Experimental Study On CNG / Diesel Dual Fuel Engine

Natural gas, which have the advantages of low cost, less pollution, abundant and mature technology and so on, is an high quality alternative fuel. It has better emissions and economic benefit compared with diesel in engine application. At present, many universities and enterprises obtain a lot of research results by invest a lot of manpower and resources to develop natural gas engines and related technologies at home. Natural gas engine control strategies, parts fatigue strength, heat load calculation&analysis, oil and gas switching, valve timing and other key technologies are simulated and experimental studied.Firstly, the CNG/diesel dual-fuel engine supply system is introduced. The physical and chemical characteristics of natural gas fuel are described. And the composition and working principle of dual fuel engine’s supply system components are descripted in detailed. The fuel supply system of CNG/diesel dual-fuel engine is analyzed. Based on the current lab condition, the overall design scheme is propsed finally, and the main system and parameters in this scheme are also introduced.Secondly, the CNG/diesel dual-fuel engine system design and construction are introduced. Electric control system is used to control the injection amount of natural gas. The electric control system is mainly composed of development board TC1728, gas nozzle driver board and photoelectric encoder. The gas injection rail controlled by the electronic control system injects gas timing and quantitantively. The inject flow characteristics of injection rail have been tested on the plateau.Thirdly, the experiment and the performance analysis for dual-fuel engine system are done. In test, four point of injectiong volume values and eight load points are set for record. Control strategy for dual fuel combustion system and the feasibility of natural gas&diesel fuel supply system are tested by the installation and test of the dual fuel engine. The bench test of every working condition has been completed by changing inject amount controlled by injection rail. The injection characteristic of the gas injection rail is verified and the bench test research of every group has been done. The test data shows that power performance is surpass around1%compared with the original machine in the dual fuel engine and the ignite diesel consumption of the dual fuel system is reduced by50%compared with diesel consumption of the original machine. The biggest replacement rate of the natural gas can reach75%and the fuel specific fuel consumption is lower than the original machine in the full load. The ignite diesel consumption is gradually decreased with the increase of the inject gas volume through the control of the inject gas volume and the exhaust temperature will gradually increase. Finally, the cost of dual fuel engine is greatly affected by the natural gas marketable price. Cost will reduce as the inject gas volume increasing when natural gas price fall down, otherwise it will rise. In addition, engine pollutants will greatly reduce by using diesel engine fueled with natural gas. Therefore, the design of the dual fuel system has achieved the expected design requirements.The experimental process of the dual fuel engine is summarized in the end and the next research contents are introduced.