Study On Control Strategy During Cold Start In Jetta CNG Spark Ignition Engine

To reduce the pollution from the vehicle, nowadays almost every countryrestrict the pollutant emissions from automobile. It comes into being the EmissionRegulations of the nation. Many experiments result show that HC emission isaggravating during the cold start and the heat of engine body, but the principle ofproducing HC emission is complex. After study the development of the emissionregulation, we can see that the exhaust emission in cold start state is tremendouscomparing to normal operation. So the new test Driving Cycle of EUIII beginssampling at engine start state. The combustion control of cold start state isbecoming significant. In the cold start state the proportion of HC and CO isaggravating, it is almost 50% to 80% of total pollutant. So the optimization andcontrol of cold start combustion is becoming one of the key technical proposals inthe emission control on the automobile engine.During the cold start state the engine works unsteady, so it can cause themistake between signal and engine real state, at the same time the catalyst has notbeen lighted up. So during the cold start state the control is in the open_loopcontrol, and tries to keep the engine work stably. So the cold start strategy is veryimportant to reduce the HC emission and enhance the stability of cold start.The new control circuit keep the sensors and the actuating mechanism such asignition system, injection system and so on. On the new control circuit ,we add anature gas engine management system. To design the new control circuit, wechoose the Infineon corporation high performance micro control unit XC167CI ascontroller. In the others control, we also chose the Infineon corporation highperformance chip. In the nature gas engine management system ,we define themain top dead center and the subordination top dead center. When the ECU detectthe main top dead center or subordination dead center, it will begin to ignite andinject to the propriety cylinder according to the cam signal. In the nature gas enginemanagement system contain the fuel open_loop control and closed_loop controlalgorithm, as well as ignition angle closed_loop control model.After the successfully debugging the nature gas engine management code, Iadd the cold start strategy on that. The cold start strategy is divided into cold startand hot start according to the difference of the coolant temperature. In the cold startstrategy , I have made some MAP to offset the fuel injection actuating mechanismand ignition energy.During the entire cold start process, the main aim is to reduce the deleteriousemission and enhance the reliability of cold start. The cold start strategy is dividedinto three depart. The first stage is that the engine is drived by electric motor. Thenext stage is to speedup the catalyst to be lighted up. The last stage is to speedupheating of nature gas engine body. The different stages have different goal, so in thedifferent stages the strategy is different. The experiments show that to adjust boththe ignition angle and the gas mixture concentration will have good effect to attainthe goal. That will take great help to reduce the HC and CO emission during theentire cold start process, as well as enhance the reliability of cold start.At last of this dissertation, I analysis the influence of the different ignitionangle and coolant temperature to reduce the HC and CO emission during the entirecold start .