A system for controlled heat generation in exhaust pipeline is studied, consisting of fuel injector and oxidation catalyst (plus connecting pipes). A 3D-CFD software (StarCD) coupled with a tailored 1D model of catalytic monolith channel (XMR) are employed for simulations of realistic, fully 3D system geometry. Exhaust gas flow, fuel injection, and distribution at the catalyst inlet is solved by 3D-CFD, while the processes inside individual representative channels are simulated by the effective 1D model. The 3D-CFD software calls iteratively the 1D channel model with proper boundary conditions and solves 3D temperature profile over the monolith, utilizing local enthalpy fluxes (including gas-solid heat transfer and reaction enthalpy) calculated by the 1D channel model.Seven representative hydrocarbons are used for characterisation of Diesel fuel composition with respect to catalytic oxidation kinetics. Each representative component possesses its own light-off behaviour (described by a global reaction kinetics) and combustion enthalpy. The impact of the following parameters on the conversion of hydrocarbons and heat release is investigated: (i) fuel composition, (ii) operating temperature of the system at the beginning of fuel injection, and (iii) system geometry, determining the flow and concentration distributions at the monolith inlet.