A numerical investigation on the effects of design and operation parameters on the performance and emissions of a marine diesel engine

Prevention of environmental pollution is very important in terms of ecological balance. Healthy life for next generation is only possible that ecological balance is protected. The human has to produce energy to survive and fossil fuels are used to generate the energy by the human. Unfortunately, environmental pollution has been increasing day by day owing to fossil fuels which are used. Energy generally obtains for purpose of heat, transportation, electricity generation, industrial production and even entertainment. All of them causes that harmful gases spread to atmosphere. Internal combustion engines emits harmful exhaust gases to air a lot. Ships and vehicles used for transportation have internal combustion engines and they contribute to air pollution. Gases caused to air pollution are named as ''emission'' and have several varieties. These emissions are nitrogen oxides (NOx), sulfur oxides (SOx), carbon monoxide (CO), soot, carbon dioxide (CO2) and hydro carbons (HC). Emissions have caused many natural catastrophes lately. Nitrogen oxides and sulfur oxides trigger acid rains and give rise to be negatively affected the soil. Carbon dioxide (CO2) going out from the exhaust gases due to in-cylinder combustion causes overheating in atmosphere. Overheating is named as ''Greenhouse Effect''. This effect is a very important risk in terms of global warming. Global warming which are sparked by overheated air has been increasing the melting of glaciers recently. Emissions damage human health vitaly too and cause some diseases. These are cancer-derived illness, respiratory diseases and skin diseases. Many international and national decisions have been come into force in order to prevent this negative effects. International Maritime Organization (IMO) determines some limits for NOx and SOx emissions within the ship exhaust gases. These are Tier I, Tier II and Tier III limits for NOx emissions. NOx emission standards are determined according to shipbuilding year and revolutions per minute (rpm) of engine. SOx emission limit values have been gradually reduced over the years. Within the scope of this study, Computational Fluid Dynamics (CFD) was used to model in-cylinder combustion, and emission and performance values of the marine diesel engine were obtained. Emission and performance values are investigated by changing some parameters which in-cylinder combustion chamber affects. These parameters are spray angle, swirl ratio, spray advance, injector nozzle diameter and spray cone angle. Power, torque, BMEP, in-cylinder mean pressure, exhaust gas temperature and BSFC are investigated as performance values. The emission values which were examined are nitrogen oxides (NOx), PM, carbon monoxide (CO), carbon dioxide (CO2), and hydro carbons (HC). Numerical results were compared with the available experimental results in order to verify the results. This study is composed from seven chapters. In the first part, ship air pollution and emission regulations are presented. Studies which investigate the emission and performance parameters for internal combustion engines in the literature are deeply explained. In the second part, general information such as classification of engines and their cycles for the internal combustion engines are presented. It is extensively presented that exhaust emissions which are from marine diesel engine are detrimental for life and environment. Besides, emission formation is described in detail, the effects of parameters on the emission and performance values of the engines are presented. In the third part, conservation equations, combustion models, turbulance models, fuel droplet evaporation models, droblet fragmentation models, nitrogen oxide (NOx) and PM emissions generation models are clearly introduced. In the fourth chapter, Computational Fluid Dynamics (CFD) modelling is presented for in-cylinder combustion process of marine diesel engine. Marine diesel engine properties, initial and boundary conditions are introduced to CFD program, AVL FIRE. Independent result from mesh number is obtained for 30000, 40000, 50000 and 70000 mesh sizes. It is seen that results do not change for more intensive mesh number than 40000 meshes. Fifth chapter is the most important part for this study. Emission and performance values are investigated by changing the parameters which in-cylinder combustion chamber affects in this chapter. These parameters are spray angle, swirl ratio, spray advance, injector nozzle diameter and spray cone angle. While 120, 125, 130, 135, 140, 145 and 150 degrees are analyzed for spray angle; 1, 1.5, 2, 2.4, 3, 3.5 and 4 values are examined for swirl ratio. Later, spray advance parameter is investigated for 700, 701, 702, 703, 704, 705 and 706 degrees. Besides, for spray cone angle; 4, 5, 6, 7, 8, 9 and 10 degrees are considered. Finally, injector nozzle diameters of 0.15, 0.2, 0.25, 0.3, 0.35, 0.4 and 0.45 mm are studied for their effects on the emission and performance values. Different combinations of spray angle and swirl ratio (7x7) are studied. Some parameters are taken as constant. These are 702 degree is for spray advance, 6 degree is for spray cone angle and 0.3 mm is for injector nozzle diameter. Spray angle, injector nozzle diameter and spray cone angle are accepted as a constant value for spray advance and swirl ratio analyzes too. Spray angle is 135 degree, injector nozzle diameter and spray cone angle values are the same which are used for spray angle and swirl ratio analyzes. And combinations are established for all of these situations (7x7). Spray angle is taken as 135 degree, spray advance is 702 degree, swirl ratio is 2.4 value and injector nozzle diameter is 0.3 mm for spray cone angle analysis. The analyzes are arranged in all spray cone angle for this conditions (7x1). Finally, injector nozzle diameters are investigated. During this analysis, spray angle, spray advance, swirl ratio and spray cone angle values are respectively taken as 135 degree, 702 degree, 2.4 ratio and 6 degree. All combinations of nozzle diameters are used to obtain the emission and performance values (7x1). Throughout the study, numerical results are obtained for a total of 112 cases. The results are presented and compared in different figures to be able to investigate all the cases considered deeply. Also, in this part; the most suitable case in terms of emission and performance values is defined and presented clearly. In the sixth chapter; validation is made by comparing numerical results with the available experimental values in this section. The seventh chapter is the last chapter in this study. In this chapter, the effects of parameters such as spray angle, swirl ratio, spray advance, spray cone angle and injector nozzle diameter on the performance and emissions of the marine diesel engine are presented and discussed. The new knowledge on the in-cylinder combustion for internal combustion engines are presented. The results show that when the spray angle values are increased, the performance values of the engine increase too. For instance; the engine power increases about 10 %. But, emission values have some different characteristics. The Hydrocarbon (HC) and carbon monoxide (CO) emissions affected more than other emissions. Nitrogen oxides (NOx) increase due to the fact that the local temperature values raise. According to the results with different swirl ratios, Extreme high swirl ratios decrease effectively the performance owing to rising of the ratios of the flow loses and the regional flame damping. For example; power and torque values decrease about 20 percent. Hydro carbon (HC), carbon monoxide (CO) and particulate matter are the most affected in terms of emissions. According to the results obtained for different spray advance values, performance parameters are increased about 5%. The combustion time and engine power are increased for the low spray advance values. While the PM, CO and HC emissions increase, the NOx emissions decrease for the high swirl ratios. The results for different spray cone angle values show that the performance values decrease as the spray cone angle increases. While the NOx, HC and CO emissions increase, the engine power and torque values decrease by about 5%. According to the results found for different injector nozzle diameters, the injector nozzle diameter is found to be the most important parameter which performance and emission values are affected. The engine power decreased by about 40% when the nozzle diameter increased by about three times. All emissions (NOx, PM, CO2, HC and CO) are strongly affected by the injector nozzle diameter parameter. The NOx emissions decrease, the rest of the emissions increase due to the increasing injector nozzle diameter. The results of the study show that the spray angle values between 135 to 145 degrees, the swirl ratio values between 1.5 to 2.4, the spray angle values between 702 to 703 degrees, the spray cone angle values between 4 to 6 degrees and the injector nozzle diameter values between 0.25 to 0.3 mm are suitable range for both the performance and emission values. Finally, it is believed that the study will help to improve the numerical models of internal combustion engines and contribute to the thermal and environmental science.