Vedran Mrzljak

Energy and Exergy Efficiency Analysis of Sealing Steam Condenser in Propulsion System of LNG Carrier

In ship propulsion systems today diesel engines are dominant, but steam propulsion systems prevail in one type of ships and that are LNG carriers. Such steam propulsion systems consist of many different components. One interesting component of these systems is sealing steam condenser analysed in this paper. Measurements of all necessary operating parameters for analysed sealing steam condenser were performed during the ship exploitation and they were used for calculating the energy and exergy efficiency of this device. Except the displayed movement of both efficiencies the reasons for those changes and proposals for possible improvements were presented. Also, it was displayed all operating parameters of sealing steam condenser that has an impact on its performance and efficiency. During the ship exploitation, improvements related to the sealing steam condenser efficiency are hard to expect because improvements would cause an increase in the steam propulsion system operating costs.

Simulation of a Two-Stroke Slow Speed Diesel Engine Using a Quasi-Dimensional Model

The paper describes a diesel engine quasi-dimensional numerical model, implemented in a previously developed 0D model. The presented model uses direct solution to the conservation equations set for cylinder pressure and zone temperatures without numerical iterations which are customary in these models. Numerical model validation was performed on a four-stroke diesel engine at four operating points. After successful validation, modifications were implemented in the numerical model allowing the simulation of a marine two-stroke diesel engine. It is important to emphasize that the simulation model logic remained unchanged. The only significant differences are the changes in the engine working processes and different calculation of the engine operating parameters which are characteristic of two-stroke engines. The results of the diesel engine simulations using the quasidimensional model were compared to the test-bed measurements of the two-stroke engine found in available literature. Good agreement between the measurements and the simulation results for the two-stroke engine has been obtained. The developed quasi-dimensional numerical model can accurately predict operating parameters of the four-stroke and the twostroke diesel engine.

Energy Power Losses and Efficiency of Low Power Steam Turbine for the Main Feed Water Pump Drive in the Marine Steam Propulsion System

Steam turbine for the main feed water pump (MFP) drive is a low power turbine, for which energy power losses and energy efficiency analysis are presented in this paper. The MFP steam turbine analysis has been performed within a wide range of turbine loads. The influence of steam specific entropy increment of the real (polytropic) steam expansion upon the MFP turbine energy power losses and energy efficiency has been investigated. During all the observed loads MFP steam turbine energy power losses were in the range between 346.2 kW and 411.4 kW. The MFP steam turbine energy power losses and energy efficiency were most significantly influenced by the steam specific entropy increment. Change in the steam specific entropy increment is directly proportional to the change in MFP turbine energy power losses, while the change in the steam specific entropy increment is reversely proportional to the MFP turbine energy efficiency change. For the observed turbine loads, the MFP steam turbine energy efficiency was in the range between 46.83% and 51.01%.

Exergy Analysis of Steam Pressure Reduction Valve in Marine Propulsion Plant on Conventional LNG Carrier

Paper has presented an exergy analysis of steam pressure reduction valve, unavoidable element in the steam propulsion plant on LNG carrier. The steam pressure reduction valve was analyzed in a wide range of steam system loads. Along with pressure decrease, through the valve also occur decrease in steam temperature and increase in steam specific entropy. The pressure decrease of the analyzed valve ranges from 4.846 MPa up to 5.027 MPa while the average steam temperature decrease for the whole observed operating range amounts 74.8 °C. At the ambient temperature of 25 °C, valve exergy destruction ranges from 121.72 kW up to 180.64 kW, while exergy efficiency amounts from 80.28 % up to 80.54 %. Variation in the ambient temperature, for the expected engine room temperature range, showed that the exergy destruction of pressure reduction valve increases and exergy efficiency decreases during the increase in the ambient temperature. The lowest average value of pressure reduction valve exergy destruction was obtained at the ambient temperature of 10 °C and amounts 152.03 kW, while at the same ambient temperature was obtained the highest average exergy efficiency of 82.77 %. The highest valve exergy destruction and the lowest exergy efficiency were obtained at the highest observed ambient temperature of 40 °C.

Turbogenerator Steam Turbine Variation in Developed Power: Analysis of Exergy Efficiency and Exergy Destruction Change

Developed power variation of turbogenerator (TG) steam turbine, which operates at the conventional LNG carrier, allows insight into the change in turbine exergy efficiency and exergy destruction during the increase in turbine power. Measurements of required operating parameters were performed in eight different TG steam turbine operating points during exploitation. Turbine exergy efficiency increases from turbine power of 500 kW up to 2700 kW, and maximum exergy efficiency was obtained at 70.13% of maximum turbine developed power (at 2700 kW) in each operating point. From turbine developed power of 2700 kW until the maximum power of 3850 kW, exergy efficiency decreases. Obtained change in TG turbine exergy efficiency is caused by an uneven intensity of increase in turbine developed power and steam mass flow through the turbine. TG steam turbine exergy destruction change is directly proportional to turbine load and to steam mass flow through the turbine—higher steam mass flow results in a higher turbine load which leads to the higher exergy destruction and vice versa. The higher share of turbine developed power and the lower share of turbine exergy destruction in the TG turbine exergy power inlet lead to higher turbine exergy efficiencies. At each observed operating point, turbine exergy efficiency in exploitation is lower when compared to the maximum obtained one for 8.39% to 12.03%.

Quasi-dimensional diesel engine model with direct calculation of cylinder temperature and pressure

Original scientific paper This paper describes the quasi-dimensional numerical model, implemented in previously developed 0D model. The presented model uses direct solution of equations for cylinder pressure and zone temperatures, without numerical iterations which are customary for these models. In the model there is shown a process of averaging from a set of small fuel spray packages (volumes) into big ones, which is a necessary precondition for the numerical stability. The model uses about fifty submodels. Simulations were performed in eight operating points, on four most sensitive engine cylinder operating parameters. Direct solution of temperature and pressure changes, in conjunction with the fuel spray packages averaging, represents a contribution to quasi-dimensional diesel engine process modelling.

Comparison of COGES and Diesel-Electric Ship Propulsion Systems

Diesel-electric ship propulsion is a frequent shipowners choice nowadays, especially on passenger ships. Despite many diesel engines advantages, their primary disadvantage is emission of pollutants. As environmental standards become more stringent, the question of optimal alternative to diesel-electric propulsion arises. COGES (COmbined Gas turbine Electric and Steam) propulsion system is one of the proposals for alternative propulsion system, primarily due to significant reduction of pollutant emissions. On the other hand, gas turbines have higher specific fuel consumption in comparison with diesel engines what represents their noticeable disadvantage. However, some analyzes suggested that COGES propulsion system could be still cost-effective in comparison to diesel-electric propulsion, particularly on passenger ships where higher initial investment can be compensated by increasing the number of passenger cabins. This paper shows a comparison of abovementioned propulsion systems, which can be useful for the optimal ship propulsion system selection.