Effect of droplet sizes on evaporation of a bi-component droplet at DME (dimethyl ether)/n-heptane-fueled engine conditions

Two fuels with the compression-ignition property similar to conventional diesel-DME and n-heptane-are selected to analyze the evaporation performance of a bi-component droplet at different internal combustion engine conditions. A multi-component evaporation model based on UNIFAC (Universal Functional Activity Coefficient ) method and the non-equilibrium evaporation law is implemented to predict the evaporation characteristics of “each component” of the DME/n-heptane droplets with different mass fractions and different initial diameters, and to find how the two main competing factors (the consumption of latent heat for evaporation and the heat transfer into the droplet) affect the evaporation behaviors of each component. Generally, reducing the mass fractions of DME, increasing the ambient temperature or increasing the relative velocity between the droplet and the ambient gas enhances the evaporation of a droplet. Decreasing initial droplet diameter reduces the “peak” evaporation rate of both components. It is interesting to find that a relative constant and high evaporation rate of DME can last for a relative long time with an appropriate mass fraction of n-heptane. It proposes a way to change the evaporation rate of each component by altering the mass fractions in the DME/n-heptane mixture, in order to control the combustion of DME/n-heptane blended fuels.