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Session: Poster session & Sponsor Exhibition
Session starts: Monday 07 October, 14:00

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Stephen Streater (Mentor Graphics)
Zhiqiu Pan (Mentor Graphics)

Abstract:
The ability to quickly and accurately model small scale vapour cycle systems is of increasing importance to virtually all sectors of the Automotive industry, and indeed other industries where the internal combustion engine is widely utilised. This is especially the case for heavy commercial vehicles, as well as small scale power generation applications, where duty cycles include prolonged periods at high engine load conditions. The realtively high capital cost and service life of machinery used in these applications makes them particularly suited to maximising the fuel economy benefits associated with Waste Heat Recovery (WHR). Concepts for automotive WHR are tending to focus on systems that use water-steam, and/or Organic Rankine Cycle (ORC) fluids, to recover heat from the vehicle’s exhaust, EGR cooler, or liquid cooling system. These small-scale Rankine Cycle systems are aimed at recovering at least some of the 60-70% of fuel energy that is normally lost to the surroundings. The recovered energy is used to heat the working fluid to a superheated vapour which is then expanded using either a turbine or a piston machine to extract useful work. This is then returned to the vehicle powertrain as either mechanical or electrical energy. The study shows how Flowmaster has extended its existing vapour cycle modelling capabilities, originally developed for water-steam systems in the Power Generation industry, to produce an ORC capability for automotive Vehicle Thermal Management System (VTMS) engineers. Important new numerical models have been developed in order to represent the key components used in the increasingly important application of automotive WHR simulation. These single component models can be successfully used to build Flowmaster system level networks and thereby allow the complete Rankine cycle to be simulated. The resulting system level model uses a recently developed solver that is based on energy conservation at every network node, thus allowing the behaviour of the entire WHR system to be predicted. In addition to the conventional water-steam cycle, the modelling approach has been successfully applied to two of the more commonly used ORC fluids to provide a better reflection of current small scale WHR concepts. Proper calibration of the component numerical models produces an excellent correlation with measured test data, thus validating their use for the design layout and development of small scale WHR systems. The study concludes that this newly developed approach to modelling automotive WHR can effectively meet the new challenges facing VTMS engineers at this time of increased powertrain electrification and engine downsizing.