Data from a two-stage axial vapor cryogenic compressor on the dual-fuel diesel–electric (DFDE) liquefied natural gas (LNG) carrier were measured and analyzed to investigate compressor energy and exergy efficiency in real exploitation conditions. The running parameters of the two-stage compressor were collected while changing the main propeller shafts rpm. As the compressor supply of vaporized gas to the main engines increases, so does the load and rpm in propulsion electric motors, and vice versa. The results show that when the main engine load varied from 46 to 56 rpm at main propulsion shafts increased mass flow rate of vaporized LNG at a two-stage compressor has an influence on compressor performance. Compressor average energy efficiency is around 50%, while the exergy efficiency of the compressor is significantly lower in all measured ranges and on average is around 34%. The change in the ambient temperature from 0 to 50 °C also influences the compressor’s exergy efficiency. Higher exergy efficiency is achieved at lower ambient temperatures. As temperature increases, overall compressor exergy efficiency decreases by about 7% on average over the whole analyzed range. The proposed new concept of energy-saving and increasing the compressor efficiency based on pre-cooling of the compressor second stage is also analyzed. The temperature at the second stage was varied in the range from 0 to −50 °C, which results in power savings up to 26 kW for optimal running regimes.

This review describes the current liquefaction systems on ships for natural gas transportation in liquid form (Liquefied Natural Gas – LNG). Since in the construction of a gas carrier an essential requirement is the selection of a liquefaction system, this paper describes the principles of operation, thermal and technological processes, as well as the advantages of each system.

A common way of measuring heavy fuel oil consumption on board a vessel is to use volumetric fuel flow meters installed at fuel systems inlets for each of the major fuel consumers. At each stage of the fuel processing cycle, certain mass fuel losses or deviations and calculation errors occur that are not counted accurately into fuel consumption figures. The goal of this paper is to identify those fuel mass losses and measuring/calculating errors and perform their quantitative numerical analysis based on actual data. Fuel mass losses defined as deviations identified during the fuel preparation process are evaporation of volatile organic compounds, water drainage, fuel separation, and leakages while errors identified are flow meter accuracy and volumetric/mass flow conversion accuracy. By utilizing statistical analysis of obtained data from engine logbook extracts from three different ships numerical models were generated for each fuel mass loss point. Measuring errors and volumetric/mass conversion errors are numerically analyzed based on actual equipment and models used onboard example vessels. By computational analysis of the obtained models, approximate percentage losses and errors are presented as a fraction of fuel quantity on board or as a fraction of fuel consumed. Those losses and errors present between 0,001% and 5% of fuel stock or fuel consumption figures for each identified loss/error point. This paper presents a contribution for more accurate heavy fuel oil consumption calculation and consequently accurate declaration of remaining fuel stock onboard. It also presents a base for possible further research on the possible influence of fuel grade, fuel water content on the accuracy of consumption calculation.

ABSTRACT

Air pollution from ships is increasing due to higher global demand of goods, and with them, global emission standards as well. These standards are prescribed by MARPOL Annex VI and the introduction of emission control areas (ECA). Ships built before 1990. do not have to comply with these rules, but ships built after the early 2000. must follow “NOx Emission Tier I”, which allows 17g/kWh NOx (for the slow speed diesel engines with <130 rpm), and selective catalytic reactors (SCR) are not necessary. Tier III NOx Emission standard was enforced in 2016 and it requires an 80% reduction in NOx emission compared to the Tier I, specifically 3.4 g/kWh, which can not be achieved without SCR or without using some other types of fuels. The focus of this paper is to do analysis how the ammonia dosage to SCR affects to the NOx formation in exhaust gasses on various engine speed (loads), as well as how it affects to some important engine parameters and specific fuel oil consumption (SFOC). The analysis was performed on Kongsberg engine room simulator (ERS), MC 90-V Model, as well as on MATLAB by using mathematical models. All external influences are excluded from the analysis like wind or rough sea. All data on different scenarios has been recorded after prolonged period to avoid inconsistencies. The results are shown graphically, and conclusions are presented.