A two-dimensional computational fluid dynamics (2D CFD) simulation of a low-speed two-stroke marine engine simulation was performed in order to investigate the performance of 2D meshes that allow the use of more complex chemical schemes and pollutant formation analysis. Various mesh density simulations were compared with a 3D mesh simulation and with the experimentally obtained cylinder pressure. A heavy fuel model and a soot model were implemented in the software. Finally, the influences of three water injection strategies were simulated and evaluated in order to investigate the capability of the model and the influence of water injection on NOx formation, soot formation, and engine performance. We conclude that the direct water injection strategy reduces NOx emissions without adversely affecting the engine performance or soot emissions. The other two strategies-Intake air humidification and direct injection of fuel-water emulsion-reduced NOx emissions but at the cost of higher soot emissions or reduced engine performance.

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%.

In this paper is presented an analysis of main and auxiliary steam energy flow streams from steam generators during the increase in steam system load at conventional LNG carrier. During the steam system load increase was presented differences in steam pressure and temperature between main and auxiliary steam flow streams. Energy power of the auxiliary flow stream is higher than energy power of the main flow stream only at the lowest steam system loads after which main flow stream takes over primacy at middle and high steam system loads. Cumulative auxiliary energy flow stream was divided on energy flow streams to each auxiliary device and energy power consumption of each auxiliary device was also investigated throughout number steam system loads. Analysis of steam production from marine steam generators presented in this paper provides insight into the operation dynamics of the entire steam propulsion system.

The scavenging process is an important part of the two-stroke engine operation. Its efficiency affects the global engine performance such as power, fuel consumption, and pollutant emissions. Slow speed marine diesel engines are uniflow scavenged, which implies inlet scavenging ports on the bottom of the liner and an exhaust valve on the top of the cylinder. A CFD model of such an engine process was developed with the OpenFOAM software tools. A 12-degree sector of the mesh was used corresponding to one of the 30 scavenging ports. A mesh sensitivity test was performed, and the cylinder pressure was compared to experimental data for the analyzed part of the process. The scavenging performances were analyzed for real operation parameters. The influence of the scavenge air pressure and inlet ports geometric orientation was analyzed. The scavenging process is analyzed by means of a passive scalar representing fresh air in the cylinder. Isosurfaces that show the concentration of fresh air were presented. The variation of oxygen and carbon dioxide with time and the axial and angular momentum in the cylinder were calculated. Finally, the scavenging performance for the various operation parameters was evaluated by means of scavenging efficiency, charging efficiency, trapping efficiency, and delivery ratio. It was found that the scavenging efficiency decreases with the engine load due to the shorter time for the process. The scavenging efficiency increases with the pressure difference between the exhaust and scavenging port, and the scavenging efficiency decreases with the increase in the angle of the scavenging ports. It was concluded that smaller angles than the industry standard of 20° could be beneficial to the scavenging efficiency. In the investigation, the charging efficiency ranged from 0.91 to over 0.99, the trapping efficiency ranged from 0.54 to 0.83, the charging efficiency ranged from 0.78 to 0.92, and the delivery ratio ranged from 1.21 to 2.03.

Potrošnja goriva i emisije štetnih plinova imaju vrlo veliki utjecaj na okoliš, a ovise o vrsti pogona vozila, konfiguraciji terena, opterećenju vozila te brzini gibanja vozila. U ovom radu provedena je simulacija potrošnje goriva i emisija štetnih tvari pomoću računalne aplikacije Advisor za automobil na određenoj dionici. Pomoću tvornički ugrađenih senzora i upravljačke jedinice motora automobila te putem OBD2 priključka, izmjerena je trenutna brzina i potrošnja goriva automobila s dizelskim motorom na dinamičnoj gradskoj dionici. Zatim su izrađeni simulacijski modeli automobila s dizelskim, benzinskim i hibridnim pogonom. Izmjereni profil brzine stvarnog automobila upotrijebljen je kao ulazni podatak u simulacijama za automobile s različitim pogonima. Usporedba rezultata dobivenih simulacijom i vrijednosti dobivenih mjerenjem na stvarnom automobilu s dizelskim pogonom poslužila je za validaciju simulacijskog modela. Pomoću računalne aplikacije Advisor izračunate su potrošnje goriva, emisije ugljikovog dioksida, neizgorenih ugljikovodika, ugljikovog monoksida te dušikovih oksida. Dobiveni rezultati su očekivani, iako su zbog dinamičnosti dionice razlike između pojedinih izvedbi pogona naglašenije nego što to sugeriraju podaci deklarirani od strane proizvođača. Najveću potrošnju goriva i najvišu emisiju štetnih tvari ima automobil s benzinskim pogonom, a najmanju automobil s hibridnim pogonom. Vrlo velik utjecaj na emisije izračunate pomoću simulacijskog modela ima činjenica da katalizator trostrukog djelovanja ugrađen u automobil s benzinskim i hibridnim pogonom postaje djelotvoran tek nakon nekog vremena od hladnog starta, odnosno nakon što se postigne odgovarajuća radna temperatura motora.

Thermodynamic (energy and exergy) analysis of steam cooling process in the marine steam propulsion plant is presented in this research. Steam cooling is performed by using Desuperheater which inject water in the superheated steam to obtain wet steam. Wet steam is used in auxiliary heaters for various heating purposes inside the marine steam propulsion system. Auxiliary heaters require wet steam due to safety reasons and for easier steam condensation after heat transfer. Analysis of steam cooling process is performed for a variety of steam system loads. Mass flow rates of cooling water and superheated steam in a properly balanced cooling process should have the same trends at different system loads -deviations from this conclusion is expected only for a notable change in any fluid temperature. Reduction in steam temperature is dependable on the superheated steam temperature (at Desuperheater inlet) because the temperature of wet steam (at Desuperheater outlet) is intended to be almost constant at all steam system loads. Energy losses of steam cooling process for all observed system loads are low and in range between 10-30 kW, while exergy losses are lower in comparison to energy losses (between 5-15 kW) for all loads except three the highest ones. At the highest system loads exergy losses strongly increase and are higher than 20 kW (up to 40 kW). The energy efficiency of a steam cooling process is very high (around 99% or higher), while exergy efficiency is slightly lower than energy efficiency (around 98% or higher) for all loads except the highest ones. At the highest steam system loads, due to a notable increase in cooling water mass flow rate and high temperature reduction, steam cooling process exergy efficiency significantly decreases, but still remains acceptably high (between 95% and 97%). Observation of both energy and exergy losses and efficiencies leads to conclusion that exergy analysis consider notable increase in mass flow rate of cooling water which thermodynamic properties (especially specific exergies) strongly differs in comparison to steam. Such element cannot be seen in the energy analysis of the same system.