Abstract:

Aiming at the lack of atomization data and unclear atomization mechanism under back pressure， we conducted both macro and micro experimental research on atomization characteristics under the back pressure of 0.1–4.1 MPa using an impinging jet injector. Based on the high-speed shadow imaging method， the spray macro-morphology of the impinging jet injector under back pressure was obtained， and the atomization angle， the spatial distribution of droplet velocity in the spray field and other data extracted. Furthermore， the microscopic parameters such as the probability density distribution of droplet size and the Sauter Mean Diameter （SMD） under back pressure were obtained by the Phase Doppler Particle Analysis （PDPA） laser measurement method. The experimental results show that high back pressure compresses the overall development of spray， reduces the atomization angle， and increases the number density of atomized droplets. With the increase of back pressure， the droplet velocity attenuates more significantly. However， the SMD of droplets shows a non-monotonic evolution law with the increase of back pressure， and the evolution law is related to the vertical distance along the nozzle outlet. At a back pressure smaller than 1.1 MPa， the SMD of droplets decreases with the increase of back pressure. At H=20 mm， when the back pressure increases from 1.1 MPa to 3.1 MPa， the SMD remains basically unchanged， while further increasing back pressure leads to gradual SMD increase. At H=30 mm， back pressure larger than 1.1 MPa results in gradual SMD increase. It is considered that the increase of back pressure leads to higher droplet number density and increases the probability of droplet collision and polymerization， explaining the increase of droplet SMD under high back pressure.

Key words: impinging jet injector, atomization, back pressure, droplet, velocity distribution, droplet size