A Study on the Combustion and Emission Characteristics of Dual-Fuel Marine Engines Using Various Alternative Fuels

Abstract

The shipping industry is being responsible for a significant proportion of climate change and global warming problems due to exhaust gas emissions from marine engines. As a result, the International Maritime Organization (IMO) emission regulations, as well as the local emission regulations, are becoming increasingly strict to protect human health and the environment. In another aspect, due to fossil fuels are being depleted resulting in the fuel price is being increased, there are urgent needs to undertake research and develop feasible alternative fuels to substitute for petroleum-based fuels aiming to meet the increasing global energy demand, thereby reducing the reliance on fossil-derived fuels, as well as minimum environmental and economic impacts. This thesis presents studies on the effects of various viable alternative fuels on the combustion and emission characteristics of four-stroke and two-stroke heavy-duty dual-fuel (DF) marine engines. The computational fluid dynamic (CFD) approach together with the support of computer simulation software (AVL FIRE and ANSYS FLUENT) were used to conduct three-dimensional (3D) simulations of the combustion and emission formations occurring inside the engine cylinder in both diesel and DF mode to analyze the in-cylinder pressure, temperature, performance and emission characteristics of the engine. The effectiveness of various viable alternative fuels, such as methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), dimethyl ether (DME), and H2+CH4 mixture, when being employed as the primary fuel in the DF mode of the engines has been analyzed and evaluated in terms of engine performance and emission formation. The numerical simulation results were then compared and showed a good agreement with the experimental results reported in the engine’s shop test technical data. The results showed significant benefits in both economic and environmental aspects of using gaseous fuels as the primary fuel in DF engines instead of diesel only in diesel engines. In particular, the researched fuels reduced exhaust gas emissions while keeping the engine power almost unchanged, even increasing the engine power in some operating modes. This thesis has also studied the effects of some operating factors that affect the combustion and emission characteristics of the engine, such as the start of injection (SOI) timing and scavenging air temperature (SAT), aiming to find a way to further increase engine power and emission performance. The study results showed that in-cylinder peak pressure and temperatures were reduced as the SOI angle reduced in both diesel and DF modes, resulting in a reduction in NO emission, however, there also were reductions in the engine power. Analyzing the effects of the SAT cooling method on the combustion and emission characteristics of the engine showed that this method not only enhanced the engine performance but also reduced exhaust gas emissions. The studies in this thesis have successfully analyzed the benefits of using various viable alternative fuels as primary fuels for heavy-duty DF marine engines, as well as the effectiveness of the SOI angle adjustment and SAT cooling methods in reducing exhaust gas emissions and keeping or enhancing engine performance of the engines to meet the emission regulations of IMO without using any emission after-treatment devices that were very rare to be found in previous studies.