The study objective is to identify to what extent the recirculation of exhaust gas from a low-speed marine diesel engine affects environmental, economic and power-related parameters in engine operation. Concentration of nitrogen oxides in exhaust gases was assumed to be the environmental parameter of an engine, specific fuel consumption as its economic parameter while effective (brake) power as its power-related parameter. Content of nitrogen oxides in exhaust gases discharged by low-speed marine diesel engines shall remain within the range of 3.4…14.4 g/(kW•h) depending on the area of marine vessel operation as specified by requirements of Annex VI MARPOL. Exhaust gas recirculation (EGR) was reviewed as a way to provide for such values. It was proven experimentally that recirculation of exhaust gas in the range of 4.7…18.8 % provides for reduction in concentration of nitrogen oxide (NO х) in the exhaust gases respectively down to 13.3…3.3 g NO x /(kW•h) depending on the rotation speed and load of diesel engine. Drop of NO х concentration in exhaust gases (as compared to NO х concentration without any circulation system used) was shown to reach 37.9…53.5%. It is proposed to apply the EGR system as a major technique to reduce NO х-emissions and bring the aforesaid parameter in compliance with requirements of international agencies. Sažetak Cilj studije je identificirati: "Do koje mjere ponovno strujanje ispušnoga plina iz sporohodnog dizelskog stroja, utječe na okolišne, ekonomske i energetske parametre pri radu stroja?" Koncentracija nitrogen oksida pri ispušnim plinovima, smatra se energetskim parametrom stroja, a specifična potrošnja goriva, kao ekonomski parametar, dok je učinkovita (konjska) snaga energetski parametar. Sadržaj nitrogen oksida pri ispušnim plinovima koje ispušta sporohodni brodski dizelski stroj, ostat će unutar dometa od 3.4…14.4g/(kW•h) ovisno o području djelovanja broda na moru, kako je specificirano zahtjevima Annexa MARPOL Konvencije Ponovno strujanje plina (EGR) odabrano je za dokazivanje tih vrijednosti. Eksperimentalno je dokazano da ponovno strujanje ispušnoga plina u dometu od 4.7…18.8% osigurava smanjenje koncentracije nitrogen oksida (NO x) pri ispušnim plinovima, prema redosljedu navođenja sve do 13.3…3.3 g NO x /kW•h ovisno o rotacionoj brzini i opterećenju dizelskoga stroja. Pad koncentracije pri ispušnim plinovima (u usporedbi s NO x) koncentracijom bez ikakva sustava cirkulacije dostigao je 37.9…53.5%. Predlaže se da se primijeni EGR sustav kao glavna tehnika smanjenja NO x emisija i da se dovede spomenuti parametar u skladu sa zahtjevima međunarodnih agencija. KEY WORDS low-speed marine diesel engine environmental indicators of diesel engine operation concentration of nitrogen oxides in exhaust gases exhaust gas recirculation (EGR) system brake power specific fuel oil consumption KLJUČNE RIJEČI sporohodni dizelski motor okolišni pokazatelji djelovanja dizelskoga stroja koncentracija nitrogen oksida pri ispušnim plinovima sustav ponovnoga strujanja plina konjska snaga specifič...

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The features of the operation of the drillship-type vessels in special ecological regions of Northern Europe are considered. The main gap in the study of these systems is to determine the optimal degree of recirculation. The requirements of the International Maritime Organization for the emission of nitrogen oxides from the exhaust gases of marine diesel engines are given. The aim of the study is to determine the optimal degree of recirculation of exhaust gases of a 16V32 STX-MAN marine diesel. During the research, the optimal degree of exhaust gas recirculation varied in the range of 0–21%, the load on the diesel—in the range of 35–95% of the rated power. It was established that in this case, the emission of nitrogen oxides decreases up to 7.7–33.6%, the specific fuel consumption increases up to 0.2–3.5%. It was also found that the use of gas recirculation in the range of 18–21% at loads of 35–55% leads to a critical increase in exhaust gas temperature. It is advisable to use exhaust gas recirculation in the range of 6–15% to ensure the environmental friendliness of the operation of the drillships. In these modes, the maximum reduction in nitrogen oxide emissions is ensured with a minimum increase in specific fuel consumption. Future studies should be directed at the development of the criteria for the environmental stability of sea vessels.

