 207– 218. [6] Huijbregts, W. M. M., and Leferink, R. G. I., ―Latest advances in the understanding of acid dewpoint corrosion: corrosion and stress corrosion cracking in combustion gas condensates‖. Anti-Corrosion Methods and Materials, Vol. 51, 2004, pp. 173–188.[7] Teetz, C., ―Beitrag zur Verminderung der Naßorrosion im Dieselmotor‖ VDI Forschungsheft, Vol. 626, 1984, pp. 1–40.

[8] Behrens, R., and Groth, K., ―Problems caused by burning heavy fuels in diesel

engines (paper 3)‖. Diesel Engine Combustion Chamber Materials for Heavy Fuel Operation, 1990, pp. 29–38. [9] Behrens, R., ―Brennstoffbedingte korrosion im dieselmotor‖. Motortechnische Zeitschrift, Vol. 49, 1988, pp. 479–485.

[10] Behrens, R., ―Fuel-related wear mechanisms in heavy oil-fuelled diesel engines, as exemplified by first piston ring (paper 8)‖. Maritime Systems Integrity, 1988,pp. 83–91.