Design And Experimental Research Of Control System For Marine LNG/Diesel Dual-Fuel Engine

Environmental pollution and oil shortages have become the two major issues which cannot be avoided in today’s society.Marine diesel engine has always been the source of shipping power.Because of being subject to these two problems,marine diesel engine has been put forward higher requirements of development.Therefore,finding alternative fuels to reduce dependence on oil and to meet increasingly stringent emissions regulations is becoming one of the directions of marine diesel engine development.Natural gas combines the advantages of rich reserves of clean energy.It’s an ideal alternative fuel.At home and abroad it has also been researched in internal combustion engine.Compared with CNG,LNG（liquefied natural gas）has a feature of high density.Application of LNG in marine diesel can solve the problem of frequent refilling.In the paper a marine diesel engine is converted into LNG/diesel dual-fuel engine.Then the electronic control system is designed and dual-fuel engine performance will also be studied.In this article a set of natural gas system designed to match X6170 for the purpose of using LNG and the installation of diesel fuel quantity regulate actuators achieve the dual-fuel engine technology that has multi-point injection quantity of natural gas working in with diesel fuel position electronically controlled.The core of its electronic control system is 16-bit high-performance dual-core microcontroller.The controller hardware is designed.The software of the control system is developed in level and modules.The important parameters of multi-point injection technology such as speed and natural gas injection timing are elaborated how to calculate.The program of operational management strategies and reasonable distribution of control system tasks are based on the characteristics of dual-fuel engine.Fuel modes management task and speed control strategy are formulated for the two fuel modes of operation.The purpose of quantitative and timing control of natural gas injection is achieved.The strategy of speed control used natural gas which is based on the idea of speed close-loop computing equivalent fuel is formulated,and in particular the control strategy for the transition of the two fuel modes operation.Ultimately the purpose of stable operation and energy conservation are obtained in dual-fuel mode under whole working conditions.Before experimental study on the performance the calibration of the dual-fuel engine is executed.It can provide necessary data for the next experimental study.Fuel mode switching test shows that in the switching process slowly changing the amount of natural gas can ruduce the speed fluctuation rate and shorten the settling time.The tests of speed control verify the speed of dual-fuel engine can be controlled using natural gas.It can meet the power requirements of marine engines.The comparative results of Propulsion conditions of two fuel modes indicate that substitution rate of diesel fuel can reach 70%,the fuel economy is better,soot emissions reduces and that NO_x emissions changes little in dual fuel mode.The change of injection timing shows that it affects NO_x little and early injection can cut down HC.In addition,the increasing of substitution rate leads to high HC emissions and exhaust temperature;at low speed the lower substitution rate the dual-fuel engine has,the higher soot emissions it exhausts;at high speed soot emissions first increases and then reduces with increasing substitution rates;Substitution rate has less affection on NO_x emissions.