This paper deals with Diesel engine control. More precisely, a model-based approach is considered to stabilise engine speed around a defined value. The model taken into account is nonlinear and contains explicitly the expression of fuel conversion efficiency. In general in the literature, this experimentally obtained quantity is modelled with either a polynomial or an exponential form (see for instance Younes, R. (1993). Elaboration d'un modele de connaissance du moteur diesel avec turbocompresseur a geometrie variable en vue de l'optimisation de ses emissions. Ecole Centrale de Lyon; Omran, R., Younes, R., Champoussin, J., & Outbib, R. (2011). New indicated mean effective pressure (IMEP) model for predicting crankshaft movement. Energy Conversion and Management, 52, 3376-3382). This paper focuses on engine speed feedback stabilisation when fuel conversion efficiency is modelled with an exponential form, which is more suitable for automative applications. Simulation results are proposed to highlight the closed-loop control performances.