The paper proposes a novel solution to control the combustion regime of Diesel engines in order to obtain NOx reduction and to minimize fuel consumption. The nonlinear dynamic model associated to a Diesel platform equipped with an EGR and VGT is estimated. The linearized and reduced state model structure has been approximated. The optimal control procedure for the air flow in the intake manifold of the cylinders and the pressure inside the combustion chamber of the Diesel engine is proposed. A multi-model control for nonlinear systems with parametric uncertainties solution is developed. Our procedure is implying the minimization of the multi-model structure by reducing the identification effort of the number of models and associated controllers. The simulation results will be implemented and validated on the experimental Diesel engine.