Experimental mild conversion of a lean burn natural gas engine with SCR to a hydrogen engine: NOx and GWP potential for marine applications

Abstract

Emissions of nitrogen oxides (NOx) from marine propulsion systems have gained public interest resulting in emission limits as defined by the International Maritime Organization (IMO) with IMO Tier III, especially for vessels operating in Emission Control Areas (ECA). The reduction of greenhouse gas emissions is also increasingly important for marine propulsion. Minimizing NOx while reducing climate impact calls for technologies such as the gas engine with aftertreatment systems, preferably with the ability to run on alternative fuels. A proven technology for reducing NOx in marine engines is the Selective Catalytic Reduction (SCR) aftertreatment system. It is also possible to avoid engine raw emissions by shifting the combustion process to lower temperature levels. Hydrogen is an alternative fuel with combustion properties enabling premixed operation at significantly higher air-fuel ratio than natural gas (NG) and thus, reducing raw NOx emissions. The study uses a systematic approach to compare emissions and efficiency of a lean-burn gas engine with a natural gas and a mild conversion hydrogen setup, utilizing two different strategies: combustion of NG with the assumption of an SCR catalyst and high raw NOx emissions and combustion of pure hydrogen using the NOx reduction potential of higher excess air. The scope of the study makes it possible to illustrate engine concepts for future applications in the displacement class of 4.8 L per cylinder. The highest efficiency of 45.3% was achieved with the natural gas engine and SCR. The concept with the lowest Global Warming Potential (GWP) was the hydrogen fueled engine under the prerequisite of using green hydrogen, accompanied by a reduction in efficiency of 0.6% compared to the efficiency optimum of NG with SCR. Assuming the use of gray hydrogen, the GWP was 48% and 52% higher than with NG and NG with SCR, respectively, at the efficiency-optimal operating points.

Effect of Variable-Nozzle-Turbocharger-Coupled Exhaust Gas Recirculation on Natural Gas Engine Emissions and Collaborative Optimization

“…In comparison to gasoline or diesel engines, natural gas engines emit lower levels of pollutants, including polycyclic aromatic hydrocarbons (PAHs), sulfur dioxide (SO 2 ), and CO. However, owing to higher combustion temperatures in the cylinder, their NOx emissions are higher [1][2][3]. Additionally, various factors, such as valve overlap angle, cylinder clearance, and incomplete combustion, result in massive CH 4 emissions from natural gas engines [4][5][6][7][8].…”

Investigation on the applicability of parameters identification of marine diesel engine SCR kinetic model based on Discrete-Grid algorithm

“…[1][2][3][4] However, marine engine combustion will produce a lot of harmful emissions such as particulate matter (PM), sulfur oxides (SOx), and nitrogen oxides (NOx), which cause severe pollution to the atmosphere and marine environment. [5][6][7][8][9][10][11] According to the statistics of the China Mobile Source Environmental Management Annual Report (2021), in 2020, the national non-road mobile sources discharged 163,000 tons of SO 2 , 425,000 tons of hydrocarbons (HC), 237,000 tons of PM, and 4.782 million tons of NOx. Among them, NOx emissions from ships accounted for 29.9%.…”

Studying the effects of manifold pressure boosting and EGR on combustion and NOx emission of hydrogen-fueled SI engine

“…However, the NO x reduction was not satisfactory under minimum performance drop range. Some other methods like SCR, 27 EGR, 28 and water injection 29 are also investigated. Among several ways to reduce NO x , EGR is considered the most effective method.…”