I wonder if a combustion process with air as oxidant can benefit by oxygen enriching the air intake? By benefit I mean if the net energy output would be positive, or negative, since the enrichment process will consume some of the energy released in combustion.
A general answer is sufficient, or an answer based on a modern motor vehicle combustion engine.
Actually a practical answer would also do. A car with variable valve timing would automatically andjust the engine compression ratio based on the oxygen level detected by the oxygen sensor. (If oxygen levels increase, variable valve timing close the intake valves earlier.)
I know some submarines do oxygen enrichment but it is unclear if it is done to achieve increased efficiency or for some other purpose.
Some clues can be had from
Engineering Science and Technology, Volume 19, Issue 1, March 2016, Pages 438-443 Effects of oxygen enriched combustion on pollution and performance characteristics of a diesel engine P.Baskar, A.Senthilkumar
THE EFFECT OF OXYGEN-ENRICHED AIR ON THE PERFORMANCE AND EXHAUST EMISSIONS OF INTERNAL COMBUSTION ENGINES ,VARADARAJA SETTY, B.E. MASTER THESIS IN MECHANICAL ENGINEERING , Texas Tech University
Reports like the following are less interesting, since spark timing is the regulating mechanism with increased oxygen levels.
J.X. Zhou, B. Moreau, Christine Mounaïm-Rousselle, Fabrice Foucher. Combustion, Performance and Emission Analysis of an Oxygen-Controlling Downsized SI Engine. Oil & Gas Science and Technology - Revue d’IFP Energies nouvelles, Institut Français du Pétrole, 2016, 71 (4), pp.49. ff10.2516/ogst/2015035ff. ffhal-01597165f