Systems and methods are disclosed that include operating an isothermal compression based combustion (IsoC) engine by injecting isothermally compressed air into a combustion engine immediately prior to a combustion event in order to increase the efficiency of the engine, improve emissions, and substantially eliminate autoignition and associated design constraints. The IsoC engine utilizes an intercooled compressor to isothermally compress air that is stored in a plurality of capacitance tanks prior to delivery of the compressed air to the combustion engine. The IsoC engine allows combustion to be selectively terminated to increase fuel efficiency, thereby resulting in a hybrid compressed air-motor and internal combustion operated IsoC engine.