Abstract The thermodynamic performance of the evaporator used in the Ford Focus liquefied petroleum gas (LPG) was calculated over the engine power range. In-vehicle tests were performed at two extreme operating temperatures so that the switchover (from gasoline to LPG) characteristics could be examined. Approximately 300 kW of thermal energy from the LPG, ∼6 g/s, is needed to realise maximum engine power output. The effect of LPG composition on engine performance was also studied, and was found to be minimal due to the fuel components having similar calorific values. Engine coolant temperatures (into and out of the evaporator) are discussed in detail because the difference between them represents the ΔTc across the evaporator, providing a basis for the calculation of the amount of thermal energy transferred into the LPG. For maximum power, using energy balance, the ΔTc was found to be about 6 K. This study concludes that the Necam evaporator performs satisfactorily. It is rated conservatively in terms of maximum power but this is a necessary safety margin for periods of lower than normal engine efficiency.
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