The effects of design parameters on the dynamic behavior of organic ranking cycle for the engine waste heat recovery

Organic Rankine Cycle (ORC) is a suitable way to recover the waste heat of internal combustion engines. Since the engine usually operates under different working conditions, the waste heat recovery system is also under unstable state. Consequently, it is quite meaningful to research the dynamic behavior of the ORC. The dynamic math model of the ORC for waste heat recovery of a natural gas engine is established by Simulink in this paper. Based on these, the effects of design parameters of evaporating pressure, condensing pressure, exhaust outlet temperature and working fluids on the ORC dynamic behavior are researched. The results indicate that the dynamic response speed of the ORC just varies a little with the design evaporating pressure, condensing pressure and exhaust outlet temperature. By contrast, different working fluids lead to quite different dynamic response speed. As a result, when designing the ORC, the working fluid should be considered much more to match the dynamic characters of the engine working condition. Furthermore, it is found that ORCs designed under different evaporating pressure, condensing pressure, exhaust outlet temperature can apply the same PID controller, while it is not suitable for ORCs with different working fluids which have quite distinctive critical temperature.