Importance of Vanadium-Catalyzed Oxidation of SO2to SO3in Two-Stroke Marine Diesel Engines

Low-speed marine diesel engines are mostly operated on heavy fuel oils, which have a high content of sulfur andash, including trace amounts of vanadium, nickel, and aluminum. In particular, vanadium oxides could catalyze in-cylinderoxidation of SO2 to SO3, promoting the formation of sulfuric acid and enhancing problems of corrosion. In the present work, thekinetics of the catalyzed oxidation was studied in a fixed-bed reactor at atmospheric pressure. Vanadium oxide nanoparticles weresynthesized by spray flame pyrolysis, i.e., by a mechanism similar to the mechanism leading to the formation of the catalyticspecies within the engine. Experiments with different particle compositions (vanadium/sodium ratio) and temperatures (300−800 °C) show that both the temperature and sodium content have a major impact on the oxidation rate. Kinetic parameters forthe catalyzed reaction are determined, and the proposed kinetic model fits well with the experimental data. The impact of thecatalytic reaction is studied with a phenomenological zero-dimensional (0D) engine model, where fuel oxidation and SOxformation is modeled with a comprehensive gas-phase reaction mechanism. Results indicate that the oxidation of SO2 to SO3 inthe cylinder is dominated by gas-phase reactions and that the vanadium-catalyzed reaction is at most a very minor pathway.