Constraining a New Type of Dark Energy Model from Present Observations

We propose a new type of dark energy (DE) model, in which the equation of state of DE ω_de is a simple function of the fractional energy density Ω_de instead of the redshift z. We assume three DE models of this type, and fit them with present observations to get constraints of DE, which are also compared with the CPL model. It is shown that a suitable ω_de (Ω_de) model can give smaller χ² or smaller errors of ω_de than that of the CPL model. This new type of DE model can help to study the essential properties and nature of DE.