This paper focuses on the designing of the engine simulation models using the Wärtsilä 31 (W31) dual fuel (DF) first-order marine engine model, operating on torque and the performance output is the engine speed. X-in-the-loop simulations are proposed using the closed-loop system of proportional integral derivative control designs with respect to manual tuning and direct synthesis techniques to test the engine’s speed and load control functionality. The model-in-the-loop simulation evaluates the performance of the engine model i.e. the model-based testing whereas the software-in-the-loop simulation verifies the engine model in a simulation environment using the W31DF UNIC control system. The simulation results show the effectiveness of the proposed testing methods with respect to stability and settling performance.