Model Based Development For Diesel Ignited Natural Gas Engine Control System And Research Of Air-path Control

With the increasingly stringent emission regulation and growing energy crisis,the study of alternative fuels of internal combustion engine is getting more and more attention,in recent years,and diesel ignited natural gas engine has become a research focus.However,diesel ignited natural gas engine suffers from high THC and CO emission and low efficiency under middle and low load,it is mainly because the diesel fuel injection strategy is not flexible and the mixture concentration in cylinder is not appropriate.By analyzing the control demand of diesel ignited natural gas engine,an integrated conrol model which consists of high pressure common rail diesel system,natural gas(NG)inlet single point system and throttle-air inlet system is built using model based development(MBD).Model based development has the advantages of graphical interface,early verification,automatic creation documents and shorter development cycle,compared with traditional development method.The diesel ignited natural gas engine control system is based on fuel-quantity-based control strategy,speed closed-loop control as the core and rail ressure closed-loop control as the foundation,and coordinately control injecting quantity of diesel,injecting quantity of NG,throttle opening degree.Rail pressure control uses feedforward and variable parameter PID closed-loop controller,and the steady-state error is less than 1 MPa,transient overshoot is less than 2 MPa,response time is less than 300 ms.Speed control and throttle position control use variable parameter PID closed-loop controller which is quite fit for engine real-time control,and achieved good control results.Based on intake quantity estimate model,developing air path control strategy which inproving the speed regulation performance under the varying duty working conditions,on the other hand,the estimate model can be used as feedforward for λ closed-loop control.Studying the effects of pre-injection timing,pre-injection quantity ratio,injection pressure,throttle opening degree on combustion and emission characteristics of engine.The results indicated that combustion performance can be optimized and THC,CO emission can be reduced by adjusting pilot diesel injection parameters and changing excess air coefficient when using the diesel ignited natural gas engine control system raised in this paper.However,there exist mutual exclusion among each optimization goal,we need trade-off to achieve performance and economical efficiency requirement.