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Potential of carbon dioxide transcritical power cycle waste-heatrecovery systems for heavy-duty truck engines

Li, Xiaoya, Tian, Hua, Shu, Gequn, Zhao, Mingru, Markides, Christos N., Hu, Chen
Applied energy 2019
carbon dioxide, computer software, controllers, diesel engines, employment, energy, energy use and consumption, factor analysis, models, trucks, waste heat recovery
Carbon dioxide transcritical power cycle (CTPC) systems are considered a new and particularly interesting technology for waste-heat recovery. In heavy-duty truck engine applications, challenges arise from the highly transient nature of the available heat sources. This paper presents an integrated model of CTPC systems recovering heat from a truck diesel engine, developed in GT-SUITE software and calibrated against experimental data, considers the likely fuel consumption improvements and identifies directions for further improvement. The transient performance of four different CTPC systems is predicted over a heavy-heavy duty driving cycle with a control structure comprising a mode switch module and two PID controllers implemented to realize stable, safe and optimal operation. Three operating modes are defined: startup mode, power mode, and stop mode. The results demonstrate that CTPC systems are robust and able to operate safely even when the heat sources are highly transient, indicating a promising potential for the deployment of this technology in such applications. Furthermore, a system layout with both a preheater and a recuperator appears as the most promising, allowing a 2.3% improvement in brake thermal efficiency over the whole driving cycle by utilizing 48.9% of the exhaust and 72.8% of the coolant energy, even when the pump and turbine efficiencies are as low as 50%. Finally, factor analysis suggests that important directions aimed at improving the performance and facilitating CTPC system integration with vehicle engines are: 1) ensuring long-duration operation in power mode, e.g., by employment in long-haul trucks; and 2)enhancing pump and turbine performance.