Experimental study on velocity and particle size characteristics of dense spray at different ambient temperatures

The microscopic characteristics of diesel spray droplets severely affect mixture formation and ignition characteristics. Aiming to reveal the droplet velocity and size characteristics under the hot atmosphere in the cylinder, this study conducted an experimental research on the microscopic characteristics of diesel fuel dense spray under evaporative environment by using a Phase Doppler Anemometry (PDA) in a flowing constant volume chamber (CVC). The test results showed that as the ambient temperature increased, the velocity of the droplets when they reached the measuring body gradually increased, and droplets with a velocity of about 350 m/s were effectively captured. Due to the enhanced evaporation characteristics of droplets at high temperature, the quantity of effective droplets captured in the measurement body increased with the rose of ambient temperature. At the same time, the proportion of large-sized droplets gradually decreased during the stable development period of spray, but when the ambient temperature was too high, the number of droplets began to decrease. At the environment temperature above 500 K, the small droplets of spray were almost all evaporated at the end of 3 ms after the start of spraying, and only the slightly larger particles were captured. The droplets of large particles decreased from 17.9 μm at 300 K to 11.2 μm at 800 K during the stable development period of the spray. The droplets of large particles are considered to be one of the reasons for the formation of carbon soot after combustion, and are the main focus of attention in the microscopic characterization of sprays. This study provides guidance for diesel engine as well as nozzle design.