Diesel/CNG Dual-fuel Engine Control Strategy And Experimental Research

Air pollution and energy crisis are major social problems today,and natural gas has the advantages of high calorific value,high octane number,and high compression ratio.These advantages make diesel/natural gas dual-fuel engines the hotspots of current research.Based on the premise of not changing the power of the original machine,the following research was conducted for the purpose of improving the economy of the dual-fuel engine and reducing emissions.In order to design the dual-fuel engine structure better,based on the physical and chemical properties of natural gas and the analysis of blended combustion,a gas supply system with a multi-point sequential injection method at the intake manifold was designed.Based on the electronically controlled high-pressure common-rail diesel engine,the demand of the electronic control system for the dual-fuel engine was analyzed.The injector and the control method of the air-jet valve were designed.The criteria for determining the cylinder working order and the jet sequence of the dualfuel engine were described.For the dual-fuel engine performance optimization,the dual-fuel engine working conditions,start-up control strategy,natural gas and pilot fuel injection control strategy,air-fuel ratio limit control strategy,and oil-gas switching control strategy were designed and optimized.The control strategy is docked with the underlying control.Through the bench test,the correctness and rationality of the logic of the control strategy are verified,and the key curves and MAP in the control strategy are calibrated.In order to analyze the performance difference between the dual fuel mode and the pure diesel mode,the two modes were tested separately under the conditions of external conditions and control parameters.The final test results show: The dual-fuel engine can smoothly switch between the two modes;in the dual-fuel mode,the engine can maintain the original power;The dual fuel mode is adopted at medium and high load,the economical advantages of the engine are obvious,and the higher of the natural gas replacement rate,the better of the economy;Using dual fuel mode at low speed of high load and high speed can effectively reduce CO2,smoke and NOX emissions.The higher natural gas replacement rate,the better the emission effect.In the dual fuel mode,the fuel combustion time is longer and the peak cylinder pressure is greater.The higher the natural gas replacement rate,the longer the combustion time and the greater the peak cylinder pressure.