Spray characteristics of fouled gasoline direct injectors under flash boiling and sub-zero temperature conditions

This study investigated the spray characteristics of a fouled injector under different ambient pressures, fuel temperatures, and flashing ratios. Four fouled injectors and a clean injector were used to analyze the effects of deposits on spray characteristics. A fouled injector, showing the greatest difference in spray characteristics compared to a clean injector, was selected as a representative fouled injector and analyzed. The near-field and far-field spray visualization were performed by using the Mie-scattering imaging technique. Quantitative indices, such as the spray angle, penetration length, and sharpness intensity, were defined to compare the spray characteristics of the fouled and clean injectors. These quantitative indices were calculated using the MATLAB image processing tool. Deposits formed differently even under the same engine operating condition, such that the spray structure was different depending on the fouled injector. In the near-field spray visualization, there were relatively large droplets and long ligaments in the fouled injector compared to the clean injector due to the low atomization performance.