Research On Combustion Phasing Control In A High-dilution Low-Temperature SFI Combustion Gasoline Engine

The high-dilution low-temperature combustion draws intensive attention,for its superiority in thermal efficiency and emissions.But it is sensitive to in-cylinder states,making the combustion phasing control challenging.The stratified-flame-ignition(SFI)combustion is realized by port fuel injection-direct injection(PFI-DI)system and spark discharge.The in-cylinder states and combustion phasing prediction models are established,and a control solution consisted of the model-based feed-forward controller and active disturbance rejection feedback controller is developed.Firstly,the research is carried out based on a four cylinder turbocharged DI gasoline engine,which is equipped with low lift camshafts,and augmented with PFI and external EGR system.The control system,based on MicroAutobox and RapidPro is developed,is proved to work well.A GT-SUITE model is developed and validated in experiments,for controller design and validations.Secondly,the in-cylinder temperature,residual gas fraction(RGF)and the combustion phasing prediction models are established.By introducing exhaust heat dissipation model and sensor delay compensation algorithm,the estimation error of RGF is within 4%.A combustion prediction model is proposed,considering that the SFI combustion has both early stage flame propagation and the subsequent auto-ignition,in dual-stage manner.Experimental validation shows the estimation errors for the start of auto-ignition and CA50 are both less than 2°CA.Thirdly,a combustion phasing control solution with the intake valve closing(IVC)and spark timing(ST)as inputs is proposed.This solution has the feed-forward term based on the inverse of the proposed prediction model,and importantly,the errors of the model are estimated and compensated via the total disturbance observer.Simulation results show that control algorithm can achieve fast tracking of the combustion phasing within 2°CA deviation during load and speed transitions.Experiment results also confirms that in load and speed condition steps,CA50 has a fluctuation within 5°CA,with the maximum pressure rise rate below 5bar/°CA.In a word,the proposed model enables the estimation of in-cylinder states and CA50,while the established solution improves the stability of SFI combustion in transients,which is promising for the practical application of SFI combustion.