A Study of Low Critical Fuel Flow in Nozzle 2003-01-1928
Dimethyl ether(DME) is a promising new alternative fuel not only diesel fuel but also power generation, fuel cell and city gas. However, the physical properties are not similar to those of conventional diesel fuel. The P-v, bulk modulus and viscosity of DME are derived as a function of temperature and pressure. As a Result, the Weber and Reynolds number of DME is very large as compared with that of diesel fuel. So, the spray characteristics of DME is not the liquid spray but similar to that of gas spray. The spray formation is strongly affected by the fuel flow in the nozzle. The Computational Fluid Dynamics (CFD) and the experiments are examined to analyze the fuel flow in the nozzle. The DME physical properties make some difference of the flow in the nozzle, comparing with those of diesel. As a CFD result, cavitation in the injection nozzle is more frequent with DME than with diesel oil. From experimental result, the temperature in the nozzle sac is higher with DME than with diesel oil. The lower bulk modulus of elasticity and density of DME makes a higher sac pressure than that of diesel oil, therefore the nozzle outlet velocity and injection rate of DME becomes higher than those of diesel oil. However, low density and low critical point of DME makes a poor spray penetration characteristics at high engine speed and load.