Use of ORCs in waste heat recovery is widely seen as a viable and promising solution for increasing energy efficiency and emission reduction efforts, with “on-board” vehicular concepts becoming increasingly popular. In this study, the potential of an ORC harnessing exhaust energy from a diesel generator is considered. Preliminary fluid selection was based on satisfactory thermodynamic performance, and expander size requirement as the limiting parameter. Both simple and recuperative ORC systems were modelled. The effect of the exhaust temperature and the high operational pressure of the ORC model were evaluated in terms of energetic and exergetic performance. For the toluene ORC, moderate pressure values were dictated by the expander size limitation, yet this can be alleviated by high exhaust temperatures. Simple ORCs required a larger heat input and had lower exergetic efficiency. Recuperative ORCs showed better thermal efficiency and lower overall exergy destruction. The expander efficiency was identified as a vital parameter for cycle design and thermodynamic performance.