Advanced bottoming cycle configurations for waste heat recovery in internal combustion engines: A pathway to hydrogen production and energy sustainability

Abstract This review presents a comprehensive and comparative analysis of four prominent bottoming cycles: the Steam Rankine Cycle (SRC), the Supercritical CO₂ Brayton Cycle (s‐CO₂), the inverse Brayton cycle (IBC), and the Air Bottoming Cycle (ABC) integrated with proton exchange membrane (PEM) electrolyzers for hydrogen production. The study evaluates each cycle through a multi‐criteria 4E framework (energy, exergy, economic, and environmental performance). The SRC system emerges as the most promising, achieving an exergy efficiency of 21.93% and a hydrogen production efficiency of approximately 57.4%. In comparison, the IBC lags with an exergy efficiency of 13.72% due to higher irreversibilities. Hybrid configurations employing thermoelectric generators (TEGs) further enhance low‐grade heat recovery, adding up to 1.2–2.4% to the overall system efficiency. The exergoeconomic analysis reveals a cost rate of $32.8/GJ for SRC‐based hydrogen systems compared to $25.58/GJ for IBC, suggesting a trade‐off between cost and performance. The integration of bottoming cycles with PEM electrolyzers presents a viable route to reduce fossil fuel dependency and greenhouse gas emissions, potentially cutting lifecycle CO₂ emissions by 12–20%. This review highlights technology synergies crucial for transitioning toward a hydrogen‐enabled circular energy economy.

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