as diesel fuel and gasoline are complex HC mixtures, if you want to simulate approximately their thermodynamic behaviour you might use a pseudo-component approach as customary made in the O&G industry. This means to know the mixture composition (and have specific lab test results) and to use a suitable software to compute the pseudo-component properties. In any case, both pure components and multiple pseudo-components are used in a EOS developed for a specific hydrocarbon mixture.
This if you are interested to replicate the thermophysical properties of the mixture only. But if your simulation has also the goal to assess the environmental risk, then probably some specific components should be tracked independently on their contribution to mixture properties. BTEX could be an example.
In principle, TMVOC could use a similar approach with some pure components and some pseudo-components. I have never used this approach in TMVOC, but in TMGAS. For one application we used an EOS with 12 components (either pure or pseudo-component) basically replicating the same EOS developed for ECLIPSE. The EOS for the oil mixture was developed using lab data and suitable software by specialists of the oil company.
In one case we used a single pseudo-component to model a HC mixture in T2VOC, when TMVOC was not yet available. The reference is Battistelli et al. (1996). Modeling of unsaturated zone contaminantion due to pipeline leackage. 1st Intl. Conf. The impact of industry on groundwater resources. Como, Italy.
The paper describes the application and the approach followed for the pseudocomponent approach, but does not report the CHEMP block. Basically we used the HC mixture composition and the properties of pure compounds to compute the mixture viscosity, average molecular weight, mixture vapor pressure, mixture density, average solubility in water, average adsorption, etc. Then we computed the CHEMP block parameters able to reproduce the average mixture properties. This approach may work until there is no much changes in mixture composition due to evaporation or dissolution, as mixture properties remain unchanged, while in the real world the mixture would be depleted by volatile and soluble compounds over time. this was pointed out in the paper looking at simulation results.
Not exactly an answer to your request for the CHEMP block parameters. But i hope it may help.