What is it about?
This study presents an experimental methodology to design, operate, and measure semi-closed-cycle oxy-fuel combustion (SCC-OFC) in reciprocating internal combustion engines. We demonstrate the approach on a full-scale 2.2 L, 4-cylinder automotive compression-ignition engine, adapted with high-pressure oxygen injection, controlled water (condensate) injection into the intake, and an exhaust drying/condensate recovery system that enables a CO₂-rich exhaust stream suitable for capture. Because SCC operation involves recirculated gases with unknown and changing composition, conventional flow and emissions measurement methods are not directly applicable. To address this, we propose a dedicated measurement and post-processing framework to estimate gas composition and mass flows across branches (intake/EGR/exhaust/capture), supported by a Monte-Carlo-based uncertainty analysis.
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Why is it important?
SCC-OFC is a promising pathway for near-zero engine-out NOx, strong reduction of pollutants in the raw exhaust, and inherent CO₂ capture capability—features that are especially relevant for hard-to-abate sectors. A key contribution is that we validate stable SCC-OFC operation on a production multi-cylinder diesel engine with only minor hardware modifications, supporting retrofit applicability rather than relying only on simulations or single-cylinder platforms. Finally, the paper provides experimental guidelines and a robust measurement methodology (including uncertainty quantification) that can help other researchers and engineers generate comparable, reliable datasets—an essential step toward scaling SCC-OFC concepts and integrating them with downstream CO₂ capture units.
Perspectives
Our results show that water/condensate injection can help manage intake conditions, but it also introduces practical challenges such as partial condensation and liquid water ingestion, which can affect the effective in-cylinder oxygen-to-fuel ratio and combustion behaviour. This highlights the need for careful control strategies and potentially alternative injection approaches. Looking ahead, SCC-OFC should be assessed at system level, considering auxiliary requirements such as oxygen supply, boosting, and pumping, which influence overall efficiency. Further optimisation is needed to balance capture-ready operation with performance. Beyond this specific pilot plant, the methodology is relevant to other advanced concepts where intake/exhaust compositions are tightly coupled (e.g., high-humidity EGR strategies). With continued development, SCC-OFC could support carbon capture in industrial power systems and marine transport, enabling concentrated CO₂ streams for separation.
Dr. Francisco José Arnau Martínez
Universitat Politecnica de Valencia
Read the Original
This page is a summary of: Experimental methodology for semi-closed cycle engines: Insights from an oxy-fuel combustion pilot plant for carbon capture, Energy Conversion and Management, May 2026, Elsevier,
DOI: 10.1016/j.enconman.2026.121264.
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