Soot Measurement Of The Combustion In The Cylinder Of GDI Engine By Laser-induced Incandescence

Gasoline direct injection engine has good power, economy performance as the special injection mode and become the main development direction of the passenger car engine. However, the particulate emission of GDI engine is higher than port fuel injection engine. What’s more, the particulate size of GDI engine is smaller than diesel engine, which is more harmful to human health. Soot is an important part of particulate. To reduce particulate emission, the formation mechanism of it which is very complex should be firstly understood. In recent years, optical measurement is increasingly important in the study of soot. Laser-induced incandescence based on two-color method is widely used.In this paper, high-temperature blackbody furnace was used to as the standard light source to get the relations between brightness temperature and gray value. Two-color calibration system was set up. The measurement was carried out on a laminar diffusion flame burner. Ethylene was chosen as the fuel, and controlling the flow of air and ethylene to get the stable flame. Nd: YAG laser was chosen as the excitation light source, then selected appropriate excitation wavelength and excitation energy to get the LII signal, and make the signal through two different wavelength filters, used the ICCD camera to acquire the signal with appropriate time and the gate pulse width. Removed background and import the picture in the MATLAB software for further processing: calculate the matrix of brightness temperature, adjust distortion points, calculate the temperature with Newton iteration method, calculate the soot volume fraction, and gray scale image enhancement processing and pseudo-color processing was proposed, then get the 2-D image of temperature and soot volume fraction.An investigation was carried out on an optical single-cylinder GDI engine with the conditions 600r/min and 7MPa fuel injection, with various injection pulse width(6500, 8000 and 9500μs). The results show that: when the fuel injection too early, injector is too closed to the piston and gasoline inject on the piston, which leads to the collected signal inaccuracy. when fuel injection angle and the acquisition time was delayed, we can get the gray scale image of LII signal, then used the burner flame calibration result to get the 2-D image of soot volume fraction in the Cylinder. With the increase of the fuel injection pulse width, soot concentration increased obviously. Most of the soot in the central region of the measured area, near the cylinder wall the soot is very thin. When the fuel injection pulse width increased from 6500μs to 8000μs to 9500μs, the pixel ratio of soot volume fraction less than 1.0×10-8 rapidly decreased from 95.49% to 70.98% to 17.26%. The pixel ratio in the range 1.0×10-8-1.0×10-7 rapidly increased from 4.43% to 26.05% to 53.46%. The pixel ratio in the range 1.0×10-7-1.0×10-6 is small, but it rapidly increased from 0.06% to 26.05% to 53.46%. In the ranges 1.0×10-6-1.0×10-5 and bigger than 1.0 × 10-5, the pixel is very few.