Inverted Brayton Cycle With Exhaust Gas Condensation

Abstract

Approximately 30% of the energy from an internal combustion engine is rejected as heat in the exhaust gases. An inverted Brayton cycle (IBC) is one potential means of recovering some of this energy. When a fuel is burnt, water and CO2 are produced and expelled as part of the exhaust gases. In an IBC, in order to reduce compression work, the exhaust gases are cooled before compression up to ambient pressure. If coolant with a low enough temperature is available, it is possible to condense some of the water out of the exhaust gases, further reducing compressor work. In this study, the condensation of exhaust gas water is studied. The results show that the IBC installed in series on a turbocharged engine can produce an improvement of approximately 5% in brake-specific fuel consumption at the baseline conditions chosen and for a compressor inlet temperature of 310 K. The main factors that influence the work output are heat exchanger pressure drop, turbine expansion ratio, coolant temperature, and turbine inlet temperature. For conditions when condensation is possible, the water content of the exhaust gas has a significant influence on work output. The hydrogen to carbon ratio of the fuel has the most potential to vary the water content and hence the work generated by the system. Finally, a number of uses for the water generated have been presented such as to reduce the additional heat rejection required by the cycle. It can also potentially be used for engine water injection to reduce emissions.

Maximizing specific work output extracted from engine exhaust with novel inverted Brayton cycles over a large range of operating conditions

“…For example, Fujii et al [11] proposed an intercooled inverted Brayton cycle or mirror gas turbine concept to improve performance. Kennedy et al [14] studied the effect of removing condensed water in the exhaust before the compressor. The benefit of this modification is the mass flow rate reduction during gases compression, which improves the overall cycle efficiency.…”