Strategies for improving premixed oxy-fuel combustion in spark-ignition engines

Oxy-fuel combustion in internal combustion engines is a promising technology that eases Carbon Capture and Storage and allows near-zero NO x powerplants. While some experimental and theoretical studies on oxy-fuel combustion engines are available in the literature, there is a lack of systematic research on dilution strategies or on the use of non-synthetic exhaust gas recirculation. This study uses a combination of 0D-1D and CFD modeling and experimental measurements to assess the use of oxygen dilution and real exhaust gas recirculation in a single-cylinder spark-ignition engine operation under oxy-fuel combustion conditions. A comparison between conventional and oxy-fuel combustion is first performed to highlight the differences between the two combustion modes. Later, taking into account the thermo-mechanical limitations and knocking restrictions, several strategies are analyzed to improve oxy-fuel combustion efficiency: exhaust gas recirculation ratio, compression ratio, and intake temperature. Results show that under oxy-fuel mode, operating at stoichiometric conditions with exhaust gas recirculation rates around 70%, reduces NO x by more than 99%, and CO and uHC by up to 89% compared to conventional combustion with air. In terms of performance, an 8 pp reduction in gross indicated efficiency could be expected; however, since knocking propensity is reduced, the compression ratio can be increased to recover about 5 pp of the efficiency drop. • Humid EGR and O 2 dilution strategies were analyzed for premixed oxy-fuel SI engines. • Combined experimental-numerical analysis defines realistic limits for OFC-ICE. • Almost zero-NO X emissions and up to 89% reduction of CO and HC are achieved. • OFC efficiency penalties can be partially recovered by increasing compression ratio. • Favorable exhaust gas composition ready for being captured with CCS technologies.