Development Of Diesel Engine Air System Based On Oxygen Sensor

The limits and measurement methods for exhaust pollutants from compression ignition engines of vehicles(CHINA ?),the most challenging regulation,is about to come on.The diesel engine can not achieve the corresponding emission limit only by improving the fuel injection precision to meet the requirements of the regulation.With the development of diesel engine,the importance of the air control system has been paid more and more attention on.Now the traditional control system use air flow as control target,the hot film air flow as a technical scheme.Because the target is not clear and the control theory is not perfect and very susceptible to matching and environmental conditions,it lead to low control precision.And it is difficult to effectively control the emission,moreover,the calibration process is complex and the adaptability is poor.In order to overcome the above shortcomings of traditional air system,this paper puts forward the concept of effective EGR rate by deeply analyzing the combustion factors of diesel engine.The new air system that the air-fuel ratio and the effective EGR rate are taken as the control targets is redesigned.Through the control of the effective EGR rate,the issue that the traditional air system has not considered of the excessive air combustion of the diesel engine and the unstable CO2 ratio in the exhaust gas is solved.The new air system is put forward through the turbocharger and the TVA as the air-fuel ratio control means,EGR valve as the control means of EGR rate by the analysis of the influencing factors of air-fuel ratio.The new scheme solves the problem of the conflict between the EGR valve and the throttle in the traditional air system.This paper also researches the strategy based on flow prediction model,which is created by sonic nozzle principle of fluid mechanics to improve the control precision of the valve of the model,to improve the control responsiveness and adaptability.The control strategy of predictive compensation PID is also studied to improve the response of closed loop control.And a fast analysis and prediction of the closed-loop difference is carried out to further improve the control effect on the air system.The new air system control strategy greatly improves the control accuracy and responsiveness and makes the combustion process more effectively control.It also simplifies the calibration and enhances the adaptability.The new air system control strategy requires oxygen concentration as a basis for control,but conventional oxygen sensors are designed for exhaust environments.The measurement of environmental temperature,measuring pressure range and dew point treatment are very different.The exhaust environment is 150?800?.The pressure is close to the atmospheric pressure.The measuring medium is easy to reach dew point.And the exhaust is easy to produce condensed water.Relatively the inlet temperature is not more than 70 ?,and the range of inlet pressure changes a lot about the range of exhaust pressure.It is difficult to reach dew point for inlet.Due to the above differences,the traditional oxygen sensor must be redevelopment to adapt to the measurement of intake air environment.According to this requirement,the heating module of the oxygen sensor,which can quickly reach the working temperature,is designed.The pressure compensation module is developed to solve the problem of intake pressure changes sharply.Through the improvement of the structure of sensor probe and the use of special coating,the water resistance of the sensor is strengthened to solve the problem of the air dew point so that the sensor can quickly enter the working mode.