SummaryThe article deals with the operational features of internal combustion engines of marine vessels during their operation in special environmental areas -Nitrogen Oxide Emission Control Areas. According to the requirements of Annex VI MARPOL, during the operation of marine diesel engines in these areas the content of nitrogen oxides in the exhaust gases should be less than 3.4 g/(kW×h). The article touches upon the possible technical measures to ensure the maintenance of the required level of nitrogen oxide emissions in the exhaust gases of marine diesel engines. The authors propose to use an exhaust gas recirculation system, with a certain amount of gases supplied back to the cylinder after preliminary cooling and mixing with air, which reduces the maximum combustion temperature to values that prevent the formation of nitrogen oxides. The experiment proved that the recirculation of exhaust gases in the 4.7 ... 18.8% range helps to reduce the concentration of nitrogen oxides in exhaust gases by 19.5 ... 48.8%. At the same time, it is necessary to ensure values that meet the requirements of international organizations aimed at protecting the air from pollution and allowing the use of marine vessels in areas of increased environmental control. SažetakČlanak se bavi operativnim značajkama brodskih motora s unutarnjim izgaranjem u posebnim područjima zaštite okoliša -područja kontrole emisija dušikovih oksida. Prema odredbama Priloga VI. MARPOL konvencije, tijekom rada brodskih dizelskih motora, u posebnim područjima sadržaj dušikovih oksida u ispušnim plinovima ne smije prelaziti 3,4 g/(kW×h). Članak se bavi potencijalnim tehničkim mjerama za održavanje određene razine emisija dušikovih oksida u ispušnim plinovima brodskih dizelskih motora. Autori predlažu uporabu sustava recirkulacije ispušnih plinova s određenom količinom plinova koji se vraćaju u cilindar nakon prethodnog hlađenja i miješanja sa zrakom, što smanjuje najvišu temperaturu izgaranja do vrijednosti koje sprječavaju stvaranje dušikovih oksida. Pokus je potvrdio da recirkulacija ispušnih plinova u rasponu od 4,7 do 18,8 % pomaže pri smanjenju koncentracije dušikovih oksida u ispušnim plinovima za 19,5 do 48,8 %. istodobno je potrebno osigurati vrijednosti koje su u skladu s propisima međunarodnih organizacija s ciljem zaštite zraka od onečišćenja i uporabe brodskih motora u područjima povećane kontrole okoliša. KEY WORDSlow-speed marine diesel environmental performance of a diesel engine concentration of nitrogen oxides in exhaust gases exhaust gas recirculation effective power specific fuel oil consumption KLJUČNE RIJEČI sporohodni brodski dizelski motori skrb za okoliš dizelskih motora koncentracija dušikovih oksida u ispušnim plinovima recirkulacija ispušnih plinova efektivna snaga specifična potrošnja goriva

The by-pass system of exhaust gas for the engine 6L20 Wartsila has been observed. The requirements of Annex VI MARPOL towards nitrogen oxide concentration in ship engine exhaust gases have been provided. The purpose of research was the determination of diesel 6L20 Wartsila by-pass exhaust gases optimum volume – at this the nitrogen oxide minimal concentration in exhaust gases is assured, the minimal increase (comparing with operation mode without by-pass) – specific effective fuel consumption, supporting of necessary thermal factor diapason of engine cylinders. The research was performed for the exhaust gas by-pass diapason 0…10 % with engine load diapason 0.55…0.85 % from nominal power. Upon experimental results it has been stated that the exhaust gas by-pass usage favors the ecological parameters of ships engine operation modes – by this at the range of exploitation load 0.55…0.85 % from nominal power the nitrogen oxide concentration in exhaust gas is decreased to 1.32….12.97 %. The exhaust gas by-pass impairs the combustion process and favors the increasing of specific effective fuel consumption and increasing the temperature of exhaust gases. The exhaust gas by-pass system effectiveness assessment should be performed by complex estimation of the following engine operation parameters: the nitrogen oxide concentration in exhaust gas, increasing of specific effective fuel consumption(SFOC), the exhaust gas temperature. As optimal degree of exhaust gas by-pass value when the maximum decrease of nitrogen oxide emission at minimal increase of fuel consumption and simultaneous engine thermal factor handling has to be considered.