Effect of SCR-regeneration on cylinder liner temperatures of a medium-speed diesel engine
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Climate change and the reduction of its effects are leading to even more stringent emission requirements for marine diesel engines. Engine manufacturers are forced to create and adapt technologies that ensure new engines comply with the emission requirements set by maritime regulatory powers. However, many of the emission reduction technologies affect the performance of an engine. Subsequent issues caused by the addition of emission reduction equipment are also probable.
Nitrogen oxides (NOx) emissions are one of the most addressed and harmful emissions emitted by a marine diesel engine. In order to be compliant to be installed on a new-built ship, a modern marine diesel engine must meet the Tier III NOx-limit set by the International Maritime Organization (IMO). In the literature part of this study, the NOx-emissions regulations are studied, along with different techniques to reduce these emissions of a diesel engine.
Selective Catalytic Reduction (SCR) is one of the most effective techniques to reduce the NOx-emissions of a diesel engine to be compliant with the IMO Tier III requirements. The SCR-system however requires a minimum exhaust gas temperature to avoid contamination of the SCR-reactor and to keep the system effective. Exhaust gas temperature (EGT) control is utilized to reach a favourable operating window for the exhaust gas aftertreatment device(s). However, the thermal efficiency of a modern marine diesel engine with sequential turbocharging is high, and thermal energy of the exhaust gas is efficiently extracted into mechanical work of the turbines. This results in low EGTs at the SCR-inlet, and additional measures need to be implemented to reach the required EGT at the SCR-reactor. These methods are also studied in the literature part.
In the experimental part of the study, the effect of increased exhaust gas temperatures, required during the regeneration of the SCR-system, on the cylinder liner temperatures of a dual-fuel marine diesel engine were studied. The study is concentrated around a medium-speed 4-stroke marine dual-fuel engine. However, the same physical principles apply for low- and high speed 4-stroke diesel engines, as well as 2-stroke engines.