Research of NOx reduction on a low-speed two-stroke marine diesel engine by using EGR (exhaust gas recirculation)–CB (cylinder bypass) and EGB (exhaust gas bypass)

Abstract

IMO Tier III, applied on 1 January 2016, forced that NOx emissions must not exceed 3.4 g/kWh for low-speed marine diesel engines (engine speed lower than 130 rpm) in NOx ECAs. And the best answer for propulsion of nautical ships presently and for the near decades is the low-speed two-stroke diesel engines. Any abatement technology that reduces NOx emissions to the expected point can be allowed. EGR is an effective technology that has been verified on automotive applications and marine diesel engines (high speed and medium speed). This paper provides an internal measure: EGR (exhaust gas recirculation) combined with CB (cylinder bypass) and EGB (exhaust gas bypass) to reduce NOx emissions. Combined with CB and EGB, the EGR system applied on the engine can reduce the NOx emissions under 3.4 g/kWh. To test the effects of the EGR system, three modes were set: non-EGR mode, low-EGR mode and ECA-EGR mode. The effects of different modes on NOx emissions, fuel consumption, engine power and emissions are investigated. As a result, it can be concluded when the engine run in the ECA-EGR mode, NOx emissions can meet the requirements of IMO Tier III.