Abstract:
In most previous studies that have been conducted on converting waste heat energy from exhaust gases into useful energy, the engine waste heat recovery system has been placed along the exhaust flow pipe where the temperature differs from the temperature just behind the exhaust valves. This means that an important fraction of the energy from the exhaust gases is still lost to the environment. The present work investigates the potential thermodynamic analysis of an integrated exhaust waste heat recovery (EWHR) system based on a Rankine cycle on an engine's exhaust manifold. The amount of lost energy contained in the exhaust gases at the exhaust manifold level, at average temperatures of 500 °C and 350 °C (for petrol and diesel), and the thermodynamic composition of these gases were determined. For heat to occur, a temperature difference (between the exhaust gas and the working fluid) at the pinch point of 20°C was considered. A thermodynamic analysis was performed on different configurations of EWHR thermal efficiencies and the selected suitable working fluids. The environmental and economic aspects of the integrated EWHR system just behind the exhaust valves of an internal combustion engine (ICE) were analysed. Among all working fluids that were used when the thermodynamic analysis was performed, water was selected as the best working fluid due to its higher thermal efficiency, availability, low cost and environmentally friendly characteristics. Using the typical engine data, results showed that almost 29.54% of exhaust waste heat can be converted. This results in better engine efficiency and fuel consumption on a global scale by gaining an average of 1 114.98 Mb and 1 126.63 Mb of petrol and diesel respectively from 2020 to 2040. It can combat global warming by recovering 56.78 1 011 MJ and 64.65 1 011 MJ of heat rejected from petrol and diesel engines, respectively. A case study of a Volkswagen Citi Golf 1.3i is considered, as it is a popular vehicle in South Africa. This idea can be applied to new-design hybrid vehicles that can use the waste heat to charge the batteries when the engine operates on fossil fuel.
