Research On Fuel Injection Quantity Diagnosis Of High Pressure Common Rail Based On Rail Pressure Characteristics

The cycle injection quantity determines the combustion in the cylinder of the diesel engine,which affects the power performance and emission performance of the whole engine.At present,the diesel engine can’t measure the cycle injection quantity in a closed-loop way;if the flow capacity of the injector is assumed to be constant,the amount of fuel injected is determined by the rail pressure and power on time.However,the flow capacity of the nozzle may change because of carbon deposition and nozzle wear,so it is necessary to carry out the research of on-line diagnosis of cycle injection quantity.At present,the academic circle mainly uses the cylinder pressure,transient speed or the change of exhaust oxygen concentration formed by fuel combustion to identify the cyclic injection quantity into the cylinder.But these methods need to pass the combustion link,so the response speed and the distinguishability are affected,and the injection quantity of a single cylinder cannot be identified quickly.The fuel injection system is the minimum execution system of fuel injection,so this paper will focus on the fuel system,find the relationship between fuel injection and fuel pressure,explore the method of identifying fuel injection quantity change by using existing rail pressure sensor,and carry out engineering verification,and get the following conclusions:1.There is a significant correlation between fuel injection quantity and fuel pressure fluctuation.The essence of the fuel injection quantity change is: the fuel rate change through the injection hole,the fuel injection quantity can be obtained by integrating the rate.The injection rate has a great influence on the fuel pressure,especially at the nozzle and the pressure on the rail.The rail pressure variation caused by injection is independent of the pressure fluctuation caused by pump oil.The influence mechanism of fuel injection on rail pressure includes two factors: fuel flow rate and pressure wave caused by needle valve opening and closing.There is a monotone linear relationship between the rail pressure drop caused by fuel injection.The change of the total amount of fuel injection caused by the change of the orifice flow capacity can be reflected by the change of rail pressure.Because of the pressure wave caused by the water hammer effect,the power up time of the injection is less than the rail pressure variation process,and multiple injection can be regarded as a single injection.2.Based on the significant correlation between rail pressure variation and fuel injection quantity,a diagnosis algorithm is proposed and applied in engineering.Generally.The response of the existing rail pressure sensor is 0.2ms,and the rail pressure accuracy can reach 0.1MPa.At present,the minimum execution cycle of batch ECU is 1ms.Therefore,based on the existing rail pressure sensor on the rail,1ms frequency can be used to collect the pressure change information.The larger the injection quantity is,the higher the initial rail pressure is,and the more significant the effect is.The lower the speed of the oil pump,the less the interference to the pressure fluctuation caused by the injection.So the operation conditions can be long pulse width,high rail pressure and low speed(low speed and high load);the actual processing of rail pressure is the key of the algorithm,and the corresponding AD sampling rate must be high enough to prevent the interference caused by other electrical drives.3.Using independent acquisition unit and rapid development prototype to carry out verification.According to the same pressure drop of rail end caused by injection,the online correction of cycle injection quantity is realized.Through this research,a method which can realize the online identification of the fuel injection quantity of a single injector is explored,which can improve the performance of the diesel engine.