OPTIMISATION OF FUEL CONSUMPTION ON LNG CARRIERS TAKING INTO ACCOUNT THE POSSIBLE USE OF GAS AND DIESEL FUEL

Porast broja i veličina brodova te stroži zakoni zahtijevaju ekonomičnost pogona te očuvanje okoliša pa se u skladu s time prati i optimizira potrošnja goriva. S ciljem testiranja hipoteze da je sve veća primjena motora na dvojna goriva (DFDE) na brodovima za prijevoz prirodnog plina (LNG) opravdana u svrhu optimizacije potrošnje goriva, provedene su dvije empirijske studije slučaja. U prvoj se analizira probna vožnja LNG broda s dizel električnim pogonom i DFDE motorima koja je pokazala najnižu specifičnu potrošnju goriva pri maksimalnom opterećenju motora u radu na prirodni plin. Rezultati druge studije učinkovitosti četiri LNG broda s različitim pogonima (parno-turbinski i DFDE) prikazuju zanemarive razlike među pogonima, no s obzirom na nepotpune podatke te procjene određenih vrijednosti dobiveni rezultati nisu reprezentativni. Studije su pokazale da motori pri izgaranju plina ne gube na efikasnosti u odnosu na izgaranje dizela, zbog čega je njihova primjena opravdana. Zbog smanjenog ispuštanja sumpornog dioksida, motori u radu na plin su ekološki prihvatljiviji, no ostaje upitan utjecaj na okoliš curenja metana.The increase in number and size of ships as well as stricter regulations require more economical propulsion and environmental safeguards, and in line with that the monitoring and optimisation of fuel consumption. In order to test the hypothesis that the increased application of Dual Fuel Diesel Electric (DFDE) engines for optimization of fuel consumption is justified, two empirical case studies were undertaken. The first case study analysed a sea trial of an LNG ship with diesel electric propulsion and DFDE engines. It showed that the lowest specific fuel consumption was at the maximal continuous rating with the engine in gas mode. The second study looked at the efficiency of four LNG ships with different propulsions (steam turbine and DFDE) and it showed negligible differences, but due to incomplete data and estimates of certain values, the results are not representative. Case studies showed that engines in gas mode are not less efficient than when in diesel mode, which justifies their application. Due to lower SOx and NOx emissions, engines in gas mode are ecologically more acceptable; however the question of the environmental impact of methane slip remains open