Abstract
This study presents a novel strategy to enhance the recovery performance of any positive displacement expander technology which aims at the maximization of the power output rather than solely its efficiency. The approach is based on an auxiliary injection of fluid under the same suction conditions as the main intake but during the closed volume expansion phase. The operating principle of the supercharging technology is firstly outlined in theoretical terms, while the benefits over a conventional configuration are numerically assessed with reference to a sliding vane expander for applications based on Organic Rankine Cycles (ORC). The holistic modelling platform used for the benchmarking is preliminarily validated over an experimental campaign in which the vane expander was installed in a heavy-duty automotive ORC system and generated up to 1.9 kW (3% of the engine mechanical power) with an overall efficiency of 51.2%. After the simulation platform is validated, the auxiliary intake line is parameterized in terms of four geometrical quantities and the effects of the supercharging with respect to baseline angular pressure trace are shown. An optimization based on a genetic algorithm is eventually performed and the resulting optimized design led to an average mechanical power increase of 50.6%.
Highlights
The need for lowering the environmental impact of transportation is of paramount importance and nowadays it is a concern of global exposure
The interest shown in the development of automotive heat to power conversion systems based on Organic Rankine
Current research projects in the engine Organic Rankine Cycles (ORC) field mostly focus on small-scale systems since in large scale applications, such as the internal combustion engines (ICE) in marine bunkers or gensets, ORC power units already have a mature technology readiness level [3]
Summary
The need for lowering the environmental impact of transportation is of paramount importance and nowadays it is a concern of global exposure. In the waste heat to power conversion field, the most valuable performance figure is eventually the net power output that an expander is able to provide rather than solely its overall efficiency For these reasons, in the current work we propose a novel concept to enhance the capabilities of positive displacement expanders which aims at maximizing the power recovery: the idea is to use a hot fluid injection at suction conditions to supercharge the expander cells during the closed volume expansion phase. A genetic algorithm is eventually employed to optimize the auxiliary intake line
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