Influence of O 2 -enriched intake air with CO 2 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.