Proposals for the use of electronic speed governing of diesel engines used for driving alternators has led to a re-examination of the dynamic behaviour of the engine for control purposes. If maximum advantage to the plant performance is to be achieved from using more complex and expensive governing devices, then better models of individual components in the power system for simulation and control studies may be necessary. This paper describes an investigation performed to model the engine in terms of a discrete system. The frequency domain properties of the model (for various numbers of cylinders) are examined and compared with the model usually assumed, as well as with the frequency response of an actual engine. A companion paper will extend this work using 2-transform techniques.