| With the continuous development of the transportation industry,oil resources are continuously exploited and over-utilized,the energy crisis and environmental pollution problems are becoming more and more serious,and the exploration and utilization of clean and alternative energy has become the theme of development in countries around the world.Natural gas has gradually become the first choice for alternative fuels due to its abundant reserves,cleanness and environmental protection.The marine natural gas engine operates stably and has good performance in the steady state process,but the transient characteristics are poor.Although the multi-point injection natural gas engine can improve the consistency of fuel distribution in each cylinder and can respond relatively quickly to load changes,it has high requirements for the coordinated control of gas and air.Therefore,the development of marine multi-point injection natural gas engine gas and air The research on synergistic mechanism and control strategy is of great significance for improving engine dynamic response characteristics,economy and emission performance.In this paper,GT-Power software is used to build a one-dimensional complete machine model of natural gas engine,and on the basis of model test verification,the effects of ignition timing,jet timing and excess air coefficient on engine performance are calculated,and then the optimal value range is determined;Quantitative analysis of the correlation shows that the excess air coefficient has a more significant impact on the power and economy of the engine,and should be the main research target,while the ignition timing and jet injection are the secondary research targets,and the optimal values are determined as 20°CA BTDC and390°CA.Taking the improvement of engine power and economy as the optimization goal,the main research target excess air coefficient is optimized.The results show that there is an optimal excess air coefficient under different working conditions,which makes the comprehensive performance of the engine better,and the results are converted into performance MAP map;in order to improve the dynamic response of the sudden increase and decrease of engine load and improve the speed fluctuation problem,based on the synergy between the gas injection amount and the air charge,a control strategy for correcting the throttle valve opening and correcting the gas injection amount is designed.The results show that when the engine load suddenly increases,the control strategy of correcting the gas injection amount can effectively reduce the peak speed deviation during acceleration,which is55.68% lower than the peak value of the basic control strategy,and the speed stabilization time is also reduced.25.70%;and the control strategy of correcting the throttle opening in the process of load shedding reduces the speed deviation slightly.In order to further improve the dynamic response of the engine,the fuzzy control algorithm was replaced by the original classical PID control,and the control algorithm was upgraded by the method of co-simulation,and the closed-loop effect of the engine speed was compared and analyzed.Under load,the two peak speed deviations during engine loading decreased by 36.86% and 68.53%,respectively,and the stabilization time was reduced by16.81%;in the process of load shedding,the speed deviation decreased by 33.52%;the stabilization time was almost unchanged.Under 50% load,the engine speed deviation decreased by 21.51% during the loading process,and the stabilization time decreased by10.83%;during the load shedding process,the speed deviation decreased by 29.21%,and the difference in stabilization time was small.It can be seen that the control strategy based on the fuzzy control algorithm can effectively improve the dynamic characteristics of the natural gas engine. |
