A study by Ford suggests that an organic Rankine cycle (ORC) waste heat recovery system using R245fa as the working fluid could supply the full vehicle accessory electrical load in a light duty vehicle on the highway cycle.
Presented at the Directions in Engine-efficiency and Emissions Research Conference in Detroit, the study showed that in city driving the ORC system would only supply about half of the accessory load requirement for a conventional engine; and only a third of the load requirement for a hybrid powertrain.
At the moment the Rankine cycle is being widely used commercially to generate power in stationary power plants – and it is also being considered as a potential waste heat recovery system for light-duty and heavy-duty vehicles.
The system includes a pump, evaporator, expander and condenser with the working fluid pumped into the evaporator where it is vapourised by heat. It then flows to the expander where it can be used to generate electricity – and then it comes back to the condenser where it cools back into a liquid and starts the cycle again.
According to the researchers, the ORC for a light-duty vehicle can generate enough electricity to partially offset or even nearly fully offset accessory load on the vehicle.
In addition, the Ford team found that the backpressure with ORC waste heat recovery under this design was a little lower than the baseline system.
