Visualization study the cross spray and combustion characteristics of diesel and methanol in a constant volume combustion chamber at cold and flare flash boiling regions

To optimize the performance of diesel/methanol dual fuel engine, fundamental research on the spray and combustion characteristics of diesel/methanol dual direct injection was conducted in a constant volume combustion chamber. The injection pressures were set as at 60 MPa, 80 MPa, 100 MPa, while the ambient pressures were set as 4 MPa and 0.01 MPa, corresponding to cold and flare flash boiling regions, respectively. The results showed that diesel/methanol cross-collision accelerated the droplet interaction, promoting more uniform mixing. Compared to the cold region, the diesel/methanol collision spray had a larger axial and radial diffusion rate and evaporation rate in the flare flash boiling region. In addition, in the flare flash boiling region, the collision length, collision width, and spray projected area of both the liquid and gas phases were significantly greater than those in the cold region. With the increase in injection pressure, the spray obtained more kinetic energy, leading to a more intense collision process and more homogeneous fuel-gas mixing. Besides, a higher injection pressure shortened the mixing time of the fuel-air mixture before collision, resulting in a smaller equivalent ratio, a smaller ignition delay, a larger flame lift-off length, and a lower soot formation.