Abstract
The global transportation sector produces approximately 20% of human-induced greenhouse gas and pollutant emissions. Road transport accounts for almost 75% of that amount. As a result, the automotive industry has invested heavily in powertrain electrification as a long-term strategy for reducing the environmental impact of urban mobility. However, in-vehicle energy storage and access to charging infrastructure are still large bottlenecks to widespread uptake of battery electric vehicles. Combined with waste heat recovery (WHR), hybrid vehicle architectures are a shortto-medium-term solution that will enable a gradual transition to a cleaner transportation system.Analysis of the waste heat recovery technological landscape identified the organic Rankine cycle (ORC) and phase-change (PCM) thermal storage as potential enablers for real-world fuel economy improvement. Vehicle-level modelling of the performance of an ORC WHR system coupled to a mild-hybrid (MHEV) powertrain found a 0.38% increase in total fuel consumption over a WLTP drive cycle – this result highlighted the limitations of ORC energy recovery with respect to thermal fluctuations.
Two powertrain concepts were identified to leverage the ORC’s suitability for steady-state operation. First, modelling of a plug-in hybrid electric vehicle (PHEV) architecture with ORC energy recovery indicated up to 8.3% reduction in fuel consumption over the WLTP drive cycle. Further, sensitivity analysis demonstrated that the thermal efficiency of the internal combustion engine (ICE) is the main driver of combined system performance.
The second concept leveraged novel solid-solid PCM technology as a thermal buffer to reduce ORC input power fluctuations in an MHEV powertrain. The latent heat storage properties of a sample material were confirmed in an experimental environment as proof-of-concept, using a bespoke prototype heat exchanger. Modelling indicated a 0.7% reduction in fuel consumption over the WLTP drive cycle, compared to a 0.38% net increase for the baseline scenario without PCM thermal stabilisation.
| Date of Award | 28 Jun 2023 |
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| Original language | English |
| Awarding Institution |
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| Sponsors | Jaguar Land Rover Ltd |
| Supervisor | Sam Akehurst (Supervisor) & Richard Burke (Supervisor) |