An investigation on the exhaust emissions of a ferryboat by experimental and theoretical methods

Marine transport is the most environmentally friendly transport mode when comparing others. However marine transport has growth day by day therefore world ship fleet has increased. For this increase marine emissions emitted by ships has became important emission source considering global emission budget. Marine emissions can be listed as nitrogen oxides (NOX), carbon dioxide (CO2), carbon monoxide (CO), sulphur dioxide (SO2), hydrocarbons (HC), particulate matters (PM) and others. Marine emissions affect environment, chemical composition of the atmosphere, climate, regional air quality and human health negatively. Global effects of marine emissions are mostly related climate changing and global warming. On the other hand local effects of marine emissions can be listed as water and soil acidification, acid rain, local climate changes and human health hazards. Therefore marine emissions are researched globally and locally to estimate emission inventories, to define hazardous effects of emissions, to research possible emission reduction technologies and to decrease emission rate of ships. Due to hazardous effects of marine emissions, environment agencies, international organizations and countries make regulations to limit marine emissions. International Maritime Organization (IMO), in 1997, make a protocol to prevent air pollution from ships. MARPOL Annex VI regulates air pollution from ships. In this regulation chapter 13 and chapter 14 define respectively emission limits of NOX and SO2. CO2 emission is regulated according to energy efficiency design index. Yet other emission kinds are not regulated. As a result of approval of the MARPOL Annex VI by member states, global and local NOX and SO2 limits adopted. SO2 limits mostly define fuel sulphur content due to source of SO2 exhaust emissions is fuel sulphur content. On the other hand NOX emissions are comprised as a result of chemical reaction of nitrogen and oxygen, which are in the burning air, at high temperatures in the combustion chamber. Briefly NOX emissions are product of the combustion processes. Due to hazardous effects of NOX emissions MARPOL Annex VI chapter 13 limits engine NOX emission rates according to construction year of the ships. There are three tier about to ships NOX emissions rates. Due to this regulations, ships have to inspect whether they are consistent with emission limits or not. NOX Technical Code define procedures to ship's emission measurement methods, calculation methods also inspection and certification methods. Direct emission measurent method is used to inspect and certification emission rate of ships. Furhtermore, direct exhaust emission measurement method used to investigate emission reduction technologies, effect of different fuel usage and engine performance evaluation. On the other hand, direct emission measurement studies provide necessary knowledge to evaluate marine emissions with emission inventory methods. Emissision inventory methods used to estimate marine emissions localy or globally. These methods can be categorized into two groups, as bottom-up method and top-down method. According to bottom-up method emission from ships are estimated with fuel consumption data and emission factor of ship. If fuel consumption data is not known according to top-down method, ship installed power, engine specific fuel consumption data, load factor and emission factor are used to calculate emission from ships. Emission factors, engine load, installed engine power and load factor data of ships are published as a result of researches. These datas are limited and not include all kind of ships. As a result of several researches emission datas are published for general type of ships like general cargo, tanker and container vessels. These datas are useful for global emission inventory estimations. However, to calculate local emission inventories, detailed knowledge of ship characteristics are needed. Due to different operating conditions or different ship characteristics, emission datas published may not reflect all kind of ships. Therefore, direct emission measurement studies provide important and precious knowledge about emission values of specific or local ships. In this study, exhaust emissions of a typical ferryboat which is shipping between Eskihisar and Topçular ports in Marmara Sea, are measured with direct emission measurement method. NOX Technical Code procedures are followed in measurements. According to E2 test cycle, direct emission measurement are applied at different engine loads. Engine brake power, engine parameters, ambient parameters, exhaust parameters and emission concentrations are measured at every load point. At the end, specific emission value of ship is estimated acorrding to NOX Technical Code and this value is compared with NOX emission limit. As a result, specific NOX emission value of ferryboat is estimated as 11.909 g/kWh and tier 1 NOX emission limit is estimated as 11.97 g/kWh. It is seen that ferryboat is consistent with tier 1 NOX emission limit. Besides, exhaust flow rate is calculated using two methods and results are compared at %75 and %100 engine load. Firstly, exhaust gas flow rate is directly determined by using pitot tubes. In the second method exhaust gas flow is calculated by carbon balance method given in the NOX Technical Code Appendix 6. Fuel consumption flow rate is calculated by specific oil consumption data given by engine manufacturer. As a result, when comparing these emission values estimated using two differen methods it is seen that emission values calculated using carbon balance method %15.22 and %16.28 higher than emission values calculated using direct exhaust flow rate determination method respectively at %75 and %100 engine load. Differences between emission values calculated by two different methods are reasonable considering uncertainty values of test results. According to regulation marine fuel sulphur content limit is %0.1 for Marmara Sea. Sulphur content of fuel used by ferry is %0.0005, so fuel used by ferry is consistent with fuel sulphur content regulation. Further, other exhaust emissions are calculated. These exhaust emission values can be listed as, CO2 (611.14 g/kWh) , CO (0.67 g/kWh), SO2 (0.1 g/kWh), HC (0.6 g/kWh), O2 (1350.1 g/kWh). In the second part of this study emission inventory methods are applied to estimate emission values for one trip of ferryboat. Emissions from ferryboat are calculated for one trip of ferryboat according to bottum up and top down methods. To estimate emissions from ships, cruise characteristics of ferryboat categorize into three goups. These categories are hotelling, manoeuvring and cruise. Then hotelling time, manoeuvring time and cruise time are determined. Ferryboat emission inventory is calculated using published load factor and emission factor values and measurement datas. Then result of emission inventory estimations are compared. As a result it is seen that, calculated NOX and CO2 emissions with emission factors published in literature and emission factor are calculated, give similar results with acceptable differences. However, other emission factors used to estimate emissions is not suitable for this type of ship. Because there are important differences between emission values estimated with literature datas and calculated with measurement results. So other emission values should be investigated for this type of ferryboat. As a result of measurements ferryboat trip phases, phase times for one trip of ferryboat, load factor of ferryboat at every phase of trip and emission values of ferryboat are defined. Finally, emission inventory of ferryboat is calculated for NOX, SO2, CO2, CO and HC emissions mothly during 1 year. Emission are calculated for 1 year as 97 (t) NOX, 0.77 (t) SO2, 4467.3 (t) CO2, 6.2 (t) CO and 5.6 (t) HC.