Engines, systems, devices, software, and methods of the present invention provide increased fuel efficiency and emission performance. The engine may include a magnesium alloy cast engine block cast as a mono-block with or without a ceramic inner core and including one or more cylinders designed to provide compression ratio of 10:1 to 14:1. Each cylinder may include one or more laser igniters, one or more supercritical fuel injectors configured to inject the fuel near or in a supercritical state, and carbon dioxide, which may be in the form of engine exhaust gas. The fuel may be diesel, gasoline, or other suitable hydrocarbons that may be cracked into smaller molecules prior to be injected into the cylinder.