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Prof. Dr. Tomislav Mrakovčić
Faculty of Engineering, University of Rijeka, 51000 Rijeka, Croatia

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Research Keywords & Expertise

0 Internal Combustion Engines
0 Fuels
0 Energy and exergy analysis
0 Marine energy systems
0 Greenhouse gases control

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Journal article
Published: 20 October 2020 in Journal of Marine Science and Engineering
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The medium-speed diesel engine in diesel-electric propulsion systems is increasingly used as the propulsion engine for liquefied natural gas (LNG) ships and passenger ships. The main advantage of such systems is high reliability, better maneuverability, greater ability to optimize and significant decreasing of the engine room volume. Marine propulsion systems are required to be as energy efficient as possible and to meet environmental protection standards. This paper analyzes the impact of split injection on fuel consumption and NOX emissions of marine medium-speed diesel engines. For the needs of the research, a zero-dimensional, two-zone numerical model of a diesel engine was developed. Model based on the extended Zeldovich mechanism was applied to predict NOX emissions. The validation of the numerical model was performed by comparing operating parameters of the basic engine with data from engine manufacturers and data from sea trials of a ship with diesel-electric propulsion. The applicability of the numerical model was confirmed by comparing the obtained values for pressure, temperature and fuel consumption. The operation of the engine that drives synchronous generator was simulated under stationary conditions for three operating points and nine injection schemes. The values obtained for fuel consumption and NOX emissions for different fuel injection schemes indicate the possibility of a significant reduction in NOX emissions but with a reduction in efficiency. The results showed that split injection with a smaller amount of pilot fuel injected and a smaller angle between the two injection allow a moderate reduction in NOX emissions without a significant reduction in efficiency. The application of split injection schemes that allow significant reductions in NOX emissions lead to a reduction in engine efficiency.

ACS Style

Vladimir Pelić; Tomislav Mrakovčić; Radoslav Radonja; Marko Valčić. Analysis of the Impact of Split Injection on Fuel Consumption and NOx Emissions of Marine Medium-Speed Diesel Engine. Journal of Marine Science and Engineering 2020, 8, 820 .

AMA Style

Vladimir Pelić, Tomislav Mrakovčić, Radoslav Radonja, Marko Valčić. Analysis of the Impact of Split Injection on Fuel Consumption and NOx Emissions of Marine Medium-Speed Diesel Engine. Journal of Marine Science and Engineering. 2020; 8 (10):820.

Chicago/Turabian Style

Vladimir Pelić; Tomislav Mrakovčić; Radoslav Radonja; Marko Valčić. 2020. "Analysis of the Impact of Split Injection on Fuel Consumption and NOx Emissions of Marine Medium-Speed Diesel Engine." Journal of Marine Science and Engineering 8, no. 10: 820.

Journal article
Published: 26 September 2020 in Journal of Marine Science and Engineering
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The energy efficiency and environmental friendliness of medium-speed marine diesel engines are to be improved through the application of various measures and technologies. Special attention will be paid to the reduction in NOx in order to comply with the conditions of the MARPOL Convention, Annex VI. The reduction in NOx emissions will be achieved by the application of primary and secondary measures. The primary measures relate to the process in the engine, while the secondary measures are based on the reduction in NOx emissions through the after-treatment of exhaust gases. Some primary measures such as exhaust gas recirculation, adding water to the fuel or injecting water into the cylinder give good results in reducing NOx emissions, but generally lead to an increase in fuel consumption. In contrast to the aforementioned methods, the use of an earlier inlet valve closure, referred to in the literature as the Miller process, not only reduces NOx emissions, but also increases the efficiency of the engine in conjunction with appropriate turbochargers. A previously developed numerical model to simulate diesel engine operation is used to analyse the effects of the Miller process on engine performance. Although the numerical model cannot completely replace experimental research, it is an effective tool for verifying the influence of various input parameters on engine performance. In this paper, the effect of an earlier closing of the intake valve and an increase in inlet manifold pressure on fuel consumption, pressure and temperature in the engine cylinder under steady-state conditions is analysed. The results obtained with the numerical model show the justification for using the Miller processes to reduce NOx emissions and fuel consumption.

ACS Style

Vladimir Pelić; Tomislav Mrakovčić; Vedran Medica-Viola; Marko Valčić. Effect of Early Closing of the Inlet Valve on Fuel Consumption and Temperature in a Medium Speed Marine Diesel Engine Cylinder. Journal of Marine Science and Engineering 2020, 8, 747 .

AMA Style

Vladimir Pelić, Tomislav Mrakovčić, Vedran Medica-Viola, Marko Valčić. Effect of Early Closing of the Inlet Valve on Fuel Consumption and Temperature in a Medium Speed Marine Diesel Engine Cylinder. Journal of Marine Science and Engineering. 2020; 8 (10):747.

