Theoretical and experimental evaluation of the spark-ignition premixed oxy-fuel combustion concept for future CO2 captive powerplants

Abstract Oxy-fuel combustion concept is one of the most promising technologies not only to avoid NOx emissions, but also to reduce CO, unburned hydrocarbons and soot emissions in combustion-based powerplants. Moreover, the concept facilitates Carbon Capture and Storage (CCS), thus promoting CO2 integration in a circular economy strategy (i.e. e-fuels production). For O2 production, Mixed Ionic-Electronic Conducting membranes (MIEC) arise as a solution to separate pure O2 from air, but its thermal requirements must be considered in order to guarantee its integration with the internal combustion engine (ICE). In this study, the combustion process using pure oxygen as oxidizer is studied in a spark ignition ICE. A numerical method to assess the combustion process and engine outputs in oxy-fuel operation, taking into account the thermo-mechanical constraints, is developed and validated with experiments. It has been concluded that the use of exhaust gas recirculation (EGR) is more appropriated than O2 for diluting the oxidizer, and the best operating strategy consists in using stoichiometric conditions and 60% to 70% EGR rate, thus having a good compromise between combustion stability and efficiency, engine integrity, and MIEC operation. It is also shown that oxy-fuel combustion reduces knocking propensity and hence, on the one hand, it provides some room for spark optimization, specially at high load; on the other hand, it allows increasing compression ratio. Both strategies are interesting to compensate the expected fuel consumption increase observed in oxy-fuel operation.