Evolution of biodiesel flow spray inside and near field in pressure swirl nozzles: Flow rate, atomization angle, and droplet size

This study developed five visualized pressure swirl nozzles with distinct apertures to improve the characteristics of biodiesel spray in industrial furnaces. Biodiesel atomization was investigated at the macroscopic and microscopic scales using high-speed cameras and laser spray detection technology. The results indicated that the flow rate of the nozzle gradually increased with aperture expansion, whereas the flow coefficient decreased. At a pressure of 0.7 MPa, the variance in the flow coefficient between nozzles with apertures of 0.7 and 1.1 mm was 0.2727. For the same apertures, an increase in pressure led to nonlinear changes in the flow coefficient and decreasing of the liquid film fragmentation length. Furthermore, spray images were subjected to spectral mean image scaling to red, green, and blue (RGB) based on light-intensity, revealing that an increase in pressure resulted in higher density of the spray. Additionally, with increasing aperture, the atomization angle generally increased. Under constant pressure, increasing the nozzle aperture led to a gradual increase in droplet size. Conversely, when the aperture was constant, the droplet size decreased with increasing fuel pressure. Similarly, higher spray pressures led to an overall decrease in the characteristic particle sizes and a reduction in atomization uniformity.