Control And Performance Optimization Of Natural Gas Engine With Micro-pilot Diesel Fuel Injection Based On Models

EEDI and pollutant emission are main indexes to evaluate engine performance.Use low carbon and clean fuel an important method to achieve marine energy saving and emission reduction.Natural gas be used as alternative fuel of marine power becomes a hot research area.Mirco pilot diesel induced ignition dual fuel engine(MPII-DFE)is one of the main application form of natural gas.MPII-DFE has multi fuel modes,multi combustion modes and a complex conbustion process.It is coupled with time lag,strong nonlinear and sensitive to lambda.Aiming at the performance optimization and operation control problem,simulation compounded with experimental study are token as the study method.From the aspect of combustion process and operation characteristic,the effect of control parameters on combustion process and engine performance is investigated deeply,and MPII-DFE performance optimization method and operation control strategy are studied.The studied results will support MPII-DFE high performance opreation control in whole operation conditions on method and theory.To investigate the economy and emission optimization method,the effect of combustion modes on combustion process and engine performance are investigated by experiment.The limitation condition of PPCI combustion mode expension to high load conditions,and engine operation parameter limitation is studied further.Control parameters configuration basis at high load condition is studied.Experimental results reveal that,lambda is proposed as the operation limit parameter of PPCI combustion mode expending.When lambda is bigger than 1.63,PPCI combustion mode is used to promote combustion speed of mixture.When lambda is smaller than 1.63,DDF added with intake throttling combustion mode is preferred.To do coorperative control at different fuel modes and different combustion modes,torque based MPII-DFE management strategy is designed.ITE modeling method is lucubrated to achieve torque-fuel mass conversion.Classification analysis and two stage modeling method is adopted.The effect of control parameters on combustion process characteristic parameters model and the effect of combustion process characteristic parameters on ITE model are built seperatly.Study results shows that control parameters can by divied into three kinds,Main injection timing,pilot injection timing,pilot fuel mass affect combustion phase.Lambda and pilot fuel mass affect combustion speed.Ignition fuel mass affect combustion center.ITE function is decomposed according to control parameters classification.Impact factors of each kind of control parameters are calculated,and then calculate ITE.Model prediction accuracy is 94%.Torque based MPII-DFE management is realized by designed ITE model.Aiming at the short of power during transient process,speed fluctuation rate big problems.Operation characteristic of MPII-DFE is analyzed from the aspect of combustion process and engine structure,and study the transient state and stable state torque tracking control strategy.Study results show that power problem at transient state and speed fluctuation problem at stable stable are mainly caused by the delay characteristic of gas combustion torque response.Diesel injection compensation strategy is proposed to speed up torque response.Combustion phase micro-adjusting strategy at steady state,combustion phase and combustion center compensation control strategy at transient state are proposed.According to the intake manifold charge and venting model,minimum gas strategy and ignition diesel follow delay are designed.Engine closed loop simulation results show that stable speed fluctuation is decreased to ±3r/min from ±4r/min.Transient speed error during sudden unload is decreased to-29r/min from-40r/min.To compensating lambda control error of open loop lambda control strategy,model based lambda closed loop control strategy is designed.Self-adaptive sliding mode control algorithm is studied to optimize the throttle position tracking performance.Control performance of twisting,LA-twisting and CA-twisting are compared by simulation and experiment.Results revealed that response rate and control accuracy can be optimized by CA-twisting algorithm,lambda control accuracy is promoted.Based on the combustion process control strategy and operation control strategy designed above,MPII-DFE control system is developed,including CAN bus based distributed hardware framework and OSI model based software framework.Software is divided into several layers,and basic control software is detailly designed.Bench test and ship test is carried out on the basis of designed control system.Start experiment,stable state governor experiment,transient state governor experiment,fuel mode switching experiment and performance test experiment are carried out to validate the control performance.Experiment results show that transient state speed fluctuation rate is 3.73% and setting time is 2s during fuel mode switching process,first class governor performance specified by GB/T 3475-2008 can be met.Transient state speed fluctuation rate is 6.6% and steady state speed fluctuation rate is 0.33% at dual fuel mode,second class governor performance can be met.Emission test results show that NOX+NMHC is 5.6395g/k W.h,and CO emission 3.9425g/k W.h,can meet the requirement of the second stage marine engine emission limitation specified by GB10597-2016.Meanwhile fuel economy at low and medium load is optimized dramatically.