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Cosmological models with time varying gravitational constant, G, and cosmological constant , in the presence of viscous fluid in Kaluza-Klein metric were investigated. The solutions to Einstein Field Equation were obtained for different types of G, with bulk coefficient ξ = ξ 0 ρ d (where ρ is density of the Universe, d is some constant) and lambda = αH 2 + βR −2 where H and R are Hubble parameter and scale factor respectively. Two possible models are suggested, one where G is proportional to H and, the other where G is inversely proportional to H. While the former leads to a non-singular model, the latter results in an inflationary model. Both Cosmological models show that the Universe is accelerating; but at the early stage of the Universe the behaviour of both models is quite different,which has been studied through the variation of decelerating parameter q with time.

In this paper, exact solutions of the Einstein field equations of the Kaluza-Klein cosmological model have been obtained in the presence of strange quark matter. We have considered the timevarying cosmological constant Λ as Λ = αH2 + βR-2, where α and β are free parameters. The solutions are obtained with the help of the equation of state for strange quark matter as per the Bag model, i.e. quark pressure p = 1/3(ρ - 4BC), where BC is Bag’s constant. We also discussed the physical implications of the solutions obtained for the model for different types of universes.

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In this paper, we have investigated the dark energy cosmological model in the presence of anisotropic fluid in Kaluza-Klein metric with generalized time-dependent lambda Λ=αH 2 + βS 2 (α, β are free parameters; H is Hubble parameter and S is normal scale factor). Considering the equation of state (EOS) p = ωρ for normal dimensions and pψ= (ω+δ)ρ for the fifth dimension, exact solutions of Einstein field equations of the anisotropic model are obtained (where p -the pressure for normal dimensions, pψ -the pressure of the fifth dimension, ρ -density of the fluid, ω -EOS parameter, and δ -skewness parameter). It is concluded that the universe at its early stage shows anisotropic behavior due to its finite value δ. The variations of ω and δ demonstrate the evolution from radiation dominated early universe to a dark energy-dominated universe. We have also investigated dark energy density, pressure, and other physical parameters. The physical parameters are dependent on free parameters and power index factor n which relates the extra dimension scale factor to the normal scale factor.