Investigation On Spray Macro Characteristics Test System Of Diesel Engine

Diesel engines are widely utilized in different fields due to superior thermal efficiency. Since these types of engines rely on fuel spray to obtain the fuel-air mixture for combustion, the spray characteristics of the fuel directly determine the fuel economy and emissions of diesel engines. Due to the complicated transient features and strong turbulence of the atomizing process, the spray characteristics should be analyzed in very effective strategies.In order to study the measuring effect of the diesel spray cone angle and penetration, an optical system was designed and built based on Schlieren method in this study. The wavelength of light beam filtrated by optical filter, the arrangement of knife edge and the distance of lens were adjusted to optimize the quality of spray images obtained by high speed camera. Measurements of spray cone angle and penetration are mainly carried out by using a new image process, which only extract the detail informations of spray boundary. The objective of this method is to decline the influence to images, which caused by the entrainment phenomenon between surrounding gas and diesel spray. For the whole spray was obtained by temporal integration in the pre-process. Image noise was eliminated by median filter, then translated the RGB images into the grayscale images for process simplification. A combination of Canny method and Ostu threshold was used for spray edge detection. Then the boundary lines was fitted by Hough transform. In the image coordinate, the spray macro characteristics were obtained. Finally verification tests proved this method had a high accuracy for actual measurement.In order to test the validation of this method in the diesel spray measurement, detailed comparisons of spray cone angle and spray penetration were conducted under various fuel injection conditions. In comparison with the results of different motor speeds, different back pressures and different nozzle sizes, the results of atomization characteristics show that, the spray cone angle increased rapidly first and then tended to be stable, the penetration increased rapidly and then slowly with time; the spray cone angle became larger and the penetration was longer as the injection pressure increased, the spray cone angle became larger but the penetration was shorter as the back pressure increased, the spray cone angle became larger and the penetration was longer as the nozzle size increased. The results are in accordance with spray theory, which confirmed this method is feasible in the actual measurement.