An Experimental Investigation on the Spray Characteristics of Dimethyl Ether(DME) 2001-01-0142
A series of tests were conducted using scattered laser light photography to study the spray characteristics of DME and diesel fuel. The photographs show that, compared with diesel fuel, DME spray displays a slower penetration, much faster evaporation, and a wider spray angle by a factor of about 2, although its general appearance is similar to that of diesel spray. Another series of tests were performed with shadow photography, in which the detailed DME spray characteristics were investigated. The results of high-speed photography show that the spray breakup time of DME is 0.2∼0.4ms, which is shorter than that of diesel fuel. Increasing the ambient density resulted in a shorter breakup time, a wider spray angle, and rapid reduction in the spray penetration and spray tip velocity. With decreasing the orifice diameter, both the spray penetration and the spray angle decrease.
The results show that the needle valve opening pressure almost has no effect on the DME spray penetration. Decreasing the needle valve opening pressure leads to a decrease in the spray angle at the beginning of the spray development, but it almost has no effect at the end of spray development. Testing was also run in engine-like ambient temperature ranging from 573K∼773K, in which no big change in the spray penetration was found with increasing either the ambient temperature or the ambient density.
The James model was used to investigate the mixing characteristics of DME spray. The calculation results agreed well with the experimental results, and showed that the DME spray has a higher air fuel equivalence ratio than diesel spray, indicating a better mixing with air in DME spray. This is one reason that DME emits low pollutant emissions. Also, the calculation results showed that increasing the ambient density or decreasing the orifice diameter would cause an increase in the air fuel equivalence ratio of DME spray.