Analysis of Late Combustion of Diesel Engine Based on Visualization of Endoscopic Imaging System

The mechanism of governing the late combustion of a diesel engine is too complex to be understood. On the other hand, shortening the duration of the late combustion is the key measure of improving the degree of constant volume and thermal efficiency alike for diesel engines application. An endoscopic imaging system is harnessed into the analysis of late combustion of typical loading conditions of 2000 rpm/700 kPa of indicated mean effective pressure (IMEP) based on a 2.2 L four-cylinder diesel engine. Both ultraviolet (UV) emissions mainly from the excited hydroxyl-radical (OH*) chemiluminescence through a 310 nm bandpass filter and direct soot luminosity images are taken, respectively, for the test operation condition, which is characterized by the pilot, pre-, and main injection at the constant injection pressure of 180 MPa. To guarantee the correct heat release rate derived from in-cylinder pressure, a capacitive proximity top dead center (TDC) sensor has been applied in this work. According to the meaning of intrinsic physical, the new polytropic index is defined. And the polytropic index and in-cylinder pressure at intake valve closure (IVC) timing are performed, respectively. Finally, the correlating trend between visible flame luminosity intensity and the pressure-derived heat release rate, as well as UV chemiluminescence imaging, was verified.