An extended rich mode engine configured and operated extremely rich of stoichiometric to produce a substantially continuous hydrogen rich engine exhaust. Oxygen enrichment devices further optimize production of hydrogen rich engine exhaust. Engines include a free piston gas generator with rich homogenous charge compression, a rich internal combustion engine cylinder system with an oxygen generator, and a rich inlet turbo-generator system with exhaust heat recovery. Oxygen enrichment devices to enhance production of hydrogen rich engine exhaust include pressure swing absorption with oxygen selective materials, and oxygen separators such as a solid oxide fuel cell oxygen separator and a ceramic membrane oxygen separator.