We have performed MD and DFT calculations to shed light onto the molecular mechanisms controlling the adsorption of DCAs onto model carbonaceous deposits. The MD simulations show that zwitterionic surfactants give stronger adsorption onto PAH-based deposits than conventional PIBSI from gasoline (iso-octane) and diesel (cetane) surrogates. This is due to the increased number of polar functional groups in the head-group, which leads to stronger bonding from additional non-covalent interactions, most notably the cation-π interactions from the quaternary ammonium group. Given the physical nature of cation-π interactions, these are not captured with non-polarisable force field parametrisations and more involved approaches are required, such as the explicit representation of π-electrons using IFF. DFT simulations, with a non-local functional that approximates Van der Waals interactions, are used to provide insights on the fundamental mechanisms underpinning the thermodynamics of adsorption, as well as validating the energetics modelled by the force field in MD simulations. The adsorption of both DCAs is slightly stronger from iso-octane than from cetane, which is due to the more pronounced molecular layering of the latter on the PAH surface.