Study On The Combustion Process Of SI Engine Based On The Indicator Diagram

The development of Automobile is facing two headache challenges: environment protection and limitation of crude oil resources. As of the automobile core, the engine can affect the car's fuel efficiency, dynamics, emission and comfort. At the same time the combustion process will determine the engine's quality. It will have practical importance to save fuel and improve power in studying SI engine's combustion process.In the SI engine's experimental test, it showed that different operation cycles had different mean indication pressure value with the engine under the same operation condition and adjusting parameters and their pressure difference was large. So it would be a fundamental theory study to research on the combustion cycles of maximizing or minimizing mean indication pressure.Based on the indicator diagram, the SI engine's combustion cycles were studied. Before calculating the combustion process, wavelet transform method was applied in this article to filter the noise. Therefore vibration and measure errors were removed. Because the accurency of heat ratio has great influence on combustion process, a new heat ratio formula was developed. Using the energy balance law, the heat transfer formula was formed and was more accruate than the former. It provided a theory support to calculate the combustion process.On the SI engine test bench, 315 test points with different speed, load, A/F, SA were tested. At each test point 2000 operation cycles were sampled. The two typical cycles'combustion process of maximizing and minimizing mean indicator pressure was analyzed. Then the operating and adjusting parameters were analyzed to study their influence on the combustion process. The result showed that even through the operating and adjusting parameter was different, the combustion process of the maximizing mean indication pressure was similar: instant heat release rate was concentrated and symmetrical. The heat release process of the minimizing mean indicator pressure was longer than the maximizing mean indicator pressure'. But the heat release was almost completed. Therefore, the main reason of different mean indicator pressure was depended on the combustion process.One improving combustion heat release model was built upon the experiment. The cylinder's pressure and temperature calculating from the model was close to the experimental data.