Simulation And Optimization On The Performance And Emissions Of Dual-fuel Marine Engine

The fuel economy and emissions of diesel / natural gas dual-fuel engine have been improved comparing to diesel engine. However, parts of the structural parameters of diesel engines are not well matched dual-fuel combustion mode, which to make the fuel economy and emission characteristics are not to achieve the desired effects. For this problem, a study of dual-fuel engine performance simulation has been done, and relevant optimization improvements have been put forward.There are diffusion combustion of diesel, premixed combustion of natural gas and mixed combustion of diesel and natural gas in dual-fuel combustion, the combustion process is very complicated. Performance simulation software currently are not available to establish dual-fuel combustion model. Based on the multi-fuel predictive combustion models "DIJet" of GT-POWER 7.3, With optimized "DIJet" combustion model for the establishment of R6160 dual-fuel engine model, the performance parameters were within the 5% of error limits after calibrating, which to prove the reliability of the whole model.Based on the calibrated model to study the impact of natural gas substitution rate, injection timing and excess air ratio on performance and emissions of dual-fuel engine. Studies have shown that: the fuel economy and NOx emission can be improved with a high natural gas substitution rate; retarded injection timing three crank angle, NOx emissions of diesel and dual-fuel engine can be improved; dual-fuel engine is sensitive to the excess air ratio, especially in the low-load conditions, low excess air ratio can improve engine combustion, so that fuel consumption reduced.To further improve NOx emission of the dual-fuel engine, the Exhaust Gas Recirculation(EGR) and the Miller cycle were simulated. Studies have shown that: the NOx emissions can be reduced using low EGR rate in the high load condition; In the low load conditions, the use of high EGR rate can improve NOx emissions, but the fuel consumption increased; early intake valve closing can get better performance than late intake valve closing, early closure of 42 degrees crank angle got the best results.