Article pubs.acs.org/EF
Investigating SO3 Formation from the Combustion of Heavy Fuel Oil in a Four-Stroke Medium-Speed Test Engine Rasmus Cordtz,†,* Jesper Schramm,† and Rom Rabe‡ †
Technical University of Denmark, 2800 Kgs, Lyngby, Denmark Rostock University, 18059 Rostock, Germany
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ABSTRACT: The validation of detailed models, in terms of SO3 formation in large marine engines operating on sulfurcontaining heavy fuel oils (HFOs), relies on experimental work. The requisite is addressed in the present work, where SO3 is measured in the exhaust gas of an 80 kW medium-speed single-cylinder HFO-fuelled test engine. SO3 formation is triggered by running the engine at altered operational conditions and speeds within 1050−1500 rpm. The test engine does not represent a large low-speed marine engine; however, the nature of high-temperature SO3 formation may well be explored with the current engine and serve as reference for further modeling studies. SO3 is measured using a continuous SO3 monitor from PENTOL GmbH. The monitor offers online SO3 readings and short sampling times, in contrast to other extractive methods. The measurement is based on SO3 capture in isopropanol prior to chemical conversion and indirect detection via light absorption in a photometer. Present results show that SO3 formation is favored by elevated pressure histories, premixed combustion, and reduced speeds. The fraction of fuel sulfur converted to SO3 is measured to be on the order of 0.5%−2.4%, corresponding to 4− 14 ppmv. SO3 and NOx are not comparable, according to thermodynamic considerations, yet both species involve the radical pool and are studied in parallel. Resulting emissions of SO3 and NOx in the exhaust gas follow a comparable trend throughout the experiments.
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INTRODUCTION Heavy fuel oil (HFO), which is used for ship propulsion in large, low-speed marine engines, contain sulfur (on the order of 3 wt %, on average). During combustion, the sulfur is rapidly converted to SO2,1,2 from which a fraction is further oxidized to SO3,3−5 which, at temperatures lower than ∼600 °C, reacts to form gaseous sulfuric acid H2SO4 from a fast reaction6 with H2O. For a typical exhaust gas, the equilibrium of eq R1 lies well to the right at temperatures of
