In this paper, a hybrid adaptive control to realize an entire enveloppe speed regulation with fast operating condition changes and input saturation constraint is proposed. It is based on a simplified nonlinear parameter varying diesel engine model which includes variable transport delays in fueling input. The proposed controller which consists of a derived piecewise continuous controller based jumping-up sub-controller and a friction and load torque observer based Lyapunov function stabilization sub-controller guarantees the closed-loop system stability and demonstrates perfectly unknown friction and load torque disturbance rejection capacities. Comparing with a linear parameter varying control, the proposed hybrid adaptive control has better performance in terms of settling time, steady state error and it allows no static state fueling input oscillation and nearly zero speed drop in presence of significant external load torque changes. Moreover, the proposed control has a very simple structure and can be implemented easily for real-time system control.