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The reported findings help to understand the treatment technology for studying shipping emissions and air pollution, especially in the context of near-zero emissions. Ship emissions primarily consist of two categories: air pollutants such as SOx, NOx, PM, CO, and NMVOCs, as well as greenhouse gases, including CO SB 2 sb , CH SB 4 sb , and N SB 2 sb O [[5], [7]]. However, 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 [[4]]. [Extracted from the article]

In recent years, due to stringent emission regulations vehicle manufacturers have been compelled to cut down noxious pollutants released from diesel engines. Different alternative solutions have been recommended to achieve this challenging task. One of these alternative solutions is the utilization of biogas in addition to the use of liquid diesel. In this regard, the current study investigates the combustion characteristics and exhaust emissions of a turbocharged, direct injection, diesel engine operating at constant speed (1800 rpm) and under dual fuel mode with diesel as the pilot fuel and biogas (generated from pig manure and corn straw) and methane enriched biogas. Simulations were carried out at four various engine loads corresponding to brake mean effective pressure (BMEP) of 0.425, 0.85, 1.275, and 1.7 MPa using GT-Power package. The BTE values of biogas-diesel were higher as compared to diesel fuel. The CO2 ratio of biogas did not impact BTE considerably. The highest BTE value of 38.22% was recorded for BG45. However, the Brake specific fuel consumption (BSFC) values for the biogas-diesel fuels were higher than that of diesel fuel operations. With respect to emissions, compared to diesel fuel operation, the hydrocarbon (HC) and CO2 of the biogas-diesel were higher, but NOx and CO pollutants were much lower. The utilization of biogas with diesel by all accounts is attractive to cut down discharges and improve performance of the engine. The engine performance did not deteriorate with up to 45% CO2 proportion in biogas. [ABSTRACT FROM AUTHOR]

Ammonia, an efficient hydrogen carrier with the advantages of lower storage cost and higher stability comparing to hydrogen, is becoming a potential solution for carbon dioxide emission reduction from marine engine. In this paper, the CH 4 /NH 3 mechanism applied to simulate the combustion process of elevated-pressure engine was experimentally verified. Then, simulations were conducted on a marine pre-chamber lean-burn engine to investigate the feasibility of dual-fuel combustion with natural gas and ammonia. The results show that the combustion of the rich mixture ignited by spark in the pre-chamber produces high-speed turbulent jet flames into the main chamber, which promotes the combustion of the lean gas mixture. Additionally, an anomalous pre-ignition pressure rise is observed at 50% natural gas addition. Finally, the performance evaluation of engine indicates that for the design of marine dual-fuel engine, the ammonia fraction range of 50%∼80% should be employed to achieve good engine thermal efficiency. • Ignition characteristic of the CH 4 /NH 3 mixtures was studied. • Gas mixture formation in the pre-combustion chamber was analyzed. • Combustion of lean main mixture was improved by rich-burn pre-combustion chamber. • Anomalous pre-ignition pressure rise in the cylinder at 50% natural gas addition. • Ammonia fraction range was evaluated to achieve high engine efficiency. [ABSTRACT FROM AUTHOR]

• A CH 4 /NH 3 mechanism is developed and experimentally verified. • Ammonia pyrolysis in the pre-combustion chamber promotes the flame propagation. • NO x emissions decreased with the further increase of ammonia (when NH 3 > 50%). • N 2 O emissions partially offset the CO 2 emission reduction effect. • Ammonia is a suitable candidate fuel applied for natural gas marine engine. As an efficient hydrogen carrier, ammonia (NH 3) has great potential to realize the target of carbon neutralization. In this paper, a natural gas-ammonia dual-fuel engine model has been established to evaluate the feasibility of ammonia application in a high-pressure medium-speed four-stroke natural gas marine engine. In order to achieve the efficient and clean combustion of ammonia, a method combining the pre-chamber ignition system with lean-burn combustion technology was proposed. In addition, a CH 4 /NH 3 combustion mechanism with reasonable accuracy was developed to simulate the combustion process of the engine. Moreover, the effect of using various ammonia concentration in the fuel on jet flame formation, thermal efficiency, unburned ammonia, and NOx and N 2 O emissions were compared. The results showed that the pyrolysis of ammonia mixtures in the pre-combustion chamber promoted the formation of jet flame, which had a "chain effect" on the turbulent kinetic energy in the main combustion chamber and further enhanced the flame propagation in lean conditions. In addition, NOx emission showed a decreasing function of the split ratio of ammonia, which was caused by the NO reduction by unburned NH 3. However, the low-temperature generation characteristics of N 2 O emissions led to the opposite trend. Furthermore, the application of ammonia increased N 2 O emissions by 0.18–0.49 g/kWh, which is about 0.06%–0.1% of nitrogen in ammonia fuel, resulting in a partial offset of CO 2 emission reduction effect. [ABSTRACT FROM AUTHOR]