Visualization Investigation On The Influence Of Injection Strategy In The Combustion Of Diesel Engine

Previous studies have shown the use of split injection can effectively reduce thecombustion noise or reduce particulate emissions in diesel engines, which shows significantimportance for energy conservation, but the mechanism is far from known. As an opticalmethod of combustion diagnostics, two-color method bears the characteristics of nointerference to burning, real-time measurement and simplicity and reliability. After40yearsof exploration and research, it has been widely used in the measurement of diesel flametemperature and soot concentration distribution.This thesis introduces the basic principles of the two-color method, the selectionwavelength, the physical significance of KL factor. Then it specifies the optical engine testsystem of two color method, the development of two-color method program which achievesinterface operation. Before the test, the calibration of fuel injection amount and camerasetup, and the verification of two-color method program have been carried out. The opticalengine can run at1200r/min speed, with electronically controlled high-pressure injectioncommon rail, where the injection pressure and waveform are flexible and adjustable. It isthe basis for different injection strategies.The influence of pre-injection on diesel combustión is analyzed with two-colormethod. The results show that under the conditions of experimental design, with theincrease of the injection interval, the peak of the combustion pressure increases, and takingthe impact of thermal stress on the cylinder head and block into consideration, pre-maininjection interval angles should not be too large. The increase of the proportion of theamount of pre-injection helps reduce cylinder pressure rise rate, decreasing the combustionnoise. With the pre-primary angle reducng or the amount of pre-injection increasing, theperiod of the ignition delay is shortened. With the pre-primary injection interval increasing,the soot oxidation rate in the late process of the incylinder combustion slows down. Withthe increase of the proportion of pre-injection quantity, soot oxidation rate changes little.Pre-injection timing and its ratio should be optimized. If the interval is too long or thequantity is too little, the pre-injection can not preheat the main injection, while if the injection interval is too small or the amount is too large, it may cause main injection to bein the oil-rich state of hypoxia, resulting in a lot of soot production.Meanwhile, the influence of post-injection on diesel combustión is analyzed withtwo-color method.. The results show that the presence of post-injection makes temperatureand total factor KL curve bimodal distribution. With the increase of the proportion of thepost-injection, the combustion pressure peak reduces. When the proportion of thepost-injection quantity increases, the total number of KL factor first increases and thendecrease, while when the ratio of the post-injection quantity becomes larger, the totalnumber of KL factor changes little. Soot oxidation rate accelerates with the spray intervalangle increasing. The interval angle and quantity of the post-injection should beoptimizated. Post-injection promotes the turbulence of the mixed gas, while the exothermiccombustion of fuel enhances the temperature of the in-cylinder. So it can increase the rateof soot oxidation, and also reduce the emissions.