Abstract
The authors applied one-dimensional (1-D) simulation and 3-D Computational Fluid Dynamics (CFD) simulation to evaluate the potential of in-cylinder control methods on a low-speed 2-stroke marine engine to reach the International Maritime Organization (IMO) Tier 3 NOx emissions standards. Reducing the combustion temperature is an important in-cylinder measure to decrease NOx emissions of marine diesel engines. Miller-cycle and Exhaust Gas Recirculation (EGR) are effective methods to reduce the maximum combustion temperature and accordingly decrease NOx emissions. The authors’ calculation results indicate that with a combination of 2-stage turbocharging, a mild Miller-cycle and 10% EGR rate, the NOx emissions can be decreased by 48% without the increased Specific Fuel Oil Consumption (SFOC) penalties; with a medium Miller-cycle and 10% EGR, NOx can be decreased by 56% with a slight increase of SFOC; with a medium Miller-cycle and 20% EGR, NOx can be decreased by 77% and meet IMO Tier 3 standards, but with the high price of a considerable increase of SFOC. The first two schemes are promising to meet IMO Tier 3 standards with good fuel economy if other techniques are combined.
Highlights
The third stage harmful emission control regulations of the International Maritime Organization (IMO) (IMO Tier 3) have been in place since 1 January 2016 [1]
Based on the analysis the characteristics of in-cylinder NOx emission control methods presented in the above literature, this paper uses a combination of Miller-cycle, Exhaust Gas Recirculation (EGR) and higher geometric Compression Ratio (CR) to decrease NOx and maintain a low engine Specific Fuel Oil Consumption (SFOC)
2-stroke marine diesel engine, the potential of in-cylinder control methods to meet the IMO Tier 3 NOx emission standard was evaluated and the following conclusions can be made: (1) By extending EVO timing, a Miller-cycle can be applied in low-speed 2-stroke marine diesel engines to decrease NOx emissions
Summary
The third stage harmful emission control regulations of the International Maritime Organization (IMO) (IMO Tier 3) have been in place since 1 January 2016 [1]. Fiedler proposed a combination of Miller-cycle, 2-stage turbocharging, 2-stage high pressure fuel injection and fuel-water-emulsification to meet the IMO Tier 3 standard [11], but for a 2-stroke marine diesel engine, the application of a Miller-cycle is more complicated than for a 4-stroke engine, as 2-stroke marine engines don’t have intake valves, and the only way of realizing a Miller-cycle is to retard the Exhaust Valve Closing (EVC) time. The test on a 2-stroke indicated that the engine can meet the IMO Tier 3 NOx limit when an EGR system is running, but with a higher Specific Fuel. This paper will investigate the influence of the Miller-cycle on a 2-stroke marine diesel engine’s combustion, NOx emissions, and fuel economy. Based on the analysis the characteristics of in-cylinder NOx emission control methods presented in the above literature, this paper uses a combination of Miller-cycle, EGR and higher geometric CR to decrease NOx and maintain a low engine SFOC
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