Research On Fast Idle Control Strategy Of Vehicle Diesel Engine

Because the number of oil vehicles in China accounts for more than 95% of the total number of motor vehicles,the national stage 6 motor vehicle emission standards have added the pollutant emission and cycle work of cold start diesel engine into the calculation results of start cycle test.At the same time,both oil vehicles and new energy vehicles have cold start problems.Therefore,it is very important to improve the overall performance of engine during cold start.In this paper,the optimal fast idling control strategy of vehicle diesel engine under different ambient temperatures is studied by means of simulation.First of all,the first cycle combustion model of diesel engine was built by AVL-FIRE software.By setting different ambient temperatures,the optimal starting speed,namely the beginning point of fast idle curve,was obtained by simulation calculation.When the ambient temperature was-10℃,the optimal starting speed was 160r/min.When the ambient temperature is higher than 0℃,the best starting speed is 200r/min;When the ambient temperature is lower than-10℃,the prototype can not start normally,and inlet air preheating auxiliary device must be installed.On this basis,the influence of injection mode on cold starting performance was further explored,and the results showed that:Under the condition of secondary pre-injection plus main injection,the pilot injection with timing of pre-injection 2 ～ pre-injection 1 ～ main injection 250℃A ～ 354℃A ～358℃A can effectively improve the combustion condition of the engine under low temperature starting condition.The pilot injection mode can also start successfully at ambient temperature of-10℃ without auxiliary preheating device.In addition,in the pilot injection mode,it is best to set the fuel injection ratio of pre-injection 2 ～ preinjection 1 ～ main injection as 3 ～ 3 ～ 4.In this mode,the combustion efficiency can be better improved and emissions can be reduced,which is conducive to the improvement of cold start performance.Secondly,the fast idle speed target speed curve was designed as starting stage,high idle steady stage,speed decline stage and idle warm up stage,and the threshold of water temperature increment was set as the judging basis for entering from high idle steady stage to idle warm up stage.On the basis of the fuel injection calculation model based on the target torque,the relationship between speed and torque is deduced by the formula,and the target torque of corresponding stage is calculated,and then the fuel injection amount of the control strategy of fast idling heater is determined.The diesel engine model built by GT-Power and the fast idle fuel injection control model built by Simulink were co-simulated.The results show that when the ambient temperature is-5℃ and 5℃,the maximum idle speed and water temperature increment threshold of the optimal fast idle warming control strategy are 1200r/min and 20℃ respectively.When the ambient temperature is 15℃,the maximum idle speed and water temperature increment threshold of the optimal fast idle warming control strategy are 1500r/min and20℃ respectively.