Chicago/Turabian Style

Vladimir Pelić; Tomislav Mrakovčić; Vedran Medica-Viola; Marko Valčić. 2020. "Effect of Early Closing of the Inlet Valve on Fuel Consumption and Temperature in a Medium Speed Marine Diesel Engine Cylinder." Journal of Marine Science and Engineering 8, no. 10: 747.

Journal article
Published: 01 May 2017 in Energy Conversion and Management
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ACS Style

Vedran Mrzljak; Igor Poljak; Tomislav Mrakovčić. Energy and exergy analysis of the turbo-generators and steam turbine for the main feed water pump drive on LNG carrier. Energy Conversion and Management 2017, 140, 307 -323.

AMA Style

Vedran Mrzljak, Igor Poljak, Tomislav Mrakovčić. Energy and exergy analysis of the turbo-generators and steam turbine for the main feed water pump drive on LNG carrier. Energy Conversion and Management. 2017; 140 ():307-323.

Chicago/Turabian Style

Vedran Mrzljak; Igor Poljak; Tomislav Mrakovčić. 2017. "Energy and exergy analysis of the turbo-generators and steam turbine for the main feed water pump drive on LNG carrier." Energy Conversion and Management 140, no. : 307-323.

Proceedings article
Published: 09 June 2013 in Volume 9: Odd M. Faltinsen Honoring Symposium on Marine Hydrodynamics
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A reliable prediction of attainable ship speed at actual seas is essential from economical and environmental aspects. At this paper a methodology for estimating the attainable speed and related fuel consumption and carbon dioxide (CO2) emissions in moderate and severe sea is proposed. The irregular sea is handled as a series of regular waves with different amplitudes and frequencies. The added resistance in regular waves is obtained by either a direct pressure integration method or an asymptotic small wavelength formula. The in-and-out-of-water-effect and ventilation of a propeller in severe seas is accounted for by a quasi-steady averaging of experimental data for different propeller submergences. The propulsion results for regular waves are used in simulating results in irregular waves. It is shown that for higher sea states this effect has much more influence on the speed loss than the added resistance in waves. The speed loss is calculated by taking into account the engine and propeller performance in actual seas as well as the mass inertia of the ship. The numerical model used for main propulsion engine modeling is based on a zero-dimensional model of an internal combustion engine. The main propulsion engine is represented by number of control volumes interconnected with links for mass and energy transfer between them. This model provides excellent prediction of engine dynamic response during transients with rather short computational time. Also, engine fuel consumption can be precisely determined which represents the basic presumption for estimation of carbon-dioxide emission. Furthermore, use of such model can be extended to determination of the lowest fuel oil consumption strategy for given sea condition and ship speed with resulting lowest possible CO2 emissions. The attainable ship speed is obtained as time series. Correlation of speed loss with sea states allows predictions of propulsive performance in actual seas.

ACS Style

Jasna Prpic-Orsic; Odd Magnus Faltinsen; Tomislav Mrakovčić. Influence of Ship Behaviour in a Seaway on CO2 Emissions. Volume 9: Odd M. Faltinsen Honoring Symposium on Marine Hydrodynamics 2013, 1 .

AMA Style

Jasna Prpic-Orsic, Odd Magnus Faltinsen, Tomislav Mrakovčić. Influence of Ship Behaviour in a Seaway on CO2 Emissions. Volume 9: Odd M. Faltinsen Honoring Symposium on Marine Hydrodynamics. 2013; ():1.

Chicago/Turabian Style

Jasna Prpic-Orsic; Odd Magnus Faltinsen; Tomislav Mrakovčić. 2013. "Influence of Ship Behaviour in a Seaway on CO2 Emissions." Volume 9: Odd M. Faltinsen Honoring Symposium on Marine Hydrodynamics , no. : 1.

Journal article
Published: 01 June 2013 in Fuel Processing Technology
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ACS Style

Zmagoslav Prelec; Tomislav Mrakovčić; Viktor Dragičević. Performance study of fuel oil additives in real power plant operating conditions. Fuel Processing Technology 2013, 110, 176 -183.

AMA Style

Zmagoslav Prelec, Tomislav Mrakovčić, Viktor Dragičević. Performance study of fuel oil additives in real power plant operating conditions. Fuel Processing Technology. 2013; 110 ():176-183.

Chicago/Turabian Style

Zmagoslav Prelec; Tomislav Mrakovčić; Viktor Dragičević. 2013. "Performance study of fuel oil additives in real power plant operating conditions." Fuel Processing Technology 110, no. : 176-183.