Research On Transient Process Of Gasoline Direct Injection HCCI Combustion

Homogeneous Charge Compression Ignition (HCCI) combustion has advantages of low fuel consumption and ultra low NOx emission. However, the challenges from the autoignition control difficulty and narrow operation region limit the practical application of this technology. A hybrid combustion mode which combines SI mode and HCCI mode in separated working regions was regarded as a promising technology for HCCI engines. The purpose of this dissertation is to study the control strategies of transient process, including engine performance behavior process within HCCI region and mode switch process between HCCI and SI.A technical solution of changing the cam profile and injection strategy simultaneously was adopted to realize the rapid and smooth switch between SI mode and HCCI mode. An electrohydraulic two-stage cam profile mechanism was designed and produced, including the fuel injection and cam profile electronic control system. An SI/HCCI hybrid engine prototype was established.On the prototype test bench, the factors which influence the HCCI transient process were analyzed based on the test results of engine emission and pressure traces. The optimized strategies and its general criteria of mode switch control were proposed. The test results show that the load change in HCCI mode is rapidly responded, and can be optimized by adjusting injection strategy; the HCCI combustion is insensitive to the engine speed change, and the combustion phase can be adjusted rapidly and smoothly by changing the injection ratio; the mode switch from HCCI to SI was easy, while the switch from SI to HCCI was difficult with combustion fluctuation; by adjusting the key factors within the switch process, such as injection mass, injection timing, spark timing, throttle opening, and so on, the switch process was optimized; the switch process was completed in 10 engine cycles, rapidly, reliably and smoothly, without any abnormal combustion such as knocking and misfiring.A dual-zone detailed chemical kinetics engine model which features stratified homogeneous mixture was developed based on the Chemkin source code. An engine cycle simulation model was established by coupling the dual-zone model and software BOOST. The engine mode was utilized to simulate the switch process. Controlling parameters such as injection ratio and injection timing was evaluated. The results provide a good explanation for the experiments.