Evolution of the scale factor a(t) as a function of time. We have represented the standard ΛCDM model (long-dashed line) and a dark fluid (solid lines) described by an equation of state p = (αρ + kρ²)c² with optimal parameters (q = 0.303471, α =  −0.76782367) and (q =  −0.383589, α =  −0.53880367). We have also represented the EdS universe p = 0 (upper dotted line) and the universe described by a linear equation of state p =  −ρc²/3 (lower dotted line).