Numerical investigation of the high pressure selective catalytic reduction system impact on marine two-stroke diesel engines

Lu, Daoyi and Theotokatos, Gerasimos and Zhang, Jundong and Tang, Yuanyuan and Gan, Huibing and Liu, Qingjiang and Ren, Tiebing (2021) Numerical investigation of the high pressure selective catalytic reduction system impact on marine two-stroke diesel engines. International Journal of Naval Architecture and Ocean Engineering, 13. pp. 659-673. ISSN 2092-6790 (https://doi.org/10.1016/j.ijnaoe.2021.09.003)

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Abstract

After-treatment systems using the selective catalytic reduction (SCR) technology have demonstrated a potential to reduce the nitrogen oxides (NOx) emissions from marine engines by more than 90% with its most typical configurations being the high pressure system (SCR-HP) and the low pressure system (SCR-LP). This study aims to investigate the impact of the SCR-HP system on a large marine two-stroke engine performance parameters by employing thermodynamic modelling. A coupled model of the zero-dimensional type is extended to incorporate the modelling of the SCR-HP system components and the control bypass valve (CBV) block. The CBV control system is modelled based on the exhaust gas minimum temperature set point, which is considered a function of the sulphur content and the exhaust receiver pressure. This model is initially validated against experimental data and subsequently employed to simulate several scenarios representing the engine operation at both healthy and degraded conditions considering the compressor fouling and the SCR reactor clogging. The derived results are analysed to quantify the impact of the SCR-HP system on the investigated engine performance. The SCR system pressure drop and the cylinder bypass valve flow cause an increase of the engine specific fuel oil consumption (SFOC) in the range 0.3 to 2.77 g/kWh. The thermal inertia of the SCR-HP system is mainly attributed to the SCR reactor, which causes a delayed turbocharger response. These effects are more pronounced at low engine loads. This study supports the better understanding of the operating characteristics of marine two-stroke diesel engines equipped with the SCR-HP system and quantification of the impact of the components degradation on the engine performance. Furthermore, it provides insights for the effective shipboard operation of these engines and the SCR-HP system.

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