Design And Implementation Of Electro-hydraulic Joint Control Multi-point Injection System For Marine Dual Fuel Engine

With the decrease of petroleum resources,the prominence of new environmental protection problems such as haze,and the gradual stringency of emission regulations,people urgently need to explore alternative fuels for petrochemical resources.Natural gas,with its high calorific value,cleanliness,non-toxicity and abundant reserves,has gradually attracted the attention of the engine industry.The Ministry of Environmental Protection and the Ministry of Transportation are vigorously promoting the application of marine natural gas and providing some policy support to ships using diesel/natural gas dual-fuel engines.Diesel/natural gas dual-fuel engine uses natural gas as its main fuel and a small amount of diesel as its ignition fuel.Compared with the original diesel engine,it has no power loss and can be easily converted between pure diesel mode and dual-fuel mode.Fuel replacement rate can reach more than 80%,which has become a new research hotspot in the industry.At present,many domestic marine main engine factories have successfully developed marine dual-fuel engines,but basically all of them adopt premixed gas supply mode and electronic single-point injection mode.These two modes are relatively backward,low safety,difficult to achieve better combustion effect and better emission level,and cannot give full play to the advantages of natural gas to enhance emission performance.In this paper,a marine diesel engine in Zichai was improved by adding a natural gas supply system and designing a matching electro-hydraulic multi-point injection system,the accuracy,balance,stability and emission of fuel supply are better than those of electronic single point injection and premixed gas supply,and the intake pipe is safe because there is no combustible gas.The main content is as follows:Firstly,the research and development status of dual-fuel engine and its gas injection system are introduced.Combining with the combustion characteristics of natural gas,the traditional diesel engine is transformed into a dual-fuel engine,and the corresponding electro-hydraulic multi-point injection system is designed to control the intake process of natural gas.Secondly,the working principle and main structure of the engine are introduced in detail.On the premise that the main structure of diesel engine is basically unchanged,the control circuit and gas supply system of natural gas are added,as well as other improved components such as gas mixing device and injector cooling system.The natural gas injection valve is installed on the cylinder head,and the natural gas is injected into the cylinder head.It mixes with air before the intake valve,and then the mixture enters the combustion chamber to realize quasi-internal mixing.Natural gas "quasi-internal mixing" mixing technology can effectively solve the potential safety hazards of tempering and fuel waste caused by premixed intake mode,and is closer to the combustion chamber than natural gas intake branch injection technology,which is conducive to shortening the reaction time of the engine and improving the engine control efficiency.Thirdly,the hardware,software and control strategy of electro-hydraulic multi-point injection system are introduced.The hardware part focuses on the design of control circuit(including timing processing signal,switching input signal,gas supply system state signal and engine state signal processing circuit),actuator circuit(including gas switch valve circuit,jet valve circuit and H bridge drive circuit)and external communication circuit;the software part mainly introduces the realization of functions,including analog acquisition and processing,condition discrimination,mode conversion control,engine fault diagnosis.The control strategy mainly includesclosed-loop control of air-fuel ratio of natural gas injection,uniform combustion control of cylinders and engine load control.Finally,a lot of validation tests have been carried out,such as ship propulsion performance test,exhaust smoke measurement test,mode conversion test and noise measurement test.The actual parameters of the engine are obtained through these tests.The data show that the power performance of the engine is the same as that of the original engine.The maximum fuel replacement rate can reach 83.9%,which can save fuel effectively.The noise of the two modes can meet the national compulsory standard,and the emission of nitrogen oxides and particulate matter is lower than that of the diesel engine.The improved dual fuel engine combined with electro-hydraulic multi-point injection system can replace the original diesel engine and provide power for ships.