The Research On Electronic Controlled Injection System And Closed-loop Control Algorithm Of Direct Injection Spark Ignition Engine

The aim of four-stroke gasoline engine design is to reduce fuel consumption greatlywhile satisfying the emission regulation and having a long durability. Direct-injectionstratified-charge (DISC) technology proved to be a valuable solution in this point becauseDISC combines the advantages of diesel engine and gasoline engine. Firstly, in partial load,GDI engine uses both stratified-charge lean-burn and quantitative control modes to avoidpumping loss. In this way, the gasoline direct injection engine has the equivalent fueleconomy as diesel engine. Secondly, in full load, the GDI engine uses premixedhomogeneous combustion mode to maintain the high power output as the ordinary gasolineengine. In the mean time, due to the effects of in-cylinder charge cooling, the GDI engineexhibits the advantage of better theoretical efficiency through higher knock-limitedcompression ratio, so it achieves better fuel economy while maintaining the same poweroutput. In addition to all above, the GDI engine provides convenience to measuring fuelconsumption precisely by avoiding the wall-wetting phenomena. Hence, it decreases fuelconsumption and emissions during cold start and enhances the transient response speed.The development and characteristics of the direct-injection spark-ignition gasolineengine are presented. Offer an overview of the difference between port-fuel-injection anddirect-injection system. The potential of enhanced fuel economy, transient response andcold-start hydrocarbon emission of optimized GDI engine is discussed. The application ofnew technologies such as high-pressure, common-rail, swirl-atomizing gasoline fuel injectorsand charge stratification to GDI is introduced. The process of fuel injection, spray atomizationand vaporization, charge cooling, mixture preparation and the in-cylinder air motion,combustion strategies are also discussed and analyzed in detail. Based on these knowledge,the research and development of test-rig for a small GDI and the design ofelectronic-controlled fuel injection system are put forward in this article. Because themanufacturing of swirl injector is not a mature technique and the cost is expensive as well, the"common-rail-valve-nozzle" typed injector which can adjust the injection parametersconveniently is developed using the characteristics of easily numeric-controlled HSV. Theinjector has the lowest injection rate of 0.9 mg/cycle and fulfills the aim of micro-injection.The enhancement of fuel economy and emission quality of GDI relies on the precisecontrol of air-fuel ratio while the improvement of power performance demands the engine speed getting steady rapidly when encountered load disturbance. In the research of this paper,air-fuel ratio feedback control system based on wide-band O₂ sensor is built-up in steadyworking condition. Because the GDI engine can be operated in multiple combustion modeand after-treatment apparatus differs from traditional gasoline engines, its control strategyunder transient working condition is therefore different. Nonlinear dynamic model of the GDIengine is proposed in this dissertation. Coupled with PID control, air-fuel ratio-dominant andspeed-dominant system simulation models are developed under the MATLAB/SIMULINKdeveloping environment using the air-fuel ratio and engine speed as feedback signals. Resultsshow the closed-loop control models not only can modify the bias of air-fuel ratio or enginespeed, but also can shorten the adjustment time of the random offset from target.The design of hardware and software of ECU is the core of electronic control system. Thereasonability of hardware design determines the reliability of electronic control system to agreat extent, and the strict and perfect design of software affects the system function directly.In this work, Intel 16-bit 80C196KB microcontroller is chosen as the main chip of the ECUand the extended peripheral circuits according to the requirements of electronic controlsystem is analyzed in detail. Modularizing design style is used in software programming. Thiswill be convenient for future function extension and co-operation. Since there are many thingsto do in matching job, a control software using the communication between PC and the ECUis developed to monitor, modify and calibrate all system parameters on-line. Practiceapplication shows the whole control system can work steadily and reliably.The last part of the paper records the test progress we processed on ZX125FMI gasolineengine. The experiment results indicate the fuel consumption, HC and NO_x decreases byabout 9.76%, 38.9%, 14.67% respectively even in homogeneous combustion mode in highidle speed operating mode of 2000 rpm compared with the carburetor-modeled engine. Inpartial load, the GDI engine has better lean burn ability and the maximum air-fuel ratio ofmixture can reach 22 while keeping stable combustion. Further improvement of fuel economyand emission can be obtained by adjusting injection timing.