Influence of O2-enriched intake air with CO2 dilution on the combustion process of an optically accessible spark-ignition engine

Abstract

Oxygen-enriched air combustion has been extensively studied, but not for internal-combustion engines. This paper presents how oxygen-enriched intake air influences early flame growth and the combustion process, and looks at how oxygen (O2) enrichment translates into resistance to carbon dioxide (CO2) dilution. The experiments were conducted with an optical single-cylinder engine instrumented with an in-cylinder pressure transducer and a high-speed camera to monitor early flame growth. During the experiments, O2 concentrations were varied from 18% to 29%, while CO2 was varied from 0% to 35%. The main findings are that O2 addition speeds up the combustion process and renders the flame more resistant to CO2 dilution. It was observed that the amount of CO2 can be significantly increased to reduce the combustion process to a level similar to that with air. Finally, laminar flame speed correlated well with early flame growth and fully developed turbulent combustion periods.