Investigation On Diluted Combustion Optimization And Knock Control Of Low-pressure GDI Engine

Nowadays, the power development and environment protection are the common problems all over the world, they also affect Chinese economy development, and the development of internal combustion engine affects these two aspects directly, so it is significant to improve the engine performance. At present, the main developing way is improving combustion process, increasing mechanical efficiency and decreasing heat loss for lower fuel consumption, and many technologies were used to reduce the emission such as HC, CO and NOx. Gasoline direct injection, diluted combustion can availably improve engine thermal efficiency and reduce harmful emission. Studies have shown that GDI engine could have a large compression ratio due to the lean mixture in the cylinder, the way of quality adjustment at part-load operating condition can reduce the throttling loss, so good economy performance will resulted from GDI technology. Exhaust gas recirculation(EGR)could reduce the in-cylinder temperature, which could result in low NOx emission, additionally, appropriate EGR ratio could also decrease the opportunity of Knock happening. This paper shown the diluted combustion optimiztion and the study about knock control for low-pressure GDI engine, and follows the main contents:1. Prepared the data acquisition (DAQ) system and the whole equipment will be used, and then upload the data of equipments to DAQ system through data communication interface, which conveniences the task data acquisition and post-processing.2. Finished the engine calibration system based on CCP protocol, communicating with control unit through Controller Area Network (CAN), which realized the data adjustment, upload and download.3. Finished engine combustion analysis system and knock signal acquisition module. The combustion analysis system has a real-time monitoring of in-cylinder pressure and analyzes the signal, then other important information will be obtained, such as heat release rate, pressure rise rate, cumulative heat release rate, IMEP, COV, and so on. What's more, real-time monitoring of knock could realized according to the analysis of cylinder pressure curve.4. Calibration system and combustion analysis system were used to monitor the engine combustion process, studied the diluted combustion law via adjusting the advanced ignition angle, A/F ratio and EGR ratio. The results demonstrate that engine has a lower cycle-to-cycle variation ratio with the EGR ratio range from 5% to 20%, and fuel consumption will decrease by 8%-21%.5. A knock signal acquisition module was used to research the method of knock controlling via adjusting the parameter such as advanced ignition angle, EGR ratio and A/F ratio. At operating conditions of stoicheiometry A/F ratio, results show that the ignition angle limited by detonation can be advanced by 2 crank angles with every 5% increase of EGR ratio.