Experimental study on the spray and mixing characteristics for equilateral triangular and circular nozzles with diesel and biodiesel under high injection pressures.

Abstract The present research work presented an experimental comparison of the fuel-air mixing quality and macro spray behaviors for the equilateral triangular and circular sprays between diesel and biodiesel, through Mie-scattering method based on a laser beam system, at different high injection pressures (120 MPa, 140 MPa, 160 MPa) and backpressures (1 MPa, 3 MPa). The results indicated that the biodiesel spray had longer spray tip penetration than the diesel spray, and also the spray tip penetration of the circular one was consistently longer than that of the equilateral triangular spray for both fuels and injection conditions. The spray tip velocity of biodiesel was higher than that of the diesel fuel, and the spray tip velocity decreases with increasing backpressure. The biodiesel spray cone angles were always smaller than the diesel spray in both major and minor planes. The spray cone angle of the circular orifice was consistently smaller than that of the equilateral triangular spray. Besides, the equilateral triangular spray discharging axis-switching phenomenon for both fuels even under the high injection pressure conditions. The increase of backpressure will decrease the number of interactions of spray cone angles in major and minor planes, while the increase of injection pressure will increase the number of interactions. Moreover, the spray axis-switching occurred earlier at the higher injection pressure, which illustrated the increase of the injection pressure was helpful to increase the equilateral triangular spray instability and deformation. The biodiesel spray was more difficult to undergo the spray axis-switching as compared to the diesel spray. Furthermore, the biodiesel spray projection area was smaller than the diesel spray in all view planes. The spray projection area of equilateral triangular spray was higher than that of the circular spray for both fuels. Meanwhile, the diesel spray had more mass of the entrained air than the biodiesel spray. The mass of the entrained air of equilateral triangular spray was higher than that of the circular spray. The combination of high injection pressure and using an equilateral triangular nozzle can mitigate the poor spray quality of biodiesel significantly. [ABSTRACT FROM AUTHOR]